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AGUAHEDIONDA WATERSHED
REGIONAL TREATMENT BMP FEASIBILITY STUDY
CITY OF CARLSBAD, CALIFORNIA
Job Number 14071-A
Exp. 06/06
Prepared for:
City of Carlsbad
1635 Faraday Avenue
Carlsbad, California 92008
760) 602-2720
Prepared by:
Rick Engineering Company
Water Resources Division
5620 Friars Road
San Diego, California 92110-2596
(619) 291-0707
September 19, 2003
LIST OF ACRONYMS
EXECUTIVE SUMMARY
CHAPTER 1 Introduction
TABLE OF CONTENTS
1.1 Background ........................................................................................................................... 1
1.2 Municipal Penn it ................................................................................................................... 1
1.3 Jurisdictional Urban Runoff Management Program (JURMP) and Watershed Urban
Runoff Management Program (Watershed URMP) ............................................................... 2
1.4 Standard Urban Stonn Water Mitigation Plan (SUSMP) and Stonn Water Standards
Manual ................................................................................................................................... 3
1.5 Regional BMPs and LEAD Method ...................................................................................... 4
1.6 Agua Hedionda Watershed Regional Treatment BMP Feasibility Study .............................. 6
CHAPTER 2 Study Area
2.1 General Description ............................................................................................................... 7
2.2 Topography ............................................................................................................................ 9
2.3 Stonn Flow Rates ................................................................................................................... 9
2.4 Land Use ................................................................................................................................ 9
2.5 Beneficial Uses of Surface Water .......................................................................................... 12
CHAPTER 3 Storm Water Pollutants and Monitoring
3 .1 General Description of Pollutants .......................................................................................... 14
3.2 Stonn Water Monitoring within the Carlsbad Hydrologic Unit (CHU) ................................ 19
3 .3 Description of Study Area Pollutants of Concern .................................................................. 24
CHAPTER 4 Description of Treatment BMPs
4.1 General BMP Categories ....................................................................................................... 30
4.2 Biofiltration (Carlsbad Stonn Water Standards Category: Bio filters) .................................. .31
4.3 Constructed Wetlands (Carlsbad Stonn Water Standards Category:
Wet Ponds or Wetlands) ........................................................................................................ 33
4.4 Extended Detention Basins (Carlsbad Stonn Water Standards Category:
Detention Basins) ................................................................................................................... 35
4.5 Infiltration (Carlsbad Stonn Water Standards Category: Infiltration Basins) ....................... .36
CHAPTER 5 General Description of Potential BMP Locations
5.1 Basis for Identification of Potential BMP Locations ............................................................. 38
5.2 Identification of Potential BMP Locations ........................................................................... .39
CHAPTER 6 Identification of Pollutants of Concern and BMP Selection Procedure
6.1 Carlsbad Storm Water Standards Manual Selection Procedure ............................................ .42
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CHAPTER 7 Methodology of BMP and Pollutant Removal Analysis
7 .1 General ................................................................................................................................... 49
7 .2 GIS W1MS Database .............................................................................................................. 49
7 .3 Ric kB MP ................................................................................................................................ 51
7.4 Overview ofBMP Sizing and Pollutant Removal Efficiencies ............................................. 57
7.5 BMP Sizing ............................................................................................................................ 59
7 .6 BMP Optimization ................................................................................................................. 63
7.7 Pollutant Load Modeling ....................................................................................................... 64
7 .8 BMP Pollutant Removal Efficiency ....................................................................................... 68
7 .9 Pollutant Load Removed ........................................................................................................ 69
7.10 Potential BMP Location Assessment.. ................................................................................... 70
CHAPTER 8 Results of Analyses
8.1 General Description of Results .............................................................................................. 73
8.2 RickBMP Results ................................................................................................................... 73
8.3 BMP Sizing and Optimization ............................................................................................... 76
8.4 Pollutant Load Modeling ....................................................................................................... 80
8.5 BMP Pollutant Removal Efficiency and Pollutant Load Removed ....................................... 80
8.6 Description of Potential BMP Locations ............................................................................... 83
CHAPTER 9 References ................................................................................................................. 151
TABLES:
Table 2-1. Land Use Distribution within the City of Carlsbad Agua Hedionda Watershed .............. 10
Table 2-2. Summary of Beneficial Uses of Surface Waters in the Agua Hedionda Watershed ........ 13
Table 3-1. 303(d) Listed Water Bodies Within the Agua Hedionda Watershed ............................... 24
Table 3-2. Carlsbad Watershed URMP-Identified Water Quality Problems .................................. 26
Table 3-3. Carlsbad Storm Water Standards-Anticipated and Potential Pollutants Generated
by Land Use Type ............................................................................................................ 28
Table 4-1. Advantages and Disadvantages of Biofiltration Designs ................................................ .32
Table 4-2. Advantages and Disadvantages of Constructed Wetland Designs ................................... 34
Table 4-3. Advantages and Disadvantages of Dry Extended Detention Pond Designs ..................... 35
Table 4-4. Advantages and Disadvantages of Infiltration Designs .................................................... 36
Table 5-1. Potential Treatment BMP Locations Identified in the Agua Hedionda Watershed ......... .41
Table 6-1. Potential Pollutants within Potential BMP Location Subwatersheds Based on
Carlsbad Storm Water Standards Manual ....................................................................... .43
Table 6-2. Potential Pollutants within Potential BMP Location Subwatersheds Based on
303 (d) List ....................................................................................................................... 44
Table 6-3. Structural Treatment Control BMP Selection Matrix ...................................................... 47
Table 7-1 . Criterion Weights byBMP ............................................................................................... 53
Table 7-2. EMC for Common Urban Runoff Pollutants based on Land Use Type ........................... 66
Table 7-3. Land Use Distribution by Subwatershed Area ................................................................. 67
Table 7-4. BMP Pollutant Removal Efficiencies ............................................................................... 68
Table 8-1. Physical Characteristics of the Potential BMP Locations and
their Respective Subwatersheds as Calculated by GIS .................................................... 7 4
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Table 8-2. GIS Calculated Scores for the Potential BMP Locations ................................................. 75
Table 8-3. BMP Sizing and Optimization Results for Biofiltration .................................................. 76
Table 8-4. BMP Sizing and Optimization Results for Extended Detention ...................................... 77
Table 8-5. BMP Sizing and Optimization Results for Wet Pond/Wetland ....................................... 78
Table 8-6. BMP Sizing and Optimization Results for Infiltration ..................................................... 79
Table 8-7. Pollutant Load Results ...................................................................................................... 80
Table 8-8. Indicator Pollutant Load Removal for Top 9 Potential BMP Locations .......................... 83
FIGURES:
Figure ES-1. Flow Chart of Parameters Used to Calculate Pollutant Load Removed ....................... ES-9
Figure 7-1. Flow Chart of Parameters Used to Calculate Pollutant Load Removed ......................... 58
Figure 8-1. City of Carlsbad BMP TSS Removal.. ............................................................................ 81
Figure 8-2. City of Carlsbad BMP Total Zn Removal.. ..................................................................... 82
EXHIBITS:
Exhibit ES-I. Carlsbad Hydrologic Unit ........................................................................................... ES-3
Exhibit ES-2. Agua Hedionda Watershed ......................................................................................... ES-5
Exhibit ES-3. City of Carlsbad Agua Hedionda Watershed Existing Land Use ............................... ES-15
Exhibit ES-4. City of Carlsbad Agua Hedionda Watershed Planned Land Use ................................ ES-16
Exhibit 2-1. City of Carlsbad Agua Hedionda Watershed Planned Land Use ................................... 11
Exhibit 6-1. City of Carlsbad 24-hour, 85th Percentile Depth of Rainfall Isopluvial Map ............... .46
Exhibit 8-lA. Agua Hedionda Watershed Potential BMP Location-
Basin 1 Existing Land Use ......................................................................................... 85
Exhibit 8-lB. Agua Hedionda Watershed Potential BMP Location-
Basin 1 Planned Land Use ......................................................................................... 86
Exhibit 8-2A. Agua Hedionda Watershed Potential BMP Location -
Basin 5 Existing Land Use ......................................................................................... 89
Exhibit 8-2B. Agua Hedionda Watershed Potential BMP Location -
Basin 5 Planned Land Use ......................................................................................... 90
Exhibit 8-3A. Agua Hedionda Watershed Potential BMP Location -
Basin 11 Existing Land Use ....................................................................................... 93
Exhibit 8-3B. Agua Hedionda Watershed Potential BMP Location -
Basin 11 Planned Land Use ....................................................................................... 94
Exhibit 8-4A. Agua Hedionda Watershed Potential BMP Location-
Basin 13 Existing Land Use ....................................................................................... 97
Exhibit 8-4B. Agua Hedionda Watershed Potential BMP Location -
Basin 13 Planned Land Use ....................................................................................... 98
Exhibit 8-5A. Agua Hedionda Watershed Potential BMP Location-
Basin 1 7 Existing Land Use ....................................................................................... 101
Exhibit 8-5B. Agua Hedionda Watershed Potential BMP Location -
Basin 17 Planned Land Use ....................................................................................... 102
Exhibit 8-6A. Agua Hedionda Watershed Potential BMP Location -
Basin 20 Existing Land Use ....................................................................................... 105
Exhibit 8-6B. Agua Hedionda Watershed Potential BMP Location -
Basin 20 Planned Land Use ....................................................................................... I 06
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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Exhibit 8-7 A. Agua Hedionda Watershed Potential BMP Location -
Basin 21 Existing Land Use ....................................................................................... 109
Exhibit 8-7B. Agua Hedionda Watershed Potential BMP Location -
Basin 21 Planned Land Use ....................................................................................... 11 0
Exhibit 8-8A. Agua Hedionda Watershed Potential BMP Location-
Basin 22 Existing Land Use ....................................................................................... 113
Exhibit 8-8B. Agua Hedionda Watershed Potential BMP Location-
Basin 22 Planned Land Use ....................................................................................... 114
Exhibit 8-9A. Agua Hedionda Watershed Potential BMP Location-
Basin 23 Existing Land Use ....................................................................................... 117
Exhibit 8-9B. Agua Hedionda Watershed Potential BMP Location -
Basin 23 Planned Land Use ....................................................................................... 118
Exhibit 8-1 OA. Agua Hedionda Watershed Potential BMP Location -
Basin 26 Existing Land Use ....................................................................................... 121
Exhibit 8-IOB.Agua Hedionda Watershed Potential BMP Location-
Basin 26 Planned Land Use ....................................................................................... 122
Exhibit 8-1 lA. Agua Hedionda Watershed Potential BMP Location-
Basin 44 Existing Land Use ....................................................................................... 125
Exhibit 8-1 IB. Agua Hedionda Watershed Potential BMP Location-
Basin 44 Planned Land Use ....................................................................................... 126
Exhibit 8-12A. Agua Hedionda Watershed Potential BMP Location -
Basin 45 Existing Land Use ....................................................................................... 129
Exhibit 8-12B.Agua Hedionda Watershed Potential BMP Location -
Basin 45 Planned Land Use ....................................................................................... 130
Exhibit 8-13A. Agua Hedionda Watershed Potential BMP Location -
Basin 90 Existing Land Use ....................................................................................... 133
Exhibit 8-13B.Agua Hedionda Watershed Potential BMP Location-
Basin 90 Planned Land Use ....................................................................................... 134
Exhibit 8-14A. Agua Hedionda Watershed Potential BMP Location -
Basin 96 Existing Land Use ....................................................................................... 137
Exhibit 8-l 4B.Agua Hedionda Watershed Potential BMP Location -
Basin 96 Planned Land Use ....................................................................................... 138
Exhibit 8-15A. Agua Hedionda Watershed Potential BMP Location-
Basin 97 Existing Land Use ....................................................................................... 141
Exhibit 8-15B.Agua Hedionda Watershed Potential BMP Location-
Basin 97 Planned Land Use ....................................................................................... 142
Exhibit 8-16A. Agua Hedionda Watershed Potential BMP Location-
Basin 98 Existing Land Use ....................................................................................... 145
Exhibit 8-16B. Agua Hedionda Watershed Potential BMP Location -
Basin 98 Planned Land Use ....................................................................................... 146
Exhibit 8-17 A. Agua Hedionda Watershed Potential BMP Location -
Basin 99 Existing Land Use ....................................................................................... 149
Exhibit 8-17B.Agua Hedionda Watershed Potential BMP Location-
Basin 99 Planned Land Use ....................................................................................... l 50
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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APPENDICES:
Appendix A: Definitions of Land Use Categories
Appendix B: Supporting Documentation for Beneficial Uses of Surface Waters for
the Agua Hedionda Watershed
Appendix C: GIS Processing Program Constants, Variables, and Equations
Appendix D: CASQA Handbook BMP Sizing Guidelines
Appendix E: Calculated BMP Pollutant Removal Efficiencies
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LIST OF ACRONY1\1S AND ABBREVIATIONS
1. 303(d) List -Clean Water Act S~ction 303(d) hnpaired Waterbodies List
2. A-area
3. ac -acres
4. ac-ft -acre-feet
5. BMP -Best Management Practice
6. BOD -Biological Oxygen Demand
7. C -Runoff Coefficient
8. CASQA -California Stormwater Quality Association
9. Cd -Cadmium
10. cfs -cubic feet per second
11. CHU -Carlsbad Hydrologic Un.it
12. COD -Chemical Oxygen Demand
13. Cu -Copper
14. EMC -Event Mean Concentration
15. FEMA -Federal Emergency Management Agency
16. FIS -Flood Insurance Study
17. GIS -Geographic Information System
18. hr-hour
19. I-Intensity
20. in -inches
21. in/hr -inches per hour
22. JURMP -Jurisdictional Urban Runoff Management Program
23. LEAD -Localized Equivalent Area Drainage
24. MBAS -detergents
25. MDP -Master Drainage Plan
26. MEP -Maximum Extent Practicable
27. mg/L -milligrams per liter
28. MLS -Mass Loading Station
29. MS4 -Multiple Separate Sewer System
30. n -Manning's Roughness Coefficient
31. NO2 -Nitrite
-32. NO3 -Nitrate
33. NPDES -National Pollutant Discharge Elimination System
34. P -Phosphorous
35. Pb -Lead
36. Q-Flow Rate
37. R -Wetted Perimeter
38. S -Slope
39. SANDAG -Sand Diego Association of Governments
40. SUSMP -Standard Urban Stormwater Mitigation Plan
41. SWRCB -State Water Resources Control Board
42. TDS -Total Dissolved Solids
43. TKN -Total Kjedahl Nitrogen
44. TMDL -Total Maximum Daily Load
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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45. TSS -Total ·suspended Solids
46. ug/L -micrograms per liter
47. URMP -Urban Runoff Management Program
48. V -Velocity
49. WIMS -Waterhsed Infonnation Management System
50. WURMP -Watershed Urban Runoff Management Program
51. Zn -Zinc
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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EXECUTIVE SUMMARY
Purpose of Report
This Regional Treatment BMP Feasibility Study has been prepared for the City of Carlsbad,
California, to analyze the effectiveness of treating storm water runoff at a regional level as an
alternative to treatment on a site-by-site basis. This plan proposes regional Best Management
Practices (BMPs) to be implemented within the Agua Hedionda Watershed to meet storm water
treatment requirements for future new development and significant redevelopment projects within
the watershed. The regional BMPs are separated into two categories: Regional Planning BMPs and
Localized Equivalent Area Drainage (LEAD) Method BMPs. Regional Planning BMPs will treat
storm water runoff from future development within the subwatersheds. The LEAD BMPs will treat
urban runoff from existing development within the subwatersheds and be used as credit toward storm
water treatment requirements for future development outside the subwatersheds.
The LEAD method is discussed in detail in the Model Standard Urban Storm Water Mitigation Plan
for San Diego County, Port of San Diego, and Cities in San Diego County (Final Model SUSMP),
jointly developed by the Copermittees, February 14, 2002, approved by the California Regional
Water Quality Control Board, San Diego Region (Regional Board), June 12, 2002.
Background
Urban runoff discharged from municipal storm water conveyance systems has been identified by
local, regional, and national research programs as one of the principal causes of water quality
impairments in most urban areas. The City of Carlsbad's existing storm water conveyance system
collects urban runoff from the streets, rooftops, driveways, parking lots, and other impervious areas,
and conveys the flows through underground storm drain systems, as well as natural and man-made
channels, directly to local beaches and lagoons. Urban runoff potentially contains a host of pollutants
such as trash and debris, bacteria and viruses, oil and grease, sediment, nutrients, metals, and toxic
chemicals. These contaminants can adversely affect receiving waters, wildlife, and public health.
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Urban runoff pollution is not only a problem during rainy seasons, but also year-round due to many
types of urban water use, such as landscape irrigation and car washing, that discharge runoff to the
storm water conveyance system (Carlsbad, 2003).
The Regional Board is the agency tasked with regulating storm water discharges in the City of San
Diego, the County of San Diego, the Port of San Diego, and the 17 municipalities in the region
(hereafter referred to as Copermittees). On February 21, 2001 the Regional Board adopted the
California Regional Water Quality Control Board San Diego Region Order No. 2001-01 NPDES
No. CAS0J08758 Waste Discharge Requirements for Discharges of Urban Runoff from the
Municipal Separate Storm Sewer Systems (MS4s) Draining the Watersheds of the County of San
Diego, the Incorporated Cities of San Diego County, and the San Diego Unified Port District
(Municipal Permit). The Municipal Permit requires the development and implementation of storm
water regulations addressing storm water pollution issues in planning and construction associated
with private and public development projects. Specifically, private and public development projects
are required to include storm water BMPs both during construction, and in the project's permanent
design, to reduce the quantity of pollutants generated and discharged from the project site, to the
maximum extent practicable (MEP).
The City of Carlsbad Public Works Department implemented the Standard Urban Storm Water
Mitigation Plan Storm Water Standards manual (hereafter referred to as the Carlsbad Storm Water
Standards manual) in April 2003. The primary objectives of the manual are to:
(1) Effectively prohibit non-storm water discharges; and
(2) Reduce the discharge of pollutants from storm water conveyance systems to the maximum
extent practicable both during construction and throughout the use of a developed site.
(Carlsbad 2003)
To address pollutants that may be generated from new development once the site is in use, the
Municipal Permit further requires that the City ensure that BMPs be implemented, as described in
the Storm Water Standards manual.
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The Carlsbad Storm Water Standards manual is based on the Final Model SUSMP. Appendix C of
the Final Model SUSMP discusses the LEAD method, which supports the basis of this regional
treatment BMP feasibility study. With the LEAD concept in mind, the City of Carlsbad proposes to
implement one or more of the proposed regional treatment BMPs within the Agua Hedionda
Watershed, giving future development and redevelopment projects the opportunity to support these
BMPs as an alternative to implementing on-site treatment BMPs. This regional approach will treat
a greater quantity of runoff than traditional on-site treatment BMPs.
The City of Carlsbad is proposing the implementation of regional BMPs for the following reasons:
• Existing desilting/detention basins throughout the Agua Hedionda watershed afford the
City the opportunity to modify the basins for water quality purposes.
• The City will oversee maintenance.
• Maintenance costs are lower for regional BMPs compared with maintenance costs of on-
site treatment BMPs (typically catch basin inserts and hydrodynamic separators).
• Equal and potentially better pollutant removal efficiencies when compared with on-site
BMPs.
• Overall increased improvement to water quality within the Agua Hedionda watershed .
• Availability ofland to site additional treatment BMPs (availability ofland to site BMPs
r. is commonly a constraint for new development and significant redevelopment projects).
• Ability to monitor BMP pollutant removal efficiencies.
Study Area
...... _,,
\~ ...r,..J ' I .J
I'
,,,A/\j: r,.,
_J' _,,I'\: Carlsbad
Hydrologlc Unit
Boundary
The focus area of this study is the Agua
Hedionda watershed, located within the
Carlsbad Hydrologic Unit (CHU) (Exhibit
ES-1). The CHU, approximately 210
square miles in area, is formed by a group
of watersheds in northern San Diego
County. The CHU (Region 9, Hydrologic
Unit 04 [904]) is comprised of the
Source: Carlsbad V\'alershed Manoa,,ment Plan (Fetxuarv 2002)
Exhibit ES-1. Carlsbad Hydrologic Unit
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following seven Hydrologic Areas (watersheds): Loma Alta Creek, Buena Vista Creek, Agua
Hedionda and Buena Creeks, Canyons de las Encinas Creek, San Marcos Creek, Cottonwood Creek,
and Escondido Creek. The CHU contains four major coastal lagoons: Buena Vista, Agua Hedionda,
Batiquitos and San Elijo (WURMP, 2003).
Agua Hedionda watershed (Hydrologic Area 904.3) (Exhibit ES-2) is the third largest watershed
within the CHU. The watershed, dominated by Agua Hedionda Creek, extends approximately 11
miles inland from the coast and is about 18,837 acres (29 .4 mi2) in area, comprising 14% of the
Carlsbad Hydrologic Unit {KTU+A, 2002). The Agua Hedionda watershed limits extend across
portions of the City of Carlsbad, City of Vista, City of Oceanside, City of San Marcos, and
unincorporated County of San Diego. Approximately 8,800 acres (13.8 mi2) are located within the
Carlsbad City limits. This study focuses only on the portion of the Agua Hedionda watershed located
in the lower (western) area, primarily within the City of Carlsbad.
Agua Hedionda Lagoon is on the 2002 Clean Water Act Section 303(d) Impaired Waterbodies List
(303(d) List) for bacterial indicators and sedimentation/siltation. Potential sources of bacterial
contamination or adverse water quality are failure of sewage lines, urban runoff, and wildlife waste.
The likely source of sedimentation/siltation is from construction sites, agricultural areas, and erosion
(natural and from construction sites).
Agua Hedionda Creek is on the 303(d) List for total dissolved solids {TDS). Increased levels in TDS
are contributed to urban runoff by pollutants such as salts from streets, fertilizers from lawns and
agricultural areas, sediment caused by soil erosion (natural and from construction sites), and
dissolved organic particles from plant and animal decay that can be washed into the storm drains.
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0
Source: Carlsbad Watershed Management Plan (February 2002)
i __ • ., ___ •
L,·.,,.•
/' / 40ft Contours I\/ Perennial Streams
/\/Intermittent Streams I •I
1111 Waterbodies
1111 1 00yr Flood Plain
500yr Flood Plain
Exhibit ES-2:
Agua Hedionda Watershed
Methodology
The strategy of this study is to identify potential locations for retrofit of existing desilting/detention
basins and then evaluate several treatment BMPs for the sites. All BMP locations, including
subwatershed areas, are located within the City of Carlsbad. The strategic design and installation of
treatment BMPs within the Agua Hedionda watershed will help reduce pollutant loads in urban
runoff before it reaches the Agua Hedionda Lagoon thus improving the overall water quality within
the watershed.
The types ofBMPs analyzed in this study are treatment control BMPs. Treatment control BMPs are
any engineered system designed and constructed to remove pollutants from urban runoff. Four
categories of treatment BMPs were considered for implementation within the scope of the study.
The categories are biofiltration, constructed wetland/wet pond, extended detention, and infiltration.
This study included selecting potential BMP locations, analyzing the locations using GIS, and
calculating BMP size, pollutant load, pollutant load removed and BMP pollutant removal efficiency.
The methodology for these analyses is described in the following subsections.
BMP Location Selection
Since 1980, the City of Carlsbad has required the construction of numerous desilting and/or
detention basins in an effort to reduce the amount of silt deposited in the local lagoons. The
City of Carlsbad is the only municipality in the County of San Diego to implement such an
extensive desilting/detention basin program to improve water quality. In June 2000, the
Public Works Department completed the Desiltation Basin Inventory, which compiled
infom1ation such as size, ownership, and condition of the basins to initiate a formal
monitoring and maintenance program. Fifty-nine basins were inventoried within the City of
Carlsbad, 21 located in the Agua Hedionda watershed.
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Potential locations for BMPs were identified based on review of · the existing
desilting/detention basin study (Carlsbad, 2000), City of Carlsbad staff recommendations,
review of topography in GIS for natural basin areas, and field observations of existing basins
and natural basin areas. Seventeen potential locations were identified and analyzed in this
report. Each location was analyzed to determine the suitability for retrofit and potential water
quality benefit.
The subwatershed areas draining to the potential treatment BMP locations vary in size from
approximately 20 acres (0.03 square miles) to approximately 720 acres (1.2 square miles).
The majority of the subwatershed areas fall in the range of approximately 70 acres (0.1
square miles) to approximately 225 acres (0.35 square miles).
GIS
A Geographic Information System (GIS) based Watershed Information Management System
database (GIS WIMS database) was designed to compile data within the Agua Hedionda
watershed for use in the selection and implementation of treatment BMPs. The following
spatial data was acquired and compiled in a GIS database to form the GIS WIMS database:
topographic data, ortho-rectified aerial imagery, existing storm drain information, land use
coverage, vegetation coverage, and soil coverage.
A GIS computer model, RickBMP, was developed to evaluate and compare various
treatment BMPs at the specific locations identified within the Agua Hedionda watershed.
RickBMP used existing information in the GIS WIMS database coupled with evaluation
matrices for the treatment BMPs from the Carlsbad Storm Water Standards manual to
determine the best treatment BMPs at each location.
Evaluation matrices were developed for each type of treatment BMP and placed into the
model so that each BMP could be rated based on location-specific and BMP-specific criteria
for its effectiveness at each potential treatment location. Each potential location was
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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evaluated for suitability to incorporate each treatment BMP based on the following criteria:
• Estimated number of dwelling units upstream,
• Existing area at the location of the treatment BMP relative to the total
area draining to the BMP,
• Available slope across the potential treatment BMP,
• Soil type at the location of the BMP, and
• Vegetation type at the location of the potential treatment BMP.
A weighted criteria matrix was established to prioritize the treatment BMPs. Weights were
assigned to each criterion based on its importance in design of a treatment BMP. Each
potential location receives a weighted total score for each of the four treatment BMPs
considered. The weighted total score for the treatment BMP indicates its suitability for the
location.
RickBMP was used to evaluate four types of treatment BMPs (biofiltration, extended
detention, wet ponds/wetlands, and infiltration) at all 17 potential treatment locations
identified within the Agua Hedionda watershed. The results of the BMP ranking were used
as an initial indicator to identify the BMP locations with the most potential for water quality
improvement. All BMP pollutant removal calculations were based on the BMP sizing
methods discussed below.
Overview of BMP Sizing and Pollutant Removal Efficiencies
Several calculations were performed to ultimately solve for the pollutant load removed for
each pollutant, by each BMP type, at each potential BMP location. The steps involved in this
calculation included determining for the following parameters: existing BMP size, required
BMP size, existing percent optimal, optimized pollutant removal efficiency, existing BMP
pollutant removal efficiency, pollutant load, and pollutant load removed. Figure ES-1 shows
a flow chart of the relationship between these parameters, which are discussed in detail in
the following subsections .
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FIGURE ES-1. FLOW CHART OF PARAMETERS USED TO CALCULATE POLLUTANT LOAD
REMOVED
Existing
BMPSize
Based on
topography
(length,
width, area,
volume)
Required
BMPSize
Based on
calculations
for length
width, area,
and volume
....
, r
Existing
Percent
Optimal
Equals Existing
BMP Size/
Required BMP
Size* 100%
Optimized BMP
Pollutant Removal
Efficiency
Value for each BMP
type for each
pollutant based on
outside sources1
Existing Pollutant
Removal Efficiency
Equals Existing
Percent Optimal*
Optimized BMP
Pollutant Removal
Efficiency
Sources: Carlsbad Watershed Management Plan, prepared by KTU+A,
Merkel & Associates, and The Rick Alexander Company (February 2002),
and The Practice of Watershed Protection, by Thomas R. Schueler and Heather
K. Holland, Article 64 (2000)
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Pollutant Load
Value for each
pollutant for each
sub watershed
based on
calculations
.... ...
, r
Pollutant Load Removed
Equals Existing Pollutant
Removal Efficiency •
Pollutant Load
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BMPSizing
The purpose of calculating the BMP size was to determine the existing BMP pollutant
removal efficiency, which is discussed further in this section. Two BMP sizes were
calculated for each BMP type at each potential BMP location: required BMP size and
existing BMP size.
The BMP sizing criteria presented in the California Stormwater Quality Association
Stormwater Best Management Practice Handbook for New Development and
Redevelopment, January 2003 (CASQA Handbook) was used to calculate the required BMP
size. Variables affecting the BMP size include BMP area, slope, volume, soil type, and water
quality flow rate or volume. The required BMP size was calculated for each potential BMP
location.
Since none of the potential BMP locations were originally designed for water quality
purposes, limitations at the potential BMP location may preclude optimizing all design
parameters of the treatment BMP (e.g., size, soil type, etc.). Therefore, the existing BMP size
was also calculated. The existing BMP size is based on measurements of topographic maps
to determine length, width, and volume.
Once the required BMP size and the existing BMP size were calculated, the existing percent
optimal was determined, which represents the fraction of the existing BMP size to the
required BMP size. The existing percent optimal signifies the existing potential BMP
location's sufficiency to function as a BMP in terms of size. The value of existing percent
optimal is the existing BMP size divided by the required BMP size, multiplied by 100 to
convert to a percentage. A hypothetical calculation of existing percent optimal is shown in
the following example for an extended detention basin:
The existing BMP size of Basin A is determined by calculating the volume based on
existing topography. The required BMP size is determined by calculating the
required volume using the following equation:
V = 0.083CdA
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Where Vis the volume of the basin (acre-ft), C is the runoff coefficient, dis the
depth of rainfall from the County of San Diego 24-hr 85th percentile storm event (in),
A is the area of the subwatershed (acres), and 0.083 is the conversion factor from
inches to feet. The runoff coefficient and subwatershed area were calculated in GIS
using RickBMP, and the depth of rainfall was determined based on the County of San
Diego 24-hr 85th percentile isopluvial map.
Existing Volume Basin A= 10 ac-fl:1 determined by topography
Required Volume Basin A= 0.083(ft/in)*(0.80)*(0.65 in)*(460 ac)
Required Volume Basin A= 20 ac-ft
Existing Percent Optimal Basin A= (10 ac-ft)/(20 ac-fl:)*(100%)
Existing Percent Optimal Basin A = 50%
If the existing BMP size is 100% optimal, it meets the BMP size requirements. Even if the
existing BMP size is 100% optimal, it will not function as a treatment BMP without specific
modifications, depending on the type of BMP. All vegetation-based BMPs (biofiltration and
wet pond/wetland) require the establishment of particular vegetation types. Extended
detention requires modifications to the inlet/outlet, forebay, etc. These variables will be
analyzed in detail during the final design phase of the specific BMPs.
Pollutant Load
The pollutant load was calculated for each potential BMP location for eleven common urban
runoff pollutants. The pollutant load is based on information presented in the 2000-2001 City
of San Diego and Copermittees National Pollutant Discharge Elimination System (NPDES)
Municipal Storm Water Monitoring Report, prepared by MEC Analytical Systems, Inc.,
2001. This report provides data that associates the event mean concentration (EMC) of the
eleven pollutants for a variety of land use types. This information was applied to each
potential BMP location subwatershed area, and an anticipated pollutant load was calculated.
The calculated pollutant load is only as accurate as the data, and due to the extreme
variability and limitations in the storm water sampling data, is not intended to represent the
true pollutant load. However, it served as a useful tool to compare the pollutant load of the
potential BMP locations to each other.
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•
BMP Pollutant Removal Efficiencies and Pollutant Load Removed
Each type of treatment BMP typically is capable of removing only a portion of the pollutant
load that it receives, even if all design parameters of the treatment BMP at the specific
treatment location are 100% optimized. Therefore, each treatment BMP type has an
efficiency associated with it, specific to each pollutant, and labeled the optimal BMP
pollutant removal efficiency.
Optimized BMP pollutant removal efficiencies for the four types of BMPs and eleven
pollutants analyzed in this report were obtained from the Carlsbad Watershed Management
Plan, prepared by KTIJ+A, Merkel & Associates, and The Rick Alexander Company
(February 2002), and The Practice of Watershed Protection, by Thomas R. Schueler and
Heather K. Holland, Article 64 (2000). These efficiencies represent the optimized BMP
pollutant removal efficiency for each type ofBMP, which was then reduced by the existing
percent optimal calculated for each of the potential BMP locations to obtain the existing
BMP pollutant removal efficiency. A hypothetical example of existing BMP pollutant
removal efficiency is presented below.
Basin A from the example in the BMP Sizing section of this Executive Summary was
calculated to be 50% optimal as an extended detention basin. The optimal BMP
pollutant removal efficiency ofTSS using extended detention is 61 %. The existing
BMP removal efficiency is the product of the calculated existing percent optimal and
the BMP type's optimized BMP pollutant removal efficiency.
Existing BMP Pollutant Removal Efficiency Basin A = (50%)*(61 %)
Existing BMP Pollutant Removal Efficiency Basin A = 30.5%
The existing BMP pollutant removal efficiency was multiplied by the pollutant load to obtain
the pollutant load removed. This calculation produced an immense data set consisting of the
pollutant load removed for each of the 11 pollutants for each of the 4 BMPs at each of the
17 BMP locations. The data set was reduced first by selecting indicator pollutants, then by
selecting the BMP at each potential location that removed the largest load of the indicator
pollutant. A complete table showing the existing BMP removal efficiency, pollutant load,
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and pollutant load removed is provided in Appendix E.
The indicator pollutants were selected based on the pollutants for which the receiving water
body is impaired. The Agua Hedionda Lagoon and Agua Hedionda Creek are the only
waterbodies within the watershed currently listed on the 303(d) List. The Lagoon is listed for
sediment and bacteria, and the creek is listed for TDS. Pollutant load data was not available
for bacteria, therefore total suspended solids (TSS) was selected as the indicator pollutant for
sediment.
Pollutant load data was not available for TDS therefore the indicator pollutant was selected
to represent the TDS load within each subwatershed. The composition of TDS includes
nutrients and dissolved metals. Potential indicator pollutants included in the EMC data set
were Total Zn, N02 & N03, Total Pb, TKN, Total Cu, and Total Cd. Although TDS includes
just the dissolved portion of these constituents, only the total ( dissolved and suspended) data
was available.
Total Zn was selected as the indicator pollutant based on the following logic:
• N02 & N03 were eliminated from consideration as the indicator pollutant because
biofilter and extended detention BMPs exhibit negative removal efficiency for these
pollutants.
• Total Cu was eliminated from consideration because there is no BMP efficiency data
available for infiltration.
• TKN was eliminated from consideration because BMP efficiency data is not available
for any of the BMPs in this analysis.
• Total Cd exhibited very low pollutant loads compared with the other pollutants •
therefore it would not be a conservative choice.
• Total Zn was selected over Total Pb because it exhibited a higher pollutant load and
lower removal efficiency, therefore it would be the most conservative choice.
Potential BMP Location Assessment
The assessment of each potential BMP location entailed review of an aerial photograph and
a GIS-based planned land use map, both with the subwatershed boundaries overlaid. The
aerial photograph (Exhibit ES-3) represented the existing condition and the GIS map (Exhibit
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ES-4) represented the ultimate condition ofland use within the Agua Hedionda watershed.
Each subwatershed was evaluated for existing undeveloped and ultimate developed areas.
The subwatersheds that were primarily comprised of existing undeveloped and ultimate
developed areas were grouped into the "Regional Planning BMP" category. The
subwatersheds that primarily consisted of existing developed areas were grouped into the
"LEAD BMP" category. The subwatersheds that primarily included existing undeveloped
and ultimate undeveloped areas were eliminated from further analysis.
The Regional Planning BMP category applies to the subwatersheds that are currently
undeveloped, but will ultimately be developed. The BMPs in this category will be funded by
and implemented for future development within the subwatershed only. The LEAD category
applies to the subwatersheds that are primarily already developed. The BMPs implemented
in this category will receive storm water treatment credit toward development outside of the
sub watershed.
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Legend:
, 1 Lower (western) ~ ~ Agua Hedionda major basin boundary /Y, Subwatershed boundaries /'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
3000 0 A 3000
Exhibit ES-3: City of Carlsbad
Agua Hedionda Watershed
Existing Land Use
Legend:
Lower (western) l\l Agua Hedionda major basin boundary
l'>l,Subwatershed boundaries "f'v Potential BMP location boundaries
ACT*
C]AGR
AUT
C COM
CJ HEA
HIG
LIG
LOW
MED
-OPE
PAR
STO
D TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
3000 0 3000 6000 Feet
City of Carlsbad
----Corporate Limit
Exhibit ES-4: City of Carlsbad
Agua Hedlonda Watershed
Planned Land Use
•
•
Potential BMP locations were also evaluated based on subwatershed area. Some BMPs were
located downstream of other BMPs; these were labeled cumulative BMPs. The subwatershed
area for the cumulative BMP included the subwatershed area for the upstream BMP. In some
cases, the cumulative subwatershed area included several upstream areas. Analyses were
performed for all potential BMP locations, however, in the final assessment, the upstream
BMP locations were eliminated from further consideration, and only the cumulative BMPs
were recommended.
The final evaluation criterion was pollutant load removed. The existing pollutant removal
load and the optimal pollutant removal load were calculated for each potential BMP location.
The potential BMP locations were sorted based on a combination of the highest pollutant
removal and the difference between existing pollutant removal and optimal pollutant
removal. The locations that had less variability between existing and optimal received a
higher weight than the ones with extreme variability. The potential BMP locations that
discharge to Agua Hedionda Creek were also given extra weight because the BMP would
improve water quality for two impaired water bodies (the creek and Lagoon).
Results and Recommendations
Seventeen potential BMP locations were analyzed in this study. Three locations are recommended
for Regional Planning BMPs, and six locations are recommended for LEAD BMPs. Seven locations
were eliminated because they are located upstream of a cumulative BMP and one location was
eliminated because the subwatershed is not developed and is zoned as open space in the planned
condition, therefore will not be developed. The potential BMP locations are summarized below.
Removal efficiencies are based on size only, and assume that the basin has already been retrofit (e.g.
proper vegetation establishment for biofilters and wet ponds/wetlands, forebay for extended
detention, etc.). Improved removal efficiencies can be achieved in most cases by increasing the size
of the basin .
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Regional Planning BMPs
The Regional Planning BMPs were not ranked because each of these BMPs is recommended.
The retrofit and implementation of these BMPs should be based on when development is
expected to occur.
Basin 20
• Located along the eastern side of Legoland Drive near the intersection of Cannon
Road and Legoland Drive, and north of Basin 17. Basin 20 is a cumulative BMP,
including the subwatershed area of Basin 17.
• Subwatershed area -93 acres.
• Planned land use-44% commercial, 35% industrial, and 21 % undeveloped.
• Recommended BMP is biofiltration.
• For TSS, existing removal efficiency is 31 %, optimal removal efficiency is 68%.
• Removal efficiency can be improved by increasing the length and width of the basin.
Basin 22
• Located along the northern side of Cannon Road, west of Basin 21 and just east of
Car Country Drive. Based on photos from the Desiltation Basin Inventory (Carlsbad,
2000), the basin was unvegetated and contained a small pool of water.
• Subwatershed area -16 acres.
• Planned land use -23% commercial, 44% industrial, and 33% undeveloped.
• Recommended BMP -biofiltration.
• For TSS, existing removal efficiency is 39%, optimal removal efficiency is 68%.
• Removal efficiency can be improved by increasing the length of the basin.
Basin 44
• Located west of the intersection of Cannon Road and El Camino Real, along the west
side of Cannon Road near Macario Drive. Based on photos from the Desiltation
Basin Inventory (Carlsbad, 2000), the basin was vegetated. Basin 44 is a cumulative
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BMP, including the subwatershed area of Basin 45.
• Subwatershed area -117 acres.
• Planned land use -25% commercial, 60% residential, and 15% undeveloped.
• Recommended BMP -biofiltration.
• Basin 44 discharges to Agua Hedionda Creek, therefore a BMP at this location would
benefit water quality in both the creek and the Lagoon.
• For TSS, existing removal efficiency is 68%, which is also the optimal removal
efficiency. For Total Zn, the existing and optimal removal efficiency is 45%.
LEADBMPs
The LEAD projects are ranked in order of recommended implementation based on the
parameters analyzed in this study. Each of the BMP locations should be investigated further
prior to final design.
Basin 90
• Also known as Cannon Lake, located between El Arbul and A venida Encinas and
south of Cannon Road. Basin 90 is a cumulative BMP, including the subwatershed
area of Basin 96.
• Subwatershed area -400 acres.
• Planned land use -56% commercial, 13% industrial, 5% residential, and 26%
undeveloped.
• Recommended BMP -wet pond/wetland.
• For TSS, existing removal efficiency is 79%, which is also the optimal removal
efficiency.
Basin 11
• The eastern-most basin evaluated in this study, located northeast of the intersection
of Palomar Airport Road and El Camino Real, directly North of El Fuerte Street. A
concrete lined swale conveys flow into the basin. The basin is vegetated and contains
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standing water based on photos from the Desiltation Basin Inventory (Carlsbad,
2000).
• Subwatershed area -163 acres.
• Planned land use -11 % commercial, 89% industrial.
• Recommended BMP -biofiltration.
• Basin 11 discharges to Agua Hedionda Creek, therefore a BMP at this location would
benefit water quality in both the creek and the Lagoon.
• For TSS, existing removal efficiency is 66%, optimal removal efficiency is 68%. For
Total Zn, the existing removal efficiency is 44%, and the optimal removal efficiency
is 45%.
• Removal efficiency can be improved by increasing the width of the basin.
Basin 97
• Located south of Tamarack Avenue approximately between La Portalada Drive and
El Camino Real. This area is not an existing detention basin; rather it is currently
used for agricultural purposes. Basin 97 is a cumulative BMP, including the
subwatershed areas of Basins 26, 98, and 99.
• Subwatershed area-719 acres.
• Planned land use -27% commercial, 64% residential, and 9% undeveloped.
• Recommended BMP -biofiltration.
• For TSS, existing removal efficiency is 7%, optimal removal efficiency is 68%. Due
to the high variability in existing and optimal removal efficiencies, further
investigation is required to determine a realistic value.
• Removal efficiency can be improved by increasing the width and length of the basin.
Basin 1
• Located adjacent to the northwest intersection of Jackspar Drive and El Camino Real.
J ackspar Drive is a residential street located midway between Cannon Road and
College Boulevard. Basin 1 supports vegetation and is regularly maintained.
• Subwatershed area -108 acres.
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• Basin 1 discharges to Agua Hedionda Creek, therefore a BMP at this location would
benefit water quality in both the creek and the Lagoon.
• Planned land use -17% commercial, 3% industrial, 60% residential, and 19%
undeveloped.
• Recommended BMP -biofiltration.
• For TSS, existing removal efficiency is 68%, which is also the optimal removal
efficiency. For Total Zn, the existing and optimal removal efficiency is 45%.
Basin 13
• Located on the eastern side of Faraday Avenue, on the southern outskirts of the
business park developments just before the road makes the final bend toward
Cannon. Vegetation and standing water were observed in the basin during a
November 2002 site visit. An irrigation system is installed along the side slopes of
the basin. Basin 13 is a cumulative BMP, including the subwatershed area of Basin
23.
• Subwatershed area -162 acres.
• Planned land use -10% commercial, 59% industrial, 21 % residential, and 9%
undeveloped.
• Recommended BMP -biofiltration.
• For TSS, existing removal efficiency is 37%, optimal removal efficiency is 68%.
• Removal efficiency can be improved by increasing the width and length of the basin.
Basin 5
• Located behind the Carlsbad Research Center near the intersection of College
Boulevard and Faraday. A major branch of the stonn drain system that collects
runoff from the surrounding industrial area drains into Basin 5, which maintains a
pennanent pool of water and provides aesthetic value as a water feature. Basin 5
includes a forebay upstream of the detention basin.
• Subwatershed area -420 acres.
• Planned land use -22% commercial and 78% industrial.
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• Recommended BMP -extended detention.
• For TSS, existing removal efficiency is 12%, optimal removal efficiency is 61 %.
• Removal efficiency can be improved by increasing the storage volume of the basin.
Conclusions
BMPs
All basins are located in the City of Carlsbad throughout the Agua Hedionda watershed.
Seventeen potential BMP locations were analyzed, fourteen existing basins and three natural
basin-like areas. Nine potential BMP locations were selected for implementation. Four types
ofBMPs were analyzed: biofiltration, extended detention, wet pond/wetland, and infiltration.
Biofiltration was the selected BMP for 7 of the 9 potential BMP locations analyzed in this
study. Biofiltration is a flow-based BMP therefore the area required was based on length and
width, rather than volume. Biofiltration and extended detention had similar pollutant removal
efficiencies, but biofiltration was slightly higher. During final design, both biofiltration and
extended detention should be re-evaluated to determine the most effective BMP.
Wet pond/wetlands were not feasible at most locations because of the significant required
volume, approximately 3 times more than that of extended detention. There is also a
requirement of a permanent pool, which would likely require a supplemental water supply
for most locations, especially during the dry season. Basin 90, also known as Cannon Lake,
was the only location that wet pond/wetlands are recommended. Basin 90 already has the
required storage volume and a permanent pool. Basin 5, which also maintains a permanent
pool, does not meet the volume requirements to function as a constructed wetland/wet pond.
The volume requirement for Basin 5 is so extensive that it would be considered a dam
subject to the jurisdictional requirements of the California Department of Water Resources
Division of Safety of Dams.
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•
•
Infiltration was also not feasible in most locations due to unfit soil type. In locations where
the soil type was optimal, the surface area was not large enough. Additional requirements are
placed on infiltration basins, including pretreatment, diversion of dry weather flows, source
control and pollution prevention BMPs to protect groundwater quality, as well as a minimum
vertical distance to groundwater. Due to these constraints, infiltration was not selected for
any of the potential BMP locations.
Closing Statement
This regional treatment BMP feasibility study has been prepared at the request of the City
of Carlsbad to determine the potential for implementation of regional storm water treatment
BMPs as an alternative to on-site treatment BMPs required for new development and
significant redevelopment projects. Existing detention/desilting basins within the Agua
Hedionda watershed will be retrofit to function as BMPs. With the implementation of
regional BMPs throughout the Agua Hedionda watershed, the City of Carlsbad aims to
improve the water quality in the receiving waters ( creeks, Lagoon, and beaches) faster and
more effectively than treatment on a site-by-site basis.
The results of this study indicate that several of the proposed basins have realistic potential
to be retrofit and function as regional storm water treatment BMPs. Some of the
recommended regional BMPs will apply the LEAD method. Since a LEAD project has never
been proposed in San Diego County, this study will be presented to the Regional Board and
the environmental community to obtain support.
This study was a preliminary investigation into the potential for regional treatment of storm
water through retrofit of existing basins. When a regional BMP is selected for
implementation, the basin and subwatershed should be analyzed in greater detail to identify
and examine parameters not included in this study. These parameters include cost analysis,
public interest/public support, accessibility, land ownership, etc. In addition, the following
BMP design parameters should be analyzed: availability of land to increase the size of the
BMP for greater efficiency; design of forebays, inlet and outlet structures for the extended
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detention basins and wet pond/wetlands; as well as installation of irrigation systems and
native vegetation for biofilters. In addition, the type of BMP recommended at each location
in this study should be re-evaluated to ensure that it is the most feasible and most effective
BMP.
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1.1 Background
CHAPTER I
INTRODUCTION
Urban runoff discharged from municipal storm water conveyance systems has been identified by
local, regional, and national research programs as one of the principal causes of water quality
impairments in most urban areas. The City of Carlsbad's storm water conveyance system collects
urban runoff from the streets, rooftops, driveways, parking lots, and other impervious areas, and
flows directly to local beaches and lagoons without receiving treatment. Urban runoff potentially
contains a host of pollutants such as trash and debris, bacteria and viruses, oil and grease, sediment,
nutrients, metals, and toxic chemicals. These contaminants can adversely affect receiving waters,
wildlife, and public health. Urban runoff pollution is not only a problem during rainy seasons, but
also year-round due to many types of urban water use, such as landscape irrigation and car washing,
that discharge runoff to the storm water conveyance system (Carlsbad 2003).
1.2 Municipal Permit
Federal Clean Water Act of 1972 was amended in 1987 to establish a framework for regulating storm
water discharges from municipal, industrial, and construction activities under the National Pollutant
Discharge Elimination System (NPDES) program. Under the Federal Clean Water Act,
municipalities throughout the nation are issued a Municipal Permit. The primary goal of the
Municipal Permit is to reduce polluted discharges from entering the storm water conveyance system
and local receiving and coastal waters and to ensure the beneficial uses of protected receiving waters
(Carlsbad 2003).
In California, the State Water Resources Control Board (SWRCB) administers the NPDES storm
water municipal permitting program. On February 21, 2001 the California Regional Water Quality
Control Board San Diego Region (Regional Board) adopted the California Regional Water Quality
Control Board San Diego Region Order No. 2001-01 NPDES No. CAS0J08758 Waste Discharge
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Requirements for Discharges of Urban Runoff from the Municipal Separate Storm Sewer Systems
(MS4s) Draining the Watersheds of the County of San Diego, the Incorporated Cities of San Diego
County, and the San Diego Unified Port District (Municipal Permit).
1.3 Jurisdictional Urban Runoff Management Program (JURMP) and Watershed
Urban Runoff Management Program (Watershed URMP)
The Municipal Permit adopted in 2001 places greater requirements on new development and
significant redevelopment projects. The Municipal Permit requires the Copermittees to develop and
implement Jurisdictional Urban Runoff Management Programs (JURMP) and Watershed Urban
RW1off Management Programs (Watershed URMP).
The JURMP contains several components, including:
• Land-Use Planning for New Development and Redevelopment
• Construction
• Existing Development
• Education
• Illicit Discharge Detection and Elimination
• Public Participation
• Assessment of Jurisdictional URMP Effectiveness
• Fiscal Analysis
The Land Use Planning for New Development and Redevelopment Component requires each
Copermittee to modify their development project approval processes. Prior to project approval,
Copermittees are tasked with conditioning each proposed project to implement measures that ensure
pollutants and urban runoff from the development will be reduced. This reduction of pollutants is
accomplished through project requirements in local permits. These conditions include specific
requirements for project proponents, such as:
• Implementing site design/landscape characteristics that maximize infiltration, provide
retention, slow runoff and minimize impervious land coverage for all development projects.
• Implementing source control BMPs for all applicable development projects.
• Providing proof of a mechanism which will ensure on going long-term maintenance of all
structural Post-Construction BMPs.
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•
The Municipal Permit acknowledges that urban runoff produced within cities and counties is often
conveyed across jurisdictional boundaries, and requires the mutual development of watershed plans
by the jurisdictions located within the San Diego region's nine hydrologic units. The Carlsbad
Watershed URMP proposes to address water quality problems within the watershed through
extensive monitoring to more accurately define the problems, through jurisdictional implementation
of the JURMPs and SUSMPs, watershed based land use planning, public participation, and
watershed education programs. The Carlsbad Watershed URMP is discussed in greater detail in
Chapter 3.
1.4 Standard Urban Storm Water Mitigation Plan (SUSMP) and Storm Water Standards
Manual
Another constituent of the Land Use Planning for New Development and Redevelopment
Component of the Municipal Permit requires Copermittees to develop Standard Urban Storm Water
Mitigation Plans (SUSMPs) to reduce pollutants from all new development and significant
redevelopment projects falling under specific priority project categories or locations. The SUSMP
includes the use of structural treatment BMPs. These BMPs should be located to infiltrate, filter or
treat a required volume or flow prior to its discharge to any receiving water body supporting
beneficial uses. This volume or flow based BMP treatment is known as the Numeric Sizing Criteria.
The Final Model SUSMP developed by the Copermittees and approved by the Regional Board on
June 12, 2002 provides an implementation guide for compliance with the Municipal Permit. The City
of Carlsbad Public Works Department implemented the Standard Urban Storm Water Mitigation
Plan Storm Water Standards manual (hereafter referred to as the Carlsbad Storm Water Standards
manual) in April 2003, which provides information on how to comply with all of the City's
permanent and construction storm water BMP requirements.
The primary objectives of the Storm Water Standards manual are to:
(1) Effectively prohibit non-storm water discharges; and
(2) Reduce the discharge of pollutants from storm water conveyance systems to the
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maximum extent practicable both during construction and throughout the use of
a developed site. To address pollutants that may be generated from new
development once the site is in use, the Municipal Permit further requires that
the City ensure that BMPs be implemented, as described in the Storm Water
Standards manual. (Carlsbad 2003)
1.5 Regional BMPs and LEAD Method
Although the Final Model SUSMP and Carlsbad Storm Water Standards manual primarily focus on
the storm water requirements of new development and significant redevelopment projects, the
opportunity to comply with storm water requirements on a regional level, rather than a project-by-
project basis, is discussed. The City of Carlsbad encourages this drainage basin approach, and
acknowledges that treating storm water from a hydrologic drainage area, rather than legally defined
parcels, can provide more efficient and cost effective methods of treatment by implementing fewer,
more effective BMPs. The Carlsbad Storm Water Standards manual requires the following criteria
for implementation of a regional BMP:
• All structural treatment control BMPs shall infiltrate, filter, and/or treat the required
runoff volume or flow prior to discharging to any receiving water body supporting
beneficial uses;
• Multiple post-construction structural treatment control BMPs for a single priority project
shall collectively be designed to comply with the numeric sizing treatment standards;
• Shared BMPs shall be operational prior to the use of any dependent development or
phase of development. The shared BMPs shall only be required to treat the dependent
development until each shared BMP is operational. If interim BMPs are selected, the
BMPs shall remain in use until permanent BMPs are operational.
The City of Carlsbad proposes to implement one or more of the proposed regional treatment BMPs
analyzed in this study within the Agua Hedionda Watershed, giving developers the opportunity to
support these BMPs as an alternative to implementing on-site treatment BMPs. This regional
approach will treat a greater quantity of runoff when compared to traditional on-site treatment BMPs.
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The Carlsbad Storm Water Standards manual is based on the Final Model SUSMP. In the Final
Model SUSMP, treatment of storm water on a regional level is identified as the Localized Equivalent
Area Drainage Method (LEAD). The LEAD method is designed to provide more efficient, integrated
storm water treatment, resulting in water quality improvements more quickly. Using the LEAD
Method, treatment BMPs are implemented for entire subwatershed areas. Appendix C of the Final
Model SUS MP discusses the LEAD method, which supports the basis of this regional treatment
BMP feasibility study.
The LEAD method provides numerous benefits, including:
• Promotes watershed-based storm water treatment by treating runoff from entire sub-
drainages;
• Protects receiving water quality and supports designated beneficial uses through
implementation of structural BMPs to the maximum extent practicable;
• Provides the flexibility required for projects in developed areas of the City where existing
infrastructure limits opportunities for efficient BMP implementation;
· • Provides increased and more cost-effective opportunities for BMPs to reside in the
public domain where BMP operation and maintenance can be assured;
• Promotes efficient and integrated implementation of regional solutions in lieu of end-of-
pipe solutions.
A regional BMP must meet the following requirements to be considered as a LEAD project:
• Located within the proximity of the project.
• Discharge to the same receiving water as the project.
• Provide for equivalent or greater pollutant load reduction than at the project site.
• Located in a drainage basin where no other requirement for treatment exists and treat
the entire flow from the drainage basin.
• BMPs must be implemented and operational before the project is complete.
• Treat runoff from an equivalent or greater impervious area than the project.
• The pollutant load reductions obtainable at the alternative LEAD method BMP must be
greater than that obtainable at the project site. (Copermittees 2002)
When the Regional Board approved the Final Model SUSMP (June 2002), each Co-Permittee was
granted the opportunity to submit 3 LEAD pilot projects for approval. At the authoring of this report,
a LEAD project has not yet been proposed to the Regional Board .
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1.6 Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
The City of Carlsbad, California, initiated this water quality study along with an update to its 1994
Master Drainage Plan (MOP). This study includes planning level investigations to identify existing
desilting/detention facilities within the Agua Hedionda watershed, and determine whether
modifications could be made to the basins so that they would function as regional storm water
treatment BMPs. The strategic design and implementation of regional treatment BMPs within the
Agua Hedionda watershed will help reduce pollutant loads before urban runoff reaches the Lagoon.
All BMP locations, including subwatershed areas, are located within the City of Carlsbad.
Any basins that are retrofit into storm water treatment BMPs would serve as regional BMPs, and
treat their respective subwatershed area. Qualifying future development and redevelopment projects
within the Agua Hedionda watershed would support these BMPs, rather than implement on-site
treatment BMPs. The City of Carlsbad is proposing the implementation of regional BMPs for the
following reasons:
• Existing desilting/detention basins located throughout the Agua Hedionda watershed can
be modified for water quality purposes.
• The City will oversee maintenance.
• Maintenance costs are lower for regional BMPs compared with maintenance costs of on-
site treatment BMPs (typically catch basin inserts and hydrodynamic separators).
• Equal and potentially better pollutant removal efficiencies.
• Overall increased improvement to water quality in the receiving waters (Agua Hedionda
Creek and Lagoon).
• Availability ofland to site additional treatment BMPs (availability ofland to site BMPs
is commonly a constraint for new development and significant redevelopment projects).
• Ability to monitor BMP pollutant removal efficiencies.
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2.1 General Description
CHAPTER2
STUDY AREA
The focus area of this study is the Agua Hedionda watershed, located within the Carlsbad Hydro logic
Unit (CHU) (Region 9, Hydrologic Unit 04 [904]). The CHU, approximately 210 square miles in
area, is formed by a group of watersheds in northern San Diego County. The CHU is comprised of
the following seven Hydrologic Areas (watersheds): Loma Alta Creek, Buena Vista Creek, Agua
Hedionda and Buena Creeks, Canyons de las Encinas Creek, San Marcos Creek, Cottonwood Creek,
and Escondido Creek. The CHU contains four major coastal lagoons: Buena Vista, Agua Hedionda,
Batiquitos and San Elijo (WURMP, 2003).
Agua Hedionda watershed (Hydrologic Area 904.3) (Exhibit ES-2) is the third largest watershed
within the CHU. The watershed, dominated by Agua Hedionda Creek, extends approximately 11
miles inland from the coast and is about 18,837 acres (29.4 mi2) in area, comprising 14% of the
Carlsbad Hydrologic Unit (KTU+A, 2002). The Agua Hedionda watershed limits extend across
portions of the City of Carlsbad, the City of Vista, the City of Oceanside, the City of San Marcos,
and unincorporated County of San Diego. Approximately 8,800 acres (13.8 mi2) are located within
the Carlsbad Corporate Boundary. This study focuses only on the portion of the Agua Hedionda
watershed located in the lower (western) area, primarily within the City of Carlsbad.
The Agua Hedionda watershed is relatively narrow at its upper and lower ends with a prominent
bulge at its midpoint. The watershed is divided into two basins. The upper basin (Hydrologic
Subarea 904.32) occupies the narrow upper end of the watershed while the lower basin (Hydrologic
Subarea 904.31) contains the midpoint bulge and tapers toward the coast and Agua Hedionda Lagoon
(KTU+A 2002).
The upper basin contains the upper reaches of Agua Hedionda Creek and the entire drainage of
Buena Creek; the western edge of the upper basin is just downstream of the confluence of these two
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streams. Buena Creek and Agua Hedionda Creek confluence near the intersection of Green Oaks
Road and Sandy Lane in the northeast portion of the watershed within the City of Vista. The upper
basin is characterized by a generally ovoid shape and is much smaller in area than the lower basin.
The upper basin exhibits a varied topography and contains a relatively large amount of undeveloped
open space {KTU+A 2002).
The western end of the lower basin is the widest part of the watershed and tapers into its narrowest
point where it terminates at the Pacific Ocean. The lower basin is similar to the upper basin in that
it also has a varied topography and contains relatively large amounts of undeveloped land. There are
two small reservoirs in the lower basin, Lake Calavera and Squires Reservoir. Agua Hedionda
Lagoon is the most notable feature of the lower basin; this important estuary is divided into three
sections by dikes associated with two highways and a railway (KTU+A 2002).
Agua Hedionda Lagoon is located east of Carlsbad State Beach approximately between Tamarack
A venue and Cannon Road (see Exhibit ES-3). The outlet of the Lagoon intersects Carlsbad State
Beach south of Tamarack Avenue. Recreational uses at Agua Hedionda Lagoon include water skiing,
personal watercraft, boardsailing, kayaking, canoeing, rowing, and fishing. The Lagoon
accommodates approximately 5,700 users annually, based on a 1997 survey provided by the Agua
Hedionda Lagoon Permit Office.
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2.2 Topography
Slopes within the watershed are generally moderate to shallow, however, become fairly steep in the
extreme upper end of the drainage on the slopes of San Marcos Mountains. Slopes are also relatively
steep on the hills along lower Agua Hedionda Creek just inland from the Lagoon and along the bluff
edges fringing the Lagoon itself. The lowest elevation in each watershed is sea level along the shore
of the Lagoon. The highest elevation watershed is approximately 1,500 feet in the San Marcos
Mountains (KTU+A, 2002).
2.3 Storm Flow Rates
The current 100-year peak flow rate in Agua Hedionda Creek at El Camino Real is 9,850 cfs, based
on the effective Federal Emergency Management Agency (FEMA) effective Flood Insurance Study
(FIS) dated June 19, 1997, (Volume I, 4, SummaryofDischarges).
2.4 Land Use
Existing land use varies throughout the watershed, from dense development in the west and
northwest portions of the watershed, to significant agriculture and vacant land in the eastern half of
the watershed. However, pockets oflight industry, commercial and residential land use can be found
throughout the watershed. Existing land use distribution is based on the San Diego Association of
Governments (SANDAG) 1995 Existing Land Use GIS coverage. In the planned condition,
residential developments occupy the area north of the Lagoon, a combination of residential and
commercial developments extend throughout the northeast part of the watershed, and a combination
of light industry and commercial developments maintain the southwest and southeast. Pockets of
open space can be found in the vicinity of the Lagoon, in the southwest, and in the north and
northeast portions of the watershed, comprising approximately 18% of the total watershed area. The
planned land use condition is based on City of Carlsbad Planned Land Use GIS coverage.
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The City of Carlsbad Planned Land Use GIS coverage was used as the source ofland use distribution
for this study to ensure the longevity of the BMPs (in terms of capacity). Exhibit 2-1 shows the
planned land use distribution of the Agua Hedionda watershed within the Carlsbad city limits. Table
2-1 presents a general summary and comparison of the land use distribution between existing
(SANDAG, 1995) and the City of Carlsbad planned conditions. Definitions for the land use
categories are provided in Appendix A.
TABLE 2-1. LAND USE DISTRIBUTION WITHIN THE CITY OF
CARLSBAD AGUA HEDIONDA WATERSHED
1995 Existing SANDAG City of Carlsbad Planned
Land Use Percent of Watershed Percent of Watershed
Total Undeveloped Land 43% 18%
Total Residential 26% 43%
Total Commercial 24%* 11%*
Total Transportation 2% 11%
Total Industrial 4% 18%
"'Note -The percentage of Total Commercial land use decreased in the planned
condition because agriculture was identified as a commercial land use in the exiting
condition, comprising 17% of the total watershed area. The planned condition
contains 0% agriculture.
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Legend:
r, , Lower (western) ~ ~ Agua Hedionda major basin boundary
ACT*
AGR
AUT
COM
D HEA
HIG
LJ LIG
LOW
MED
-OPE
PAR
STO
CJ TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
N
3000 o A 3000 6000 Feet
City of Carlsbad
----Corporate Limit
Exhibit 2-1: City of Carlsbad
Agua Hedionda Watershed
Planned Land Use
•
2.5 Beneficial Uses of Surface Water
Beneficial uses are the uses of water necessary for the survival or well being of humans, plants and
wildlife. These uses of water serve to promote the tangible and intangible economic, social, and
environmental goals of humankind. Beneficial uses can be found in the Water Quality Control Plan
for the San Diego Basin (San Diego Basin Plan) prepared by the California Regional Water Quality
Control Board, dated September 8, 1994. Beneficial uses are separated into categories for inland
surface waters, coastal waters, reservoirs and lakes, and ground waters.
The beneficial uses of Agua Hedionda Lagoon, as listed in the San Diego Basin Plan, are the
following: industrial service supply, contact water recreation, non-contact water recreation,
commercial and sport fishing, aquaculture, estuarine habitat, wildlife habitat, marine habitat,
migration of aquatic organisms, rare, threatened, or endangered species, and shellfish harvesting.
Relevant excerpts from the San Diego Basin Plan containing definitions and listing the beneficial
uses of Agua Hedionda Creek, Buena Creek, Letterbox Canyon, and Agua Hedionda Lagoon are
provided in Appendix B of this report. Table 2-2 summarizes the beneficial uses of these surface
waters .
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TABLE 2-2. SUMMARY OF BENEFICIAL USES OF SURFACE WATERS IN THE
AGUA HEDIONDA WATERSHED
Agua Hedionda Watershed
Location Buena Creek Agua Bedionda
Creek
Hydrologic Unit 904.32 904.32/ Basin Number 904.31
-
Beneficial Uses Municipal and Municipal and
Domestic Supply Domestic Supply
(MUN) (MUN)
Agricultural Supply Agricultural Supply
(AGR) (AGR)
Industrial Services Industrial Services
Supply (IND) Supply (IND)
Contact Water Contact Water
Recreation (REC-1) Recreation (REC-1)
Non-contact Water
Non-contact Water Recreation (REC-2)
Recreation (REC-2)
Warm Freshwater
Warm Freshwater Habitat (WARM)
Habitat (WARM)
Wildlife Habitat
Wildlife Habitat (WILD)
(WILD)
Source: Water Quality Control Plan for the San Diego Basin. Regional Board, 1994.
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Letterbox Canyon Agua Hedionda
Lagoon
904.31 904.31
Municipal and Industrial Services
Domestic Supply Supply (IND)
(MUN)
Contact Water
Agricultural Supply Recreation (REC-1)
(AGR)
Non-contact Water
Industrial Services Recreation (REC-2)
Supply (IND)
Commercial and
Contact Water Sport Fishing
Recreation (REC-1) (COMM)
Non-contact Water Estuarine Habitat
Recreation (REC-2) (EST)
Warm Freshwater Wildlife Habitat
Habitat (WARM) (WILD)
Rare, Threatened,
Wildlife Habitat or Endangered
(WILD) Species (RARE)
Marine Habitat
(MAR)
Aquaculture
(AQUA)
Migration of
Aquatic Organisms
(MIGR)
Shellfish Harvesting
(SHELL)
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CHAPTER3
STORM WATER POLLUTANTS AND MONITORING
3.1 General Descriptions of Pollutants
A wide variety of pollutants can be found in storm water runoff from watersheds in urban areas.
Many common pollutants to urban runoff have been categorized and described in documents such
as the Final Model SUSMP. Sometimes a pollutant in one category can also contain pollutants from
other categories. For example, sediment is a common pollutant in urban runoff, but particles from
other pollutants such as heavy metals and nutrients can attach themselves to sediment particles.
Therefore, when sediment is removed from runoff, other pollutants are potentially removed as well.
The following discussion provides definitions of urban runoff pollutants and potential treatment
BMPs based on the Final Model SUSMP.
3.1.1 Trash and Debris
Trash (such as paper, plastic, polystyrene packing foam, and aluminum materials) and
biodegradable organic matter (such as leaves, grass cuttings, and food waste) are common
waste products on the landscape. The presence of trash and debris may have a significant
impact on the recreational value of a water body and aquatic habitat. Excess organic matter
can create a high biochemical oxygen demand in a stream and thereby lower its water quality.
Also, in areas where stagnant water exists, the presence of excess organic matter can promote
septic conditions resulting in the growth of undesirable organisms and the release of odorous
and hazardous compounds such as hydrogen sulfide.
Trash and debris are best removed with detention basins and filtration, but can also be
removed by drainage inserts or hydrodynamic separators .
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3.1.2 Total Suspended Solids (TSS)
Total suspended solids can include both organic and inorganic material, such as silt, decaying
plant and animal matter, industrial waste, and sewage. Sediment is a common pollutant in
the suspended solids category, and includes all other pollutant particles that attach to the
sediment particles, such as bacteria. Sediment is a soil or another surficial material eroded
and then transported or deposited by the action of wind, water, ice, or gravity. Sediment can
increase turbidity, clog fish gills, reduce spawning habitat, lower young aquatic organism
survival rates, smother bottom dwelling organisms, and suppress aquatic vegetation growth.
Reducing suspended solids load can have a beneficial impact on a number of the pollutant
categories. Suspended solids are best removed through detention basins, infiltration basins,
wetlands, and filtration, but can also be removed by hydrodynamic separators and biofilters.
3.1.3 Total Dissolved Solids (TDS)
Total dissolved solids differ from suspended solids because these particles can pass through
a filter. These materials include carbonate, bicarbonate, chloride, sulfate, phosphate, nitrate,
calcium, magnesium, sodium, organic ions, and other ions. A certain level of these ions in
water is necessary for aquatic life. However, changes in TDS concentrations can be harmful.
Similar to TSS, high concentrations of TDS may reduce water clarity, contribute to a
decrease in photosynthesis, combine with toxic compounds and heavy metals, and lead to an
increase in water temperature. Increased levels in TDS are contributed to urban runoff by
pollutants such as salts from streets, fertilizers from lawns and agricultural areas, sediment
caused by soil erosion and from construction sites, and dissolved organic particles from plant
and animal decay that can be washed into the storm drains. Because of the large amount of
pavement in urban areas (increased impervious area), natural settling areas have decreased,
and dissolved solids are carried through storm drains to creeks, rivers, and the ocean.
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3.1.4 Metals
Metals are raw material components contained in non-metal products such as fuels,
adhesives, paints, and other coatings. Metals of concern include cadmium, chromium,
copper, lead, mercury, and zinc. Lead and chromium have been used as corrosion inhibitors
in primer coatings and cooling tower systems. At low concentrations naturally occurring in
soil, metals are not toxic. However, at higher concentrations, certain metals can be toxic to
aquatic life. Humans can be impacted from contaminated groundwater resources and
bioaccumulation of metals in fish and shellfish. Environmental concerns, regarding the
potential for release of metals to the environment, have already led to restricted metal usage
in certain applications.
Heavy metals can be effectively removed through wetlands and filtration, but can also be
removed by biofilters, detention basins, and infiltration basins.
3.1.5 Bacteria and Viruses
Bacteria and viruses are ubiquitous microorganisms that thrive under certain environmental
conditions. Their proliferation is typically caused by the transport of animal or human fecal
wastes from the watershed. Water containing excessive bacteria and viruses can alter the
aquatic habitat and create a harmful environment for humans and aquatic life. Also, the
decomposition of excess organic waste causes the increased growth of undesirable organisms
in the water.
Bacteria can be effectively removed through infiltration basins, a disinfecting process such
as ultra-violet irradiation or ozonation, but can also be removed by filtration.
3.1.6 Oil and Grease
Oil and grease are characterized as high-molecular weight organic compounds. Primary
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sources of oil and grease are petroleum hydrocarbon products, motor products from leaking
vehicles, esters, oils, fats, waxes, and high molecular-weight fatty acids. Introduction of these
pollutants to the water bodies are made possible through the wide uses and applications of
some of these products in municipal, residential, commercial, industrial, and construction
areas. Elevated concentrations of oil and grease content can negatively impact the wildlife
that comes in contact with surface water, as well as decrease the aesthetic value and quality
of the water body.
Oil and grease are effectively removed through filtration, but can also be removed by
biofilters.
3.1.7 Organic Compounds
Organic compounds are carbon-based. Commercially available or naturally occurring organic
compounds are found in pesticides, solvents, and hydrocarbons. Organic compounds can, at
certain concentrations, indirectly or directly constitute a hazard to life or health. When
rinsing off objects, toxic levels of solvents and cleaning compounds can be discharged to
storm drains. Dirt, grease, and grime retained in the cleaning fluid or rinse water may also
adsorb levels of organic compounds that are harmful or hazardous to aquatic life.
High organic compound removal efficiency has not been achieved by a BMP according to
the Final Model SUSMP. However, organic compounds can be removed at moderate
efficiency through filtration.
3.1.8 Oxygen Demanding Substances
This category includes biodegradable organic material as well as chemicals that react with
dissolved oxygen in water to form other compounds. Proteins, carbohydrates, and fats are
examples of biodegradable organic compounds. Compounds such as ammonia and hydrogen
sulfide are examples of oxygen demanding compounds. The oxygen demand of a substance
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can lead to depletion of dissolved oxygen in a water body and possible development of septic
conditions. The ease of breakdown of the substance often determines its impact as a
pollutant. Leaves and branches break down very slowly in the environment and though they
have a very high oxygen demand during their breakdown, it occurs so slowly that it does not
normally affect the dissolved oxygen in the storm water. Dissolved organic compounds,
such as sugars and methanol, can be rapidly absorbed by bacteria and can cause a more
dramatic effect by quickly reducing dissolved oxygen levels.
High oxygen demanding substance removal efficiency has not been achieved by a BMP
according to the Final Model SUS MP. However, oxygen demanding substances can be
removed at moderate efficiency through detention basins, infiltration basins, wetlands, or
filtration.
· 3.1.9 Pesticides
Pesticides (including herbicides) are chemical compounds commonly used to control
nuisance growth or prevalence of organisms. Excessive application of a pesticide may result
in runoff containing toxic levels of its active component.
According to the Final Model SUSMP, it is unknown whether any treatment BMP is highly,
or even moderately, effective in pesticide removal. However drainage inserts and
hydrodynamic separators are rated as having a low removal efficiency for pesticides.
3.1.10 Effects of Storm Water Pollutants
Toxicity
A vast number of pollutants or secondary effects of pollutants can cause toxicity in storm
water. An oxygen demanding substance is a good example of a pollutant that causes toxicity
as a secondary effect. If bacteria in storm water break down the oxygen demanding
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substance, thereby depleting the oxygen, the storm water will become toxic due to a lack of
oxygen. Since in most cases it is not possible to identify a specific pollutant that causes
toxicity, it is difficult to evaluate treatment BMPs for effectively treating runoff to a nontoxic
state. To date, there is not a treatment technology available to treat specifically for toxicity.
However, relating to the previous example, if a treatment BMP was used remove bacteria,
the oxygen demanding substance would not have been broken down, and the water would
not be toxic due to a lack of oxygen. Therefore, it is possible that toxicity can be reduced or
removed by treating for other known pollutants in the runof£
Eutropliication
Natural eutrophication is the process by which water bodies gradually age and become more
productive. It normally takes thousands of years to progress. However, humans have greatly
accelerated this process in many water bodies around the world. Cultural or anthropogenic
eutrophication is water pollution caused by excessive plant nutrients.
Humans add excessive amounts of plant nutrients (primarily phosphorus, nitrogen, and
carbon) to water bodies in various ways. Runoff from agricultural fields, field lots, urban
lawns, and golf courses are sources of these nutrients. Also, large amounts of phosphates can
be contained in detergents. Untreated, or partially treated, domestic sewage is another major
source. Phosphorus is the key nutrient in eutrophicated water bodies. The excessive growth,
or ''blooms," of algae promoted by these phosphates can lead to oxygen depletion and
resultant organism and fish kills.
3.2 Storm Water Monitoring within the Carlsbad Hydrologic Unit (CHU)
The Carlsbad Watershed URMP (January 2003) provides a detailed description of the water quality
monitoring programs within the CHU, which are on-going in an effort to accurately assess the
condition of water quality within the receiving waters. The Watershed URMP also identifies the
major water quality problems within the CHU, and a plan of action to address these problems. The
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following discussion is based on Section II of the Watershed URMP.
3.2.1 Storm Water Monitoring Programs
The Watershed URMP presents a compiled list of the storm water monitoring programs
throughout the CHU and separates them into three groups: regional, core, and process
studies. Regional monitoring programs encompass a large spatial area and are designed to
answer questions concerning the ecological health of the entire Southern California coastline,
with components including water and sediment quality, fish, benthos, birds, etc. The core
monitoring programs include individual monitoring performed by jurisdictions and
monitoring performed collectively by the Copermittees. Process studies are short-term
evaluations designed to answer specific questions, such as DNA-ribotyping for bacterial
source identification in a watershed and source identification studies used for the
development of Total Maximum Daily Loads (TMDLs) for 303(d) listed impaired water
bodies.
The core monitoring program includes the following components applicable to the CHU:
mass loading station (MLS) monitoring, urban stream bioassessment monitoring, ambient
bay, lagoon, and coastal receiving water monitoring, coastal storm drain outfall monitoring,
and dry weather monitoring.
MLS Monitoring
One of the 12 MLSs within the San Diego area is located in Agua Hedionda Creek in an
earthen channel under the El Camino Real Bridge crossing immediately downstream of the
confluence of Agua Hedionda Creek and Calavera Creek. Runoff from the Agua Hedionda
Watershed, including Buena Creek, drains through one main artery to Agua Hedionda
Lagoon. The contributing runoff area covers over 15,100 acres (11 % of the CHU), however,
much of that located outside the Carlsbad city limits.
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The MLS at Agua Hedionda Creek has been monitored by the Copermittees since the 1998-
1999 wet weather season. The limited historical monitoring record represents four years and
twelve storm events for which sampling has been performed. It is important to note that the
constituents monitored at this location have not been consistent and data gaps exist.
Therefore, the historical monitoring data has limitations in its use for trend analysis.
Samples collected from the MLSs are analyzed for the following parameters:
• Inorganic chemicals -Ammonia, Biochemical Oxygen Demand (BOD), Chemical
Oxygen Demand (COD), total and dissolved phosphorus, nitrate, nitrite, total hardness,
Total Kjedahl Nitrogen {TKN) Total Dissolved Solids (TDS), Total Suspended Solids
(TSS), Turbidity, and detergents (MBAS).
• Metals {Total and Dissolved) -Antimony, arsenic, cadmium, chromium, copper, lead,
nickel, selenium, zinc.
• Organophosphate pesticides -Diazinon, chlorpyrifos.
• Toxicity Testing-Using Ceriodaphnia dubia, Selenastrum capricornutum, and Hyalella
azteca.
Data from the MLS monitoring was used to develop the event mean concentration (EMC)
of 11 pollutants based on land use type. This EMC analysis was conducted by MEC
Analytical Systems, Inc., and the results are presented in the 2000-2001 City of San Diego
and Copermittees National Pollutant Discharge Elimination System (NPDES) Municipal
Storm Water Monitoring Report, prepared by MEC Analytical Systems, Inc., 2001. The EMC
analysis was used in the pollutant load model performed in this regional treatment BMP
feasibility study.
Bioassessment Monitoring
Two of the bioassessment monitoring sites established in 2001 are located within the Agua
Hedionda watershed. These stations are part of a group of 20 monitoring stations and 5
reference stations throughout six hydrologic units in the San Diego area. Bioassessment
monitoring is used to provide a characterization of benthic communities within each
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watershed. Detailed analyses of the bioassessment monitoring conducted in 2001 is
presented in the San Diego County Municipal Co-Permitees 2001-2002 Urban Runoff
Monitoring, Final Report, prepared by MEC Analytical Systems, Inc., 2002 (WURMP
2003).
Coastal Storm Drain Outfall Monitoring
Coastal storm drain outfall monitoring began in 2002. This program monitors bacteria levels
in urban runoff from coastal storm drains. This information can be evaluated in conjunction
with MLS results to identify the higher priority outfalls/watershed areas for remedial efforts.
The program is coordinated with the extensive monitoring program conducted by the San
Diego County Department of Environmental Health (WURMP 2003).
Dry Weather Monitoring
Dry weather monitoring has been conducted within the City of Carlsbad since 1995. In
compliance with the Municipal Permit, the City conducts field screening and analytical
monitoring at various sampling locations during the dry weather season (May 1st through
September 301\ During 2002, twenty of the 74 monitoring locations were located in the
Agua Hedionda watershed. The purpose of the dry weather monitoring program is to detect
and eliminate illicit connections and illegal discharges to the storm drain system, minimizing
the negative impacts of human activities on receiving water bodies. The dry weather
monitoring program consists of the following components:
• Field screening observations.
• Field sampling for analytical testing
• Laboratory analytical testing
Information collected from dry weather monitoring is also used to characterize dry weather
discharges in the storm drain system and identify conveyances that are discharging elevated
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pollutants. Follow-up studies and source investigations are conducted as necessary, to detect
and eliminate the sources of these pollutants (D-Max 2002).
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3.3 Description of Study Area Pollutants of Concern
Pollutants of concern in the Agua Hedionda watershed were determined based on the Water Quality
Control Plan for the San Diego Basin (San Diego Basin Plan), the Clean Water Act Section 303(d)
List, and the Carlsbad Storm Water Standards manual.
3.3.1 San Diego Basin Plan
Based on the San Diego Basin Plan Table 4-8, "Receiving Waters Impacted by Pollution
from Stormwater and Urban Runoff," pollutants of concern in Agua Hedionda Lagoon
include coliform bacteria or other microbes.
3.3.2 Clean Water Act
Agua Hedionda Lagoon and Agua Hedionda Creek are listed as impaired water bodies on the
303(d) List dated March 19, 2002 for the constituents discussed below and shown in Table
3-1 . Agua Hedionda Lagoon was listed on the original 303( d) List dated 1998 for high
coliform count and sedimentation/siltation. Agua Hedionda Creek is listed on the 303( d) List
for total dissolved solids (TDS). Table 3-1 summarizes the 303( d) listed water bodies within
the project area.
TABLE 3-1. 303(d) LISTED WATER BODIES
WITHIN THE AGUA HEDIONDA WATERSHED
Pollutant Year of Listing Location
Sedimentation/Siltation 1998 Agua Hedionda Lagoon
Bacterial Indicators 1998 Agua Hedionda Lagoon
Total Dissolved Solids 2002 Agua Hedionda Creek
Source: 2002 CWA Section 303(d) List of Water Quahty Lnmted Segments, Reg10nal Board, 2003 .
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3.3.3 Watershed URMP
The "potential water quality problems" identified in the Watershed URMP were selected
based on storm water sampling data collected from two MLSs within the CHU. One of the
monitoring stations was the Agua Hedionda Creek station and the other was the Escondido
Creek station. Both stations yielded the same constituents of concern. Table 3-2 is a
reproduction of Table 4-11 from the Watershed URMP, and summarizes the potential water
quality problem, priority, and comments and proposed activity.
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Table 3-2. CARLSBAD WATERSHED URMP -IDENTIFIED WATER QUALITY PROBLEMS
Potential Water High Comments and Proposed Activity
Quality Problem Priority?
Fecal Coliform Yes Fecal Coliform has been identified as a potential constituent of concern (COC) from
or Bacterial the 2002 data assessment. Bacteria are identified as a pollutant in the 1998 303(d) list
Indicators for the watershed. Addressing water quality issues which limit recreational and other
opportunities is important to watershed Copermittees both s a quality oflife issue and
to ensure the long term economic health of the region.
Activity: Bacteria Source Investigation Project
Diazinon No Diazinon levels were exceeded at the two MLSs in the watershed. The six data points
collected so far, although all exceeded water quality standards, are not sufficient to
define a course of action. The data collected in other watersheds indicates that
Copermittees should consider addressing the use of pesticides in the region as an
important component of proactive storm water runoff management activities.
Activity: Integrated Pest Management
Total Dissolved No Municipal and domestic water supplies can be compromised by a variety of factors that
Solids include urban runoff, imported water sources, etc. Monitoring the constituents of
concern in the subwatersheds will assist Copermittees in future planning efforts to
address this water quality issue.
Activity: Data Collection and Management
Sedimentation/ Yes Total suspended solids and turbidity were found to exceed reference standards at the
Siltation Agua Hedionda Creek MLS. Lagoons in the watershed are listed for sedimentation and
siltation. This may be an indication of ecological trends and future assessment can aid
the evaluation of the appropriateness of watershed programs.
Activity: SUSMP Implementation
Activity: Ambient Bay and Lagoon Monitoring Program
Activity: Data Collection and Management
Eutrophication/ No The 303(d) listing several water bodies for Eutrophication. Eutrophication is
Nutrients potentially detrimental to aquatic habitat due to changes in the levels of oxygen as
nutrient levels fluctuate. Some evidence on nitrate and other nutrients found. Collect
existing data to determine cause(s) or sources(s).
Activity: Consider grant funding to implement projects to remediate.
Activity: Data Collection and Management.
Note: A~ua Hedionda La~oon is not on the 303(d) Listfor Eutrophication.
Source: Carlsbad Watershed URMP, 2003.
3.3.4 Carlsbad Storm Water Standards Manual
The Carlsbad Storm Water Standards manual requires that new development or significant
redevelopment in priority project categories implement a treatment BMP selection process
that includes referring to a matrix of anticipated and potential pollutants by land use type to
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determine pollutants of concern for the new development, and a matrix of treatment control
BMPs to select a BMP to remove the pollutants of concern from the new development.
While this study is not prepared for a new development or significant redevelopment project,
the same process can be applied to determine anticipated and potential pollutants by land use
type within the watershed. Table 2 from the Carlsbad Storm Water Standards manual was
reproduced as Table 3-3 below, and shows the priority project categories and general
pollutant categories. Based on the Carlsbad Storm Water Standards manual, the Agua
Hedionda watershed includes all of the land uses that are listed as priority project categories;
therefore, the pollutants of concern include all of the general pollutant categories.
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TABLE 3-3. CARLSBAD STORM WATER STANDARDS-ANTICIPATED AND POTENTIAL POLLUTANTS
GENERATED BY LAND USE TYPE
General Pollutant Categories
Priority Heavy Organic Trash Oxygen Oil& Bacteria
Project Sediment Nutrients Metals Compounds & Demanding Grease & Pesticides
Categories Debris Substances Viruses
Detached
Residential X X X X X X X
Development
Attached
Residential X X X pO> p(2) p X
Development
Commercial
Development
>100,000 ft2
p(I) pO> p(2) X p(S) X p(3) p(S)
Automotive X X(4)(S) X X Repair Shops
Restaurants X X X X
Hillside
Development X X X X X X
>5,000 ft2
Parking Lots p(I) p(I) X X pO> X p(I)
Streets,
Highways, X p(I) X x<◄> X p(S) X
and Freewavs
X = anticipated
P = potential
(3) A potential pollutant if landscaping exists on-site.
(4) A potential pollutant if the project includes uncovered parking areas.
(5) A potential pollutant if land use involves food or animal waste products.
(6) Including petroleum hydrocarbons.
(5) Including solvents.
Source: Carlsbad Storm Water Standards Manual, 2003.
Since the Agua Hedionda watershed contains all of the listed land use types, all of the
general pollutant categories are likely generated. See Exhibit 2-1 for the planned land use
distribution within the Agua Hedionda watershed .
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CHAPTER4
DESCRIPTION OF TREATMENT BMPs
4.1 General BMP Categories
The type of BMPs analyzed for the Agua Hedionda Watershed Storm Water Regional Treatment
BMP Feasibility Study is treatment control BMPs. A treatment control BMP is any engineered
system designed and constructed to remove pollutants from urban runoff. Pollutant removal is
achieved by simple gravitational settling of particulate pollutants, filtration, biological uptake, media
adsorption or any other physical, biological, or chemical process. This report does not preclude the
study of source control or non-structural BMPs such as public education or street sweeping. Source
control BMPs are the first line of defense against storm water pollution.
Four categories of treatment BMPs were considered for implementation within the scope of the study
(biofiltration, extended detention, wet ponds/constructed wetlands, and infiltration), based on
categories listed in the Carlsbad Storm Water Standards manual. The manual requires projects in
priority project categories to select a single or combination of the following treatment control BMPs
for from its "Structural Treatment Control BMP Selection Matrix" (Table 4 of the Carlsbad Storm
Water Standards Manual, reproduced in this report as Table 6-3 in Chapter 6), which includes the
following BMP types: biofilters, detention basins, infiltration basins, wet ponds or wetlands,
filtration, hydrodynamic separators, or drainage inserts. For the purposes of this study, only the first
four categories were analyzed. The intention of this study is to retrofit existing desilting/detention
basins to provide regional treatment of storm water runoff. Therefore, filtration devices,
hydrodynamic separators, and drainage were determined not to be appropriate treatment alternatives.
For each category of treatment BMPs, the discussions in this chapter provide a definition of the
category as it applies to this study, and a summary of the advantages and disadvantages of various
treatment BMPs within the category as they apply to this project. This chapter provides a summary
comparing the advantages and disadvantages of all of the treatment BMPs and a summary of
expected ranges of pollutant removal efficiencies for each treatment BMP.
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4.2 Biofiltration (Carlsbad Storm Water Standards Category: Biofilters)
Biofiltration is a process that uses vegetation for the purpose of slowing water velocity and filtering
out pollutants. The term "biofilter" may represent any of several different treatment BMP designs
for biofiltration. The following biofilters, "grass swale", and "bioretention area or dry swale" as
described below, were considered for this study for the potential BMP locations that do not contain
year-round standing water. Bio:filtration rated as a promising BMP for many potential BMP
locations.
The grass swale bio:filter is typically a section of turf grass or other vegetative cover with a
vegetation height greater than or equal to the depth of flow during a design storm, and parallel to the
treatment area, such as a median between parking rows. Grass swales typically have limited removal
efficiencies for most pollutants because they do not retain or infiltrate runoff. Their functionality
is generally limited to :filtration of sediment and pollutants that are attached to sediment.
Additionally, grass swales may export bacteria if they are used as recreational areas for dog walking.
The bioretention area or dry swale biofilter is a vegetated channel that temporarily retains water,
allowing time for it to filter through the channel substrate. The bioretention area or dry· swale
biofilter may also be considered a linear wetland. Bioretention areas can be expected to have greater
pollutant removal capabilities than grass swales. The pollutant removal capabilities of a bioretention
area or dry swale are similar to the pollutant removal capabilities of wetlands because they employ
retention, biological uptake of pollutants, filtration by vegetation and by soil, and potentially
infiltration.
4.2.1 Pollutant Removal Capabilities
Biofilters are rated in the Carlsbad Storm Water Standards manual as having medium
removal efficiency for sediment, heavy metals, oil and grease, low removal efficiency for
nutrients, trash and debris, and oxygen demanding substances, and unknown removal
efficiency for organic compounds, bacteria, and pesticides. However, the Carlsbad Storm
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Water Standards manual does not define the term "biofilter" or clarify any difference
between grass swales and bioretention areas. The advantages and disadvantages of the
biofilter designs that were considered are described below in Table 4-1. All statements
regarding installation or maintenance cost or levels of difficulty to install or maintain are
relative to other treatment BMPs considered in this study only.
TABLE 4-1. ADV ANT AGES AND DISADVANTAGES OF BIOFILTRATION DESIGNS
Grass Swale .. -
a --Advantages Disadvantages a
Low cost to install and maintain • Not practical for large watersheds due to large area
Easy to maintain (although frequent maintenance requirement. Practical application is limited to
is required, typical maintenance activity includes watersheds up to approximately 5 acres.
mowing grass, and can be incorporated into • Easily short circuited by concentrated flow
regular landscaping schedules) • Low pollutant removal capability
Aesthetic value • May export bacteria, especially if anfmal sources
within swale generate bacteria or if swale is used
for dog walking.
• Requires large area
• Requires frequent maintenance
• Requires irrigation
Bioretention Area or Dry Swale
dvantages Disadvantages Ill
a
High pollutant removal capability because biological • Should be located adjacent to ex1stmg riparian
uptake, filtration, and infiltration processes are vegetation to facilitate volunteer riparian vegetation
incorporated growth; however, this may create construction
Reduces channel erosion by reducing channel slope access conflicts
Low to medium cost to install depending on the • Requires extensive environmental permitting
channel gradient, low cost to maintain • Requires large area
Easy to maintain when designed properly, should
only require maintenance of vegetation including
removing/replacing invasive species until
appropriate vegetation is established.
Maintenance needs diminish with time as appropriate
vegetation matures
Potential habitat value
Aesthetic value
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4.3 Constructed Wetlands (Carlsbad Storm Water Standards Category: Wet Ponds or
Wetlands)
Wet ponds are constructed basins that maintain a permanent pool of water throughout the year and
treat incoming storm water runoff by settling and algal uptake. The primary pollutant removal
mechanism in a wet pond is settling. Constructed wetlands are similar to wet ponds, but are
shallower and support more vegetation. As storm water runoff enters the constructed wetland, it is
temporarily retained and pollutant removal is achieved by biological uptake of pollutants, filtration
by vegetation and by soil, and potentially infiltration. Constructed wetlands are among the most
effective storm water treatment practices in terms of pollutant removal capabilities, and may also
offer aesthetic value and habitat value. A disadvantage of constructed wetlands as a retrofit
treatment BMP in an already developed region is the large area and volume required. To provide
treatment for a drainage area, the constructed wetland area should be between approximately 1 % to
2% of the drainage area. Some compact package treatment wetlands exist that are commonly known
as "wetlands in a barrel." Wetlands in a barrel are self-contained wetland systems, approximately
10-feet in diameter, that promote settling of larger particles and biological uptake of smaller
particles. However, the treatment area that the package can handle is limited, typically one to two
units are required per acre of drainage area.
Due to the extensive required area/volume, wetlands/wet ponds are only feasible at one potential
BMP location (Basin 90/Cannon Lake) within the Agua Hedionda Creek watershed.
4.3.1 Pollutant Removal Capabilities
Wet ponds or wetlands are rated in the Carlsbad Storm Water Standards manual as having
high removal efficiency for sediment and heavy metals, medium removal efficiency for
nutrients, and oxygen demanding substances, and unknown removal efficiency for organic
compounds, trash and debris, bacteria, oil and grease, and pesticides. The Carlsbad Storm
Water Standards manual does not clarify any difference between wet ponds or wetlands. The
advantages and disadvantages of wet ponds, wetlands, and wetlands in a barrel are described
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below in Table 4-2. All statements regarding installation or maintenance cost or levels of
difficulty to install or maintain are relative to other treatment BMPs considered in this study
only.
TABLE 4-2. ADV ANT AGES AND DISADVANTAGES OF
CONSTRUCTED WETLAND DESIGNS
Wet Ponds ---Advantages Disadvantages
Low to medium cost to install and maintain • Low pollutant removal capability
May be created as a retrofit to an existing detention • Detriment to flood control when located in lower
basin portion of watershed
Flood control benefit if located in upper portion of • Difficult to maintain permanent pool in arid climate
watershed or if drainage area is too small
Aesthetic value • Requires large area
• May provide mosquito habitat
• Potential to attract wildlife habitat, which may be an
additional source of bacteria
Constructed Wetlands --.,
R 11 m --Advantages Disadvantages a
·"
High pollutant removal capability • Should be located adjacent to existing riparian
Low to medium cost to install depending on the vegetation to facilitate volunteer riparian vegetation
channel gradient, low cost to maintain growth; however, this may create construction
Easy to maintain when designed properly should access conflicts
only require maintenance of vegetation including • Requires extensive environmental permitting
removing/replacing invasive species until • Requires large area
appropriate vegetation is established • Difficult to maintain permanent pool in arid climate
Maintenance needs diminish with time as appropriate or if drainage area is too small
vegetation matures • May export nutrients
Potential habitat value • Potential to attract wildlife habitat, which may be an
Aesthetic value additional source of bacteria
Public education value
Wetlands in a Barrel -----Advantages Disadvantages
High pollutant removal capability • Not practical for large watersheds because many
Compact unit does not require large area units would be required (1 to 2 units per impervious
Easy to maintain acre are required). Practical application is limited to
watersheds up to approximately 5 acres
• Units contain many small parts with high potential
for clogging; therefore units may require frequent
maintenance
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4.4 Extended Detention Basins (Carlsbad Storm Water Standards Category: Detention
Basins)
Detention basins are constructed basins that provide storage volume for storm water runoff to reduce
the peak flow rate of runoff. Extended detention basins are basins whose outlets have been designed
to detain the storm water runoff from a water quality design storm for a minimum period of time
( e.g., 24 hours) to allow particles and associated pollutants to settle. Wet extended detention ponds
(wet ponds) maintain a permanent pool. Wet ponds are discussed above. Dry extended detention
ponds do not maintain a permanent pool. Extended detention was on of the most promising BMPs
for many of the potential BMP locations.
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4.4.1 Pollutant Removal Capabilities
Detention basins are rated in the Carlsbad Storm Water Standards manual as having high
removal efficiency for sediment, trash and debris, medium removal efficiency for nutrients,
heavy metals, oxygen demanding substances, oil and grease, and unknown removal
efficiency for organic compounds, bacteria, and pesticides. The advantages and
disadvantages of dry extended detention ponds are described below in Table 4-3. All
statements regarding installation or maintenance cost or levels of difficulty to install or
maintain are relative to other treatment BMPs considered in this study only.
TABLE 4-3. ADVANTAGES AND DISADVANTAGES OF
DRY EXTENDED DETENTION POND DESIGNS
Dry Extended Detention Pond
Advantages Disadvantages
Low to medium cost to install, low cost to maintain • Requires large area
May be created as a retrofit to an existing detention • Low pollutant removal effectiveness expected
basin • Potential detriment to flood control when located in
Easy to maintain lower portion of watershed
Potential flood control benefit if located in upper
portion of watershed
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4.5 Infiltration (Carlsbad Storm Water Standards Category Infiltration Basins)
Infiltration is the downward entry of water into the surface of the soil or the flow of a fluid through
pores or small openings, commonly used in hydrology to denote the flow of water into soil material.
Infiltration BMPs are systems in which the majority of the dry weather urban runoff or runoff from
small storms is infiltrated into the soil rather than discharged to a surface water body. Infiltration
systems may include ponds, vaults, trenches, or dry wells.
Infiltration is not a viable option for any of the potential BMP locations due to soil type, area
restraints, and limitations set forth in the Carlsbad Storm Water Standards manual.
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4.5.1 Pollutant Removal Capabilities
Infiltration is rated in the Carlsbad Storm Water Standards manual as having high removal
efficiency for sediment and bacteria, medium removal efficiency for nutrients, heavy metals,
and oxygen demanding substances, and unknown removal efficiency for organic compounds,
trash and debris, oil and grease, and pesticides. The advantages and disadvantages of
infiltration are described below in Table 4-4. All statements regarding installation or
maintenance cost or levels of difficulty to install or maintain are relative to other treatment
BMPs considered in this study only.
TABLE 4-4. ADV ANT AGES AND DISADVANTAGES OF INFll,TRATION DESIGNS
Infiltration -Advantages Disadvantages
High pollutant removal capability • Requires permeable soils which are not common in
San Diego
• Potential groundwater interaction; should only be
used where groundwater is a minimum of 10 feet
below the bottom of the deepest portion of the
infiltration basin
• Difficult to maintain, requires fine grading for
replacement of filter material
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CHAPTERS
GENERAL DESCRIPTION OF POTENTIAL BMP LOCATIONS
5.1 Basis for Identification of Locations
The approach of this study was to identify locations of current desilting/detention basins and evaluate
their suitability to be retrofit for use as regional treatment BMPs. Potential locations for BMPs were
identified based on review of existing desilting/detention basins located within the Agua Hedionda
watershed (Carlsbad, 2000), City of Carlsbad staff recommendations, review of topography in GIS
for natural basin areas, and field observations of existing basins and natural basin areas. Thirty-six
basins were identified, and 17 potential locations were analyzed in this report. Each location was
analyzed to determine the suitability for retrofit and potential water quality benefit.
5.1.1 Carlsbad Desiltation Basin Inventory
Since 1980, the City of Carlsbad has required the construction of numerous desilting and/or
detention basins in an effort to reduce the amount of silt deposited in the local lagoons. The
City of Carlsbad is the only municipality in the County of San Diego to implement such an
extensive desilting/detention basin program to improve water quality. In June 2000, the
Public Works Department completed the Desiltation Basin Inventory, which compiled
information such as size, ownership, and condition of the basins to initiate a formal
monitoring and maintenance program. Fifty-nine basins were inventoried within the City o ·
Carlsbad, 21 located within the Agua Hedionda watershed.
5.1.2 Field Visits
Rick Engineering Company conducted field visits of the 21 existing basins to identify the
existing basins that could be further analyzed. A determination of potential for each basin
was made based on visual observation of the basin and the tributary existing and ultimate
land uses. Nine of the 21 existing basins were eliminated from further study for the following
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reasons:
• Located immediately adjacent to the Lagoon, retrofit activities may disturb existing
habitat within the Lagoon;
• Located at the top of a slope;
• Located within close proximity to a residential area;
• Basin no longer exists.
Twelve of the 21 existing basins from the Desi/talion Basin Inventory were identified as
opportunities for water quality enhancement. In addition, three other opportunities for water
quality enhancement were identified during the field visits, for a subtotal of 15 potential
BMP locations (21 existing basins from the Desi/talion Basin Inventory, minus 9 existing
basins from the Desiltation Basin Inventory, plus 3 other opportunities from field visits).
Prior to field verification, these locations were initially identified by visual examination in
GIS of tributary canyons on maps showing topographic contours, orthophoto, and storm
drains. Two locations appeared to have natural basin-like contours and large capacity, and
could be retrofit as extended detention basins or wet ponds/constructed wetlands. The third
location is currently a concrete-lined channel that could be replaced with an earthen and/or
riprap-lined channel incorporating a series of drop structures to reduce the channel slope and
establish vegetation.
5.1.3 Recommendations by City Staff
City staff identified two additional potential BMP locations, resulting in a total of 17
potential BMP locations. One basin is an existing desilting basin connected to the storm
drain system that did not appear in the Desi/tation Basin Inventory (Basin 96). The other
potential BMP location is Cannon Lake (Basin 90), which is also connected to the storm
drain system. These two locations were included in the BMP analysis.
5.2 Identification of Potential BMP Locations
Using the methods previously described a total of 17 potential treatment BMP locations were
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identified. The subwatershed areas draining to the potential BMP locations vary in size from
approximately 20 acres (0.03 square miles) to approximately 720 acres (1.2 square miles). The
majority of the subwatershed areas fall in the range of approximately 70 acres (0.1 square miles) to
approximately 225 acres (0.35 square miles). The potential BMP locations and the subwatershed
boundaries are shown on Exhibit ES-3 and Exhibit ES-4.
Some potential BMP locations are located downstream of other potential BMP locations. This occurs
in Basins 13, 20, 21, 44, 90, and 97. All data associated with the subwatersheds of these basins, such
as area and land use distribution, is cumulative. For example, Basin 20 is located downstream of
Basin 17. Therefore, data associated with the subwatershed draining to Basin 20 includes data
associated with the subwatershed draining to Basin 17.
Table 5-1 presents the 17 potential treatment locations that were identified for the Agua Hedionda
watershed, along with their associated subwatershed areas, and the existing basin area. The potential
treatment BMP location names are consistent with the names given in the Desi/tation Basin
lnvento,y whenever possible (Carlsbad, 2000). Basins not identified in the inventory were given
arbitrary numerical names .
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TABLE 5-1. POTENTIAL BMP LOCATIONS IDENTIFIED IN THE
AGUA HEDIONDA WATERSHED
Potential BMP Location
Name
Basin 1
Basin 5
Basin 11
Basin 13
Basin 17
Basin 20
Basin 21
Basin 22
Basin 23
Basin 26
Basin 44
Basin 45
Basin 90
Basin 96
Basin 97
Basin 98
Basin 99
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Total Subwatershed
Area (mi2)
0.17
0.66
0.25
0.25
0.03
0.14
0.16
0.03
0.05
0.12
0.18
0.11
0.62
0.04
1.12
0.18
0.43
Rick Engineering Company-Water Resources Division 41
Subwatershed
Area (acres)
108
420
163
162
19
93
104
16
33
79
117
72
400
23
719
117
274
Existing Basin Area
(acres)
0.6
2.4
1.7
0.5
0.5
0.2
0.1
0.1
0.4
0.3
1.8
0.5
8.4
0.3
0.3
0.4
0.3
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CHAPTER6
IDENTIFICATION OF POLLUTANTS OF CONCERN AND BMP
SELECTION PROCEDURE
6.1 Carlsbad Storm Water Standards Manual Selection Procedure
Procedures outlined in the Carlsbad Storm Water Standards manual were used to determine the
pollutants of concern and appropriate BMPs for each potential BMP location subwatershed area.
Although this is a regional study with already developed subwatersheds, these procedures can be
used to identify pollutants generated within the subwatersheds and applicable treatment BMPs.
These procedures are listed below:
• Determine whether the project is a priority project or a standard project by completing
the "Stormwater Requirements Applicability Checklist" located in Appendix A of the
Carlsbad Storm Water Standards manual.
Each potential BMP location analyzed in this study would be considered a "priority
project" based on the checklist.
• Determine the types of BMPs (site design, source control, individual priority project,
treatment control) required for the project type based on those listed in Table 1 of the
Carlsbad Storm Water Standards manual.
Table 1 shows the types ofBMPs that are required for each priority category. Since
this study is not a new development or redevelopment project, site design, source
control, and individual priority project categories are not applicable. However, these
types of BMPs would be required for the new development or significant
redevelopment projects that will use the regional treatment BMPs.
• Determine anticipated and potential pollutants from Table 2 of the Carlsbad Storm
Water Standards manual.
Table 6-1 is a comprehensive list of the pollutants that may be generated within each
subwatershed. The table was derived from "Table 3-3. Anticipated and Potential
Pollutants Generated by Land Use Type." in Chapter 3 of this report, which is a
reproduction of"Table 2." from the Carlsbad Storm Water Standards manual. Table
3-3 presents anticipated and potential pollutants based on land use type. Since the
subwatersheds in this study are larger than a single development, they contain
multiple land use types, therefore are more likely to generate the entire array of
pollutants.
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TABLE 6-1. POTENTIAL POLLUTANTS WITHIN POTENTIAL BMP LOCATION SUBWATERSHEDS
BASED ON CARLSBAD STORM WATER STANDARDS MANUAL
Sediment Nutrients Heavy Organic Trash& Oxygen Oil & Bacteria Pesticides
Metals Compounds Debris Demanding Grease & Viruses
Substances
BASIN 1 X X X X X X X X X
BASIN 5 X X X X X X X X X
BASIN 11 X X X X X X X X X
BASIN 13 X X X X X X X X X
BASIN 17 X X X X X X X X
BASIN20 X X X X X X X X X
BASIN21 X X X X X X X X X
BASIN22 X X X X X X X X X
BASIN23 X X X X X X X X X
BASIN26 X X X X X X X X X
BASIN44 X X X X X X X X X
BASIN 45 X X X X X X X X X
BASIN90 X X X X X X X X X
BASIN96 X X X
BASIN97 X X X X X X X X X
BASIN98 X X X X X X X X X
BASIN99 X X X X X X X X X
• Identify the receiving water that each potential BMP location discharges to.
The receiving water for each of the potential BMP locations is ultimately the Agua
Hedionda Lagoon: Region 9, Hydrologic Unit 04, Hydrologic Area 3, Hydrologic
Subarea 1 (904.31 ). Basins 1, 11, 44, and 45 discharge to Agua Hedionda Creek,
Hydrologic Subarea (904.31 ), prior to discharge to the Lagoon.
• Identify receiving waters that are listed on the most recent 303(d) List and identify the
pollutants for which the water bodies are impaired.
Agua Hedionda Lagoon is on the 2002 303(d) List for bacterial indicators and
sedimentation/siltation. Agua Hedionda Creek is on the 2002 303(d) List for total
dissolved solids (TDS). Table 6-2 shows the pollutants of concern based on the
303( d) list for each potential treatment location.
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•
TABLE 6-2. POTENTIAL POLLUTANTS WITHIN
POTENTIAL BMP LOCATION SUBWATERSHEDS
BASED ON 2002 303(d) LIST
Sediment Bacteria TDS
BASIN 1 X X X
BASIN 5 X X
BASIN 11 X X X
BASIN 13 X X
BASIN 17 X X
BASIN20 X X
BASIN 21 X X
BASIN22 X X
BASIN23 X X
BASIN26 X X
BASIN44 X X X
BASIN 45 X X X
BASIN90 X X
BASIN96 X X
BASIN97 X X
BASIN98 X X
BASIN99 X X
• Evaluate conditions of concern in a drainage study report that considers the project
area 's location, topography, soil and vegetation conditions, percent impervious area,
natural and infrastructure drainage features, and any other relevant hydrologic and
environmental factors to be protected specific to the project area's watershed. Other
requirements of the drainage study are discussed in Section C.l.C of the Carlsbad Storm
Water Standards manual.
Because this study is in the planning phase, it was not appropriate to prepare a
drainage study. A drainage study will still be required for future new development
and significant redevelopment projects that will utilize the regional treatment BMPs.
• Incorporate site design and source control BMPs.
Site design, source control, and individual priority project category BMPs are not
applicable to this study, however will be required for future new development and
significant redevelopment projects that will utilize the regional treatment BMPs.
• Design a single or combination of treatment control BMPs designed to infiltrate, filter,
and/or treat runoff from the project footprint to one of the "Numeric Sizing Treatment
Standards" listed in Table 3 of the Carlsbad Storm Water Standards manual. Table 3
states that BMPs must be sized based on volume or flow rate. Design volume-based
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BMPs to mitigate the volume of runoff produced from a 24-hour 85th percentile storm
event, as determined from isopluvial maps contained in the County of San Diego
Hydrology manual. Design flow-based BMPs to mitigate the maximum flow rate of
runoff produced from a rainfall intensity o/0.2 inches of rainfall per hour for each hour
of a storm event.
The volume-based BMPs analyzed in this study ( extended detention, wetland/wet
pond, and infiltration) were sized using the 85th percentile rainfall depth. The flow-
based BMP (biofiltration) was sized using 0.2 inches per hour. The County of San
Diego 85th percentile isopluvial map showing the City of Carlsbad is provided in
Exhibit 6-1.
• Compare the list of pollutants/or which the receiving water body is impaired (303(d)
List).
The pollutants of concern are sediment and bacteria for all potential BMP locations
and, in addition, TDS for Basins 1, 11, 44, and 45. Although several pollutants of
concern were identified based on the Carlsbad Storm Water Standards manual, those
pollutants on the 303(d) List were determined to be the most significant, and were
the basis of the BMP selection.
• Use Table 4 in the Carlsbad Storm Water Standards manual to select a BMP that
maximizes pollutant removal.
Table 4 has been reproduced and is shown in this report as Table 6-3.
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•
Legend:
Lower (western) l\l Agua Hedionda major basin boundary N Subwatershed boundaries
/\/ Potential BMP location boundaries
Precipitation
0.60 Rainfall (inches)
Date of Aerial Photograph: February 2002
Source of lsopluvial Map:
County of San Diego, July 2, 2001
3000 0 A 3000 6000 Feet
Exhibit 6-1 City of Carlsbad
24-hour, 85th Percentile
Depth of Rainfall lsopluvial Map
TABLE 6-3. STRUCTURAL TREATMENT CONTROL BMP SELECTION MATRIX
Pollutant
of Treatment Control BMP Categories
Concern
Bio filters Detention Infiltration Wet Ponds Drainage Filtration Hydrodynamic
Basins Basins11> or Wetlands Inserts Separator
Svstems12>
Sediment M H H H L H M
Nutrients L M M M L M L
Heavy M M M H L H L Metals
Organic u u u u L M L Compounds
Trash & L H u u M H M Debris
Oxygen
Demanding L M M M L M L
Substances
Bacteria u u H u L M L
Oil& M M u u L H L Grease
Pesticides u u u u L u L
(I) Including trenches and porous pavement.
(2) Also known as hydrodynamic devices and baffle boxes.
L: Low removal efficiency
M: Medium removal efficiency
H: High removal efficiency
U: Unknown removal efficiency
Sources: Guidance Specifying Management Measures/or Sources of Nonpoint Pollution in Coastal Waters (1993),
National Stonnwater Best Management Practices Database (200 I), and Guide for BMP Selection in Urban Developed
Areas (2001).
Source: Carlsbad Storm Water Standards Manual, 2003.
The four types of BMPs analyzed in this study were Bio-filters, Detention Basins, Infiltration Basins,
and Wet Ponds or Wetlands. Drainage Inserts, Filtration, and Hydrodynamic Separators were
eliminated because they did not support the goals of the study, to evaluate the potential to retrofit an
existing desilting/detention basin for use as a regional treatment BMP.
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CHAPTER7
METHODOLOGY OF BMP AND POLLUTANT REMOVAL ANALYSIS
7.1 General
The basis of analysis for this study was a Geographic Information System (GIS) database. The GIS
database was used for two purposes, first to process the program RickBMP, discussed in detail in
this chapter, second to extract specific information such as area and land use specific to each BMP
location subwatershed area for further analysis to determine BMP sizing, pollutant loading, and BMP
removal efficiencies.
7.2 GIS WIMS Database
A GIS-based Watershed Information Management System database (GIS WIMS database) was
designed to compile data such as topographic contours, ortho-rectified aerial imagery, existing storm
drain information, land use coverage, vegetation coverage, and soil coverage. This data is discussed
below.
7.2.1 Topographic Data
The topographic data used to prepare the GIS based MDP for the City of Carlsbad and the
Agua Hedionda Watershed Storm Water Regional Treatment BMP Feasibility Study was
supplied by the City of Carlsbad in GIS format with two-foot contours and spot elevations.
The topographic data was flown on July 17, 2001 by Merrick & Company and is on the NAD
83 datum. The topographic data was used to establish the drainage basin boundaries and the
slope of the drainage basin in the area of the proposed treatment BMPs.
7.2.2 Ortho-Rectified Aerial Imagery
The ortho-rectified aerial imagery was provided by the City of Carlsbad. This information
was generated by Merrick & Company when preparing the topographic data.
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7.2.3 Existing Storm Drain Information
The City of Carlsbad supplied the existing storm drain information from their GIS database.
This information contains storm drain pipes, sizes, inlet and outlet locations, material types,
structure types, and invert elevations (where available) for existing storm drains within the
City. The storm drain information was compiled in 2001 and is currently undergoing field
verification. Therefore, the data is not yet comprehensive for the entire study area. Data for
some storm drains may not be included because they could not be located in the field or the
data could not be obtained from record drawings. The storm drain information was suitable
to determine drainage boundaries and approximate slopes. However, storm drain
information must be verified from field surveys for use during final design of any treatment
BMP.
7.2.4 Land Use Coverage
The ultimate watershed land use coverage was obtained from the City of Carlsbad in GIS
format. The land use data is based on the planned condition. The land use coverage was
used in the model to evaluate treatment BMPs and to predict influent pollutant loads to the
treatment BMPs.
7 .2.5 Vegetation Coverage
The vegetation coverage was obtained from the City of Carlsbad in GIS format. This
information was utilized in the RickBMP analysis of the treatment BMPs.
7 .2.6 Soil Coverage
The soil coverage was obtained from the San Diego Association of Governments
(SANDAG) for areas outside the corporate boundaries and the City of Carlsbad for areas
within the corporate boundaries, in GIS format. The SANDAG soil coverage is based on the •
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United States Department of Agricultural Soil Survey for San Diego County. This
information was used as a factor to evaluate the potential treatment BMPs.
7.3 RickBMP
A GIS computer model, RickBMP, was used to evaluate and rank the four types of treatment BMPs
from the Carlsbad Storm Water Standards manual (biofiltration, extended detention, wet
ponds/wetlands, and infiltration) at all 17 potential BMP locations that were identified in the
watersheds. The ranking of each type of BMP at each potential BMP location was an initial
indicator of which BMPs might be appropriate for each location. Further analyses were preformed
to size each BMP at each location and are discussed in further detail in this chapter.
7.3.1 Purpose ofRickBMP
RickBMP was developed to evaluate and compare various treatment BMPs at specific
.. potential treatment locations discussed in Chapter 6. RickBMP used existing information
in the GIS WIMS database coupled with drainage basin information developed for the
potential BMP locations and evaluation matrices for the BMPs from the Carlsbad Storm
Water Standards manual to detennine the best treatment BMPs for the potential locations.
7.3.2 Model Development
In order to evaluate the potential BMP locations that were identified in the Agua Hedionda
watershed, the drainage basin boundaries for each potential BMP location (subwatersheds)
were added to the GIS WIMS database and evaluation matrixes were set up to pull
information from the GIS WIMS database for each of these subwatersheds.
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7.3.3 Subwatersheds
The subwatersheds for the potential BMP locations identified in Chapter 6 were prepared in
AutoCAD and overlain into the GIS WIMS database model as a drawing exchange file ( dxf).
Arclnfo was used to read the dxf coverage as polygons. All of the data utilized in the GIS
WIMS database such as land use, soil type, and vegetation coverage was then compiled to
analyze the characteristics of each subwatershed. The existing basin area at each potential
treatment BMP was also prepared in AutoCAD and read by· Arclnfo in the same manner as
the subwatershed boundaries. Each potential treatment BMP polygon was linked to the
polygon for the corresponding subwatershed and calculations were performed that compared
the characteristics of the potential treatment BMP with the characteristics of the area draining
to it.
7.3.4 Evaluation Matrices for Potential Treatment BMPs
Evaluation matrices were developed for each type of treatment BMP and placed into the
model so that each treatment BMP could be rated based on location-specific and BMP-
specific criteria for its effectiveness at each potential treatment location. These criteria are
described below.
Each potential treatment location was evaluated for suitability to incorporate each treatment
BMP based on the following criteria: estimated number of dwelling units upstream ( dwelling
units), area of the potential BMP relative to the total area draining to the potential treatment
BMP (relative area), available slope across the potential treatment BMP (slope), soil type at
the location of the potential treatment BMP (soil type), and vegetation type at the location
of the potential treatment BMP (vegetation). These criteria were processed by GIS globally
for all treatment BMPs and potential treatment locations. A weighted criteria matrix was
established to prioritize the treatment BMPs. Weights were assigned to each criterion based
on its importance in design of a treatment BMP. The criterion weights varied based on the
treatment BMP. Table 7-1 summarizes the weights assigned to each criterion for each •
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treatment BMP. The reasoning behind the selected weights for each criterion is detailed
below.
TABLE 7-1. CRITERION WEIGHTS BY TREATMENT BMP
Treatment Dwelling Relative Slope Soil Vegetation Total BMP Units Area Type
Biofilters 0.3 0.1 0.5 0.05 0.05 1.0
Wetlands 0.3 0.25 0.2 0.05 0.2 1.0
Detention 0.0 0.6 0.35 0.05 0.0 1.0
Basins
Infiltration 0.0 0.2 0.1 0.7 0.0 1.0
Dwelling Units Criterion -The dwelling units criterion is based on the concept that a certain
amount ofbaseflow will be required to support a vegetative system such as a biofilter or a
wetland, and that this baseflow will typically originate from over-irrigating in residential
areas. The estimated number of dwelling units in a basin is calculated in the GIS processing
by multiplying the total acreage of low, medium, and high density residential land use in the
basin by estimated densities for these land uses. The following densities were selected from
the 2003 San Diego County Hydrology Manual: 2.9 dwelling units per acre or less, 14.5
dwelling units per acre or less, and 43.0 dwelling units per acre for low, medium, and high
land use, respectively. This criterion was given a weight of 30 percent for the biofilter
treatment BMP and the wetland treatment BMP because these vegetative systems will require
baseflow for support. This criterion was given a weight of0 percent for the remaining BMPs
( detention and infiltration) because these treatment BMPs do not rely on a constant source
of water to support vegetation.
Relative Area Criterion -The relative area criterion is based on the amount ofland estimated
to be required to site the treatment BMP. The area of each potential treatment BMP location
and the area of the subwatershed draining to each potential treatment BMP location were
calculated by the GIS program. The equations for this criterion vary by treatment BMP. To
provide treatment through a biofilter or wetland, the treatment BMP acreage should be
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between 1-2 percent of the acreage of the basin. For infiltration and detention, a certain
amount of storage volume is required to accommodate the storm water.
In order to determine the appropriate volume, numeric sizing criteria from the Final Model
SUS MP were considered, as well as standards set forth by the Division of Safety of Dams
(DSOD). The numeric sizing criterion selected from the Final Model SUSMP for design of
volume-based treatment BMPs such as detention basins or infiltration basins is that the
treatment BMP should treat the volume of runoff equivalent to 0.6 inches of rainfall over the
subwatershed area, converted to runoff by multiplying by the runoff coefficient for the
subwatershed area. The DSOD standards were considered to preclude designing any berms
that would be considered jurisdictional dams. Based on DSOD criteria, the storage volume
depth must be less than 25 feet. Therefore, a potential treatment BMP location with relative
area that can provide storage volume equal to 0.6 inches ofrainfall multiplied by the runoff
coefficient for the subwatershed and the subwatershed area in. less than 25 feet of depth
would meet this criterion. The rainfall of0.6 inches is built into the RickBMP software. City
of Carlsbad procedure is to use the 24-hour 85th percentile depth of rainfall based on County
of San Diego isopluvial maps (Exhibit 6-1 ). Since the RickBMP results were only used as
an initial indicator in the BMP analysis process, the RickBMP program was not modified to
use the 85th percentile. However, all BMP sizing calculations presented in this report were
based on the 85th percentile rainfall for the location of the BMP, which varied between 0.6
and 0.69.
Slope Criterion -The slope criterion also varies by treatment BMP. For biofiltration and the
wetlands, the flattest slope is ideal to slow the velocity through the treatment BMP and
provide the longest hydraulic residence time. These treatment BMPs may still be
constructible at steeper slopes; however, the construction and maintenance costs would be
higher. For detention and infiltration, a moderate slope is acceptable. However, at the steeper
slopes, less volume may be available for storage within the 25-foot height limit discussed
previously for the relative area criterion.
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In order to calculate the slope across the treatment BMPs, the upstream and downstream
node elevations were manually recorded in the treatment BMP polygons in AutoCAD (the
elevations were not calculated by GIS). The slope was calculated by the GIS program by
detennining the length across the treatment BMP and dividing by the difference in elevation.
Soil Criterion -The soil criterion considers the hydrologic properties of the soil in the
treatment BMP polygon, which describe the soils capacity to store and/or infiltrate water.
This criterion is the most critical factor for the success of an infiltration treatment BMP.
Therefore, this criterion carries a 70 percent weight for the infiltration treatment BMP. If the
soil is not penneable, infiltration will not occur in a 48-72 hour time period. Any longer
ponding time may lead to mosquito breeding and vector problems. For the other treatment
BMPs, a less penneable hydrologic soil group is acceptable. The hydrologic soil group(s)
at the potential treatment BMP location were calculated by the GIS program.
Vegetation Criterion -Scruh chaparral, riparian, and bog marsh are the three indicator
vegetation species used in the GIS analysis. Bog marsh was not present within any of the
basins therefore will not be discussed further in this report. The vegetation criterion was not
given a high criterion weight for any of the treatment BMPs because the resolution of the
vegetation layer is very generalized. However, this criterion was considered for the
vegetative treatment BMPs (the biofilter treatment BMP and the wetland treatment BMP)
because in order for these systems to become established they should be located in proximity
to existing environments that support vegetation. This criterion also considers that chaparral
should not be disturbed. Therefore the GIS processing of this criterion included searching
for the presence of riparian vegetation and/or chaparral, and gave priority to sites with
riparian vegetation and without chaparral. The vegetation group(s) at the potential treatment
BMP location were calculated by the GIS program. This criterion was given a weight of 0
for the non-vegetative treatment BMPs .
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The vegetation coverage data is not completely up to date, therefore vegetation establishment
should be determined through a biological survey during detailed design of each treatment
BMP.
7.3.5 RickBMP Results
During the GIS processing routine, each potential treatment location receives a raw score
between O and 10 (10 being the best) for each criterion for each of the four treatment BMPs
shown in Table 7-1. The scores are determined by equations designed to estimate how well
a potential treatment location meets the criteria for siting the treatment BMP based on the
GIS attributes in the subwatershed polygons and potential treatment BMP polygons. The
equations vary based on the treatment BMP. The raw scores for each criterion are then
multiplied by the associated weights for the criterion for the treatment BMP, and the
weighted results for each criterion are summed, resulting in a weighted total score for the
treatment BMP. The equations used in the GIS program to assign the raw scores are provided
in Appendix C. Each potential treatment BMP location receives a weighted total score for
each of the four treatment BMPs considered. The weighted total score for the treatment
BMP indicates its suitability for the location.
7.3.6 Auditing ofRickBMP Results
Several criteria that are also important to the siting of a treatment BMP such as existing
water quality data, public interest/public support, cost, land ownership, accessibility, and
existing vegetation health are not processed in the GIS program. Therefore, further study of
the sites is required after the results of the GIS program are tabulated. The post GIS
processing activities include evaluation of existing water quality data, site visits, public
information meetings, and cost estimating, which would be conducted during the design
phase. Within the scope of this study, each BMP was further analyzed based on the sizing
criteria presented in the CASQA BMP Handbook for New Development and
Redevelopment.
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•
•
•
Also, data utilized and/or processed by GIS, such as vegetation coverage and dwelling units,
may not be accurate due to outdated sources and generalization. All data presented in this
study should be re-evaluated during the design phase of the BMPs.
7.4 Overview ofBMP Sizing and Pollutant Removal Efficiencies
Several calculations were performed to ultimately solve for the pollutant load removed for each
pollutant, by each BMP type, at each potential BMP location. The steps involved in this calculation
included determining for the following parameters: existing BMP size, required BMP size, existing
percent optimal, optimized pollutant removal efficiency, existing BMP pollutant removal efficiency,
and pollutant load. Figure 7-1 is flow chart that shows the relationship between these parameters,
which are discussed in detail in the following subsections .
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FIGURE 7-1. FLOW CHART OF PARAMETERS USED TO CALCULATE POLLUTANT LOAD
REMOVED
Existing
BMPSize
Based on
topography
(length,
width, area,
volume)
Required
BMPSize
Based on
calculations
for length
width, area,
and volume
-
Existing
Percent
Optimal
Equals Existing
BMP Size/
Required BMP
Size* 100%
Optimized BMP
Pollutant Removal
Efficiency
Value for each BMP
type for each
pollutant based on
outside sources1
..
Existing Pollutant
Removal Efficiency
Equals Existing
Percent Optimal *
Optimized BMP
Pollutant Removal
Efficiency
Sources: Carlsbad Watershed Management Plan, prepared by KTU+A,
Merkel & Associates, and The Rick Alexander Company (February 2002),
and The Practice of Watershed Protection, by Thomas R. Schueler and Heather
K. Holland, Article 64 (2000)
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Pollutant Load
Value for each
pollutant for each
subwatershed
based on
calculations
Pollutant Load Removed
Equals Existing Pollutant
Removal Efficiency *
Pollutant Load
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7.5 BMP Sizing
The purpose of calculating the BMP size was to determine the existing BMP pollutant removal
efficiency, which is discussed further in this section. Two BMP sizes were calculated for each BMP
type at each potential BMP location: required BMP size and existing BMP size.
The BMP sizing criteria presented in the California Stormwater Quality Association Stormwater
Best Management Practice Handbook for New Development and Redevelopment, January 2003
(CASQA Handbook) was used to calculate the required BMP size. Variables affecting the BMP size
include BMP area, slope, volume, soil type, and water quality flow rate or volume. The required
BMP size was calculated for each potential BMP location.
Since none of the potential BMP locations were originally designed for water quality purposes,
limitations at the potential BMP location may preclude optimizing all design parameters of the
treatment BMP (e.g., size, soil type, etc.). Therefore, the existing BMP size was also calculated. The
existing BMP size is based on measurements of topographic maps to determine length, width, and
volume.
The sizing parameters for each type of treatment BMP are discussed in the following subsections.
7 .5.1 Biotlltration
The biofilter BMPs were sized based on the design and sizing guidelines for "Vegetated
Swale" in the CASQA handbook. The guidelines for required size include:
• Flow rate determined by local requirements. The flowrate for the biofilter BMPs
analyzed in this study was calculated by the following equation:
Q =CIA
Where Q is the flowrate (cfs), C is the runoff coefficient for the subwatershed, I is
the intensity (in/hr), and A is the area of the subwatershed (acres). The runoff
coefficient was calculated in GIS using RickBMP as a function of land use and soil
type, the intensity was provided in the Carlsbad Storm Water Standards manual (0.2
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in/hr), and the area was calculated in GIS using RickBMP.
• Swale should be designed so that the water level does not exceed 2/3rds the height
of the grass· or 4 inches, whichever is less, at the design treatment rate. It was
assumed that the maximum water level was 4 inches.
• Longitudinal slopes should not exceed 2.5%. Longitudinal slopes were assumed to
be 2.5% for all potential BMP locations even though most existing slopes were less.
A steeper slope typically results in a shallower depth.
• Trapezoidal channels are recommended. Trapezoidal channels with 3: 1
(horizontal:vertical) side slopes were assumed for all potential BMP locations.
• The width of the swale should be determined using Manning's equation:
V = (1.486/n)*(R213)*(S112)
Where Vis the velocity of flow (feet per second), n is Manning's coefficient, R is the
hydraulic radius (feet), and Sis the longitudinal slope.
The CASQA handbook specifies a value of 0.25 for Manning's n. The Rick
Engineering Company DOS-based program Trapezoidal Channels was used to solve
Manning's equation. Input parameters included flowrate, bottom width, Manning's
n, longitudinal slope, and side slopes. The bottom width was the only variable in the
calculation. The existing bottom width measured from a topographic map was
initially input at each potential BMP location. The flow depth calculated by the
program was the governing parameter; if the calculated flow depth was greater than
4 inches, the bottom width was increased and the program was re-run. This iteration
continued until the flow depth was less than or equal to 4 inches. A flow depth ofless
than or equal to 4 inches on the first iteration indicated an adequate existing bottom
width.
• A hydraulic residence time of 10 minutes was assumed at each potential BMP
location. The hydraulic residence time and velocity were used to determine the
required length of the biofilter. The trapezoidal channels program calculated the
velocity. The required length is the product of hydraulic residence time and velocity,
or 100-feet, whichever is greater.
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• Other design parameters outlined in the CASQA handbook essential to the
biofiltration BMP design were not considered in these preliminary BMP sizing
calculations. The BMP size (area or volume) was considered as the only parameter
in the sizing calculations because often times the required area is not available, and
adequate size is the first step toward a successful BMP. All other BMP guidelines
must be analyzed during final design of the selected BMPs.
The existing BMP size was determined based on measurements oflength and width from a
topographic map.
7.5.2 Extended Detention
The extended detention BMPs were sized based on the design and sizing guidelines for
"Extended Detention Basin" in the CASQA handbook. The guidelines for required BMP size
include:
• Capture volume determined by local requirements. The Carlsbad Storm Water
standards manual specifies that volume-based BMPs shall be sized based on the 24-
hr 85th percentile storm event depth of rainfall. This value varies between 0.60 in and
0.69 in within the Agua Hedionda watershed. The required volume (capture volume,
or water quality volume) was calculated using the following equation:
V=0.083CdA
Where V is the volume of the basin (acre-ft), C is the runoff coefficient, d is the
depth of rainfall from the 24-hr 85th percentile storm event (in), A is the area of the
subwatershed (acres), and 0.083 is the conversion factor from inches to feet. The
runoff coefficient and subwatershed area were calculated in GIS using RickBMP, and
the depth of rainfall was determined based on the County of San Diego 24-hr 85 th
percentile isopluvial map.
• Several other guidelines are outlined in the CASQA h~dbook, such as length to
width ratio and basin depth, however volume was the only parameter considered for
this preliminary extended detention sizing.
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• Other design parameters outlined in the CASQA handbook essential to the extended
detention BMP design were not considered in these preliminary BMP sizing
calculations. The BMP size (area or volume) was considered as the only parameter
in the sizing calculations because often times the required area is not available, and
• adequate size is the first step toward a successful BMP. All other BMP guidelines
must be analyzed during final design of the selected BMPs.
The existing extended detention basin size was determined by calculating the volume of the
basin. Volume was calculated by determining the area of the basin at each topographic
contour using a planimeter, and inputting the data into the computer program PondPack by
Haestad Methods.
7.5.3 Wet Ponds/Constructed Wetland
The wet pond/wetland BMPs were sized based on the design and sizing guidelines for "Wet
Ponds" and "Constructed Wetlands" in the CASQA handbook (the volume parameter is the
same for both BMPs). The guidelines for required size include:
• Capture volume determined by local requirements. The capture volume is the same
for wet ponds/constructed wetlands as extended detention basins.
• Permanent pool volume is recommended equal tb twice the capture volume. The
capture volume was multiplied by two to get the recommended permanent pool
volume. The total volume is the sum of the capture volume and permanent pool
volume.
• Other design parameters outlined in the CASQA handbook essential to the wet
pond/wetland BMP design were not considered in these preliminary BMP sizing
calculations. The BMP size ( area or volume) was considered as the only parameter
in the sizing calculations because often times the required area is not available, and
adequate size is the first step toward a successful BMP. All other BMP guidelines
must be analyzed during final design of the selected BMPs.
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The existing basin size was the same as that calculated for extended detention.
7 .5.4 Infiltration
The infiltration BMPs were sized based on the design and sizing guidelines for "Infiltration
Basin" in the CASQA handbook. The guidelines for required size include:
• Capture volume determined by local requirements. The capture volume is the same
for infiltration basins as wet ponds/constructed wetlands and extended detention
basins.
• Basin invert area was determined by the following equation:
A =V/kt
Where A is the invert area (acres), Vis the capture volume (acre-ft), k is 0.5 times
the lowest field-measured hydraulic conductivity (ft/hr), and t is the drawdown time
(48 hr). Volume was calculated using the equation specified in subsection 7.3.1 in
this chapter. The minimum acceptable hydraulic conductivity of0.043 ft/hr was used
because field data is not available.
• Other design parameters essential to the BMP design were not considered in the
infiltration BMP sizing calculation. The BMP size (area or volume) was considered
as the only parameter in the sizing calculations because often times the required area
is not available, and adequate size is the first step toward a successful BMP. All
other BMP guidelines must be analyzed during final design of the selected BMPs.
The existing basin size was the same as that calculated for extended detention.
7 .6 BMP Optimization
Once the required BMP size and the existing BMP size were calculated, the percent optimal was
determined, which represents the fraction of the existing BMP size to the required BMP size. The
value of percent optimal is the existing BMP size divided by the required BMP size, multiplied by
100 to get a percentage. A calculation of percent optimal is shown in the following example for an
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extended detention basin:
The existing BMP size of Basin A is determined by calculating the volume based on existing
topography. The required BMP size for extended detention is determined by calculating the
required volume using the following equation:
V=0.083CdA
Where Vis the volume of the basin (acre-ft), C is the runoff coefficient, dis the depth of
rainfall from the 24-hr 85 th percentile storm event (in), A is the area of the subwatershed
(acres), and 0.083 is the conversion factor from inches to feet. The runoff coefficient and
subwatershed area were calculated in GIS using RickBMP, and the depth of rainfall was
determined based on the County of San Diego 24-hr 85th percentile isopluvial map.
Existing Volume Basin A= 10 ac-ft
Required Volume Basin A= 20 ac-ft
Percent Optimal Basin A= (10 ac-ft)/(20 ac-fl:)*(100%)
Percent Optimal Basin A = 50%
If the existing BMP size is 100% optimal, it meets the size requirements of the BMP. Even if the
existing BMP size is 100% optimal, it will not function as a treatment BMP without specific
modifications, depending on the type of BMP. All vegetation-based BMPs (biofiltration and wet
pond/wetland) require the establishment of particular vegetation types. Extended detention requires
modifications to the inlet/outlet, forebay, etc. These variables will be analyzed in detail during the
final design phase of the specific BMPs.
7.7 Pollutant Load Modeling
A spreadsheet-based model was used to model the pollutant loads from the subwatersheds of the
potential treatment locations within the Agua Hedionda watershed. The spreadsheet model
calculates pollutant loads in tons or pounds for a given depth of rainfall over the subwatershed area.
The spreadsheet model is similar to that used by the City of San Diego and Copermittees National
Pollutant Discharge Elimination System (NPDES) Municipal Storm Water Monitoring Program.
The pollutant load was calculated for each potential BMP location for eleven common urban runoff
pollutants. The pollutant load is based on information presented in the 2000-2001 City of San Diego
and Copermittees National Pollutant Discharge Elimination System (NPDES) Municipal Storm
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Water Monitoring Report, prepared by MEC Analytical Systems, Inc., 2001 (MEC Report). This
report provides data that associates the event mean concentration (EMC) of the eleven pollutants for
a variety of land use types. This information was applied to each potential BMP location
subwatershed area, and an anticipated pollutant load was calculated. The calculated pollutant load
is only as accurate as the data, and due to the extreme variability and limitations in the storm water
sampling data, is not intended to represent the true pollutant load. However, it served as a useful tool
to compare the pollutant load at the potential BMP locations with each other.
The pollutant loads for each subwatershed are based on the land use distribution within the
subwatershed, the event mean concentration (EMC) of pollutant that originates from each land use
type, and the volume of runoff from the subwatershed. The required input parameters for this type
of pollutant load modeling are: the area of each type of land use within the subwatershed in acres,
the EMC for the modeled pollutants that originate from each type ofland use in terms of mass per
volume of runoff ( e.g., milligrams per liter), the runoff coefficient for each land use type, and the
depth of rainfall in the subwatershed. The area of each land use type within the subwatershed was
calculated by GIS. The EMC for the pollutants for each land use was obtained from the above-
mentioned MEC Report Table 7-2 presents the land use categories that were used in this study and
the EMC data assigned to each land use type based on data from the MEC Report. The runoff
coefficient for each subwatershed was calculated by GIS based on the land use types and soil types
within the subwatershed.· The depth of rainfall selected for modeling is the 24-hour 85th percentile,
based on the numeric sizing criteria for volume-based treatment BMPs given in the Storm Water
Standards manual. The land use areas, runoff coefficients, and depths of rainfall for the
subwatersheds are presented in Table 7-3 . The resulting data set was comprised of a pollutant load
(tons or pounds) for the eleven pollutants for each subwatershed area .
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TABLE 7-2. EMC FOR COMMON URBAN RUNOFF POLLUTANTS BASED ON LAND USE TYPE
Land Use Category TSS (mg/I) BOD COD Total P Diss. P
(ml?/1) (ml?/U (m~/1) (mg/I)
Active Parks (ACT) 111 19 90 0.52 0.3
Passive Parks (PAS) 111 19 90 0.52 0.3
Open Space Reserves and 69 12 17 0.16 0.11
Preserves (OPE)
Agriculture (AGR) 69 12 17 0.16 0.11
Low Density Residential 196 17 93 0.41 0.31
(10W)
Medium Density Residential 196 17 93 0.41 0.31
(MED)
High Density Residential 196 17 93 0.41 0.31
ffiIG)
Commercial (COM) 111 19 90 0.52 0.3
Storefront Commercial (STO) 142 9.7 103 0.44 0.17
Auto Dealerships (AUT) 142 9.7 103 0.44 0.17
Parking (PAR) 142 9.7 103 0.44 0.17
Freeway (FRE) 142 9.7 103 0.44 0.17
Other Transportation and 131 15 66 0.53 0.36
Maintenance (TRA)
Light Industry (LIG) 131 15 66 0.53 0.36
Heavy Industry (HEA) 131 15 66 0.53 0.36
Military (MIL) 131 15 66 0.53 0.36
Water(WAT) 0 0 0 0 0
Vacant and Undeveloped 69 12 17 0.16 0.11
Land(VAC)
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TKN NO1&NO3 Total Pb
(ml?/1) (ml?/1) (ul?/1)
2.11 1.05 16
2.11 1.05 16
0.79 1.1 23
0.79 1.1 23
2.17 1.12 23
2.17 1.12 23
2.17 1.12 23
2.11 1.05 16
1.781 0.833 23
1.781 0.833 23
1.781 0.833 23
1.781 0.833 23
1.76 1.12 31
1.76 1.12 31
1.76 1.12 31
1.76 1.12 31
0 0 0
0.79 1.1 23
Total Cu Total Zn Total Cd
(ul?/1)
27
27
15
15
34
34
34
27
52
52
52
52
31
31
31
31
0
15
(ul?/1) (ul?/1)
254 0.75
254 0.75
46 0.38
46 0.38
276 0.67
276 0.67
276 0.67
254 0.75
368 2
368 2
368 2
368 2
143 0.71
143 0.71
143 0.71
143 0.71
0 0
46 0.38
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TABLE 7-3. LAND USE DISTRIBUTION BY SUBWATERSHED AREA
Subwatershed Runoff 24-hour 85th Sum of
Coefficient Percentile Area Land Use Distribution Area (acres)
Rainfall (acres) AGR AUT COM IDG LIG LOW MED Depth (in)
BASIN 1 0.42 0.650 108.05 0 0 0 0 3.10 0 65.28
BASIN 5 0.63 0.650 420.08 0 0 32.18 0 325.79 0 0
BASIN 11 0.56 0.690 163.34 0 0 0 0 146.05 0 0
BASIN 13 0.38 0.640 129.03 0 0 0 0 95.78 9.37 25.38
BASIN 17 0.36 0.615 19.17 0 0 15.82 0 0 0 0
BASIN20 0.48 0.613 92.87 0 0 36.86 0 32.92 0 0
BASIN21 0.34 0.613 104.41 0 0 36.93 0 33.89 0 0
BASIN22 0.37 0.610 16.39 0 0 0 0 7.20 0 0
BASIN23 0.36 0.645 32.68 0 0 0 0 0 0 17.93
BASIN26 0.53 0.656 79.02 0 0 0 0 0 0 56.80
BASIN44 0.34 0.638 45.01 0 0 6.15 54.69 0 0 15.68
BASIN 45 0.33 0.643 72.40 0 0 5.29 29.22 0 0 6.54
BASIN90 0.65 0.600 399.68 22.62 84.60 30.94 0 51.11 0 21.18
BASIN96 0.34 0.600 22.72 22.62 0 0 0 O.Ql 0 0
BASIN97 0.53 0.643 719.34 0 0 66.96 52.86 0 0 407.68
BASIN98 0.51 0.663 116.86 0 0 35.01 0 0 0 46.85
BASIN99 0.55 0.656 274.47 0 0 0 7.34 0 0 182.81
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OPE TRA VAC
20.93 18.74 0
0 62.11 0
0 17.28 0
14.63 16.56 0
3.13 0 0.22
18.83 4.03 0.22
25.50 7.87 0.22
5.36 3.83 0
9.28 5.47 0
5.07 17.15 0
18.14 22.75 0
16.68 14.67 0
102.45 86.78 0
0 0.09 0
65.69 126.15 0
20.79 14.22 0
39.36 44.96 0
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7 .8 BMP Pollutant Removal Efficiency
Each type of treatment BMP typically is capable of removing only a portion of the pollutant load that
it receives, even if all design parameters of the treatment BMP at the specific treatment location are
optimized. Therefore, each treatment BMP has an efficiency associated with it, specific to each
pollutant. The efficiency of the BMP may also be reduced due to site-specific limitations.
Optimized removal efficiencies for the four types of BMPs and eleven pollutants analyzed in this
report were obtained from the Carlsbad Watershed Management Plan, prepared by KTU+A, Merkel
& Associates, and The Rick Alexander Company (February 2002), and The Practice of Watershed
Protection, by Thomas R. Schueler and Heather K. Holland, Article 64. These BMP pollutant
removal efficiencies represent the optimal BMP removal efficiency, which was then reduced by the
percent optimal for each of the potential BMP locations to obtain the existing BMP pollutant
removal efficiency. Table 7-4 shows the BMP pollutant removal efficiencies that were used in this
study.
TABLE 7-4. BMP POLL UT ANT REMOVAL EFFICIENCIES
Optimized Removal Efficiency
Pollutant Biofllter Wet Extended Detention Inflltration
Pond
TSS 68% 79% 61% 95%
BOD 69% 45% 28% 88%
COD 69% 45% 28% 88%
Total P 29% 49% 20% 100%
Diss. P 40% 62% -11% 100%
TK.N NIA NIA NIA NIA
N02&N03 -25% 36% -2% 82%
Total Pb 67% 74% 54% 98%
Total Cu 42% 58% 29% NIA
TotalZn 45% 65% 29% 99%
Total Cd 42% 50% 32% NIA
These optimized removal efficiencies were applied to each potential BMP location to determine the
existing BMP pollutant removal efficiency by multiplying the optimized removal efficiency shown
in Table 7-4 by the percent optimal. The optimized removal efficiency is equal to the value in Table
7-4, and was used to detennine the highest anticipated pollutant removal at each location, if the BMP
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were 100% optimized. A hypothetical example of existing BMP pollutant removal efficiency is
presented below.
Basin A from the example in the BMP Sizing section 7.6 of this chapter was calculated to be
50% optimal as an extended detention basin. Toe optimal BMP pollutant removal efficiency
ofTSS using extended detention is 61 %. Toe existing BMP removal efficiency is the product
of the calculated existing percent optimal and the BMP type's optimized BMP pollutant
removal efficiency.
Existing BMP Pollutant Removal Efficiency Basin A= (50%)*(61 %)
Existing BMP Pollutant Removal Efficiency Basin A= 30.5%
7 .9 Pollutant Load Removed
Toe existing BMP removal efficiency was multiplied by the calculated pollutant load to obtain the
pollutant load removed. This calculation produced an immense data set consisting of the pollutant
load removed for each of the 11 pollutants for each of the 4 BMPs at each of the 17 BMP locations .
The data set was reduced first by selecting indicator pollutants, then by selecting the BMP at each
potential location that removed the largest load of the indicator pollutant(s).
The indicator pollutants were selected based on the pollutants for which the receiving water body
is impaired. Toe Agua Hedionda Lagoon and Agua Hedionda Creek are the only waterbodies within
the watershed currently listed on the 303(d) List. Toe Lagoon is listed for sediment and bacteria, and
the creek is listed for TDS. Pollutant load data was not available for bacteria therefore total
suspended solids (TSS) was selected as the indicator pollutant for sediment.
The indicator pollutants were selected based on the pollutants for which the receiving water body
is impaired. Toe Agua Hedionda Lagoon and Agua Hedionda Creek are the only waterbodies within
the watershed currently listed on the 303( d) List. Toe Lagoon is listed for sediment and bacteria, and
the creek is listed for TDS. Pollutant load data was not available for bacteria, therefore total
suspended solids (TSS) was selected as the indicator pollutant for sediment.
Pollutant load data was not available for TDS therefore the indicator pollutant was selected to
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represent the TDS load within each subwatershed. The composition ofTDS includes nutrients and
dissolved metals. Potential indicator pollutants included in the EMC data set were To~al Zn, NOi &
NO3, Total Pb, TKN, Total Cu, and Total Cd. Although TDS includes just the dissolved portion of
these constituents, only the total ( dissolved and suspended) data was available.
Total Zn was selected as the indicator pollutant based on the following logic:
• NO2 & NO3 were eliminated from consideration as the indicator pollutant because biofilter
and extended detention BMPs exhibit negative removal efficiency for these pollutants.
• Total Cu was eliminated from consideration. because there is no BMP efficiency data
available for infiltration.
• TKN was eliminated from consideration because BMP efficiency data is not available for any
of the BMPs in this analysis.
• Total Cd exhibited very low pollutant loads compared with the other pollutants therefore it
would not be a conservative choice.
• Total Zn was selected over Total Pb because it exhibited a higher pollutant load and lower
removal efficiency, therefore it would be the most conservative choice.
7.10 Potential BMP Location Assessment
The assessment of each potential BMP location entailed review of an aerial photograph and a GIS-
based planned land use map, both with the subwatershed boundaries overlaid. The aerial photograph
represented the existing condition and the GIS map represented the ultimate condition of land use
within the Agua Hedionda watershed. Each subwatershed was evaluated for existing undeveloped
and ultimate developed areas. The subwatersheds that were primarily comprised of existing
undeveloped and ultimate developed areas were grouped into the "Regional Planning BMP"
category. The subwatersheds that primarily consisted of existing developed areas were grouped into
the "LEAD BMP" category. The subwatersheds that primarily included existing undeveloped and
ultimate undeveloped areas were eliminated from further analysis.
The Regional Planning BMP category applies to the subwatersheds that are currently undeveloped,
but will ult!mately be developed. The BMPs in this category will be funded by and implemented for
future development within the subwatershed only. The LEAD category applies to the subwatersheds
that are primarily already developed. The BMPs implemented in this category will receive storm
water treatment credit toward development outside of the subwatershed.
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Potential BMP locations were also evaluated based on subwatershed area. Some BMPs were located
downstream of other BMPs; these were labeled cumulative BMPs. The subwatershed area for the
cumulative BMP included the subwatershed area for the upstream BMP. In some cases, the
cumulative subwatershed area included several upstream areas. Analyses were performed for all
potential BMP locations, however, in the final assessment, the upstream BMP locations were
eliminated from further consideration, and only the cumulative BMPs were recommended.
The final evaluation criterion was pollutant load removed. The existing pollutant removal load and
the optimal pollutant removal load were calculated for each potential BMP location. The potential
BMP locations were sorted based on a combination highest pollutant removal and difference
between existing pollutant removal and optimal pollutant removal. The locations that had less
variability between existing and optimal received a higher weight than the ones with extreme
variability. The potential BMP locations that discharge to Agua Hedionda Creek were also given
extra weight because the BMP would improve water quality for two impaired water bodies (the creek
and Lagoon) .
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CHAPTERS
RESULTS OF ANALYSES
8.1 General Description of Results
Several analyses were performed for the 17 potential BMP locations identified within the Agua
Hedionda watershed. First, RickBMP, a GIS-based program, was performed to obtain information
such as subwatershed area and soil type. Next, BMP sizing calculations were performed to obtain
the required BMP size. The existing BMP size was determined based on physical characteristics of
the basins such as length, width, and volume. The pollutant load for each subwatershed area, the
BMP pollutant removal efficiency, and the pollutant load removed based on type of BMP were also
calculated. This chapter presents a summary of the results from these analyses.
8.2 RickBMP Results
Table 8-1 presents the GIS-calculated data describing the physical characteristics of the
subwatersheds and the potential BMP locations that were used to determine the scores for suitability
of each treatment BMP at each of the potential locations. Some of these parameters, such as
subwatershed area, runoff coefficient, basin area, and soil type were used in the BMP sizing
calculations. See Exhibit ES-3 and Exhibit ES-4 for the proposed BMP locations .
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TABLE 8-1. PHYSICAL CHARACTERISTICS OF THE POTENTIAL BMP LOCATIONS AND THEIR () RESPECTIVE SUBWATERSHEDS AS CALCULATED BY GIS
Potential Subwatershed SW SW Basin Basin Vegetation Area
BMP (SW)Area Runoff Dwelling Area Basin (acres) Soil
Location (acres) Coefficient, Units, (acres) Slope Chaparral Riparian <Basin) C DU
Basin l 108 0.60 712 0.6 0.00 0.0 0.0
Basin 5 420 0.85 0 2.4 0.00 2.4 0.0
Basin 11 163 0.85 0 l.7 0.03 0.0 0.0
Basin 13 162 0.74 277 0.5 0.00 0.0 0.0
Basin 17 19 0.73 0 0.5 0.00 0.0 0.0
Basin20 93 0.71 0 0.2 0.00 0.0 0.0
Basin 21 104 0.68 0 0.1 0.00 0.0 0.0
Basin 22 16 0.64 0 0.1 0.02 0.0 0.0
Basin23 33 0.53 195 0.4 0.00 0.4 0.0
Basin 26 79 0.62 619 0.3 0.00 0.3 0.0
Basin 44 117 0.66 964 l.8 0.00 0.02 0.0
Basin45 72 0.64 495 0.5 0.00 0.4 0.0
Basin 90 400 0.65 231 8.4 0.00 0.0 0.0
Basin 96 23 0.20 0 0.3 0.00 0.0 0.0
Basin 97 720 0.63 5,210 0.3 0.04 0.0 0.0
Basin 98 117 0.64 511 0.4 0.03 0.4 0.0
Basin 99 274 0.59 2,099 0.3 0.03 0.3 0.0
The characteristics of each watershed and potential BMP location were used to generate scores for
each location. Table 8-2 shows the scores that each potential BMP location received for each BMP
type. These scores were used as an initial indicator of which BMPs would be appropriate at each
location.
Infiltration and wetland scored well for many potential BMP locations however were eliminated due
to size constraints after evaluation of the BMP sizing calculations. Biofiltration scored lower based
on the RickBMP results than on BMP sizing calculations. RickBMP considers the likelihood of
vegetation establishment based on existing vegetation and dry weather flow, which are not factors
in the BMP sizirig calculation. Vegetation can also be established through temporary irrigation,
therefore biofiltration can still be an effective BMP in areas without dry weather flow.
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D
D
D
B
A
A
C
C
D
C
D
D
D
~ ()
D
D
•
The other parameter considered by RickBMP that affected results is the presence of chaparral. If this
vegetation was present in any of the basins, the score was lowered due to vegetation disturbance
restrictions. The GIS vegetation coverage may be outdated or inaccurate, therefore a biological
survey is recommended to detennine the presence of vegetation species. The presence of chaparral
was not considered in the BMP sizing calculations.
TABLE 8-2. GIS CALCULATED SCORES FOR THE POTENTIAL BMP
LOCATIONS
Potential BMP Biofiltration Wetland
Location Score Score
Basin 1 8.7 7.05
Basin 5 5.5 3.25
Basin 11 2.9 3.35
Basin 13 6.1 4.45
Basin 17 6.75 6.0
Basin20 6.15 4.5
Basin 21 5.9 4.25
Basin 22 4.9 3.85
Basin 23 5.7 3.75
Basin 26 8.7 6.45
Basin44 6.1 4.75
Basin 45 5.5 3.25
Basin 96 6.35 5.0
Basin 97 7.9 6.85
Basin 98 5.5 5.05
Basin 99 5.5 5.05
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Detention
Score
6.55
6.55
6.55
6.95
7.0
7.0
6.75
6.75
6.55
6.75
6.55
6.55
7.0
6.75
6.55
6.55
Infiltration
Score
2.0
2.0
2.0
7.6
9.0
9.0
2.0
1.5
2.0
2.0
2.0
2.0
9.0
2.0
2.0
2.0
KH:RC:ncliReport/14071-A.00I
09-19-03
Basin
1
5**
11
13
17
20
21
22
23
26
44
45
90
96
97
98
99
8.3 BMP Sizing and Optimization
The following subsections show the results of the BMP sizing and optimization calculations.
8.3.1 Biofiltration
Table 8-3 shows the results of the biofiltration sizing and optimization calculations. The
percent optimal was calculated based on the existing length and width versus the required
length and width. If the existing length was greater than or equal to the required length, but
the width was less than required, the percent optimal equaled the existing width divided by
the required width. If both the existing length and width were short, the percent optimal was
calculated based on the parameter that would yield the most conservative results.
TABLE 8-3. BMP SIZING AND OPTIMIZATION RESULTS FOR BIOFILTRATION
SW Runoff Q Existing Existing Existing Required Required Required Required Exis~
Area* C (cfs) Slope Length, ft. Top Slope Bottom Top Length, ft. o/i
(acres) Width, ft. Width, ft. Width, ft. (Cale) OptiL
(Cale) (Cale)
108 0.60 13 0.000 248 122 0.025 120 122 234 100%
420 0.85 71 0.000 120 112 0.025 475 478 270 23%
163 0.85 28 0.030 408 186 0.025 190 192 270 97%
162 0.74 24 0.000 146 130 0.025 135 138 270 54%
19 0.73 3 0.000 204 32 0.025 30 32 228 89%
93 0.71 13 0.000 120 60 0.025 88 90 264 45%
104 0.68 14 0.000 60 72 0.025 95 97 264 23%
16 0.64 2 0.020 79 72 0.025 70 71 138 57%
33 0.53 3 0.000 190 110 0.025 108 109 138 100%
79 0.62 10 0.000 408 44 0.025 68 70 264 63%
117 0.66 15 0.000 400 240 0.025 238 239 132 100%
72 0.64 9 0.000 396 68 0.025 66 68 258 100%
400 0.65 52 0.000 2568 164 0.025 350 352 270 47%
23 0.20 1 0.000 270 40 0.025 38 39 132 100%
719 0.63 91 0.040 256 64 0.025 600 602 270 11%
117 0.64 15 0.030 856 28 0.025 100 102 270 27%
274 0.59 32 0.030 242 6 0.025 215 217 270 3%
*SW Area is the Subwatershed Area
**Basin 5 was sized based on the forebay, not the actual basin because the basin maintains a permanent pool.
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•
8.3.2 Extended Detention
Table 8-4 shows the results of the extended detention sizing and optimization calculations.
The percent optimal was calculated based on the existing volume versus the required volume.
Increasing the volume of the basin can increase the percent optimal. The percent optimal
represents the expected BMP performance based on the assumption that the basin has already
been retrofit to function as a BMP (i.e., modified outlet structures, etc.).
TABLE 8-4. BMP SIZING AND OPTIMIZATION RESULTS FOR EXTENDED DETENTION
Basin Subwatershed RunoffC 85th Required Capture Existing Existing
Area (acres) Percentile Volume (ac-ft) Volume (ac-ft) % Optimal
Rainfall (in)
I 108 0.60 0.65 3.51 1.08 31%
5 420 0.85 0.65 19.34 3.84 20%
11 163 0.85 0.69 7.98 7.14 89%
13 162 0.74 0.64 6.38 3.20 50%
17 19 0.73 0.62 0.72 0.23 32%
20 ... 93 0.71 0.61 3.37 0.56 17%
21 104 0.68 0.61 3.63 0.39 11%
22 16 0.64 0.61 0.53 0.33 61%
23 33 0.53 0.65 0.93 2.17 100%
26 79 0.62 0.66 2.68 0.44 17%
-44 117 0.66 0.64 4.12 2.24 54%
45 72 0.64 0.64 2.48 2.85 100%
90 400 0.65 0.60 12.99 46.44 100%
96 23 0.20 0.60 0.23 0.71 100%
97 719 0.63 0.64 24.28 0.27 1%
98 117 0.64 0.66 4.13 --· --· 99 274 0.59 0.66 8.85 0.74 8%
*Basin 98 is an existing concrete channel, therefore it was sized for the volume-based BMPs
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Basin
I
5
11
13
17
20
21
22
23
26
44
45
90
96
97
98
99
8.3.3 Wet Pond/Wetland
Table 8-5 shows the results of the wet pond/wetland sizing and optimization calculations.
The percent optimal was calculated based on the existing volume versus the required volume.
Increasing the volume of the basin can increase the percent optimal. The percent optimal
represents the expected BMP performance based on the assumption that the basin has already
been retrofit to function as a BMP (i.e., modified outlet structures, etc.).
TABLE 8-5. BMP SIZING AND OPTIMIZATION RESULTS FOR WET POND/WETLAND
Required Capture Required Permanent Total Required Existing Existing
Volume (acre-ft) Pool Volume (ac-ft) Volume (ac-ft) Volume (ac-ft) % Optimal
3.51 7.02 10.53 1.08 10%
19.34 38.68 58.02 3.84 7%
7.98 15.97 23.95 7.14 30%
6.38 12.76 19.15 3.20 17%
0.72 1.43 2.15 0.23 11%
3.37 6.74 IO.IO 0.56 6%
3.63 7.25 10.88 0.39 4%
0.53 1.07 1.60 0.33 20%
0.93 1.86 2.79 2.17 78%
2.68 5.36 8.03 0.44 6%
4.12 8.24 12.36 2.24 18%
2.48 4.97 7.45 2.85 38%
12.99 25.98 38.97 46.44 100%
0.23 0.45 0.68 0.71 100%
24.28 48.57 72.85 0.27 0%
4.13 8.27 12.40 --· --· 8.85 17.71 26.56 0.74 3%
*Basin 98 is an existing concrete channel, therefore it was sized for the volume-based BMPs
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•
Basin
-
-
I
5
11
13
17
20
21
22
23
26
44
45
90
96
97
98
99
8.3.4 Inftltration
Table 8-6 shows the results of the infiltration sizing and optimization calculations. The
following criteria were used to determine the percent optimal:
• If Soil Type = A and Existing Storage Volume >= Capture Volume, %Optimal = 90
If Soil Type = B and Existing Storage Volume >= Capture Volume, %Optimal = 50
If Soil Type= C and Existing Storage Volume >= Capture Volume, %Optimal = 20
If Soil Type= D, %Optimal= 0
• If Sqil Type = A and Existing Storage Volume < Capture Volume, % Optimal =
0.9*%Capture Volume
If Soil Type = B and ·Existing Storage Volume < Capture Volume, % Optimal =
0.5*%Capture Volume
If Soil Type= C and Existing Storage Volume< Capture Volume,% Optimal=
0.2*%Capture Volume
If Soil Type= D, %Optimal= O
• The same criteria were repeated for area.
TABLE 8-6. BMP SIZING AND OPTIMIZATION RESULTS FOR INFILTRATION
Required Existing %of Soil % Optimal Required Existing % of Area
·Capture Storage Capture Type based on Invert Basin
Volume Volume Volume Volume Area (ac) Area (ac)
. (acre-ft) (ac-ft)
3.51 1.08 31% 4 0% 3.43 0.61 18%
19.34 3.84 20% 4 0% 18.89 2.36 12%
7.98 7.14 89% 4 0% 7.80 1.67 21%
5.44 3.20 59% 2 29% 5.31 0.46 9%
0.72 0.23 32% I 28% 0.70 0.54 77%
3.37 0.56 17% I 15% 3.29 0.18 5%
3.63 0.39 11% 3 2% 3.54 0.12 3%
0.53 0.33 61% 3 12% 0.52 0.12 23%
0.93 2.17 233% 4 0% 0.91 0.44 48%
2.68 0.44 17% 3 3% 2.62 0.33 13%
1.68 2.24 134% 4 0% 1.64 1.76 108%
2.48 2.85 115% 4 0% 2.43 0.5 21%
12.99 46.44 358% 4 0% 12.69 8.35 66%
0.23 0.71 312% I 90% 0.22 0.27 122%
24.28 0.27 1% 3 0% 23.72 0.28 1%
4.13 ----4 0% 4.04 0.37 9%
8.85 0.74 8% 4 0% 8.65 0.25 3%
¾Optimal
based on
Area
0%
0%
0%
4%
69%
5%
1%
5%
0%
3%
0%
0%
0%
100%
0%
0%
0%
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8.4 Pollutant Load Results
Table 8-7 shows the results of the pollutant load calculations.
TABLE 8-7. POLLUTANT LOAD RESULTS
Basin SW Area* TSS BOD COD Total P Diss. P TKN NO2& Total Total Total Total
1
5
11
13
17
20
21
22
23
26
44
45
90
96
97
98
99
(acres) NO, Pb Cu Zn Cd
Mass Mass Mass Mass Mass Mass Mass (lbs) Mass Mass Mass Mass
(tons) (tons) (tons) (lbs) (lbs) (ibs) (lbs) (lbs) (lbs) (lbs)
108 6 1 3 6 20 126 78 2 2 14 0.04
420 26 3 14 32 144 724 452 12 12 61 0.29
163 10 1 5 12 54 262 167 5 5 21 0.11
162 6 1 3 7 30 163 104 3 3 15 0.06
19 1 0.1 0 1 3 19 11 0.2 0.3 2 0.01
93 4 1 2 5 18 109 70 2 2 11 0.04
104 3 0.4 2 4 14 84 56 1 1 8 0.03
16 0.5 0.1 0.2 1 2 13 10 0.2 0.2 1 0.01
33 1 0.1 1 1 5 31 20 0.4 1 3 0.01
79 6 1 3 6 20 129 72 2 2 15 0.04
117 5 0.5 2 5 17 112 67 1 2 13 0.04
72 3 0.3 1 3 10 64 40 1 1 7 0.02
400 21 2 11 27 86 555 385 9 12 65 0.32
23 0.4 0.1 0.1 0.2 1 9 12 0 0 1 0.00 )
719 48 5 23 55 173 1136 642 14 18 133 0.38 \ _
117 7 1 4 8 26 173 102 2 3 20 0.06
274 20 2 9 21 68 445 261 6 7 52 0.15
*SW Area is the Subwatershed Area
8.5 BMP Pollutant Removal Efficiency and Pollutant Load Removed
The BMP pollutant removal efficiency calculation produced an immense data set consisting of the
pollutant removal efficiency for each of the 11 pollutants for each of the 4 BMPs at each of the 17
BMP locations. The data set was used to determine the pollutant load removed by multiplying the
existing BMP pollutant removal efficiency by the pollutant load. The data set was reduced first by
selecting indicator pollutants, then by selecting the BMP at each potential location that removed the
largest load of the indicator pollutant. Figure 8-1 shows the BMP TSS Load Removal for each
potential BMP location, and Figure 8-2 shows the BMP Total Zn Load Removal for the potential
BMP locations that discharge to Agua Hedionda Creek.
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• Figure 8-1. City of Car d BMP TSS Removal
35 · · · .. · · · .. · · .. · ... • · · · · · · .. -·-• --· · · --· -· · -..• · ·
30 --------.
25
u,
C 0 ~
"O 20
QI > 0 E QI 15 ~
Cl)
Cl)
I-
10
5
0 J~ ,ccJJ. JJ. [I ,...... I
" c}~
~~
~ "" .._~ ~ ~ ri" 'l,'l, ~ ,e, ~ ,t, o.,<::l o.,~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ c}~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~
Basin
□TSS Removed Existing with Modifications (tons} TSS Removed Potential (tons}
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r r
-----·1
;
j
__J
I I
I I I
I 7
I -l
r
I
~
I -l
~ o.,'b o.,°->
c}~ c}~ c}~
~~ ~~ ~~
KH:RC:nd/Report/14071-A.00 1
09-19-03
Figure 8-2. City of Carlsbad BMP Total Zn Removal
25 -· ----··-· ·-·······--· -·-·······---· -···-· ·-···· · ·
20 ·
-;;
.Cl :::. 15
"Cl GI > 0 E &
i!5 ! 10
5 .
o--------
BASIN 1 BASIN 11
Basin
□Total Zn Removed Existing with Modifications (lbs)
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BASIN44
Total Zn Removed Potentia@§su
BASIN45
i ----,
KH:RC:nd/Report/14071-A.001
03
Table 8-8 shows the summary of BMP pollutant removal efficiency and pollutant load removed by
the top 9 potential BMP locations. A complete table showing all pollutants for all BMP types for all
potential BMP locations is provided in Appendix E.
TABLE 8-8. INDICATOR POLLUTANT LOAD REMOVAL FOR
TOP 9 POTENTIAL BMP LOCATIONS
Regional Potential BMP TSS Total Zn*
LEAD Location and
BMP Planning Load Removed % Load (lbs) Removed % BMPType BMP (tons) (tons) Removed (lbs) Removed
X Basin 1: Biofilter 5.50 3.74 68% 14.2 6.40 45%
X Basin 5: 26.24 3.18 12% NIA* NIA NIA
Extended Detention
X Basin 11: Biofilter 9.18 6.05 66% 20.0 8.73 44%
X Basin 13: Biofilter 6.56 2.41 37% NIA NIA NIA
X Basin 20: Biofilter 3.77 1.16 31% NIA NIA NIA
X Basin 22: Biofilter 0.51 0.20 39% NIA NIA NIA
X Basin 44: Biofilter 4.87 3.31 68% 13.1 5.88 45%
X Basin 90: Wet Pond 23.05 18.21 79% NIA NIA NIA
X Basin 97: Biofilter 48.21 3.48 7% NIA NIA NIA
*Total Zn was only considered for basins that discharge to Agua Hedionda Creek.
8.6 Description of Potential BMP Locations
Seventeen potential BMP locations were analyzed in this study. Three locations are recommended
for Regional Planning BMPs, and six locations are recommended for LEAD BMPs. Seven locations
were eliminated because they are located upstream of a cumulative BMP and one location was
eliminated because the subwatershed is not developed and is zoned as open space in the planned
condition, therefore will not be developed. The potential BMP locations are summarized below.
Removal efficiencies are based on size only, and assume that the basin has already been retrofit (e.g.
proper vegetation establishment for biofilters and wet ponds/wetlands, forebay for extended
detention, etc.). Improved removal efficiencies can be achieved in most cases by increasing the size
of the basin.
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8.6.1 Basin 1
Basin 1 is located adjacent to the northwest intersection of J ackspar Drive and El Camino Real.
J ackspar Drive is a residential street located midway between Cannon Road and College Boulevard.
Basin 1 supports vegetation and is regularly maintained.
The subwatershed area ( 108 acres) is primarily developed in the existing condition, however pockets
of planned residential and light industry development remain vacant. Planned land use comprises
of 17% commercial, 3% industrial, 60% residential, and 19% undeveloped. Exhibit 8-IA shows the
existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-IB shows the
planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 1 is recommended as a LEAD BMP because the subwatershed area is primarily developed.
Basin 1 discharges to Agua Hedionda Creek, therefore a BMP at this location would benefit water
quality in both the creek and the Lagoon.
The recommended BMP type is biofiltration. For TSS, the existing pollutant removal efficiency is
68%, which is also the optimal pollutant removal efficiency. For Total Zn, the existing and optimal
pollutant removal efficiency is 45%. The pollutant load removed ranked 6th out of the 6 LEAD
BMPs, likely because Basin 1 has the smallest subwatershed area of all the potential LEAD BMP
locations.
Recommended modifications to Basin 1 include clearing of existing vegetation, establishment of
native, low growing vegetation appropriate for biofiltration, and adjusting the slope to 2.5%. The
existing width and length are optimal for a biofilter, so additional area is not required. A temporary
irrigation system may also be required to establish vegetation. Native species typically do not require
irrigation once established.
Overall, the basin was ranked 4th out of 6 LEAD BMPs because it requires minimal retrofit and
discharges to the creek. Basin 1 did not rank higher because it rated the lowest in pollutant load
removed, even though it is of adequate size.
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•
I)./, Subwatershed boundary 1/'v Potential BMP location boundary
Date of Aerial Photograph: February 2002
RICK ENGI'\lEERING C01vf P\1\ Y
1-·,
111111,·1:•
< ,lllor,11.1 111 ~ti. " I 'Jl...fl I 800 0 A 800 1600 Feet
Exhibit 8-1 A:
Agua Hedionda Watershed
Potential BMP Location
Basin 1 Existing Land Use
Legend:
1)/,Subwatershed boundary
/\/ Potential BMP location boundary
ACT*
D AGR
D AUT
D COM
C]HEA
HIG
C]LIG
C]LOW
MED
-OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
RICK ENGr\JEERING C01\[PANY
·,I
11111,,.
lill'lfll '1 .::.(,1/1 800 800 1600 Feet
Agua Hedionda Watershed
Potential BMP Location
Basin 1 Planned Land Use
•
8.6.2 Basin 5
Basin 5 is located behind the Carlsbad Research Center near the intersection of College Boulevard
and Faraday. A major branch of the storm drain system that collects runoff from the surrounding
industrial area drains into Basin 5, which maintains a permanent pool of water and provides aesthetic
value as a water feature. Basin 5 includes a forebay upstream of the detention basin.
The subwatershed area ( 420 acres) is primarily developed in the existing condition, however pockets
of planned light industry development remain vacant. Planned land use comprises of 22%
commercial and 78% industrial. Exhibit 8-2A shows the existing land use conditions based on a
2002 aerial photograph of the basin. Exhibit 8-2B shows the planned land use conditions based on
the City of Carlsbad General Plan as of May 2003.
Basin 5 is recommended as a LEAD BMP because the subwatershed area is primarily developed.
The recommended BMP type is extended detention. Although Basin 5 maintains a permanent pool,
it is not feasible as a wet pond/wetland because the required volume is more than three times the
existing volume. The required volume is so immense that the basin would be considered a
jurisdictional dam subject to requirements of the Division of Safety of Dams.
For TSS, the existing pollutant removal efficiency is 12%, and the optimal pollutant removal
efficiency is 61 %. Although the existing pollutant removal efficiency is fairly low, the pollutant load
removed ranked 2nd out of 6 LEAD BMPs because it treats a large subwatershed (2nd largest among
the subwatersheds in this study).
Recommended modifications to Basin 5 include increasing the size of the basin and redesign of the
forebay and outlet structure to meet BMP requirements. Also, the volume of the basin should be
recalculated during final design because it may have a greater capacity than assumed in this report
due to the permanent pool (i.e., the topographic map used to calculate the volume may have been
inaccurate due to the permanent pool).
• Overall, the basin was ranked 6th out of 6 LEAD BMPs because it requires significant modifications
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that may not be feasible due to the unavailability of additional area and inability to adjust aesthetic
features. If the basin were enlarged, it may require additional water supply to maintain the permanent
pool/aesthetic feature.
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I)./, Subwatershed boundary I\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
800 0
N
A 800 1600 Feet
Exhibit 8-2A:
Agua Hedlonda Watershed
Potential BMP Location
Basin 5 Existing Land Use
Legend:
1)/,Subwatershed boundary
/\/ Potential BMP location boundary
ACT*
AGR
AUT
COM
D HEA
HIG
LIG
LOW
MED
-OPE
PAR
STO
CJ TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
R!Ck ENcr,rnERING COl'vfR\NY
111 l 1.-a::•
.,It 1hl111111. r) 1111 "\ t IIJ '>I..CI 17
B-5
800 800 1600 Feet
Exhibit 8-2B:
Agua Hedlonda Watershed
Potential BMP Location
Basin 5 Planned Land Use
l
•
8.6.3 Basin 11
Basin 11, the eastern-most basin evaluated in this study, is located northeast of the intersection of
Palomar Airport Road and El Camino Real, directly North of El Fuerte Street. A concrete lined
swale conveys flow into the basin. The basin is vegetated and contains standing water based on
photos from the Desiltation Basin Inventory (Carlsbad, 2000).
The subwatershed area (163 acres) is primarily developed in the existing condition, however pockets
of planned light industry development remain vacant. Planned land use comprises of 11 %
commercial and 89% industrial. Exhibit 8-3A shows the existing land use conditions based on a
2002 aerial photograph of the basin. Exhibit 8-3B sho~s the planned land use conditions based on
the City of Carlsbad General Plan as of May 2003.
Basin 11 is recommended as a LEAD BMP because the subwatershed area is primarily developed.
Basin 11 discharges to Agua Hedionda Creek, therefore a BMP at this location would benefit water
quality in both the creek and the Lagoon.
The recommended BMP type is biofiltration. For TSS, the existing pollutant removal efficiency is
66% and the optimal pollutant removal efficiency is 68%. For Total Zn, the existing pollutant
removal efficiency is 44% and optimal pollutant removal efficiency is 45%. The pollutant load
removed ranked 4th out of the 6 LEAD BMPs.
Recommended modifications to Basin 11 include clearing of existing vegetation, establishment of
native, low growing vegetation appropriate for biofiltration, increasing the width by approximately
10 feet, and adjusting the slope to 2.5%. A temporary irrigation system may also be required to
establish vegetation. Native species typically do not require irrigation once established.
Overall, the basin was ranked 2nd out of 6 LEAD BMPs because it requires minimal retrofit and
discharges to the creek .
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This Page Intentionally Left Blank
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-Legend:
/)I, Subwatershed boundary 1/'v Potential BMP location boundary
Date of Aerial Photograph: February 2002
RICK ENGI'<F.ERING COtvf PM Y
, .. 1. ... 1.;,
~ lhl1t1111.,9"Jll1.",'}1t L j 1Jl-O 11 800 0 A 800 1600 Feet
Exhibit 8-3A:
Agua Hedionda Watershed
Potential BMP Location
Basin 11 Existing Land Use
Legend:
I;:./, Subwatershed boundary 1/'v Potential BMP location boundary
ACT*
AGR
CJ AUT
c::::J COM
D HEA
D HIG
c:::::J LIG
LOW
C]MED
-OPE
O PAR
STO
LJ TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
in Appendix A
.,
City of Carlsbad
----~corporate Limit
.
I . . ' ( ,.
'I
111-
[
Key to land use abbreviations is provided
====:::::L-----------------------------~-•"-----~-'-~
800 800 1600 Feet
•
I I I.
._ . .,j I
Exhibit 8-3B:
Agua Hedionda Watershed
Potential BMP Location
Basin 11 Planned Land Use
8.6.4 Basin 13
Basin 13 is located on the eastern side of Faraday Avenue, on the southern outskirts of the business
park developments just before the road makes the final bend toward Cannon. Vegetation and
standing water were observed in the basin during a November 2002 site visit. An irrigation system
is installed along the side slopes of the basin. Basin 13 is a cumulative BMP, including the
subwatershed area of Basin 23.
The subwatershed area ( 162 acres) is primarily developed in the existing condition, however pockets
of planned light industry, low density residential, and medium density residential development
remain vacant. Planned land use comprises of 10% commercial, 59% industrial, 21 % residential, and
9% undeveloped. Exhibit 8-4A shows the existing land use conditions based on a 2002 aerial
photograph of the basin. Exhibit 8-4B shows the planned land use conditions based on the City of
Carlsbad General Plan as of May 2003.
Basin 13 is recommended as a LEAD BMP because the subwatershed area is primarily developed.
The recommended BMP type is biofiltration. For TSS, the existing pollutant removal efficiency is
37%, and the optimal pollutant removal efficiency is 68%. The pollutant load removed ranked 5th
out of 6 LEAD BMPs.
Recommended modifications to Basin 13 include clearing of existing vegetation, establishment of
native low growing vegetation appropriate for biofiltration, increasing the length by up to 130 feet,
and adjusting the slope to 2.5%. The existing irrigation system should be inspected to ensure that it
would be adequate to establish vegetation.
Overall, the basin was ranked 5th out of 6 LEAD BMPs because it requires significant modifications
that may not be feasible due to the unavailability of additional area.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 95
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 96
KH:RC:nd/Report/14071-A.00I
09-19-03
~ Subwatershed boundaries /'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
I 11 800 0 A 800 1600 Feet -----
Exhibit 8-4A:
Agua Hedionda Watershed
Potential BMP Location
Basin 13 Existing Land Use
Legend:
N, Subwatershed boundaries /'v Potential BMP location boundaries
ACT*
AGR
AUT
LJ COM
HEA
HIG
LIG
LOW
MED
-OPE
[7 PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
8.-13
~\ Jl
A 800 0 800
•
1600 Feet
H,.
... I I ~1
I
I j
I
, I
Exhibit 8-4B:
Agua Hedionda Watershed
Potential BMP Location
Basin 13 Planned Land Use
8.6.5 Basin 17
Basin 17 is located along the eastern side of Lego land Drive near the intersection of Cannon Road
and Legoland Drive. The basin was observed dry and unvegetated during a November 2002 site
visit.
The subwatershed area (19 acres) is primarily undeveloped in the existing condition. Planned land
use comprises of 83% commercial and 17% undeveloped. Exhibit 8-5A shows the existing land use
conditions based on a 2002 aerial photograph of the basin. Exhibit 8-5B shows the planned land use
conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 17 is not recommended for consideration as a BMP at this time because the subwatershed area
is tributary to Basin 20, a cumulative BMP. A regional treatment BMP (biofiltration) is
recommended at Basin 20, which will treat runoff from the Basin 17 subwatershed.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 99
KH:RC:nd/Report/14071-A.001
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 100
KH:RC:nd/Report/14071-A.001
09-19-03
/Y, Subwatershed boundary
/\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
800 0 800 1600 Feet
Exhibit 8-SA:
Agua Hedionda Watershed
Potential BMP Location
Basin 17 Existing Land Use
Legend:
~ Subwatershed boundary f\/ Potential BMP location boundary
ACT*
AGR
AUT
COM
HEA
HIG
LIG
LOW
c:::J MED
-OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
800 0 A 800 1600 Feet
Exhibit 8-5B:
T
• 11 r.
, ." I 11.
--I ..
◄ -•
Agua Hedionda Watershed
Potential BMP Location
Basin 17 Planned Land Use
•
8.6.6 Basin 20
Basin 20 is located along the eastern side of Lego land Drive near the intersection of Cannon Road
and Lego land Drive, and north of Basin 17. Basin 20 is a cumulative BMP, including the
subwatershed area of Basin 17.
The subwatershed area (93 acres) is primarily undeveloped in the existing condition. Planned land
use comprises of 44% commercial, 3 5% industrial, and 21 % undeveloped. Exhibit 8-6A shows the
existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-6B shows the
planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 20 is recommended as a Regional Planning BMP because the subwatershed area is primarily
undeveloped.
The recommended BMP type is biofiltration. For TSS, the existing pollutant removal efficiency is
31 %, and the optimal pollutant removal efficiency is 68%. The pollutant load removed was not
ranked because it is recommended that this BMP be implemented prior to development of the
subwatershed.
Recommended modifications to Basin 20 include establishment of native low growing vegetation
appropriate for biofiltration, increasing the length by up to 145 feet, increasing the width by up to
30 feet, and adjusting the slope to 2.5%. A temporary irrigation system may also be required to
establish vegetation. Native species typically do not require irrigation once established .
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 103
KH:RC:nd/Report/14071-A.001
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 104
KH:RC:nd/Report/14071-A.00I
09-19-03
I)/, Subwatershed boundaries 1/'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
800 0
N
A 800 1600 Feet
Exhibit 8-&A:
Agua Hedlonda Watershed
Potential BMP Location
Basin 20 Existing Land Use
Legend:
I)./, Subwatershed boundaries I'\/ Potential BMP location boundaries
ACT*
AGR
AUT
LJ COM
D HEA
HIG
LIG
LOW
MED
-OPE
PAR
STO
CJ TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
inA endixA
RICK ENGI"\1FERIT\G CO~fR\1\ Y
1111•1•
~ 111!11 111., l ., , 4t,l11) l}J.O lJ 800 800 1600 Feet
[]
Exhibit 8-6B:
Agua Hedionda Watershed
Potential BMP Location
Basin 20 Planned Land Use
8.6.7 Basin 21
Basin 21 is located along the northern side of Cannon Road, just west of Armada Drive, and directly
south of the eastern end of the Lagoon. Based on photos from the Desiltation Basin Inventory
(Carlsbad, 2000), the basin was unvegetated and contained standing water.
The subwatershed area (104 acres) includes the subwatershed areas of Basin 17 and Basin 20. The
portion of the subwatershed that does not include Basin 17 and Basin 20 is primarily undeveloped
in the existing condition and in the planned condition, therefore, a BMP is recommended at Basin
20 rather than Basin 21.
Exhibit 8-7 A shows the existing land use conditions based on a 2002 aerial photograph of the basin.
Exhibit 8-7B shows the planned land use conditions based on the City of Carlsbad General Plan as
ofMay2003.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 107
KH:RC:nd/Report/14071-A.001
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 108
KH:RC:nd/Report/14071-A.001
09-19-03
I)./, Subwatershed boundaries "/'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
800 0 A 800 1600 Feet
Exhibit 8-7A:
Agua Hedionda Watershed
Potential BMP Location
Basin 21 Existing Land Use
Legend:
I)/, Subwatershed boundaries /'v Potential BMP location boundaries
ACT*
AGR
AUT
COM
D HEA
HIG
LIG
LOW
MED
-OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
800
Ii
• •
0 A 800 1600 Feet
• -11!
r
(
.. , .. L
-'
Exhibit 8-78:
Agua Hedionda Watershed
Potential BMP Location
Basin 21 Planned Land Use
8.6.8 Basin 22
Basin 22 is located along the northern side of Cannon Road, west of Basin 21 and just east of Car
Country Drive. Based on photos from the Desi/talion Basin Inventory (Carlsbad, 2000), the basin
was unvegetated and contained a small pool of water.
The subwatershed area (16 acres) is primarily undeveloped in the existing condition. Planned land
use comprises of23% commercial, 44% industrial, and 33% undeveloped. Exhibit 8-8A shows the
existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-8B shows the
planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 22 is recommended as a Regional Planning BMP because the subwatershed area is primarily
undeveloped.
The recommended J:3MP type is biofiltration. For TSS, the existing pollutant removal efficiency is
39%, and the optimal pollutant removal efficiency is 68%. The pollutant load removed was not
ranked because it is recommended that this BMP be implemented prior to development of the
subwatershed.
Recommended modifications to Basin 22 include establishment of native vegetation, increasing the
length by up to 60 feet, and adjusting the slope to 2.5%. A temporary irrigation system may also be
required to establish vegetation. Native species typically do not require irrigation once established.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 111
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 112
KH:RC:ndiReport/14071-A.001
09-19-03
•
I:!+/, Subwatershed boundary 1/'v Potential BMP location boundary
Date of Aerial Photograph: February 2002
800 0 800 1600 Feet
Exhibit 8-BA:
Agua Hedionda Watershed
Potential BMP Location
Basin 22 Exisiting Land Use
Legend:
~ Subwatershed boundary 1/'v Potential BMP location boundary
ACT*
AGR
AUT
COM
HEA
HIG
LIG
LOW
LJ MED
-OPE
PAR
STO
t7 TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
800 0 A 800
I l
1600 Feet
/;
Exhibit 8-8B:
Agua Hedlonda Watershed
Potential BMP Location
Basin 22 Planned Land Use
8.6.9 Basin 23
Basin 23 is located southwest of the intersection of El Camino Real and College Boulevard, along
the south side of the residential street Milton Drive. During site visit (November 2002), the basin
was observed with established vegetation and standing water.
The subwatershed area (33 acres) is approximately 40% undeveloped in the existing condition.
Planned land u~e comprises of 17% commercial, 55% residential, and 28% undeveloped. Exhibit
8-9A shows the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit
8-9B shows the planned land use conditions based on the City of Carlsbad General Plan as of May
2003.
Basin 23 is not recommended for consideration as a BMP at this time because the subwatershed area
is tributary to Basin 13, a cumulative BMP. A regional treatment BMP (biofiltration) 1s
recommended at Basin 13, which will treat runoff from the Basin 23 subwatershed.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 115
KH:RC:ndiR.eport/14071-A.001
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 116
KH:RC:nd/Report/14071-A.001
09-19-03
I
I)./, Subwatershed boundary /'v Potential BMP location boundary
Date of Aerial Photograph: February 2002
800 0 A 800 1600 Feet
Exhibit 8-9A:
Agua Hedlonda Watershed
Potential BMP Location
Basin 23 Existing Land Use
Legend:
N, Subwatershed boundary 1/'v Potential BMP location boundary
ACT*
AGR
C JAUT
CJ COM
CJ HEA
HIG
LIG
LOW
MED
OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
RICK ENGI'\1FERING CO:tvfR\NY
u t 1u•
.J;I • 11,r 1, I I Jt, ll'IJ 1•'1.JJ'11
N
800 0 A
II'"
• I •
t
I
rf ..
---. -~
Exhibit 8-9B:
Agua Hedionda Watershed
800 1600 Feet Potential BMP Location
Basin 23 Planned Land Use
8.6.10 Basin 26
Basin 26 is located east of the intersection of El Camino Real and Tamarack A venue, near the
northeast comer of Tamarack A venue and Pontiac Drive. Based on photos from the J)esiltation
Basin Inventory (Carlsbad, 2000), the basin was vegetated.
The subwatershed area (79 acres) is primarily developed in the existing condition. Planned land use
comprises of 22% commercial, 72% residential, and 6% undeveloped. Exhibit 8-1 OA shows the
existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-1 OB shows
the planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 26 is not recommended for consideration as a BMP at this time because the subwatershed area
is tributary to Basin 97, a cumulative BMP. A regional treatment BMP (biofiltration) is
recommended at Basin 97, which will treat runoff from the Basin 26 subwatershed.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 119
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 120
KH:RC:nd/Report/14071-A.00J
09-19-03
•
1)./, Subwatershed boundary f\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
RICK ENGJ'\TEERING CbMB\1\ Y
11 l l1t
i 11 or 1 1 jf,lfJ) l(Jl.07117 800 0 A 800 1600 Feet
Exhibit 8-1 OA:
Agua Hedlonda Watershed
Potential BMP Location
Basin 26 Existing Land Use
Legend:
~ Subwatershed boundary 1/'v Potential BMP location boundary
ACT*
CJ AGR
1=i AuT l -,J COM
D HEA
HIG
CJ LIG
CJ LOW
CJ MED
OPE
PAR
STO C JTRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
800 0 800 1600 Feet
Exhibit 8-1 OB:
Agua Hedionda Watershed
Potential BMP Location
Basin 26 Planned Land Use
•
8.6.11 Basin 44
Basin 44 is located west of the intersection of Cannon Road and El Camino Real, along the west side
of Cannon Road near Macario Drive. Based on photos from the Desiltation Basin Inventory
(Carlsbad, 2000), the basin was vegetated. Basin 44 is a cumulative BMP, including the
subwatershed of Basin 45.
The subwatershed area (117 acres) is primarily undeveloped in the existing condition. Planned land
use comprises of25% commercial, 60% residential, and 15% undeveloped. Exhibit 8-1 lA shows
the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-1 lB shows
the planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 44 is recommended as a Regional BMP because the subwatershed area is primarily
undeveloped.
The recommended BMP type is biofiltration. For TSS, the existing pollutant removal efficiency is
68%, which is also the optimal pollutant removal efficiency. The pollutant load removed was not
ranked because it is recommended that this BMP be implemented prior to development of the
subwatershed.
Recommended modifications to Basin 44 include clearing of existing vegetation, establishment of
native low growing vegetation appropriate for biofiltration, and adjusting the slope to 2.5%. A
temporary irrigation system may also be required to establish vegetation. Native species typically do
not require irrigation once established .
Agua,Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 123
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 124
KH:RC:nd/Report/14071-A.001
09-19-03
Legend:
/)I, Subwatershed boundaries 1/'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
800 0 A 800 1600 Feet
Exhibit 8-11A:
Agua Hedlonda Watershed
Potential BMP Location
Basin 44 Exisiting Land Use
Legend:
I)/, Subwatershed boundaries 1/'v Potential BMP location boundaries
ACT*
AGR
AUT
LJ COM
LJ HEA D HIG
LIG
LOW
MED
OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
RICK ENGI'\TFERING CO!v1R\1'\Y
I 1•1.-
;J,! h f t 11\ ,,1 I l I ti.JI 'I l 800 0 A 800 1600 Feet
Exhibit 8-11 B:
Agua Hedionda Watershed
Potential BMP Location
Basin 44 Planned Land Use
8.6.12 Basin 45
Basin 45 is located west of the intersection of Cannon Road and El Camino Real, along the west side
of Cannon Road, just east of Basin 44. Based on photos from the Desiltation Basin Inventory
(Carlsbad, 2000), the basin was not vegetated and contained standing water.
The subwatershed area (72 acres) is approximately 50% developed in the existing condition. Planned
land use comprises of 27% commercial, 49% residential, and 23% undeveloped. Exhibit 8-12A
shows the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-12B
shows the planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 45 is not recommended for consideration as a BMP at this time because the subwatershed area
is tributary to Basin 44, a cumulative BMP. A regional treatment BMP (biofiltration) is
recommended at Basin 44, which will treat runoff from the Basin 45 subwatershed.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 127
KH:RC:nd/Report/14071-A.001
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 12 8
KH:RC:nd/Report/14071-A.00I
09-19-03
1)/, Subwatershed boundary
/\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
800 0 A 800 1600 Feet
Exhibit 8-12A:
Agua Hedionda Watershed
Potential BMP Location
Basin 45 Existing Land Use
Legend:
~ Subwatershed boundary /'v Potential BMP location boundary
ACT*
AGR
O AUT
C]COM
CJ HEA
HIG
LIG
_]LOW
c:=J MED
-OPE
PAR
STO
CJ TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
800
/
L
0 A 800 1600 Feet
/
/
11
Exhibit 8-12B:
Agua Hedlonda Watershed
Potential BMP Location •
Basin 45 Planned Land Use
•
8.6.13 Basin 90
Basin 90, also known as Cannon Lake, is located between El Arbul and A venida Encinas and south
of Cannon Road. Cannon Lake is enclosed by a residential area, where residents have built small
docks for boats. Basin 90 is a cumulative BMP, including the subwatershed area of Basin 96.
The subwatershed area ( 400 acres) is primarily developed in the existing condition. Planned land use
comprises of 56% commercial, 13% industrial, 5% residential, and 26% undeveloped. Exhibit 8-13A
shows the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-13B
shows the planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 90 is recommended as a LEAD BMP because the subwatershed area is primarily developed.
The recommended BMP type is wet pond/wetland. For TSS, the existing pollutant removal
efficiency is 79%, which is also the optimal pollutant removal efficiency. The pollutant load
removed ranked 3rd out of 6 LEAD BMPs.
Recommended modifications to Basin 90 include establishment of native wetland vegetation and
addition of a forebay. The volume of Basin 90 is adequate for a wet pond/wetland.
Overall, the basin was ranked 1st out of 6 LEAD BMPs because it requires minimal modifications
and would treat a large subwatershed area .
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 131
KH:RC:nd.iReport/ 14071-A.00 I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 132
KH:RC:ndiReport/14071-A.001
09-19-03
Legend:
/1;!+/, Subwatershed boundaries 1/'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
RICK ENGI"\1EERING COMPAI'\Y
I
,., ... I:"
~ 11,lo.Oll•"z;"• (ilt)'11~17
N
1000 0 A 1000 2000 Feet
Exhibit 8-13A:
Agua Hedionda Watershed
Potential BMP Location
Basin 90 Existing Land Use
Legend:
I)./, Subwatershed boundaries 1/'v Potential BMP location boundaries
ACT
l AGR
AUT
(7COM
r=:J HEA
HIG
LIG
LOW
MED
-OPE
PAR
STO
C]TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
1000 1000 2000 Feet
Exhibit 8-13B:
Agua Hedionda Watershed
Potential BMP Location
Basin 90 Planned Land Use
8.6.14 Basin 96
Basin 96 is located behind the parking lot of the northeast comer of the Carlsbad Company Stores,
near Car Country Drive. This basin was not recorded in the Desiltation Basin Inventory (Carlsbad,
2000).
The subwatershed area (19 acres) comprises of a portion of the Flower Fields in the existing
condition. Although the planned land use is undeveloped, it is assumed that the area will remain
developed with agricultural land use. Exhibit 8-l 4A shows the existing land use conditions based
on a 2002 aerial photograph of the basin. Exhibit 8-14B shows the planned land use conditions based
on the City of Carlsbad General Plan as of May 2003.
Basin 96 is not recommended for consideration as a BMP at this time because the subwatershed area
is tributary to Basin 90, a cumulative BMP. A regional treatment BMP (wet pond/wetland) is
recommended at Basin 90, which will treat runoff from the Basin 96 subwatershed.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 13 5
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 136
KH:RC:nd/Report/14071-A.001
09-19-03
/;!./, Subwatershed boundary /'v Potential BMP location boundary
Date of Aerial Photograph: February 2002
800 0 800 1600 Feet
Exhibit 8-14A:
Agua Hedionda Watershed
Potential BMP Location
Basin 96 Existing Land Use
Legend:
/Y, Subwatershed boundary 1/'v Potential BMP location boundary
ACT*
AGR
AUT
COM
CJ HEA
HIG
-LIG
LOW
MED
OPE
PAR
STO
C]TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
RICK ENGI"\TEERING CbI'vf PANY
... l 1.-i::
t> llllot 111. I 1•1 "5 h 11,l ) l-1111'
N
800 0 A 800 1600 Feet
Exhibit 8-14B:
Agua Hedlonda Watershed
Potential BMP Location
Basin 96 Planned Land Use
•
8.6.15 Basin 97
Basin 97 is located south of Tamarack Avenue approximately between La Portalada Drive and El
Camino Real. This area is not an existing detention basin; rather it is currently used for agriculture.
Basin 97 is a cumulative BMP, including the subwatershed areas of Basins 26, 98, and 99.
The subwatershed area (719 acres) is primarily developed in the existing condition. Planned land use
comprises of 27% commercial, 64% residential, and 9% undeveloped. Basin 97 would treat the
largest subwatershed of all the potential BMP locations in this study. Exhibit 8-1 SA shows the
existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-lSB shows
the planned land use conditions based on the City of Carlsbad General Plan as of May 2003 .
Basin 97 is recommended as a LEAD BMP because the subwatershed area is primarily developed.
The recommended BMP type is biofilter. For TSS, the existing pollutant removal efficiency is 7%,
and the optimal pollutant removal efficiency is 68%. The pollutant load removed ranked 1st out of
6LEADBMPs.
Since Basin 97 is currently an agricultural area, it would be designed and built as new construction,
rather than retrofit. Several challenges to the implementation of this BMP include land acquisition
and determination of beneficial uses within the subwatershed. Additional investigation into the
feasibility of the implementation of this BMP is required. However, a regional BMP at this location
would provide significant removal of pollutants from urban runoff within the Agua Hedionda
watershed.
Although this location requires further study, it was ranked 3rd out of 6 LEAD BMPs because it
would treat an immense subwatershed area .
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 139
KH:RC:nd/Report/14071-A.00 I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 140
KH:RC:nd/Report/14071-A.001
09-19-03
•
/)I, Subwatershed boundaries 1/'v Potential BMP location boundaries
Date of Aerial Photograph: February 2002
RICK ENGii'JEERING CbtvIB\NY
.. ,, 1-ri l! •,ld
11 l 1,,.
I) 11 or 1, }:!I :! (fl) 'H-41'11 1000 0 A 1000 2000 Feet
Exhibit 8-1 SA:
Agua Hedionda Watershed
Potential BMP Location
Basin 97 Existing Land Use
I
Legend:
I)./ Subwatershed boundaries /'v Potential BMP location boundaries
ACT*
AGR
AUT
COM
HEA
HIG
C]LIG
LOW
MED
OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
1000 0 A 1000 2000 Feet
Exhibit 8-15B:
Agua Hedionda Watershed
Potential BMP Location
Basin 97 Planned Land Use
•
8.6.16 Basin 98
Basin 98 is located along Tamarack A venue north of Pontiac Drive, just south of Basin 26. Basin
98 is not an existing detention basin, it is currently a concrete lined channel. The original intention
for this basin was to remove the concrete, install a series of drop structures, and establish native
vegetation to retrofit as a biofilter. However, the available area is too narrow and would have to be
widened by an unrealistic amount in order to be considered a BMP. Additionally, Basin 98
discharges to Basin 97.
The subwatershed area ( 117 acres) is primarily undeveloped in the existing condition. The planned
land use comprises of 42% commercial, 40% residential, and 18% undeveloped. Exhibit 8-16A
shows the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-16B
shows the planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 98 is not recommended for consideration as a BMP at this time because it is not a feasible
retrofit and the subwatershed area is tributary to Basin 97, a cumulative BMP. A regional treatment
BMP (biofilter) is recommended at Basin 97, which will treat runoff from the Basin 98
subwatershed .
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 143
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
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09-19-03
/),/, Subwatershed boundary
/\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
RICK ~:NGI"\TEERING C'DJ\tf P\t--Y
-I "' 1 I lfl I I I Cbl1Jj "'JI 1)!11i 800 0 800 1600 Feet
Exhibit 8-1 &A:
Agua Hedionda Watershed
Potential BMP Location
Basin 98 Existing Land Use
Legend:
/)I, Subwatershed boundary f\/ Potential BMP location boundary
ACT*
:~~
COM
HEA
HIG
B UG
LOW
CJ MED
-OPE
PAR
STO
0 TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
RICK ENGINEERING CoMP\NY
,.!II I t h
ml
10 11 f,1ru '"I 111 :;,>' (I ) 1-4 800 0 A 800 1600 Feet
Exhibit 8-16B:
Agua Hedionda Watershed
Potential BMP Location
Basin 98 Planned Land Use
8.6.17 Basin 99
Basin 99 is located north of Tamarack Avenue between Sierra Morena Avenue/Milan Drive and
Regent Road. This area is not an existing detention basin, it is a depression within a natural channel.
At the authoring of this report, the Regional Board does not allow modifications of natural drainages
to serve as BMPs.
The subwatershed area (117 acres) is primarily undeveloped in the existing condition. The planned
land use comprises of 42% commercial, 40% residential, and 18% undeveloped. Exhibit 8-17 A
shows the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-17B
shows the planned land use conditions based on the City of Carlsbad General Plan as of May 2003.
Basin 98 is not recommended for consideration as a BMP at this time because the Regional Board
does not allow modifications, and the subwatershed area is tributary to Basin 97, a cumulative BMP.
A regional treatment BMP (biofilter) is recommended at Basin 97, which will treat runoff from the
Basin 98 subwatershed.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division 14 7
KH:RC:nd/Report/14071-A.00I
09-19-03
This Page Intentionally Left Blank
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 148
KH:RC:ncliReport/14071-A.00I
09-19-03
Legend:
I),/ Subwatershed boundary
/\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
~ RIC)( I\ 1{ ;J ;ERL T(; COiv[P,\!'\ y
~a, 11, 800 0 A 800 1600 Feet
Exhibit 8-17 A:
Agua Hedionda Watershed
Potential BMP Location
Basin 99 Existing Land Use
Legend:
I!!,./, Subwatershed boundary
/\/ Potential BMP location boundary
ACT*
AGR
AUT
COM
HEA
HIG
LIG
LOW
CJ MED
-OPE
PAR
STO
TRA
VAC
Source: City of Carlsbad General Plan Land Use
as of May 2003
* Key to land use abbreviations is provided
in Appendix A
800 0 A 800 1600 Feet
Exhibit 8-17B:
Agua Hedionda Watershed
Potential BMP Location
Basin 99 Planned Land Use
•
CHAPTER9
REFERENCES
California Regional Water Quality Control Board, San Diego Region. September 8, 1994. Water
Quality Control Plan for the San Diego Basin.
California Regional Water Quality Control Board San Diego Region. February 21 , 2001. California
Regional Water Quality Control Board San Diego Region Order Number 2001-01 NPDES
No. CAS0108758 Waste Discharge Requirements for Discharges of Urban Runoff from the
Municipal Separate Storm Sewer Systems (MS4s) Draining the Watersheds of the County of
San Diego, the Incorporated Cities of San Diego County, and the San Diego Unified Port
District (Municipal Permit).
California Regional Water Quality Control Board San Diego Region. 2003. 2002 CWA Section
303(d) List of Water Quality Limited Segment (Approved by USEPA July 2003).
www.swrcb.ca.gov/tmdl/docs/2002reg9303dlist.pdf
California Stormwater Quality Association. January 2003. Stormwater Best Management Practice
Handbook New Development and Redevelopment.
City of Carlsbad, City of Encinitas, City of Escondido, City of Oceanside, City of San Marcos, City
of Solana Beach, City of Vista, County of San Diego. January 2003. Watershed Urban
Runoff Management Program Carlsbad Hydrologic Unit.
City of Carlsbad Public Works Department. June 2000. Desiltation Basin Inventory.
City of Carlsbad Public Works Department. April 2003. Standard Urban Storm Water Mitigation
Plan Storm Water Standards, A Manual for Construction & Permanent Storm Water Best
Management Practices Requirements.
County of San Diego Department of Public Works Flood Control Section. 2003. San Diego County
Hydrology Manual.
D-Max Engineering. September 5, 2002. City of Carlsbad Dry Weather Field Screening and
Analytical Monitoring Program 2002.
Federal Emergency Management Agency. June 19, 1997. Flood Insurance Study San Diego County
California and Unincorporated Areas.
KTU+A, Merkel & Associates, Inc., The Rick Alexander Company. February 2002. Carlsbad
Watershed Management Plan, A Management Plan for the Coastal Watersheds of the
Carlsbad Hydrologic Unit .
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 151
KH:RC:ndiReport/14071-A.001
09-19-03
MEC Analytical Systems, Inc. 2001. 2000 -2001 City of San Diego and Copermittees National
Pollutant Discharge Elimination System (NPDES) Municipal Storm Water Monitoring
Program, Final Report.
San Diego Copermittees. February 14, 2002. Model Standard Urban Storm Water Mitigation Plan
for San Diego County, Port of San Diego, and Cities in San Diego County (Approved by
SDRWQCB 6/12/02).
Thomas R. Schueler and Heather K. Holland. 2000. "Comparative Pollutant Removal Capability of
Stormwater Treatment Practices." The Practice of Watershed Protection. Center for
Watershed Protection, Ellicott City, Maryland.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division 152
KH:RC:nd/Report/14071-A.001
09-19-03
APPENDIX A
DEFINITIONS OF LAND USE CATEGORIES
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division
KH:RC:nd/Report/14071-A.00 I
09-19-03
Table A.1
Key to Land Use Category Abbreviations
See attached support material for descriptions of the land use within each category
Category Estimated Percent
Land Use Category Abbreviation Impervious
Open Space Reserves and Preserves OPE 0
Passive Parks PAS 40
Agriculture AGR 20
Water WAT 100
Low Density Residential LOW 25
Medium Density Residential MED 45
High Density Residential HIG 65
Commercial COM 90
Storefront Commercial STO 95
Auto Dealerships AUT 95
Parking PAR 95
Active Parks ACT 50
Freeway FRE 95
Other Transportation and Maintenance TRA 90
Light Industry LIG 90
Heavy Industry HEA 95
Military MIL 90
•
•
Rick Engineering Hydrologic Land Use Codes
LOW -Low Density Residential
Spaced Rural Residential -Single family homes located in rural areas with lot sizes of
approximately 1 to 10 acres. Homes in areas of lower densities are coded as agricultural
or vacant, not residential. Rural residential estates may have small orchards, fields or
small storage buildings associated with the residential dwelling unit.
Residential Recreation -Active neighborhood parks that are for the use of residents only
such as fenced in areas that may contain pools, tennis and basketball courts, barbecues
and a community meeting room.
MED -Medium Density Residential
Single Family Residential -Single family detached housing units, on lots smaller than 1
acre. Newer developments may include clubhouses, recreation areas, pools, tennis, etc.
located within and associated with the residential development, if a separate parcel/lot
designation does not exist.
Residential Under Construction -Usually located near existing residential developments.
BIG-High Density Residential
Multifamily Residential -Attached housing units, two or more units per structure;
includes duplexes, townhouses, condominiums, apartments, and SRO's in Centre City.
Newer developments may include clubhouses, recreation areas, pools, tennis, etc. located
within and associated with the residential development, if a separate parcel/lot
designation does not exist.
Mobile Home Parks -Includes mobile home parks with 10 or more spaces that are
primarily for residential use. (RV parks are included within the commercial recreation
category)
COM -Commercial
Group Quarters Residential -Jails/Prisons/Border Patrol Holding Station, dormitories,
military barracks, monastery.
Other -Convalescent or retirement homes not associated with or within a health care
facility, rooming houses, half-way houses, California Conservation Corps, Honor Camps
and other correctional facilities.
Hotels/Motels/Resorts -Hotels, motels, and other transient accommodations with three or
less floors. Commonly found along freeways and prime commercial areas. Hotels and
motels that have four or more floors. Primarily found in downtown areas and near tourist
attractions. Resorts with hotel accommodations that usually contain recreation areas.
Examples of resorts would be La Costa Resort and Spa, Lawrence Welk, and the Olymic
Resort in Carlsbad near the airport.
Communications and Utilities -TV and radio broadcasting stations, relay towers,
electrical power generating plants, water and sewage treatment facilities.
Wholesale Trade -Usually located near transportation facilities. Structures are usually
large and cover the majority of the parcel. Examples are clothing and supply. Also
includes swap meet areas .
1 of5
Other Retail -Other retail land uses not classified.
Specialty Commercial Centers -Tourist or specialty commercial shopping areas such as
Seaport Village, Marina Village, Ferry Landing at Coronado, Bazaar del Mundo, Flower
Hill, Glasshouse Square, The Lumberyard, Park Plaza at the Village, Promenade,
Belmont Park, Del Mar Plaza.
Office -High rise buildings with more than 4 stories containing banking, offices for
business and professional services (finance, insurance, real estate), some retail activities
and restaurants.
Office -Low rise buildings with less than 5 stories containing banking, offices for
business and professional services (finance, insurance, real estate), some retail activities
and restaurants.
Government/Civic Centers -Large government office buildings or centers ( outside of
military reservations) and civic centers, or city halls of local governments. Also includes
the Chamber of Commerce buildings and DMV Offices.
Public Services -Cemetery, churches, libraries, post offices, fire/police/ranger stations,
missions, cultural facilities, museums, art galleries, social service agencies, humane
societies, historic sites and observations.
Hospitals -UCSD, VA Hospitals, Balboa Naval Hospital, and all other hospitals.
Other Health Care -Medical centers and buildings or offices, health care services and
other health care facilities. Smaller medical offices and facilities may be included with
office, strip commercial or other surrounding uses.
Schools -SDSU, SMSU, UCSD, other universities and colleges, junior colleges, senior
high schools, junior high schools and middle schools, elementary schools, school district
offices.
Other Schools -Includes adult schools, non-residential day care and nursery schools.
Tourist Attraction -Sea World, Zoo, Wild Animal Park.
Stadiums/sports arenas -Sports Arena and Qualcomm Stadium.
Racetracks -Del Mar, El Cajon speedway, Carlsbad raceway, San Luis Ray Downs.
Convention Centers -Centre City, Embarcadero.
Marinas -Includes marinas such as Oceanside Harbor, Quivira Basin, Shelter Island,
Harbor Island, Embarcadero and Chula Vista marina.
Olympic Training Center -Olympic Training Center in Chula Vista.
Other Recreation -RV parks, drive-in theaters, campgrounds, boys/girls clubs, YMCA's,
rifle ranges, swim clubs, and stand-alone movie theaters. Also includes tennis clubs
without golf, casinos, rodeo grounds and senior recreation centers.
Beaches -Active. Accessible sandy areas along the coast or major water bodies (San
Diego and Mission Bay) allowing swimming, picnicking, and other beach related
recreational activities. Usually has parking associated with it.
Commercial Under Construction -Usual located near existing commercial or residential
areas.
HEA -Heavy Industry
Heavy Jndushy -Shipbuilding, airframe, and aircraft manufacturing. Usually located
close to transportation facilities and commercial areas. Parcels are typically large, 20-50
acres.
Extractive lndustly -Mining, sand and gravel extraction, salt evaporation.
2 of5
Junkyard/dumps/landfills -The landscape should show visible signs of the activity. Also
include auto wrecking/dismantling and recycling centers.
LIG -Light Industry
Industrial Parks -Office/industrial uses clustered into a center. The primary uses are
industrial but may include high percentages of other uses in service or retail activities.
Light Indust,y-General -All other industrial uses and manufacturing not included in the
categories above. These are not located inside of parks, but are usually along major
streets or clustered in certain areas. Includes manufacturing uses such as lumber,
furniture, paper, rubber, stone, clay, and glass; as well as light industrial uses as auto
repair services and recycling centers. Mixed commercial and office uses (if not large
enough to be identified separately) are also included. General industrial areas are
comprised of 75 percent or more of industrial uses (manufacturing, warehousing, and
wholesale trade).
Warehousing/Public Storage -Usually large buildings located near freeways, industrial
or strip commercial areas. Public self-storage buildings are typically long, rectangular
and closely spaced.
Industrial Under Construction -Usually located near existing industrial or commercial
developments.
ACT -Active Parks
Parks -Active -Recreation areas and centers containing one or more of the following
activities: tennis or basketball courts, baseball diamonds, soccer fields, or swings.
Examples are Robb Field, Morley Field, Diamond Street Recreation Center, Presidio
Park. Smaller neighborhood parks with a high level of use are also included as active
parks.
PAS -Passive Parks
Parks -Passive -State, regional, and local parks, National monuments which allow
public access and have some sort of improvements or developments and facilities.
Examples are Cabrillo National Monument, Sunset Cliffs.
Golf Courses-Public and private golf courses in the region.
Golf Course Clubhouses -Clubhouses, swimming and tennis facilities and parking lots
associated with the golf course.
TRA -Other Transportation and Maintenance
Airports -Commercial Airports -Lindbergh Field only.
Milita,y Ailports -Airports owned and operated by the military. Found on military
bases.
General Aviation Ailports -All general aviation airports.
Airstrips
Rail Stations/Transit Centers/Seaports -Major transit centers ( e.g. Oceanside Transit
Center, El Cajon Transit Center), rail stations (e.g. Santa Fe Depot, Solana Beach
Station), Coaster stations (Oceanside, Carlsbad Village, Carlsbad Poinsettia, Encinitas,
Solana Beach, Sorrento Valley, Old Town, San Diego), major trolley stations, and
3 of5
•
seaport tern1inals (Port of SD). Parking areas associated with these uses are included.
Transit centers within shopping centers are included within the shopping center category.
Railroad Right-of-Ways -All railroad ROWs.
Other Transportation -Maintenance yards and their associated activities, transit yards,
and walking bridges.
Marine Terminals -National City and I 0th Street (Centre City) marine terminals.
FRE -Freeway .
Freeway -Divided roadways with 4 or more lanes, restricted access, grade separations,
and rights of way greater than 200 ft. wide. Includes all right of way and interchange
areas, but not frontage roads.
PAR-Parking
Center City Parking -Swface -All surface parking lots found in the center city plan area.
Center City Parking -Structures -All large parking structures found in the center city
plan area.
Park and Ride Lots -Stand alone parking areas that are not associated with any land use.
These are usually located near freeways.
Swface Street Right-of-Ways-All street ROWs.
Regional Shopping Centers -Contain I to 5 major department stores, and usually have
more than 50 tenants. Typically are larger than 40 acres in size.
Community Commercial -Smaller in size than the regional shopping centers. Contain a
junior department store or variety store (i.e. a Target Center with other commercial
stores) as a major tenant and have 15 to 50 other tenants. Smaller in size, 8 to 20 acres.
May also have a variety store (i.e. Target, Home Depot or Price/Costco) by itself.
Neighborhood Shopping Centers -Usually less than IO acres in size with on-site parking.
Includes supermarket and drug store centers not identified as community commercial.
May include office uses that are not large enough to code separately. Neighborhood
centers with over 100,000 sq.ft. are inventoried by the Chamber of Commerce, and The
Union Tribune (Copely) also collects data on neighborhood centers.
AUT -Auto Dealerships
Auto Dealerships -Includes National City Mile of Cars and Carlsbad's Car Country,
among others.
STO -Store-front Commercial
Store-front Commercial -Includes commercial activities found along major streets (not
in planned centers), with limited on-site parking. May include mixed office uses that are
not large enough to be identified as separate area. Also may include mixed residential
uses, i.e. residential on top of commercial, or residential units adjacent to commercial
establishments.
MIL -Military Use
Milita,y Use -Defense installations, operational facilities, maintenance facilities (non-
weapons), research and development, supply and storage (non-weapons), community
support facilities and any other military use that does not fall in other categories.
4 of5
Milita,y Training -Academic, operational and combat training facilities, training ranges,
and special purpose training ranges.
Milita,y Weapons -Weapons assembly, maintenance and storage facilities.
OPE -Open Space Reserves and Preserves
Open Space Reserves, Preserves -Wildlife and nature preserves, lands set aside for open
space, and parks with limited development and access. Examples are Torrey Pines State
Reserve, Penasquitos Canyon Reserve, San Elijo Ecological Preserve, Nature
Conservancy properties.
Other Beaches -Passive. Other sandy areas along the coastline with limited parking and
access (beaches along cliffs, or near preserves).
Landscape Open Space -Actively landscaped areas within residential neighborhoods
such as greenbelt areas, hillsides with planted vegetation (trees/shrubs), among others.
AGR-Agriculture
Orchards and Vineyards
Intensive Agriculture -Nurseries, greenhouses, flO\yer fields, dairies, livestock, poultry,
equine ranches, row crops and grains.
Extensive Agriculture-Pasture, fallow.
VAC-Vacant and Undeveloped Land
Vacant
WAT-Water
Bays, Lagoons
Inland Water -Lakes, reservoirs, and large ponds.
*Source of definitions -SANDAG 1995 Existing Land Use
5 of5
APPENDIXB
SUPPORTING DOCUMENTATION FOR BENEFICIAL USES OF SURFACE WATERS
FOR THE AGUA HEDIONDA WATERSHED
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division
KH :RC:nd/Report/14071-A.001
09-19-03
, ..
(
WATER QUALITY CONTROL PLAN
FOR THE SAN DIEGO BASIN (9)
SEPTEMBER 8, 1994
CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD
SAN DIEGO REGION
·-.\t,
• naturally occurring pollutant concentrations phiifcal, chemical, :J!~{cal, and el ~homic
prevent the attainrJJ;~pt of the use; or facto;~_~;. '.he uses listea°'iQ~~ection 101~,£~)(2)
·:;~1.,.. . are prot_~·c~1on and propagati.,,of fish, shellljsh,
• natural, ephemeral, intermittent or low flow and wil~j!e, and recreation (i.e., fishablel
con_,.ditions or water ·1~_y,els prevent the · bl ) · ..... -. . sw1mma e uses • . .. ,,t,!,~~"'-''""',...,'"'i""
attainment of the use; or -\~ . ~. . . . . 's'(-.,~;;,;,ic;,•:!<'.;,;;::i.:J?i',,,·~ffer..-,
• huml i,aused conditions "!'l'+sources 0F'"""'s"J!fi,lf j:ji;7}{i(''lJS£ ·
pollution'~:~~vent the a~tainme_nt't~h~he use}1 D£1::IIIIIT10NS
and cannot:\be remedied or woula causJ{ rllVI I J
more enviro~1?ry_ental damage to corfect tha~i:
to leave in plal ~; or ~;
:,J . !\
. :';.~ dams, diversions~\,or other types of~
.:~~,;:
1
hydrologic modificat\pns preclude th&l-'-
·r,:~~~tainment of the use, -~?, ~-is not feasibl~,
tQ,,,restore the water boay'\to its origimiP
condition or to operate suchlnodification i6~ ·'"Jf.1.. • ~-~(• a way,.-that would result in the attainment oe >1t ,.. fl•: the use·;.or ~-\'!'i' .. ~~ :\,. ~
• physical ccinditions related to the naturalt
. features of the vvater body, such as the lackk: ,_Q.. ,~·•:t:. , .. ·'.tt.. of a proper suo~~rate, cover, flow, depth,t,~
·:_::--1,i. pools, riffles,and'tl(~_ !ike, unrelated to watedtl'
· ·:.t.,_~uality,_ preclude ati~J .r,;ient of aquatic life~-
wotect1on uses; or ·lt--· ~
• ~a~h ols more stringe_nt th:~fhe controls foJ
efflu~J.,. limitations in Clea~~'~\o/ater Act~
Sectionsr-301 (bl and 306 would result in{1 ·~ ~ substantial'. and widespread economic and~
social imp~~h... ~~
'<ti"'. \~ '·~f};., . tf
... (7) States may_ n~t remf.r.~ designated uses if (a) ~t·
:·,:;_._ they are existing uses,.,.unless a use requiring ~
·<L more stringent criteria is"1agded, or (bl such uses ~~
··-r~.will be attained by impleme111ing effluent limits :l:
·•ynder Clean Water Act Sections 301 (bl and h.
30l, .. and by jmple~enting bJ'i ttGrr1anagement 8
prac~,ces for nonpomt source control [40 CFR ,;;~
1 31 . i"0(h) 1. "<f:!'-; h;· -~ ~ . . ;•t t., ~-~
(8) If existing u~~s are higher than those specified in 'j
In 1972, the Stat~ Board adopted a uniform list and
description of beneficial uses to be applied
· throughout all basins of the State. During the 1994
Basin Plan update, beneficial use definitions were
revised and some new beneficial uses were added.
Overall, the following twenty-three beneficial uses
are now defined statewide and are designated within
the San Diego Region:.
Municipal and Domestic Supply (MUN) -Includes
uses of water for community, military, or· individual
water supply systems including, but not limited to,
drinking water supply.
Agricultural Supply (AGRJ -Includes uses of water
for farming, horticulture, or ranching including, but
not limited to, irrigation, stock watering, or support
of vegetation for range grazing.
Industrial Process Supply (PROCJ -Includes uses of
water for industrial activities that depend primarily
on water quality.
Industrial Service Supply (IND) -Includes uses of
water for industrial activities that do not depend
primarily on water quality including, but not limited
to, mining, cooling water supply, hydraulic
conveyance, gravel washing, fire protection, or oil
well re-pressurization.
water qualitv\,s_~andards, a state must revise its :f
A~r,~ standards to ret ect the uses actually being ?j1
1.,\\,:~. attained (40 CFR l~\:O(i)]. :~
Ground Water Recharge (GWR) -Includes uses of
water for natural or artificial recharge of ground
water for purposes of future extraction, maintenance
of water quality, or halting of saltwater intrusion into
freshwater aquifers.
•
-~9) If the designated uses·id,o not include the uses l\
\~eecified in ~ection 101:_\~.l (2) of the Clean r~ ~~ .. \~r. Ac~, or 1f t~e state wa,~~s to remove a use ~
spec_1f1ed in Section 101 (a) (2.)., the state must ~
condu·c\.~ "use attainability ah'ti7~~s" (40 CFR ~i
131 . 1 0(J) ]. A use attainability · analysis is f[
defined in 3~.0_ CFR 131 .3(g) as a . ,\'Jh!!J.ctured ~
scientific ass}s,_~pent of the factors affect ing the ?~
attainment of '•}t,e use which may include ]
BENEFICIAL USES ' ,,, 3
Freshwater Replenishment (FRSH) -l11cludes uses of
water for natural or artificial mainten·ance of surface
water quantity or quality (e.g., salinity).
Navigation (NA VJ -Includes uses
of water for shipping, travel, or
other transportation by private,
military, or commercial vessels.
September 8, 1994
Hydropower Generation (POW) -Includes uses of
water for hydropower generation.
Contact Water Recreation (REC-1) -Includes uses of
water for recreational · activities involving body
contact with water, where ingestion of water is
reasonably possible. These uses include, but are not
limited to, swimming, wading, water-skiing, skin and
SCUBA diving, surfing, white water activities,
fishing, or use of natural hot springs.
Non-contact Water Recreation (REC-2)-Includes the
uses of water for recreational activities involving
proximity to water, but not normally involving body
contact with water, where ingestion of water is
reasonably possible. These uses include, but are not
limited to, picnicking, sunbathing, hiking,
beachcombing, camping, boating, tidepool and
marine life study, hunting, sightseeing, or aesthetic
enjoyment in conjunction with the above activities.
Commercial and Sport Rshing (COMM) -Includes
the uses of water for commercial or recreational
collection of fish, shellfish, or other organisms
including, but not limited to, uses involving
organisms intended for human consumption or b'ait
purposes.
Aquaculture (AQUA) -Includes the uses of water for
aquaculture or mariculture operations including, but
not limited to, propagation, cultivation, maintenance,
or harvesting of aquatic plants and animals for
human consumption or bait purposes.
Warm Freshwater Habitat (WARM) -Includes uses
of water that support warm water ecosystems
including, but not limited to, preservation or
enhancement of aquatic habitats, vegetation, fish or
wildlife, including invertebrates.
Cold Freshwater Habitat (COLD) -Includes uses of
water that support cold water ecosystems including,
but not limited to, preservation or enhancement of
aquatic habitats, vegetation, fish or wildlife,
including invertebrates.
Inland Saline Water Habitat (SAL) -Includes uses of
water that support inland saline water ecosystems
including, but not limited to, preservation or
enhancement of aquatic saline habitats, vegetation,
fish, or wildlife, including invertebrates.
Estuarine Habitat (EST) -Includes uses of water that
support estuarine ecosystems including, but not
limited to, preservation or enhancement of estuarine
habitats, vegetation, fish, shellfish, or wildlife (e.g.,
estuarine mammals, waterfowl, shorebirds).
BENEFICIAL USES 2-4
Marine Habitat (MARJ -Includes uses of water that
support marine ecosystems including, but not limited
to, preservation or enhancement of marine habitats,
vegetation such as kelp, fish, shellfish, or wildlife
(e.g., marine mammals, shorebirds).
Wildlife Habitat (WILD) -Includes uses of water that
support terrestrial ecosystems including, but not
limited to, preservation and enhancement of
terrestrial habitats, vegetation, wildlife (e.g.,
mammals, birds, reptiles, amphibians, invertebrates),
or wildlife water and food sources.
Preservation of Biological Habitats of Special
Significance (BIOL) -Includes uses of water that
support designated areas or habitats, such as
established refuges, parks, sanctuaries, ecological
reserves, or Areas of Special Biological Significance
(ASBS), where the preservation or enhancement of
natural resources requires special protection.
The following coastal waters have been designated
as ASBS in the San Diego Region. For detailed
descriptions of their boundaries, see the discussion
on ASBS in Chapter 5, Plans and Policies:
• San Diego -La Jolla Ecological Reserve, San
Diego County
• Heisler Park Ecological Reserve, Orange County
• San Diego Marine Life Refuge, San Diego County
The following areas are designated Marine Life
Refuges by the California legislature. A legal
description of the boundaries of each marine life
refuge is contained in the Fish and Game Code of
California, Division 7 (Refuges), Chapter 1 (Refuges
and Other Protected Areas), Article 6 (Marine Life
Refuge):
• San Diego Marine Life Refuge, San Diego County
• Laguna Beach Marine Life Refuge, Orange
County
• Newport Beach Marine Life Refuge, Orange
County
• South Laguna Beach Marine Life Refuge,
Orange County
• Dana Point Marine Life Refuge, Orange County
• Doheny Beach Marine Life Refuge, Orange
County
• Niguel Marine Life Refuge, Orange County
• Irvine Coast Marine Life Refuge, Orange County
• City of Encinitas Marine Life Refuge, San Diego
County
The following areas are designated Ecological
Reserves by the Fish and Game Commission
(California Code of Regulations, Title 14, Section
September 8, 1 994
)
•
•
630). A legal description of the boundaries of each
ecological reserve is on file at the California
Department of Fish and Game headquarters, 141 6
Ninth Street, Sacramento:
• Batiquitos Lagoon Ecological Reserve, San Diego
County
• Blue Sky Ecological Reserve, San Diego County
• Buena Vista Lagoon Ecological Reserve, San
Diego County
• Heisler Park Ecological Reserve, Orange County
• McGinty Mountain Ecological Reserve, San
Diego County
• San Diego -La Jolla Ecological Reserve, San
Diego County
• San Dieguito Lagoon Ecological Reserve, San
Diego County
• San Elijo Lagoon Ecological Reserve, San Diego
County
Rare, Threatened, or Endangered Species (RARE) -
Includes uses of water that support habitats
necessary, at least in part, for the survival and
successful maintenance of plant or animal species
established under state or federal law as rare,
threatened or endangered.
Migration of Aquatic Organisms (MIGRJ -Includes
uses of water that support habitats necessary for
migration, acclimatization between fresh and salt
water, or other temporary activities by aquatic
organisms, such as anadromous fish.
Spawning, Reproduction, and/or Early Development
(SPWNJ -Includes uses of water that support high
quality aquatic habitats suitable for reproduction and
early development of fish. This use is applicable
only for the protection of anadromous fish.
Shellfish Harvesting (SHELL) -Includes uses of water
The following are designated Natural Preserves by that support habitats suitable for the collection of
the State Park and Recreation Commission (Public filter-feeding shellfish (e.g., clams, oysters and
Resources Code, Division 5, Chapter 1, Article 1 ). mussels) for human consumption, commercial, or
A legal description of each natural preserve is on file sport purposes. .
at the California Department of Parks and Recreation . ~~~.a~~~~:tf!~~~i•i~~1~~4iii,~?'~
headquarters, 1416 Ninth Street, Sacramento: }t E X J S 1:/4.JV . G A tffe D
• San ~ateo Creek Wetland Natural Preserve, San f PO TEN7J/'AL BENEE/£/AL
Diego County ~! · A'' ~· r,/
• Los Penasquitos Marsh Natural Preserve, San ~ US£ .. tF-' ··)~
Diego County r~ ~
The following area is designated a National Estuarine I iT . ~wat~r re~o~rce; of 1
th~-~3'h Die~~ Region hav~
Research Reserve by the National Oceanic and !i . een , ex en~i~e Y eve ?JJ~ over e_ years -~
At h · Ad · • t t· (NOAA) (C t 1 2 If, today s existing benef1c1al uses will probaoly mosp enc mIms ra 10n oas a one J,tl • • ,1P1•· • • ,.,,1
M t A t f 1972 d d S t. 315 ~ continue into the f. uture. Smee the adopt1on.rof the anagemen c o as amen e ec 10n , · ti?. 8 . Pl . 1975~h • 1 d ~w· d
16 USC 1461). A le al descri tion of the ~ asin an in • .,ffe• ". c anges in ~n use ~~~-ems an . . g . p 1J resultant changes in water quality haveJ ed to some boundaries of the national estuarine research reserve '4: b t .J..f d'f' t' f b'{fJ; f" . 1 • • 0 A Off' f O 'f. su sequery,:t•' mo 1 1ca ions o . ,ene 1cIa use 1s on file at the N A headquarters, ice o cean · d • t·~ M' d'f' t· &-':h I b
d C I R M t NOAA es1gna 11,ms. inor mo 1 1ca 1cm.s ave a so een an oasta esource anagemen , , ;\g" • • • ,,,r
Washington, D.C., 20235: i :~:Jc';!i"u:: ~~;~~:~~;;irron °1 somLe of !,~e
• Tijuana River National Estuarine Research . :,•~ ,:\~ ' The beneficial use desi gnations describe f in this Reserve, San Diego County ' ,,.~ ~ ~ chapter are catenrfzed as "existing" p rp..-potentia/"
The following area is designated a National Wildlife
Refuge by the U.S. Fish and Wildlife Service. A legal
description of the boundaries of the national wildlife
refuge is on file at the U.S. Fish and Wildlife Service
headquarters, Southern California Complex, 2736
Loker Avenue West, Suite A, Carlsbad, California
92008:
• Sweetwater Marsh National Wildlife Refuge, San
Diego County
BENEFICIAL USES
~ beneficial us_~~,:#An existing be·nef-i , · · use can be ~ establis.~;11.!:>V demonstrati~g.)~T
.f • Fis~g, swimming, ~9~r;; uses have actually
,. occurred since Novem ber 28, 1975; or ·,
• The water q,utir:V'f~and quantity is suitab1~$'
• 5
allow the. use to be attained. .,#-ff?"'
~ .. :'1111'"". '
Existing beneficial uses were oriQjJ!ji~ determined as
part of a use survey of WJU:er resources in the
Region described in Chapti:i'r 1 , History of Basin
September 8, 1994
APPENDIXC
GIS PROCESSING PROGRAM CONSTANTS, VARIABLES, AND EQUATIONS
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division
KH:RC:nd!Report/14071-A.001
09-19-03
•
ESTIMATED PERCENT IMPERVIOUS AND RUNOFF COEFFICIENT BY SOIL TYPE FOR EACH LAND USE CATEGORY
LU_Cat LU Abr LU Num LU Percent Impervious C SoilA C_SoilB C_SoilC C SoilD
Active Parks ACT 1 50 0.55 0.58 0.60 0.63
Passive Parks PAS 2 40 0.48 0.51 0.54 0.57
Open Space Reserves and Preserves OPE 3 0 0.20 0.25 0.30 0.35
Agriculture AGR 4 20 0.34 0.38 0.42 0.46
Low Density Residential LOW 5 25 0.38 0.41 0.45 0.49
Medium Density Residential MED 6 50 0.55 0.58 0.60 0.63
HiQh Density Residential HIG 7 80 0.76 0.77 0.78 0.79
Commercial COM 8 90 0.83 0.84 0.84 0.85
Storefront Commercial STO 9 95 0.95 0.95 0.95 0.95
Auto Dealerships AUT 10 95 0.95 0.95 0.95 0.95
Parking PAR 11 95 0.95 0.95 0.95 0.95
Freeway FRE 12 95 0.95 0.95 0.95 0.95
Other Transportation and Maintenance TRA 13 90 0.83 0.84 0.84 0.85
LiQht Industry LIG 14 ,go 0.83 0.84 0.84 0.85
Heavy Industry HEA 15 95 0.95 0.95 0.95 0.95
Military MIL 16 90 0.83 0.84 0.84 0.85
Water WAT 17 100 0.95 0.95 0.95 0.95
Vacant and Undeveloped Land VAC 18 0 0.20 0.25 0.30 0.35
•
Lisi of EquaUon• used within GIS procn1lng routine to calculate scorH for Heh trwatm.nt dwice at Heh locatloft
FIELD IN TABLE Constant or -In GIS pnx;esslng code -shown In r ... output data for eedl potonUIII ~--
TABLE lndlcaln whether lho oons"'"t or variable -lo lho -,_....,linQ lho •oo draining lo lho potonllal -mont locotlon (BASIN) or to lho -,.......,11ng lho ootontial treatment locotion (BMP)
TYPE lndlc.etes wholhor lho field Is e user entered oonstanl (USER) or• -lhal Is allaAated by the GIS procaslng (CALCULATED)
SAMPLE 5-npte-,. lho l'll)e of data cc,nta;nod In lho r,e111. For r,e111s of TYPE• USER. lho sample shown ii lho IIClullf user entered constant
DESCRIPTIOII OesolpUon of lho constant Of -roe1c1
EQUATION
FIELD IN TABLE TABLE TYPE SAMPLE UNITS DESCRIPTION EQUATION
Runoff coetrcient for auta draining to lhe polentJal treatment location based on land UH and
sol typo (odditlonllf back up allachod .,_. runoff coefflc:lentl for eedl land use/ sol typo
BASIN C BASIN CALCULATED 0.67 _,. combination)
BASIN AC BASIN CALCULATED 36U acres T olal area nraininn to the DOtential tratment location
LOW AC BASIN CALCULATED 5'.5 -Totaf aroa of LOW land use within BASIN
MED AC BASIN CALCULA TEO 5' 5 acres Totaf aroa of MEO land use within BASIN
HIG AC BASIN CALCULATED 5'.5 -Total see of HIG land use within BASIN
BMP AC BMP CALCULATED 0.37 acres Total •ee ol ootentlal hatment location
BMP SI.OPE BMP CALCULATED 005 fOOlllool 1~ aaoss DDlenUal treatment "2icaUon
BMP PIPE BMP CALCULATED y none Y or N· Indicate, 'fll'hether 8" e,:istlna storm dnm ..,_ Wlterseds lhe DDlential treatment loca11nr
BMP RIPARIAN AC BMP CALCULA TEO 0.09 acres Total a,u of nrunwi ~ nwnrmnirv within BMP
8MP BOGMAR AC BMP CALCULA TEO 0.00 acres Total area of ~marsh -latiorl ............ --wtuw. BMP
BMP SCRUBCHAP AC BMP CALCULATED 0.09 acres Total ... ol saub/chal)anllf -•I.Ion ~-within BMP
BASIN OU BASIN CALCULATED 67 none Estmated number of_.._ units within the area --. to the oolenti:al treatment location •12 9"LOW AC\+11• 5•MED ACl+l•J"HIG ACl
BASIN OLU BASIN CALCULATED LOW none Dominant land ... within lho ... ~ lo the potential ~ .. -, locollon cl.and UM cal,__ with wllhln BASIN
BMP SOit. BMP CALCULATED 1 none Dominant _.,. sol --wUhin lhe DDlentlal treatmenl kK:ation 11 = A. 2 :s 8 3 • C 4 = •-IOI .......... wlth--•test--withii BASIN
IF BASIN_OU >• 250 THEN BIO_DU_RES • 10
1 lo 10 nosult -'--lho polontlal ~eament locotion meets ~ unit criterion (or IF 200 « BASIN_DU < 250 THEN BIO_DU_RES = 5
BIO DU RES BMP CALCULATED 5 none lliolilers IF BASIN OU < 200 THEN BIO DU RES • 0
IF BMP _AC>= (0.02.BASIN_AC) THEN BIO_AC_RES • 10
IF (0015"8ASIN_AC) o BMP _AC< co.02·BAS1N_AC) THEN BIO_AC_RES • 8
1 to 10 result -'--lho polentlal ~-enl locotJon ,,_ OYOlable ••• criteria for IF (001•BAS1N_AC) <= BMP _AC< (0.015'BASIN_AC) THEN BIO_AC_RES = 6
BIO AC RES BMP CALCULATED 5 none Biofflers If BMP AC< I0.01"8ASIN ACI THEN BIO AC RES••
IF BMP _SLOPE<> 0 005 THEN BIO_SI.OPE_RES • 10
IF 0.005 < BMP _SLOPE<= 0.02 THEN BIO_SLOPE_RES = 8
IF O 02 < BMP _SI.OPE<= 0.10 THEN BIO_SI.OPE_RES = •
IF O 10 < BMP_SI.OPE 0020THENBIO_SlDPE_RES •2
BIO SLOPE RES BMP CALCULATED 5 none 1 to 10 nosult -'--the ...._,.., -local.Ion meets """'" atteria for Booriters IF BMP SI.OPE> 0.2 THEN BIO SI.OPE RES= 0
IF BMP _S01L = 1 THEN BIO_SOll_RES = 10
IF BMP _SOit. = 2 THEN BIO_SOll_RES • 9
If BMP SOil • 3 THEN 810 SOil RES • 5
BIO SOil RES BMP CALCULATED 5 none 1 lo 10 nosult -'--the oolentlal ~-ent locotion meets IOil ---for Bloll!ers IF BMP -SOil = ◄ THEN BIO -SOil -RES = 1
IF BMP _SCRUBCHAP • 0 AHO (BMP _BOGMAR > 0 OR BMP _RIPARIAN> 0)
THEN BIO_VEG_RES • 10
IF BMP _SCRUBCHAP • 0 ANO (BMP _BOGMAR • 0 ANO BMP _RIPARIAN• 0)
1 to 10 resut -'--the polonlief -ent loco11on meets vege1atlon group criteria for THEN BIO VEG RES • 5
BIO VEG RES BMP CALCULATED 5 none Blordlers IF BMP SCRUBCHAP > 0 THEN BIO VEG RES = 1
BIO DU WT USER 0.30 none w--·---to -unil Q1terfan '°' Bioflten 0.3
BIO AC WT USER 0.10 none w-... ~ to relative •eaotterlon lotllloR1ers 0.1
BIO SI.OPE WT USER 0.50 none We
,, __ -lo •-crtterlon for BJordlers 0.5
BIO SOIL WT USER 0.05 none w-1as -lo sol atterlon for Blolil1ers 0.05
BIO VEG WT USER 0.05 none w-1-• -to.-... -crtterion for Bk>fitera 0.05
BIO_TOTAL • (BIO_OU_WT"BIO_OU_RES)
• (BIO_AC_WT"IIIO_AC_RES) + (BIO_SLOPE_WT"BIO_SI.OPE_RES)
BIO TOTAL BMP CALCULATED 1.1 none W"""'ted total oa,,e for the..,.......,~■-locotion lo,• Blolilter I ♦IBIO SOil WT"BIO SOil RES\ +IBIO VEG wr·BIO VEG RES\
IF BASIN OU>= 250 THEN WET OU RES= 10
1 to 10 ,-A -'--the potential ~utment locotlon meets dwetlr,g d criterion for IF 200 <•-BASlN_DU c 250 THEN_ WET _DU_RES = 5
WET OU RES BMP CALCULATED 5 none Watlands IF BASIN OU < 200 THEN WET OU RES • 0
IF BMP _AC>= co.02·BAS1N_AC) THEN WET _AC_RES = 10
IF (0.015"BASIN_AC) <• BMP _AC< (o.02•BAS1N_AC) THEN WET_AC_RES • 8
1 to 10 nosult •'--the polonllal ~-loco11on meets --... attsil for If (0.01"BASIN_AC) .._ BMP _AC< (0.015"BASIN_AC) THEN WET_AC_RES • 6
WET AC RES BMP CALCULATED 5 none Weuands IF BMP AC< (0.01"8ASIN AC) THEN WET AC RES• 4
IF BMP _SI.OPE o 0.005 THEN WET_SI.OPE_RES • 10
IF 0.005 < BMP _SI.OPE<• 0.02 THEN WET_SI.OPE_RES • 8
IF 0.02 < BMP _SLOPE o 0.10 THEN WET_SLOPE_RES = •
IF 0.10 < BMP _SI.OPE o 0.20 THENWET_SI.OPE_RES = 2
WET SI.OPE RES BMP CALCULATED 5 none 1 to 10 result • ,--the ootentlal -locol.lon rMOtl •-criteria lot Woltands IF BMP SI.OPE > 0.2 THEN WET SI.OPE RES • 0
IF BMP _SOit. = 1 THEN WET _SOIL_RES • 10
IF BMP_SOll • 2 THEN WET_S01L_RES • 9
IF BMP _SOil • 3 THEN WET_SOll_RES • 5
WET SOIL RES BMP CALCULATED 5 none 1 lo 10 nosult • .__ lhe--.tlal hamonl locotion meets lOll--aiteria lo, Wetlands IF BMP SOil • • THEN WET SOil RES • 1
CartsbodWOMP _BMPEquatlons.xts S-11. 8/29"03 1 of 2
IF BMP _SCRUBCHAP • 0 ANO (BMP _BOGMAR > 0 OR BMP _RIPARIAN > 0)
THEN WET VEG RES• 10
IF BMP _SCRUBCHAP • 0 ANO (BMP _BOGMAR • 0 ANO BMP _RIPARIAN= 0)
1 lo 10 '""11. --lhe potenllol treatment loc8tion meob vegetation group r:rilorla ror THENWET_VEG_RES= 5
WET VEG RES BMP CAI.CUI.ATEO 5 none Wetlands IF BMP SCRUBCHAP > 0 THEN WET VEG RES • 1
WET OU WT USER 030 none Wairtrn assinn.n to dweUina unit criterion for Wetlands 03
WET N:, WT USER 025 none w to re!aUYe •ea criterion ror WeUands 0.25
WET SI.OPE WT USER 020 none w--ass__, to __,_ criterion for Wetlands 02
WET SOIL WT USER 0.05 none w-t essianed to IOI criterion for WeOands 005
WET VEG WT USER 0.20 _,., Wmnru ns..-to -.n11Uon crilerion for Wetlands 02
WET _TOTAi.. (WET _ou_wrWET _ou_RES)
+ (WET _N:._WT'WET _N:._RES) • (WET _SLOPE_WT'WET _SI.OPE_RES)
WET TOTAi. BMP CAI.CUI.A TED 7.7 none Weimted total score for Che notential ireatment loc-etion for a Wetland +IWET SOIL WT-WET SOIi. RESl +IWET VEG WT'WET VEG RESl
IF BMP _N;,. (BASIN_AC•BASIN_C'O 6125) THEN DET_AC_RES = 10
IF (BASIN_N:.•BASIN_C'0.<125) co BMP _N:. < (BASIN_AC"BASlN_C'O 6125)
1 lo 10 rnull • -well lhe potential-locetion ,,_Is..,._ areacrilorla lo, THEN OET _N:._RES • 8
DET AC RES BMP CAI.CUlA TEO 5 none Ootenoon Basins IF BMP N:, < !BASIN N:."IIASIN c·o.4/251 THEN OET AC RES • 5
IF BMP _SI.OPE<> 0.05 THEN OET _SI.OPE_RES • 10
IF 0.05 < BMP _SLOPE o 0.10 THEN OET_SI.OPE_RES • 5
t 1o 10 rnu11. --lho potenlial 1roa1ment 1oa111on rneeb slope critorla ro, Ootenoon IF 0.10 < BMP _SLOPE<• 0 20 THEN DET _SlOPE_RES = 2
DET SLOPE RES BMP CAI.CUlA TEO 5 none Basins IF BMP SI.OPE> 02 THEN OET SLOPE RES= 0
IF BMP SOIL • 1 THEN DET SOil RES • 10
IFBMP-SOII. •2THENOET-SOll-RES•9
I lo 10 resut. '-well lhe polenllal 1roalment location meels sol group crileria for Ootonllon IF BMP -SOIL • 3 THEN DET-SOil -RES = 5
DET SOil RES BMP CALCUlA TED 5 none Basm IF BMP-SOIL •4 THENDET-SOll-RES = 1
DET AC WT USER 0.60 none w.-.t ms--lo relative •ea criterion for Detention Basm 06
DET SLOPE WT USER 0.35 none w lo --crita1Dn far Detention Besn 035
OET SOIL WT USER 0.05 none w-1 ass-lo IOI criterion for Detention BasN 005
IF BMP PIPE= Y THEN DET TOTAi. = 0
IF BMP =PIPE= N THEN DET::TOTAI. =. (DET _Ac_wT·DET _AC_RES)
DET TOTAi. BMP CAI.CUlA TED 77 none W......,ed lolal ICON! for Ille ootential IAlalmenl locetion lor ■ Detention Basin ♦ !OET SLOPE wrOET SI.OPE RES\ •IDET SOIL WT·OET SOIL RES\
IF BMP_AC >= (BASIN_N:,•BASIN_C'0.6125) THEN INF _AC_RES • 10
IF (BASIN_Ac·BAS1N_c·o.4/25) <• BMP_N:. < (BASIN_N:."IIASIN_C'O 6125)
I lo 10 resut. --!he potential 1reatment """'11on rMets .....-..,.criteria for THEN INF _N:._RES = 8
INF N:, RES BMP CAI.CUlA TEO 5 none -IF BMP N:, < IBASIN N:,•BASIN C'O 41251 THEN INF AC RES• 5
IF BMP_SLOPE o 0.05THEN INF_SLOPE_RES • 10
IF O 05 < BMP _SLOPE<• 0.10 THEN INF _SLOPE_RES • 5
IF O 10 < BMP _SI.OPE<• 0 20 THEN INF _SLOPE_RES = 2
INF SLOPE RES BMP CALCUI.ATED 5 none 1 lo 10 ,_. '-well !he notential 1roalmenl loc■tion meela • ..._ criteria for tnfillrallon IF BMP SLOPE> 0.2 THEN INF SI.OPE RES • 0
IF BMP _SOil • 1 THEN INF _SOIL_RES • 10
IF BMP _SOIL= 2 THEN INF ~SOIL_RES • 8
IF BMP SOil • 3 THEN INF SOIL RES • 0
INF SOIL RES BMP CAI.ClllATEO 5 none 1 ID 10 reMlft •'-well !ho ootonllal 1reatmenl loc■tion meela so1--critorla lor lnli1nltlon IF BMP-SOIL =4 THEN INF-SOil-RES •0
INF AC WT BMP USER 0.20 none w--. a...-:i to relative ere.a criterion for lnfflration 0.2
INF SLOPE WT USER 0.10 none w--1 ass---to ----criterion for lnBtraUon 01 INF SOIL WT USER 0.70 none w losolcrll-lor lnfilnllion 07
INF _TOTAi. •+(INF _N:._WT•INF _-'C_RES)
INF TOTAi. BMP CAI.CIA.A TEO 77 none W.-...t lollll ""°'e for !he """"'lial 1roatment location lo, lnR1ra1lon • (INF SI.OPE wT·INF SLOPE RESI ♦ (INF SOil WT.INF SOil RES\
IF BMP_N:. u0.1 THEN HYO_AC_RES • 10
IF 0.05 <• BMP _N:, < 0.1 THEN HYO_N:,_RES = 8
1 lo 10 resull • --lho potenlial 1reatmenl """'11on meets,,,,_ ■ree criteria lo, IF002 <= BMP_N:. <005THEN HYO_-'C_RES • 5
HYO -'C RES BMP CAI.CUI.A TED 5 none ............... .,-....Ion IF BMP -'C < 0 02 THEN HYO N:. RES = 2
IF BMP SLOPE >• 0 05 THEN HYO SLOPE RES • 10
IF 0.05; BMP _SLOPE•• 0.02 THEN HYO_SlOPE_RES = 5 1 lo 10 resull • __ ,,,.potential,, __ -meela slope criteria lo, Hydrodynamic IF 0.02 > BMP _SLOPE>= 0.01 THEN HYO_SI.OPE_RES • 2
HYO SLOPE RES BMP CAI.CUlA TEO 5 none --IF BMP SI.OPE < 0.01 THEN HYO SLOPE RES • 0
HYO -'CWT USER 0.30 none w--aa•-to relatNe area criterion for ---1c -tors 0.3
HYO SLOPE WT USER 0.70 none w-------to---c:rilerlon for __,,le ___ 0.7
THEN HYO_TOTAI. • + (HYO_-'C_WT"HYO_N:._RES)
HYO TOTAi. 8\IP CAI.CIJI.ATED 77 none w-1ec11o1a1"""" for lhe ...,_,11811roatmen1 tocaUon ro, • ............... ., -......,. + !HYO SI.OPE wr•HYO SLOPE RESI
IF BMP_N:. >• 0.3 THEN Fll_N:._RES • 10
IF 0.2 <• BMP AC < 0 3 THEN Fil N:. RES = 8
I lo 10 resull • '--lhe -ial 1reatmenl localoon meels --area crllert■ for IF 0.1 o BMP ::N:. < 0 2 THEN Fll=-'C=RES • 5
FIL -'C RES BMP CAI.CUI.ATEO 5 none Fillratlon IF BMP N:, <O 1 THEN Fil AC RES= 2
IF BMP _SLOPE>• 0 05 THEN FIL_SLOPE_RES • 10
IF O.OS > BMP _SLOP£ >-s 0.02 THEN FJL_SLOPE_RES • 5
IF 0.02 > BMP _SLOPE>• 0.01 THEN Fll_SLOPE_RES • 2
Fil SLOPE RES BMP CAI.CUI.ATED 5 none 1 lo 10 ----!he oalmenl """'11on meelS....., crllorla lor Fl1rallon IF BMP SLOPE< 0.01 THEN Fil SLOPE RES= 0
Fil AC WT USER 030 none w---·-torelaUve Fl1rellon 0.3
Fil SI.OPE WT USER 0.70 none w lo Flllretlon 0.7
Fll_TOTAI. = + (Fll_-'C_WT'Fll_N:._RES)
Fil TOTAi. BMP CAI.CIJI.ATEO 7.7 none W....._led lolal .-e lo, lho nnl""lial ~oalment -for Fl1raticxt + /Fil SI.OPE WT.Fil SLOPE RES\
2ol 2
APPENDIXD
CASQA HANDBOOK BMP SIZING GUIDELINES
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company-Water Resources Division
KH:RC:nd/Report/14071-A.00I
09-19-03
. Caliform Stormwater Quality Association
.· Stor water Best Management Practice
Handbook
New ~ lopment and Redevelopme nt
Vegetated Swale -(-e., Ofll-1 '2A'Tl~30
Description
Vegetated swales are open, shallow channels with vegetation
covering the side slopes and bottom that collect and slowly
convey runoff flow to downstream discharge points. They are
designed to treat runoff through filtering by the vegetation in the
channel, filtering through a subsoil matrix, and/or infiltration
into the underlying soils. Swales can be natural or manmade.
They trap particulate pollutants (suspended solids and trace
metals), promote infiltration, and reduce the flow velocity of
stormwater runoff. Vegetated swales can serve as part of a
stormwater drainage system and can replace curbs, gutters and
storm sewer systems.
California Experience
Caltrans constructed and monitored six vegetated swales in
southern California. These swales were generally effective in
reducing the volume and mass of pollutants in runoff. Even in
the areas where the annual rainfall was only about 10 inches/yr,
the vegetation did not require additional irrigation. One factor
that strongly affected performance was the presence of large
numbers of gophers at most of the sites. The gophers created
earthen mounds, destroyed vegetation, and generally reduced the
effectiveness of the controls for TSS reduction.
Advantag~s
■ If properly designed, vegetated, and operated, swales can
serve as an aesthetic, potentially inexpensive urban
development or roadway drainage conveyance measure with
significant collateral water quality benefits.
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www .cabmphandbooks.com
Design Considerations
■ Tributary Area
■ Area Required
■ Slope
■ Water Availability
Targeted Constituents
✓ Sediment ...
✓ Nutrients • ✓ Trash •
✓ Metals ...
✓ Bacteria •
✓ Oil and Grease ...
✓ Organics ...
Legend (Removal Effectiveness)
• Low ■ High
... Medium
Storm water
Quality
Association
1 of 13
/ ~ ' ' TC ~;38\0frASI ~~Jl=T~ Ii{)·~·,. Vegetated Swale
■ Roadside ditches should be regarded as significant potential swale/buffer strip sites and
should be utilized for this purpose whenever possible.
Limitations
■ Can be difficult to avoid channelization.
■ May not be appropriate for industrial sites or locations where spills may occur
■ Grassed swales cannot treat a very large drainage area. Large areas may be divided and
treated using multiple swales. ·
■ A thick vegetative cover is needed for these practices to function properly.
■ They are impractical in areas with steep topography.
■ They are not effective and may even erode when flow velocities are high, if the grass cover is
not properly maintained.
■ In some places, their use is restricted by law: many local municipalities require curb and
gutter systems in residential areas.
■ Swales are mores susceptible to failure if not properly maintained than other treatment
BMPs.
Design and Sizing Guidelines
■ Flow rate based design determined by local requirements or sized so that 85% of the annual
runoff volume is discharged at less than the design rainfall intensity.
■ Swale should be designed so that the water level does not exceed 2/3rds the height of the
grass or 4 inches, which ever is less, at the design treatment rate.
■ Longitudinal slopes should not exceed 2.5%
■ Trapezoidal channels are normally recommended but other configurations, such as
parabolic, can also provide substantial water quality improvement and may be easier to mow
than designs with sharp breaks in slope.
■ Swales constructed in cut are preferred, or in fill areas that are far enough from an adjacent
slope to minimize the potential for gopher damage. Do not use side slopes constructed of
fill, which are prone to structural damage by gophers and other burrowing animals.
■ A diverse selection of low growing, plants that thrive under the specific site, climatic, and
watering conditions should be specified. Vegetation whose growing season corresponds to
the wet season are preferred. Drought tolerant vegetation should be considered especially
for swales that are not part of a regularly irrigated landscaped area.
■ The width of the swale should be determined using Manning's Equation using a value of
0.25 for Manning's n.
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Construction/Inspection C-onsiderations
■ Include directions in the specifications for use of appropriate fertilizer and soil amendments
based on soil properties determined through testing and compared to the needs of the
vegetation requirements.
■ Install swales at the time of the year when there is a reasonable chance of successful
establishment without irrigation; however, it is recognized that rainfall in a given year may
not be sufficient and temporary irrigation may be used.
■ If sod tiles must be used, they should be placed so that there are no gaps between the tiles;
stagger the ends of the tiles to prevent the formation of channels along the swale or strip.
■ Use a roller on the sod to ensure that no air pockets form between the sod and the soil.
■ Where seeds are used, erosion controls will be necessary to protect seeds for at least 75 days
after the first rainfall of the season.
Performance
The literature suggests that vegetated swales represent a practical and potentially effective
technique for controlling urban runoff quality. While limited quantitative performance data
exists for vegetated swales, it is known that check dams, slight slopes, permeable soils, dense
grass cover, increased contact time, and small storm events all contribute to successful pollutant
removal by the swale system. Factors decreasing the effectiveness of swales include compacted
soils, short runoff contact time, large storm events, frozen ground, short grass heights, steep
slopes, and high runoff velocities and discharge rates.
Conventional vegetated swale designs have achieved mixed results in removing particulate
pollutants. A study performed by the Nationwide Urban Runoff Program (NURP) monitored
three grass swales in the Washington, D.C., area and found no significant improvement in urban
runoff quality for the pollutants analyzed. However, the weak performance of these swales was
attributed to the high flow velocities in the swales, soil compaction, steep slopes, and short grass
height.
Another project in Durham, NC, monitored the performance of a carefully designed artificial
swale that received runoff from a commercial parking lot. The project tracked 11 storms and
concluded that particulate concentrations of heavy metals (Cu, Pb, Zn, and Cd) were reduced by
approximately 50 percent. However, the swale proved largely ineffective for removing soluble
nutrients.
The effectiveness of vegetated swales can be enhanced by adding check dams at approximately
17 meter (50 foot) increments along their length (See Figure 1). These dams maximize the
retention time within the swale, decrease flow velocities, and promote particulate settling.
Finally, the incorporation of vegetated filter strips parallel to the top of the channel banks can
help to treat sheet flows entering the swale.
Only g studies have been conducted on all grassed channels designed for water quality (Table 1).
The data suggest relatively high removal rates for some pollutants, but negative removals for
some bacteria, and fair performance for phosphorus .
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TC-30 Vegetated Swale
Table 1 Grassed swale pollutant removal efficiency data
Removal Efficiencies (% Removal}
Study TSS TP TN NOa Metals Bacteria Type
Caltrans 2002 77 8 67 66 83-90 -33 dryswales
Goldberg 1993 67.8 4.5 -31.4 42-62 -100 grassed channel
Seattle Metro and Washington 60 45 --25 2-16 -25 grassed channel Department of Ecology 1992
Seattle Metro and Washington 83 29 --25 46-73 -25 grassed channel Department of Ecology, 1992
Wang et al., 1981 Bo ---70-80 -dryswale
Dorman et al., 1989 98 18 -45 37-81 -dryswale
Harper, 1988 87 83 84 Bo 88-90 -dryswale
Kercher et al., 1983 99 99 99 99 99 -dry swale
Harper, 1988. 81 17 40 52 37-69 -wetswale
Koon, 1995 67 39 -9 -35 to 6 -wet swal~
While it is difficult to distinguish between different designs based on the small amount of
available data, grassed channels generally have poorer removal rates than wet and dry swales,
although some swales appear to export soluble phosphorus (Harper, 1988; Koon, 1995). It is not
clear why swales export bacteria. One explanation is that bacteria thrive in the warm swale
soils.
Siting Criteria
The suitability of a swale at a site will depend on land use, size of the area serviced, soil type,
slope, imperviousness of the contributing watershed, and dimensions and slope of the swale
system (Schueler et al., 1992). In general, swales can be used to serve areas ofless than 10 acres,
with slopes no greater than 5 %. Use of natural topographic lows is encouraged and natural
drainage courses should be regarded as significant local resources to be kept in use (Young et al.,
1996).
Selection Criteria (NCTCOG, 1993)
■ Comparable performance to wet basins
■ Limited to treating a few acres
■ Avail~bility of water during dry periods to maintain vegetation
■ Sufficient available land area
Research in the Austin area indicates that vegetated controls are effective at removing pollutants
even when dormant. Therefore, irrigation is not required to maintain growth during dry
periods, but may be necessary only to prevent the vegetation from dying.
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The topography of the site should permit the design of a channel with appropriate slope and
cross-sectional area. Site topography may also dictate a need for additional structural controls.
Recommendations for longitudinal slopes range between 2 and 6 percent. Flatter slopes can be
used, if sufficient to provide adequate co11-veyance. Steep slopes increase flow velocity, decrease
detention time, and may require energy dissipating and grade check. Steep slopes also can be
managed using a series of check dams to terrace the swale and reduce the slope to within
acceptable limits. The use of check dams with swales also promotes infiltration.
Additional Design Guidelines
Most of the design guidelines adopted for swale design specify a minimum hydraulic residence
time of 9 minutes. This criterion is based on the results of a single study conducted in Seattle,
Washington (Seattle Metro and Washington Department of Ecology, 1992), and is not well
supported. Analysis of the data collected in that study indicates that pollutant removal at a
residence time of 5 minutes was not significantly different, although there is more variability in
that data. Therefore, additional research in the design criteria for swales is needed. Substantial
pollutant removal has also been observed for vegetated controls designed solely for conveyance
(Barrett et al, 1998); consequently, some flexibility in the design is warranted.
Many design guidelines recommend that grass be frequently mowed to maintain dense coverage
near the ground surface. Recent research (Colwell et al., 2000) has shown mowing frequency or
grass height has little or no effect on pollutant removal.
Summary of Design Recommendations
1) The swale should have a length that provides a minimum hydraulic residence time of
at least 10 minutes. The maximum bottom width should not exceed 10 feet unless a
dividing berm is provided. The depth of flow should not exceed 2/ 3rds the height of
the grass at the peak of the water quality design storm intensity. The channel slope
should not exceed 2.5%.
2) A design grass height of 6 inches is recommended.
3) Regardless of the recommended detention time, the swale should be not less than
100 feet in length.
4) The width of the swale should be determined using Manning's Equation, at the peak
of the design storm, using a Manning's n of 0.25.
5) The swale can be sized as both a treatment facility for the design storm and as a
conveyance system to pass the peak hydraulic flows of the 100-year storm if it is
located "on-line." The side slopes should be no steeper than 3:1 (H:Y).
6) Roadside ditches should be regarded a~ significant potential swale/buffer strip sites
and should be utilized for this purpose whenever possible. If flow is to be introduced
through curb cuts, place pavement slightly above the elevation of the vegetated areas.
Curb cuts should be at least 12 inches wide to prevent clogging.
7)
January 2003
Swales must be vegetated in order to provide adequate treatment of runoff. It is
important to maximize water contact with vegetation and the soil surface. For
general purposes, select fine, close-growing, water-resistant grasses. If possible,
divert runoff (other than necessary irrigation) during the period of vegetation
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TC-30 Vegetated Swale
establishment. Where runoff diversion is not possible, cover graded and seeded
areas with suitable erosion control materials.
Maintenance
The useful life of a vegetated swale system is directly proportional to its maintenance frequency.
If properly designed and regularly maintained, vegetated swales can last indefinitely. The
maintenance objectives for vegetated swale systems include keeping up the hydraulic and
removal efficiency of the channel and maintaining a dense, healthy grass cover.
Maintenance activities should include periodic mowing (with grass never cut shorter than the
design flow depth), weed control, watering during drought conditions, reseeding of bare areas,
and clearing of debris and blockages. Cuttings should be removed from the channel and
disposed in a local composting facility. Accumulated sediment should also be removed
manually to avoid concentrated flows in the swale. The application of fertilizers and pesticides
should be minimal.
Another aspect of a good maintenance plan is repairing damaged areas within a channel. For
example, if the channel develops ruts or holes, it should be repaired utilizing a suitable soil that
is properly tamped and seeded. The grass cover should be thick; if it is not, reseed as necessary.
Any standing water removed during the maintenance operation must be disposed to a sanitary
sewer at an approved discharge location. Residuals (e.g., silt, grass cuttings) must be disposed
in accordance with local or State requirements. Maintenance of grassed swales mostly involves
maintenance of the grass or wetland plant cover. Typical maintenance activities are
summarized below:
■ Inspect swales at least twice annually for erosion, damage to vegetation, and sediment and
debris accumulation preferably at the end of the wet season to schedule summer
maintenance and before major fall runoff to be sure the swale is ready for winter. However,
additional inspection after periods of heavy runoff is desirable. The swale should be checked
for debris and litter, and areas of sediment accumulation.
■ Grass height and mowing frequency may not have a large impact on pollutant removal.
Consequently, mowing may only be necessary once or twice a year for safety or aesthetics or
to suppress weeds and woody vegetation.
■ Trash tends to accumulate in swale areas, particularly along highways. The need for litter
removal is determined through periodic inspection, but litter should always be removed
prior to mowing.
■ Sediment accumulating near culverts and in channels should be removed when it builds up
to 75 mm (3 in.) at any spot, or covers vegetation.
■ Regularly inspect swales for pools of standing water. Swales can become a nuisance due to
mosquito breeding in standing water if obstructions develop (e.g. debris accumulation,
invasive vegetation) and/ or if proper drainage slopes are not implemented and maintained.
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Vegetated Swale
Cost
Construction Cost
TC-30
Little data is available to estimate the difference in cost between various swale designs. One
study (SWRPC, 1991) estimated the construction cost of grassed channels at approximately
$0.25 per ft2. This price does not include design costs or contingencies. Brown and Schueler
(1997) estimate these costs at approximately 32 percent of construction costs for most
stormwater management practices. For swales, however, these costs would probably be
significantly higher since the construction costs are so low compared with other practices. A
more realistic estimate would be a total cost of approximately $0.50 per ft2, which compares
favorably with other stormwater management practices .
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TC-30
Table 2 Swale Cost Estimate (SEWRPC, 1991)
Unit Cost
Component Unit Extent Low Moderate High Low
MobHization I Swale 1 $107 $274 $441 $107
Demobllizatlon-Ught
SilB Preparatia,
Clearingb._ ............. Aas 0.5 $2,200 $3,800 $5,400 $1,100 Grubbing'! .............. Aas 0.25 $3,800 $5,200 $8,600 $QSO General Yd3 372 $2.10 $3.70 $5.30 $781 Excavation" .. _ ........
LewtandTffl" ........ Yd2 1,210 $0.20 $0.35 $0.50 $242
Silas Development
Salvaged TopsoQ
Yd2 1,210 $0.40 $1.00 $1.60 $464 Seed, and Mulch' ..
SocfJ •....... _, •.......•.. Yd2 1,210 $1.20 $2.40 $3.60 $1,452
subtotal -----$5,118
Contingencies Swale 1 25'1ri 25% 25'1ri $1,27Q
Total -----$8395
Source: (SEWRPC, 1991)
Note: MobifmilionldomobHization refers to the organlZBllai and plarmlng involved In establishing a vegetative swale.
• Swale has a bottom width of 1.0 foot, a top Width of 10 feet With 1:3 side slopes, and a 1,000-foot length.
b Area cleared = (top width + 1 o feet) x swale length.
c Area grubbed = (top width x swale length).
dVofume excavated = (0.67 x top width x swale depth) x swale length (parabolic cross-section).
• Area 1llled = (top width+ 8Cswale depth2:) x swale length {parabolic cross-section).
3(top width)
'Area seeded= area cleared x 0.5.
• Area sodded = area cleared x 0.5.
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Vegetated Swale
Total Cost
Moderate High
$274 $441
$1,QOO $2,700
$1,300 $1,650
$1,376 $1,Q72
$424 $605
$1,210 $1,Q38
$2,Q04 $4,358
$Q,388 $13,660
$2.347 $3,415
$11 7a5 $17075
January 2003
• Vegetated Swale
Table 3 Estimated Maintenance Costs (SEWRPC. 19911
Component Unit Cost
I.awn Mawing $O.85 / 1,000ft2/mowing
General Lawn Cara $9.O0 / 1,00Off'/year
Swale Debris and Utter $0.10 / I near foot/ year
Ramcnal
Grass Reseeding with $0.a0/yd2
Mulch and Fertilizer
Program Administration and $0.15 / llnear ft>ot I year,
SwalelnspecBon plus $25 / Inspection
Total ..
January 2003
Swale Size
(Depth and Top Width)
1.5 Foot Depth, One-3-Foot Depth, 3-Foot
Foot Bottom Width, Bottom Width. 21-Foot
10-FootTop Width TopWldth
SD.14 /llnmrfoot $0.21 /Dnesrfoot
SD.18 /linearfoot $0.28 I ftnear foot
SD.1O /llnearfoot $0.10 /linear foot
SD.O1 /llnearfoot $O.O1 /finearfoot
SD.15 llinearfoot $0.15 /finearfoot
$0.51 f linear foot $ 0.75 I llne• foot
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Comment
Lawn maintenance area=(fop
width + 10 f99t) x length. Maw
eight times per year
Lawn maintenance area= (top
wid1h + 1Ofeat) xleng1h
-
Ania rewgetated equals 1 %
of lawn maintonancearaa per
ymr
Inspect four times per yaer
-
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TC-30 Vegetated Swale
Maintenance Cost
Caltrans (2002) estimated the expected annual maintenance cost for a swale with a tributary
area of approximately 2 ha at approximately $2,700. Since almost all maintenance consists of
mowing, the cost is fundamentally a function of the mowing frequency. Unit costs developed by
SEWRPC are shown in Table 3. In many cases vegetated channels would be used to convey
runoff and would require periodic mowing as well, so there may be little additional cost for the
water quality component. Since essentially all the activities are related to vegetation
management, no special training is required for maintenance personnel.
References and Sources of Additional Information
Barrett, Michael E., Walsh, Patrick M., Malina, Joseph F., Jr., Charbeneau, Randall J, 1998,
"Perlormance of vegetative controls for treating highway runoff," ASCE Journal of
Environmental Engineering, Vol. 124, No. 11, pp. 1121-1128.
Brown, W., and T. Schueler. 1997. The Economics of Stormwater BMPs in the Mid-Atlantic
Region. Prepared for the Chesapeake Research Consortium, Edgewater, MD, by the Center for
Watershed Protection, Ellicott City, MD.
Center for Watershed Protection (CWP). 1996. Design ofStormwater Filtering Systems.
Prepared for the Chesapeake Research Consortium, Solomons, MD, and USEPA Region V,
Chicago, IL, by the Center for Watershed Protection, Ellicott City, MD.
Colwell, Shanti R., Horner, Richard R., and Booth, Derek B., 2000. Characterization of
Performance Predictors and Evaluation of Mowing Practices in Bio.filtration Swales. Report
to King County Land And Water Resources Division and others by Center for Urban Water
Resources Management, Department of Civil and Environmental Engineering, University of
Washington,Seattle, WA
Dorman, M.E., J. Hartigan, R.F. Steg, and T. Quasebarth. 1989. Retention, Detention and
Overland Flow for Pollutant Removal From Highway Stormwater Runoff. Vol.1. FHWA/RD
, 89/202. Federal Highway Administration, Washington, DC.
Goldberg. 1993. Dayton Avenue Swale Bio.filtration Study. Seattle Engineering Department,
Seattle, WA.
Harper, H. 1988. Effects ofStormwater Management Systems on Groundwater Quality.
Prepared for Florida Department of Environmental Regulation, Tallahassee, FL, by
Environmental Research and Design, Inc., Orlando, FL.
Kercher, W.C., J.C. Landon, and R. Massarelli. 1983. Grassy swales prove cost-effective for
water pollution control. Public Works, 16: 53-55.
Koon, J. 1995. Evaluation of Water Quality Ponds and Swales in the Issaquah/East Lake
Sammamish Basins. King County Surface Water Management, Seattle, WA, and Washington
Department of Ecology, Olympia, WA.
Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side
Of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs.
Stormwater 3(2): 24-39.Oakland, P.H. 1983. An evaluation of stormwater pollutant removal
10 of 13 California Stormwater BMP Handbook
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Vegetated Swale TC-30
through grassed swale treatment. In Proceedings of the International Symposium of Urban
Hydrology, Hydraulics and Sediment Control, Lexington, KY. pp. 173-182.
Occoquan Watershed Monitoring Laboratory. 1983. Final Report: Metropolitan Washington
Urban Runoff Project. Prepared for the Metropolitan Washington Council of Governments,
Washington, DC, by the Occoquan Watershed Monitoring Laboratory, Manassas, VA.
Pitt, R., and J. McLean. 1986. Toronto Area Watershed Management Strategy Study: Humber
River Pilot Watershed Project. Ontario Ministry of Environment, Toronto, ON.
Schueler, T. 1997. Comparative Pollutant Removal Capability of Urban BMPs: A reanalysis.
Watershed Protection Techniques 2(2):379-383.
Seattle Metro and Washington Department of Ecology. 1992. Bio.filtration Swale Performance:
Recommendations and Design Considerations. Publication No. 657. Water Pollution Control
Department, Seattle, WA.
Southeastern Wisconsin Regional Planning Commission (SWRPC). 1991. Costs of Urban
Nonpoint Source Water Pollution Control Measures. Technical report no. 31. Southeastern
Wisconsin Regional Planning Commission, Waukesha, WI.
U.S. EPA, 1999, Stormwater Fact Sheet: Vegetated Swales, Report# 832-F-99-006
http://www.epa.gov/owm/mtb/vegswale.pdf, Office of Water, Washington DC.
Wang, T., D. Spyridakis, B. Mar, and R. Horner. 1981. Transport, Deposition and Control of
Heavy Metals in Highway Runoff. FHWA-WA-RD-39-10. University of Washington,
Department of Civil Engineering, Seattle, WA.
Washington State Department of Transportation, 1995, Highway Runoff Manual, Washington
State Department of Transportation, Olympia, Washington.
Welborn, C., and J. Veenhuis. 1987. Effects of Runoff Controls on the Quantity and Quality of
Urban Runoff in Two Locations in Austin, TX. USGS Water Resources Investigations Report
No. 87-4004. U.S. Geological Survey, Reston, VA.
Yousef, Y., M. Wanielista, H. Harper, D. Pearce, and R. Tolbert. 1985. Best Management
Practices: Removal of Highway Contaminants By Roadside Swales. University of Central
Florida and Florida Department of Transportation, Orlando, FL.
Yu, S., S. Barnes, and V. Gerde. 1993. Testing of Best Management Practices for Controlling
Highway Runoff. FHWA/VA-93-R16. Virginia Transportation Research Council,
Charlottesville, VA.
Information Resources
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual. www.mde.state.md. us/ environment/wma/stormwatermanual. Accessed May 22,
2001.
Reeves, E. 1994. Performance and Condition of Biofilters in the Pacific Northwest. Watershed
Protection Techniques 1(3):117-119.
January 2003 California Stormwater BMP Handbook
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TC-30 Vegetated Swale
Seattle Metro and Washington Department of Ecology. 1992. Bio.filtration Swale Performance.
Recommendations and Design Considerations. Publication No. 657. Seattle Metro and
Washington Department of Ecology, Olympia, WA.
USEPA 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in
Coastal Waters. EPA-840-B-92-002. U.S. Environmental Protection Agency, Office of Water.
Washington, DC. ·
Watershed Management Institute (WMI). 1997. Operation, Maintenance, and Management of
Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency, Office
of Water. Washington, DC, by the Watershed Management Institute, Ingleside, MD.
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Vegetated Swale
-~;§05~,~·~ r L
Notation:
Provide for scour
proleClion.
(a) Cross section of swale with check dam.
l = longth or swalo lmpo1a1dmont ,,., por chock dam (ft) (b) Dimensional \'lt'W' or swale lmpoandment area.
01 = Oopttl or c:helck dam (ft)
Sa = Bottom alpo or ,wale (Ml)
W = Top width or check dam (rt)
W8 = Bottom width or check dam (ft)
Z1&z = Ratio or horizontal to vertical change In awale slclo alopo (Ml)
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TC-30
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)
Wet Ponds
Description
Wet ponds (a.k.a. stormwater ponds, retention ponds, wet extended
detention ponds) are constructed basins that have a permanent pool
of water throughout the year (or at least throughout the wet season)
and differ from constructed wetlands primarily in having a greater
average depth. Ponds treat incoming storrnwater runoff by settling
and biological uptake. The primary removal mechanism is settling
as stormwater runoff resides in this pool, but pollutant uptake,
particularly of nutrients, also occurs to some degree through
biological activity in the pond. Wet ponds are among the most
widely used stormwater practices. While there are several different
versions of the wet pond design, the most common modification is
the extended detention wet pond, where storage is provided above
the permanent pool in order to detain storrnwater runoff and
promote settling. The schematic diagram is of an on-line pond that
includes detention for larger events, but this is not required in all
areas of the state.
California Experience
Caltrans constructed a wet pond in northern San Diego County (I-5
and La Costa Blvd.). Largest issues at this site were related to vector
control, vegetation management, and concern that endangered
species would become resident and hinder maintenance activities.
Advantages
■ If properly designed, constructed and maintained, wet basins
can provide substantial aesthetic/recreational value and wildlife
and wetlands habitat.
■ Ponds are often viewed as a public amenity when integrated into a
park setting.
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TC-20
Design Considerations
■ Area Required
■ Slope
■ Water Availability
■ Aesthetics
■ Environmental Side-effects
Targeted Constituents
✓ Sediment
✓ Nutrients
✓ Trash
✓ Metals
✓ Bacteria
✓ Oil and Grease
✓ Organics
Legend (Removal Effectiveness)
• .. Low ■ High
Medium
:f:i['•}i •r::.:,r.J i:._~~-;::'\., ,~,,.-·/i>; t
'(}'!'-. ..
.. -, California
Stormwater
Quality
Association ,.
■
.A
■
■
■
■
■
1 of 15
TC-20 Wet Ponds
■ Due to the presence of the permanent wet pool, properly designed and maintained wet basins
can provide significant water quality improvement across a relatively broad spectrum of
constituents including dissolved nutrients.
■ Widespread application with sufficient capture volume can provide significant control of channel
erosion and enlargement caused by changes to flow frequency relationships resulting from the
increase of impervious cover in a watershed.
Limitations
■ Some concern about safety when constructed where there is public access.
■ Mosquito and midge breeding is likely to occur in ponds.
■ Cannot be placed on steep unstable slopes.
■ Need for base flow or supplemental water if water level is to be maintained.
■ Require a relatively large footprint
■ Depending on volume and depth, pond designs may require approval from the State Division of
Safety of Dams
Design an·d Sizing Guidelines
■ Capture volume determined by local requirements or sized to treat 85% of the annual runoff
volume.
■ Use a draw down time of 48 hours in most areas of California. Draw down times in excess of 48
hours may result in vector breeding, and should be used only after coordination with local vector
control authorities. Draw down times ofl~ss than 48 hours should be limited to BMP drainage
areas with coarse soils that readily settle and to watersheds where warming may be detrimental
to downstream fisheries.
■ Permanent pool volume equal to twice the water quality volume.
■ Water depth not to exceed about 8 feet.
■ Wetland vegetation occupying no more than 25% of surface area.
■ Include energy dissipation in the inlet design and a sediment forebay to reduce resuspension of
accumulated sediment and facilitate maintenance.
■ A maintenance ramp should be included in the design to facilitate access to the forebay for
maintenance activities and for vector surveillance and control.
■ To facilitate vector surveillance and control activities, road access should be provided along
at least one side of BMPs that are seven meters or less in width. Those BMPs that have
shoreline-to-shoreline distances in excess of seven meters should have perimeter road access
on both sides or be designed such that no parcel of water is greater than seven meters from
the road.
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Constructi.on/lnspecti.on Considerati.ons
■ In areas with porous soils an impermeable liner may be required to maintain an adequate
permanent pool level.
■ Outlet structures and piping should be installed with collars to prevent water from seeping
through the fill and causing structural failure.
■ Inspect facility after first large storm to determine whether the desired residence time has been
achieved.
Performance
The observed pollutant removal of a wet pond is highly dependent on two factors: the volume of the
permanent pool relative to the amount of runoff from the typical event in the area and the quality of
the base flow that sustains the permanent pool. A recent study (Caltrans, 2002) has documented
that if the permanent pool is much larger than the volume of runoff from an average event, then
displacement of the permanent pool by the wet weather flow is the primary process. A statistical
comparison of the wet pond discharge quality during dry and wet weather shows that they are not
significantly different. Consequently, there is a relatively constant discharge quality during storms
that is the same as the concentrations observed in the pond during ambient (dry weather)
conditions. Consequently, for most constituents the performance of the pond is better characterized
by the average effluent concentration, rather than the "percent reduction," which has been the
conventional measure of performance. Since the effluent quality is essentially constant, the percent
reduction observed is mainly a function of the influent concentrations observed at a particular site.
The dry and wet weather discharge quality is, therefore, related to the quality of the base flow that
sustains the permanent pool and of the transformations that occur to those constituents during their
residence in the basin. One could potentially expect a wide range of effluent concentrations at
different locations even if the wet ponds were designed according to the same guidelines, if the
quality of the base flow differed significantly. This may explain the wide range of concentration
reductions reported in various studies.
Concentrations of nutrients in base flow may be substantially higher than in urban stormwater
runoff. Even though these concentrations may be substantially reduced during the residence time of
the base flow in the pond, when this water is displaced by wet weather flows, concentrations may still
be quite elevated compared to the levels that promote eutrophication in surface water systems.
Consequently comparing influent and effluent nutrient concentrations during wet weather can make
the performance seem highly variable.
Relatively small perennial flows may often substantially exceed the wet weather flow treated.
Consequently, one should also consider the load reduction observed under ambient conditions when
assessing the potential benefit to the receiving water.
Siting Criteria
Wet ponds are a widely applicable stormwater management practice and can be used over a broad
range of storm frequencies and sizes, drainage areas and land use types. Although they have limited
applicability in highly urbanized settings and in arid climates, they have few other restrictions. Wet
basins may be constructed on-or off-line and can be sited at feasible locations along established
drainage ways with consistent base flow. An off-line design is preferred. Wet basins are often
utilized in smaller sub-watersheds and are particularly appropriate in areas with residential land
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uses or other areas where high nutrient loads are considered to be potential problems (e.g., golf
courses).
Ponds do not consume a large area (typically 2-3 percent of the contributing drainage area);
however, these facilities are generally large. Other practices, such as filters or swales, may be
"squeezed" into relatively unusable land, but ponds need a relatively large continuous area. Wet
basins are typically used in drainage basins of more than ten acres and less than one square mile
(Schueler et al., 1992). Emphasis can be placed in siting wet basins in areas where the pond can also
function as an aesthetic amenity or in conjunction with other stormwater management functions.
Wet basin application is appropriate in the following settings: (1) where there is a need to achieve a
reasonably high level of dissolved contaminant removal and/or sediment capture; (2) in small to
medium-sized regional tributary areas with available open space and drainage areas greater than
about 10 ha (25 ac.); (3) where base flow rates or other channel flow sources are relatively consistent
year-round; (4) in residential settings where aesthetic and wildlife habitat benefits can be
appreciated and maintenance activities are likely to be consistently undertaken.
Traditional wet extended detention ponds can be applied in most regions of the United States, with
the exception of arid climates. In arid regions, it is difficult to justify the supplemental water needed
to maintain a permanent pool because of the scarcity of water. Even in semi-arid Austin, Texas, one
study found that 2.6 acre-feet per year of supplemental water was needed to maintain a permanent
pool of only 0.29 acre-feet (Saunders and Gilroy, 1997): Seasonal wet ponds (i.e., ponds that
maintain a permanent pool only during the wet season) may prove effective in areas with distinct wet
and dry seasons; however, this configuration has not been extensively evaluated.
Wet ponds may pose a risk to cold water systems because of their potential for stream warming.
When water remains in the permanent pool, it is heated by the sun. A study in Prince George's
County, Maryland, found that stormwater wet ponds heat stormwater by about 9°F from the inlet to
the outlet (Galli, 1990).
Additional Design Guidelines
Specific designs may vary considerably, depending on site constraints or preferences of the designer
or community. There are several variations of the wet pond design, including constructed wetlands,
and wet extended detention ponds. Some of these design alternatives are intended to make the
practice adaptable to various sites and to account for regional constraints and opportunities. In
conventional wet ponds, the open water area comprises 50% or more of the total surface area of the
pond. The permanent pool should be no deeper than 2.5 m (8 feet) and should average 1.2 -2 m (4-6
feet) deep. The greater depth of this configuration helps limit the extent of the vegetation to an
aquatic bench around the perimeter of the pond with a nominal depth of about 1 foot and variable
width. This shallow bench also protects the banks from erosion, enhances habitat and aesthetic
values, and reduces the drowning hazard.
The wet extended detention pond combines the treatment concepts of the dry extended detention
pond and the wet pond. In this design, the water quality volume is ·detained above the permanent
pool and released over 24 hours. In addition to increasing_the residence time, which improves
pollutant removal, this design also attenuates peak runoff rates. Consequently, this design
alternative is recommended.
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Pretreatment incorporates design features that help to settle out coarse sediment particles. By
removing these particles from runoff before they reach the large permanent pool, the maintenance
burden of the pond is reduced. In ponds, pretreatment is achieved with a sediment forebay. A
sediment forebay is a small pool (typically about 10 percent of the volume of the permanent pool).
Coarse particles remain trapped in the forebay, and maintenance is performed on this smaller pool,
eliminating the need to dredge the entire pond.
There are a variety of sizing criteria for determining the volume of the permanent pool, mostly
related to the water quality volume (i.e., the volume of water treated for pollutant removal) or the
average storm size in a particular area. In addition, several theoretical approaches to determination
of permanent pool volume have been developed. However, there is little empirical evidence to
support these designs. Consequently, a simplified method (i.e., permanent pool volume equal to
twice the water quality volume) is recommended.
Other design features do not increase the volume of a pond, but can increase the amount of time
stormwater remains in the device and eliminate short-circuiting. Ponds should always be designed
with a length-to-width ratio of at least 1.5:1, where feasible. In addition, the design should
incorporate features to lengthen the flow path through the pond, such as underwater berms designed
to create a longer route through the pond. Combining these two measures helps ensure that the
entire pond volume is used to treat stormwater. Wet ponds with greater amounts of vegetation often
have channels through the vegetated areas and contain dead areas where stormwater is restricted
from mixing with the entire permanent pool, which can lead to less pollutant removal.
Consequently, a pond with open water comprising about 75% of the surface area is preferred.
Design features are also incorporated to ease maintenance of both the forebay and the main pool of
ponds. Ponds should be designed with a maintenance access to the fore bay to ease this relatively
routine (every 5-7 year) maintenance activity. In addition, ponds should generally have a drain to
draw down the pond for vegetation harvesting or the more infrequent dredging of the main cell of the
pond.
Cold climates present many challenges to designers of wet ponds. The spring snowmelt may have a
high pollutant load and a large volume to be treated. In addition, cold winters may cause freezing of
the permanent pool or freezing at inlets and outlets. Finally, high salt concentrations in runoff
resulting from road salting, and sediment loads from road sanding, may impact pond vegetation as
well as reduce the storage and treatment capacity of the pond.
One option to deal with high pollutant loads and runoff volumes during the spring snowmelt is the
use of a seasonally operated pond to capture snowmelt during the winter and retain the permanent
pool during warmer seasons. In this option, proposed by Oberts (1994), the pond has two water
quality outlets, both equipped with gate valves. In the summer, the lower outlet is closed. During
the fall and throughout the winter, the lower outlet is opened to draw down the permanent pool. As
the spring melt begins, the lower outlet is closed to provide detention for the melt event. The,
manipulation of this system requires some labor and vigilance; a careful maintenance agreement
should be confirmed.
Several other modifications may help to improve the performance of ponds in cold climates.
Designers should consider planting the pond with salt-tolerant vegetation if the facility receives road
runoff. In order to counteract the effects of freezing on inlet and outlet structures, the use of inlet
and outlet structures that are resistant to frost, including weirs and larger diameter pipes, may be
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useful. Designing structures on-line, with a continuous flow of water through the pond, will also help
prevent freezing of these structures. Finally, since freezing of the permanent pool can reduce the
effectiveness of pond systems, it is important to incorporate extended detention into the design to
retain usable treatment area above the permanent pool when it is frozen.
Summary of Design Recommendations
(1) Facility Sizing -The basin should be sized to hold the permanent pool as well as the
required water quality volume. The volume of the permanent pool should equal twice the
water quality volume.
(2) Pond Configuration -The wet basin should be configured as a two stage facility with a
sediment forebay and a main pool. The basins should be wedge-shaped, narrowest at the
inlet and widest at the outlet. The minimum length to width ratio should be 1.5 where
feasible. The perimeter of all permanent pool areas with depths of 4.0 feet or greater
should be surrounded by an aqu.atic bench. This bench should extend inward 5-10 feet
from the perimeter of the permanent pool and should be no more than 18 inches below
normal depth. The area of the bench should not exceed about 25% of pond surface. The
depth in the center of the basin should be 4 -8 feet deep to prevent vegetation from
encroaching on the pond open water surface.
(3) Pond Side Slopes -Side slopes of the basin should be 3:1 (H:V) or flatter for grass
stabilized slopes. Slopes steeper than 3:1 should be stabilized with an appropriate slope
stabilization practice.
(4) Sediment Forebay -A sediment forebay should be used to isolate gross sediments as they
enter the facility and to simplify sediment removal. The sediment forebay should consist
of a separate cell formed by an earthen berm, gabion, or loose riprap wall. The forebay
should be sized to contain 15 to 25% of the permanent pool volume and should be at least
3 feet deep. Exit velocities from the forebay should not be erosive. Direct maintenance
access should be provided to the forebay. The bottom of the forebay may be hardened
(concrete) to make sediment removal easier. A fixed vertical sediment depth marker
should be installed in the forebay to measure sediment accumulation.
(5) Outflow Structure -Figure 2 presents a schematic representation of suggested outflow
structures. The outlet structure should be designed to drain the water quality volume
over 24 hours with the orifice sized according to the equation presented in the Extended
Detention Basin fact sheet. The facility should have a separate drain pipe with a manual
valve that can completely or partially drain the pond for maintenance purposes. To allow
for possible sediment accumulation, the submerged end of the pipe should be protected,
and the drain pipe should be sized to drain the pond within 24 hours. The valve should
be located at a point where it can be operated in a safe and convenient manner.
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For on-line facilities, the principal and emergency spillways must be sized to provide 1.0
foot of freeboard during the 25-year event and to safely pass the 100-year flood. The
embankment should be designed in accordance with all relevant specifications for small
dams.
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(6)
(7)
"When Pond is Sized for
lockable Overflow Grates for Larger Stonns \
Overflow and Outlet Pipe Are Sized for Peak Shavings
Stiff Steel Screen for Tresh Skimmer
Open on Top and -eottom
\ ~~
~ > 4D of Riser
__ ,-Pond Bottom Dreln Valve
Sediment Removal; that is V5NR < 2.6 Size Base to Prevent Hydrostatic Uplift
Front View
Overflow for Large Stonn Peak"Shaving
Negatively Sloped Pipe at Least
1 ft (0.3 m} below Pond's Surface
(bl
(c) Side View
Splitter Box -When the pond is designed as an off-line facility, ·a splitter structure is used
to isolate the water quality volume. The splitter box, or other flow diverting approach,
should be designed to convey the 25-year event while providing at least 1.0 foot of
freeboard along pond side slopes.
Vegetation -A plan should be prepared that indicates how aquatic and terrestrial areas
1 will be vegetatively stabilized. Wetland vegetation elements should be placed along the
aquatic bench or in the shallow portions of the permanent pool. The optimal elevation for
planting of wetland vegetation is within 6 inches vertically of the normal pool elevation.
A list of some wetland vegetation native to California is presented in Table 1.
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Table 1 California Wetland Vegetation
Botanical Name Common Name
BACCHARIS SALICIFOLIA MULE FAT
FRANKENIA GRANDIFOLIA HEATH
SALIX GOODINGII BLACK WILLOW
SALIX LASIOLEPIS ARROYO WILLOW
SAMUCUS MEXICANUS MEXICAN ELDERBERRY
HAPLOPAPPUSVENETUS COAST GOLDENBRUSH
DISTICHIS SPICATA SALT GRASS
LIMONIUM CALIFORNICUM COASTAL STATICE
ATRIPLEX LENTIFORMIS COASTAL QUAIL BUSH
BACCHARIS PILULARIS CHAPARRAL BROOM
MIMULUS LONGIFLORUS MONKEY FLOWER
SCIRPUS CALIFORNICUS BULRUSH
SCIRPUS ROBUSTUS BULRUSH
1YPHA LATIFOLIA BROADLEAF CATTAIL
JUNCUS ACUTUS RUSH
Maintenance
The amount of maintenance required for a wet pond is highly dependent on local regulatory
agencies, particular health and vector control agencies. These agencies are often extremely
concerned about the potential for mosquito breeding that may occur in the permanent pool. Even
though mosquito fish (Gambusia affinis) were introduced into a wet pond constructed by Caltrans in
the San Diego area, mosquito breeding was routinely observed during inspections. In addition, the
vegetation at this site became sufficiently dense on the bench around the edge of the pool that
mosquito fish were unable to enter this area to feed upon the mosquito larvae. The vegetation at this
site was particularly vigorous because of the high nutrient concentrations in the perennial base flow
(15.5 mg/L N03-N) and the mild climate, which permitted growth year round. Consequently, the
vector control agency required an annual harvest of vegetation to address this situation. This harvest
can be very expensive.
On the other hand, routine harvesting may increase nutrient removal and prevent the export of these
constituents from dead and dying plants falling in the water. A previous study (Faulkner and
Richardson, 1991) documented dramatic reductions in nutrient removal after the first several years
of operation and related it to the vegetation achieving a maximum density. That content then
decreases through the growth season, as the total biomass increases. In effect, the total amount of
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nutrients/m2 of wetland remains essentially the same from June through September, when the
plants start to put the P back into the rhizomes. Therefore harvesting should occur between June
and September. Research also suggests that harvesting only the foliage is less effective, since a very
small percentage of the removed nutrients is taken out with harvesting.
Since wet ponds are often selected for their aesthetic considerations as well as pollutant removal,
they are often sited in areas of high visibility. Consequently, floating litter and debris are removed
more frequently than would be required simply to support proper functioning of the pond and outlet.
This is one of the primary maintenance activities performed at the Central Market Pond located in
Austin, Texas. In this type of setting, vegetation management in the area surrounding the pond can
also contribute substantially to the overall maintenance requirements.
One normally thinks of sediment removal as one of the typical activities performed at stormwater
BMPs. This activity does not normally constitute one of the major activities on an annual basis. At
the concentrations ofTSS observed in urban runoff from stable watersheds, sediment removal may
only be required every 20 years or so. Because this activity is performed so infrequently, accurate
costs for this activity are lacking.
In addition to regular maintenance activities needed to maintain the function of wet ponds, some
design features can be incorporated to ease the maintenance burden. In wet ponds, maintenance
reduction features include techniques to reduce the amount of maintenance needed, as well as
techniques to make regular maintenance activities easier.
One potential maintenance concern in wet ponds is clogging of the outlet. Ponds should be designed
with a non-clogging outlet such as a reverse-slope pipe, or a weir outlet with a trash rack. A reverse-
slope pipe draws from below the permanent pool extending in a reverse angle up to the riser and
establishes the water elevation of the permanent pool. Because these outlets draw water from below
the level of the permanent pool, they are less likely to be clogged by floating debris.
Typical maintenance activities and frequencies include:
■ Schedule semiannual inspections for burrows, sediment accumulation, structural integrity of the
outlet, and litter accumulation.
■ Remove accumulated trash and debris in the basin at the middle and end of the wet season. The
frequency of this activity may be altered to meet specific site conditions and aesthetic
considerations.
■ Where permitted by the Department of Fish and Game or other agency regulations, stock wet
ponds/constructed wetlands regularly with mosquito fish (Gambusia spp.) to enhance natural
mosquito and midge control.
■ Introduce1 mosquito fish and maintain vegetation to assist their movements to control
mosquitoes, as well as to provide access for vector inspectors. An annual vegetation harvest in
summer appears to be optimum, in that it is after the bird breeding season, mosquito fish can
provide the needed control until vegetation reaches late summer density, and there is time for re-
growth for runoff treatment purposes before the wet season. In certain cases, more frequent
plant harvesting may be required by local vector control agencies.
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■ Maintain emergent and perimeter shoreline vegetation as well as site and road access to facilitate
vector surveillance and control activities.
■ Remove accumulated sediment in the forebay and regrade about every 5-7 years or when the
accumulated sediment volume exceeds 10 percent of the basin volume. Sediment removal may
not be required in the main pool area for as long as 20 years.
Cost
Construction Cost
Wet ponds can be relatively inexpensive stormwater practices; however, the construction costs
associated with these facilities vary considerably. Much of this variability can be attributed to the
degree to which the existing topography will support a wet pond, the complexity and amount of
concrete required for the outlet structure, and whether it is installed as part of new construction or
implemented as a retrofit of existing storm drain system.
A recent study (Brown and Schueler, 1997) estimated the cost of a variety of stormwater
management practices. The study resulted in the following cost equation, adjusting for inflation:
where:
C = Construction, design and permitting cost;
V = Volume in the pond to include the 10-year storm (ft3).
Using this equation, typical construction costs are:
$45,700 for a 1 acre-foot facility
$232,000 for a 10 acre-foot facility
$1,170,000 for a 100 acre-foot facility
In contrast, Caltrans (2002) reported spending over $448,000 for a pond with a total permanent
pool plus water quality volume of only 1036 m3 (o.8 ac.-ft.), while the City of Austin spent $584,000
(including design) for a pond with a permanent pool volume of 3,100 m3 (2.5 ac.-ft.). The large
discrepancies between the costs of these actual facilities and the model developed by Brown and
Schueler indicate that construction costs are highly site specific, depending on topography, soils,
subsurface conditions, the local labor, rate and other considerations.
Maintenance Cost
For ponds, the annual cost of routine maintenance has typically been estimated at about 3 to 5 .
percent of the construction cost; however, the published literature is almost totally devoid of actual
maintenance costs. Since ponds are long-lived facilities (typically longer than 20 years), major
maintenance activities are unlikely to occur during a relatively short study.
Caltrans (2002) estimated annual maintenance costs of $17,000 based on three years of monitoring
of a pond treating runoff from 1. 7 ha. Almost all the activities are associated with the annual
vegetation harvest for vector control. Total cost at this site falls within the 3-5% range reported
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above; however, the construction costs were much higher than those estimated by Brown and
Schueler (1997). The City of Austin has been reimbursing a developer about $25,000/yr for wet pond
maintenance at a site located at a very visible location. Maintenance costs are mainly the result of
vegetation management and litter removal. On the other hand, King County estimates annual
maintenance costs at about $3,000 per pond; however, this cost likely does not include annual
extensive vegetation removal. Consequently, maintenance costs may vary considerably at sites in
California depending on the aggressiveness of the vegetation management in that area and the
frequency oflitter removal.
References and Sources of Additional Information
Amalfi, F.A., R. Kadlec, R.L. Knight, G. O'Meara, W.K. Reisen, W.E. Walton, and R. Wass. 1999. A
Mosquito Control Strategy For The Tres Rios Demonstration Constructed Wetlands. CH2M Hill,
Tempe, AZ, 140 pp.
Bannerman, R., and R. Dodds. 1992. Unpublished data. Bureau of Water Resources Management,
Wisconsin Department of Natural Resources, Madison, WI.
Borden, R. C., J.L. Dorn, J.B. Stillman, and S.K. Liehr; 1996. Evaluation of Ponds and Wetlands for
Protection of Public Water Supplies. Draft Report. Water Resources Research Institute of the
University of North Carolina, Department of Civil Engineering, North Carolina State University,
Raleigh, NC.
Brown, W., and T. Schueler. 1997. The Economics of Stormwater BMPs in the Mid-Atlantic Region.
Prepared for the Chesapeake Research Consortium, Edgewater, MD, by the Center for Watershed
Protection; Ellicott City, MD.
Caltrans, 2002, Proposed Final Report: BMP Retrofit Pilot Program, California Dept. of
Transportation Report CTSW-RT-01-050, and Sacramento, CA.
City of Austin, TX. 1991. Design Guidelines for Water Quality Control Basins. Public Works
Department, Austin, TX.
City of Austin, TX. 1996. Evaluation of Non-Point Source Controls: A 319 Grant Project. Draft
Water Quality Report Series, Public Works Department, Austin, TX.
Cullum, M. 1985. Stormwater Runoff Analysis at a Single Family Residential Site. Publication 85-1.
University of Central Florida, Orlando, FL. pp. 247-256.
Dorman, M.E., J. Hartigan, R.F. Steg, and T. Quasebarth. 1989. Retention, Detention and Overland
Flow for Pollutant Removal From Highway Stormwater Runoff. Vol. 1 Research Report.
FHWA/RD 89/202. Federal Highway Administration, Washington, DC.
Dorothy, J.M., and K. Staker. 1990. A preliminary Survey For Mosquito Breeding In Stormwater
Retention Ponds In Three Maryland Counties. Mosquito Control, Maryland Department of
Agriculture, College Park, MD. 5 pp.
Driscoll, E.D. 1983. Performance of Detention Basins for Control of Urban Runoff Quality.
Presented at the 1983 International Symposium on Urban Hydrology, Hydraulics and Sedimentation
Control, University of Kentucky, Lexington, KY.
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Emmerling-Dinovo, C. 1995. Stormwater detention basins and residential locational decisions.
Water Resources Bulletin, 31(3):515-52.
Faulkner, S. and Richardson, C., 1991, Physical and chemical characteristics of freshwater wetland
soils, in Constructed Wetlands for Wastewater Treatment, ed. D. Hammer, Lewis Publishers, 831
pp.
Gain, W.S. 1996. The Effects of Flow Path Modification on Water Quality Constituent Retention in
an Urban Stormwater Detention Pond and Wetland System. Water Resources Investigations
Report 95-4297. U.S. Geological Survey, Tallahassee, FL.
Galli, F. 1990. Thermal Impacts Associated with Urbanization and Stormwater Best Management
Practices. Prepared for the Maryland Department of the Environment, Baltimore, MD, by the
Metropolitan Council of Governments, Washington, DC.
Glick, Roger, 2001, personal communication, City of Austin Watershed Protection Dept., Austin, TX.
Holler, J.D. 1989. Water Quality Efficiency Of An Urban Commercial Wet Detention Stormwater
Management System At Boynton Beach Mall in South Palm Beach County, FL. Florida Scientist
52(1):48-57.
Holler, J.D. 1990. Nonpoint Source Phosphorous Control By A Combination Wet Detention/
Filtration Facility In Kissimmee, FL. Florida Scientist 53(1):28-37.
Horner, R.R., J. Guedry, and M.H. Kortenhoff. 1990. Improving the Cost Effectiveness of Highway
Construction Site Erosion and Pollution Control. Final Report. Washington State Transportation
Commission, Olympia, WA:
Kantrowitz .I. and W. Woodham 1995. Efficiency of a Stormwater Detention Pond in Reducing
Loads of Chemical and Physical Constituents in Urban Stream flow, Pinellas County, Florida.
Water Resources Investigations Report 94-4217. U.S. Geological Survey, Tallahassee, FL.
Martin, E. 1988. Effectiveness of an urban runoff detention pond/wetland system. Journal of
Environmental Engineering 114(4):810-827.
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design Manual.
http://www.mde.state.md.us/environment/wma/stormwatermanual.
McLean, J. 2000. Mosquitoes In Constructed Wetlands: A Management Bugaboo? In T.R
Schueler and H.K Holland [eds.], The Practice of Watershed Protection. pp. 29-33. Center for
Watershed Protection, Ellicott City, MD.
Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side •
Of Stormwater Runoff Management: Disease Vectors Associated With Structural BMPs.
Stormwater 3(2): 24-39.
Oberts, G.L. 1994. Performance of stormwater ponds and wetlands in winter. Watershed Protection
Techniques 1(2):64-68.
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Oberts, G.L., P.J. Wotzka, and J.A. Hartsoe. 1989. The Water Quality Performance of Select Urban
Runoff Treatment Systems. Publication No. 590-89-062a. Prepared for the Legislative Commission
on Minnesota Resources, Metropolitan Council, St. Paul, MN.
Oberts, G.L., and L. Watzka. 1988. The water quality perlormance of a detention basin wetland
treatment system in an urban area. In Nonpoint Source Pollution: Economy, Policy, Management
and Appropriate Technology. American Water Resources Association, Middleburg, VA.
Occoquan Watershed Monitoring Laboratory. 1983. Metropolitan Washington Urban Runoff Project.
Final Report. Prepared for the Metropolitan Washington Council of Governments, Washington, DC,
by the Occoquan Watershed Monitoring Laboratory, Manassas, VA.
Ontario Ministry of the Environment. 1991. Stormwater Quality Best Management Practices.
Marshall Macklin Monaghan Limited, Toronto, Ontario.
Protection Agency, Office of Water, Washington, DC, by the Watershed Management Institute,
Ingleside, MD.
Santana, F.J., J.R. Wood, R.E. Parsons, and SJ{. Chamberlain. 1994. Control Of Mosquito Breeding
In Permitted Stormwater Systems. Sarasota County Mosquito Control and Southwest Florida Water
Management District, Brooksville, FL., 46 pp.
Saunders, G. and M. Gilroy, 1997. Treatment of Nonpoint Source Pollution with Wetland/ Aquatic
Ecosystem Best Management Practices. Texas Water Development Board, Lower Colorado River
Authority, Austin, TX.
Schueler, T. 1997a. Comparative pollutant removal capability of urban BMPs: A reanalysis.
Watershed Protection Techniques 2(4):515-520.
Schueler, T. 1997b. Influence of groundwater on perlormance of stormwater ponds in Florida.
Watershed Protection Techniques 2(4):525-528.
Urbonas, B., J. Carlson, and B. Vang. 1994. Joint Pond-Wetland System in Colorado. Denver Urban
Drainage and Flood Control District, Denver, CO.
U.S. Environmental Protection Agency (USEPA). 1995. Economic Benefits of Runoff Controls. U.S.
Environmental Protection Agency, Office of Wetlands, Oceans, and Watersheds, Washington, DC.
Watershed Management Institute (WMI). 1997. Operation, Maintenance, and Management of
Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency, Office of
Water, Washington, DC, by the Watershed Management Institute, Ingleside, MD.
Water Environment Federation and ASCE, 1998, Urban Runoff Quality Management, WEF Manual
of Practice No. 23 and ASCE Manual and Report on Engineering Practice No. 87.
Wu, J. 1989. Evaluation of Detention Basin Perlormance in the Piedmont Region of North Carolina.
Report No. 89-248. North Carolina Water Resources Research Institute, Raleigh, NC.
Yousef, Y., M. Wanielista, and H. Harper. 1986. Design and Effectiveness of Urban Retention Basins.
In Urban Runoff Quality-Impact and Quality Enhancement Technology. B. Urbonas and L.A.
Roesner (Eds.). American Society of Civil Engineering, New York, New York. pp. 338-350.
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Information Resources
Center for Watershed Protection (CWP). 1995. Stormwater Management Pond Design Example for
Extended Detention Wet Pond. Center for Watershed Protection, Ellicott City, MD.
Center for Watershed Protection (CWP). 1997. Stormwater BMP Design Supplement for Cold
Climates. Prepared for U.S. Environmental Protection Agency, Office of Wetlands, Oceans and
Watersheds, Washington, DC, by the Center for Watershed Protection, Ellicott City, MD.
Denver Urban Drainage and Flood Control District. 1992. Urban Storm Drainage Criteria Manual-
Volume 3: Best Management Practices. Denver Urban Drainage and Flood Control District,
Denver, CO.
Galli, J. 1992. Preliminary Analysis of the Performance and Longevity of Urban BMPs Installed in
Prince George's County, Maryland. Prince George's County, Maryland, Department of Natural
Resources, Largo, MD.
MacRae, C. 1996. Experience from Morphological Research on Canadian Streams: Is Control of the
Two-Year Frequency Runoff Event the Best Basis for Stream Channel Protection? In Effects of
Watershed Development and Management on Aquatic Ecosystems. American Society of Civil
Engineers. Snowbird, UT. pp. 144-162.
Minnesota Pollution Control Agency. 1989. Protecting Water Quality in Urban Areas: Best
Management Practices. Minnesota Pollution Control Agency, Minne·apolis, MN.
U.S. Environmental Protection Agency (USEPA). 1993. Guidance Specifying Management Measures
for Sources of Nonpoint Pollution in Coastal Waters. EPA-840-B-92-002. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
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INFLOW
MAXIMUM SAFETY STORM LIMIT
•
January 2003
' POND BUFFER (25 FEET MINIMUM)
25'
Cp, or 2 YEAR LEVEL
S7 ED LEVEL
-::-AQUATIC
PERMANENT POOL
6 lo 8 FEET DEEP
[-BENCH ~
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RISER IN
EMBANKMENT
PLAN VIEW
PROFILE
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Constructed Wetlands
Description
Constructed wetlands are constructed basins that have a
permanent pool of water throughout the year ( or at least
throughout the wet season) and differ from wet ponds primarily
in being shallower and having greater vegetation coverage. The
schematic diagram is of an on-line pond that includes detention
for larger events, but this is not required in all areas of the state.
A distinction should be made between using a constructed
wetland for storm water management and diverting storm water
into a natural wetland. The latter practice is not recommended
and in all circumstances, natural wetlands should be protected
from the adverse effects of development, including impacts from
increased storm water runoff. This is especially important
because natural wetlands provide storm water and flo9d control
benefits on a regional scale.
Wetlands are among the most effective stormwater practices in
terms of pollutant removal and they also offer aesthetic value. As
stormwater runoff flows through the wetland, pollutant removal
is achieved through settling and biological uptake within the
wetland. Flow through the root systems forces the vegetation to
remove nutrients and dissolved pollutants from the stormwater.
California Experience
The City of Laguna Niguel in Orange County has constructed
several wetlands, primarily to reduce bacteria concentrations in
dry weather flows. The wetlands have been very successful in this
regard. Even though there is not enough perennial flow to maintain
the permanent pool at a constant elevation, the wetland vegetation
has thrived.
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TC-21
Design Considerations
■ Area Required
■ Slope
■ Water Availability
■ Aesthetics
■ Environmental Side-effects
Targeted Constituents
✓ Sediment
✓ Nutrients
✓ Trash
✓ Metals
✓ Bacteria
✓ Oil and Grease
✓ Organics
Legend (Removal Effectiveness)
•
J;.
Low ■ High
Medium
uca11tomla
Stormwater
Ouallty
Association
■
J;.
■
■
■
■
■
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TC-21 Constructed Wetlands
Advantages
■ If properly designed, constructed and maintained, wet basins can provide substantial
wildlife and wetlands habitat.
■ Due to the presence of the permanent wet pool, properly designed and maintained wet
basins can provide significant water quality improvement across a relatively broad spectrum
of constituents including dissolved nutrients.
■ Widespread application with sufficient capture volume can provide significant control of
channel erosion and enlargement caused by changes to flow frequency relationships
resulting from the increase of impervious cover in a watershed.
Limitations
■ There may be some aesthetic concerns about a facility that looks swampy.
■ Some concern about safety when constructed where there is public access.
■ Mosquito and midge breeding is likely to occur in wetlands.
■ Cannot be placed on steep unstable slopes.
■ Need for base flow or supplemental water if water level is to be maintained.
■ Require a relatively large footprint
■ Depending on volume and depth, pond designs may require approval from the State
Division of Safety of Dams
Design and Sizing Guidelines
■ Capture volume determined by local requirements or sized to treat 85% of the annual runoff
volume.
■ Outlet designed to discharge the capture volume over a period of 24 hours.
■ Permanent pool volume equal to twice the water quality volume.
■ Water depth not to exceed about 4 feet.
■ Wetland vegetation occupying no more than 50% of surface area.
■ Include energy dissipation in the inlet design and a sediment forebay to reduce resuspension
of accumulated sediment and facilitate maintenance.
■ A maintenance ramp should be included in the design to facilitate access to the forebay for
maintenance activities and for vector surveillance and control.
■ To facilitate vector surveillance and control activities, road access should be provided
along at least one side of BMPs that are seven meters or less in width. Those BMPs that
have shoreline-to-shoreline distances in excess of seven meters should have perimeter road
access on both sides or be designed such that no parcel of water is greater than seven
meters from the road.
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Constructed Wetlands TC-21
Construction/Inspection Considerations
■ In areas with porous soils an impermeable liner may be required to maintain an adequate
permanent pool level.
■ Outlet structures and piping should be installed with collars to prevent water from seeping
through the fill and causing structural failure.
■ Inspect facility after first large storm to determine whether the desired residence time has
been achieved.
Performance
The processes that impact the performance of constructed wetlands are essentially the same as
those operating in wet ponds and similar pollutant reduction would be expected. One concern
about the long-term performance of wetlands is associated with the vegetation density. If
vegetation covers the majority of the facility, open water is confined to a few well defined
channels. This can limit mixing of the stormwater runoff with the permanent pool and reduce
the effectiveness as compared to a wet pond where a majority of the area is open water.
Siting Criteria
Wet ponds are a widely applicable stormwater management practice and can be used over a
broad range of storm frequencies and sizes, drainage areas and land use types. Although they
have limited applicability in highly urbanized settings and in arid climates, they have few other
restrictions. Constructed wetlands may be constructed on-or off-line and can be sited at feasible
locations along established drainage ways with consistent base flow. An off-line design is
preferred. Constructed wetlands are often utilized in smaller sub-watersheds and are
particularly appropriate in areas with residential land uses or other areas where high nutrient
loads are considered to be potential problems (e.g., golf courses).
Wetlands generally consume a fairly large area (typically 4-6 percent of the contributing
drainage area), and these facilities are generally larger than wet ponds because the average
depth is less.
Wet basin application is appropriate in the following settings: (1) where there is a need to
achieve a reasonably high level of dissolved contaminant removal and/or sediment capture; (2)
in small to medium-sized regional tributary areas with available open space and drainage areas
greater than about 10 ha (25 ac.); (3) where base flow rates or other channel flow sources are
relatively consistent year-round; (4) in settings where wildlife habitat benefits can be
appreciated.
Additional Design Guidelines
Constructed wetlands generally feature relatively uniformly vegetated areas with depths of one
foot or less and open water areas (25-50% of the total area) no more than about 1.2 m (4 feet)
deep, although design configuration options are relatively flexible. Wetland vegetation is
comprised generally of a diverse, local aquatic plant species. Constructed wetlands can be
designed on-line or off-line and generally serve relatively smaller drainage areas than wet
ponds, although because of the shallow depths, the footprint of the facility will be larger than a
wet pond serving the same tributary area.
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TC-21 Constructed Wetlands
The extended detention shallow wetland combines the treatment concepts of the dry extended
detention pond and the constructed wetland. In this design, the water quality volume is
detained above the permanent pool and released over 24 hours. In addition to increasing the
residence time, which improves pollutant removal, this design also attenuates peak runoff rates.
Consequently, this design alternative is recommended.
Pretreatment incorporates design features that help to settle out coarse sediment particles. By
removing these particles from runoff before they reach the large permanent pool, the
maintenance burden of the pond is reduced. In ponds, pretreatment is achieved with a sediment
forebay. A sediment forebay is a small pool (typically about 10 percent of the volume of the
permanent pool). Coarse particles remain trapped in the forebay, and maintenance is
performed on this smaller pool, eliminating the need to dredge the entire pond.
Effective wetland design displays "complex microtopography." In other words, wetlands should
have zones of both very shallow ( <6 inches) and moderately shallow ( <18 inches) wetlands
incorporated, using underwater earth berms to create the zones. This design will provide a
longer flow path through the wetland to encourage settling, and it provides two depth zones to
encourage plant diversity.
There are a variety of sizing criteria for determining the volume of the permanent pool, mostly
related to the water quality volume (i.e., the volume of water treated for pollutant removal) or
the average storm size in a particular area. In addition, several theoretical approaches to
determination of permanent pool volume have been developed. However, there is little
empirical evidence to support these designs. Consequently, a simplified method (i.e.,
permanent pool volume equal to twice the water quality volume) is recommended.
Design features are also incorporated to ease maintenance of both the fore bay and the main pool
of ponds. Ponds should be designed with a maintenance access to the forebay to ease this
relatively routine (every 5-7 year) maintenance activity. In addition, ponds should generally
have a drain to draw down the pond for vegetation harvesting or the n:iore infrequent dredging
of the main cell of the pond.
Summary of Design Recommendations
(1) Facility Sizing -The basin should be sized to hold the permanent pool as well as the
required water quality volume. The volume of the permanent pool should equal
twice the water quality volume.
(2) Pond Configuration -The wet basin should be configured as a two stage facility with
a sediment forebay and a main pool. The basins should be wedge-shaped, narrowest
at the inlet and widest at the outlet. The minimum length to width ratio should be
1.5 where feasible. The depth in the center of the basin should be about 4 feet deep to
prevent vegetation from encroaching on the pond open water surface.
(3) Pond Side Slopes -Side slopes of the basin should be 3:1 (H:V) or flatter for grass
stabilized slopes. Slopes steeper than 3:1 should be stabilized with an appropriate
slope stabilization practice.
(4) Sediment Forebay -A sediment forebay should be used to isolate gross sediments as
they enter the facility and to simplify sediment removal. The sediment forebay
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Constructed Wetlands TC-21
should consist of a separate cell formed by an earthen berm, gabion, or loose riprap
wall. The forebay should be sized to contain 15 to 25% of the permanent pool volume
and should be at least 3 feet deep. Exit velocities from the forebay should not be
erosive. Direct maintenance access should be provided to the forebay. The bottom of
the forebay may be hardened (concrete) to make sediment removal easier. A fixed
vertical sediment depth marker should be installed in the forebay to measure
sediment accumulation.
(5) Splitter Box -When the pond is designed as an off-line facility, a splitter structure is
used to isolate the water quality volume. The splitter box, or other flow diverting
approach, should be designed to convey the 25-year event while providing at least 1.0
foot of freeboard along pond side slopes.
( 6) Vegetation -A plan should be prepared that indicates how aquatic and terrestrial
areas will be vegetatively stabilized. Wetland vegetation elements should be placed
along the aquatic bench or in the shallow portions of the permanent pool. The
optimal elevation for planting of wetland vegetation is within 6 inches vertically of
the normal pool elevation. A list of some wetland vegetation native to California is
presented in the wet pond fact sheet.
Maintenance
The amount of maintenance required for a constructed wetland is highly dependent on local
regulatory agencies, particular health and vector control agencies. These agencies are often
extremely concerned about the potential for mosquito breeding that may occur in the
permanent pool.
Routine harvesting of vegetation may increase nutrient removal and prevent the export of these
constituents from dead and dying plants falling in the water. A previous study (Faulkner and
Richardson, 1991) documented dramatic reductions in nutrient removal after the first several
years of operation and related it to the vegetation achieving a maximum density. Vegetation
harvesting in the summer is recommended.
Typical maintenance activities and frequencies include:
■ Schedule semiannual inspections for burrows, sediment accumulation, structural integrity of
the outlet, and litter accumulation.
■ Remove accumulated trash and debris in the basin at the middle and end of the wet season.
The frequency of this activity may be altered to meet specific site conditions and aesthetic
considerations.
■ Where permitted by the Department of Fish and Game or other agency regulations, stock
wet ponds/constructed wetlands regularly with mosquito fish (Gambusia spp.) to enhance
natural mosquito and midge control.
■ Introduce mosquito fish and maintain vegetation to assist their movements to control
mosquitoes, as well as to provide access for vector inspectors. An annual vegetation harvest
in summer appears to be optimum, in that it is after the bird breeding season, mosquito fish
can provide the needed control until vegetation reaches late summer density, and there is
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TC-21 Constructed Wetlands
time for re-growth for runoff treatment purposes before the wet season. In certain cases,
more frequent plant harvesting may be required by local vector control agencies.
■ Maintain emergent and perimeter shoreline vegetation as well as site and road access to
facilitate vector surveillance and control activities.
■ Remove accumulated sediment in the forebay and regrade about every 5-7 years or when the
accumulated sediment volume exceeds 10 percent of the basin volume. Sediment removal
may not be required in the main pool area for as long as 20 years.
Cost
Construction Cost
Wetlands are relatively inexpensive storm water practices. Construction cost data for wetlands
are rare, but one simplifying assumption is that they are typically about 25 percent more
expensive than storm water ponds of an equivalent volume. Using this assumption, an equation
developed by Brown and Schueler (1997) to estimate the cost of wet ponds can be modified to
estimate the cost of storm water wetlands using the equation:
where:
C = Construction, design, and permitting cost;
V = Wetland volume needed to control the 10-year storm (ft3).
Using this equation, typical construction costs are the following:
$ 57,100 for a 1 acre-foot facility
$ 289,000 for a 10 acre-foot facility
$ 1,470,000 for a 100 acre-foot facility
Wetlands consume about 3 to 5 percent of the land that drains to them, which is relatively high
compared with other storm water management practices. In areas where land value is high, this
may make wetlands an infeasible option.
Maintenance Cost
For ponds, the annual cost of routine maintenance has typically been estimated at about 3 to 5
percent of the construction cost; however, the published literature is almost totally devoid of
actual maintenance costs. Since ponds are long-lived facilities (typically longer than 20 years),
major maintenance activities are unlikely to occur during a r~latively short study.
References and Sources of Additional Information
Amalfi, F.A., R. Kadlec, R.L. Knight, G. O'Meara, W.K. Reisen, W.E. Walton, and R. Wass. 1999.
A mosquito control strategy for the Tres Rios Demonstration Constructed Wetlands. CH2M Hill,
Tempe, AZ, 140 pp.
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Constructed Wetlands TC-21
Borden, R. C., J.L. Dorn, J.B. Stillman, and S.K. Liehr; 1996. Evaluation of Ponds and Wetlands
for Protection of Public Water Supplies. Draft Report. Water Resources Research Institute of
the University of North Carolina, Department of Civil Engineering, North Carolina State
University, Raleigh, NC.
City of Austin, TX. 1991. Design Guidelines for Water Quality Control Basins. Public Works
Department, Austin, TX.
Cullum, M. 1985. Stormwater Runoff Analysis at a Single Family Residential Site. Publication
85-1. University of Central Florida, Orlando, FL. pp. 247-256.
Dorothy, J.M., and K. Staker. 1990. A Preliminary Survey for Mosquito Breeding in Stormwater
Retention Ponds in Three Maryland Counties. Mosquito Control, Maryland Department of
Agriculture, College Park, MD. 5 pp.
Faulkner, S. and Richardson, C., 1991, Physical And Chemical Characteristics of Freshwater
Wetland Soils, in Constructed Wetlands for Wastewater Treatment, ed. D. Hammer, Lewis
Publishers, 831 pp.
Gain, W.S. 1996. The Effects of Flow Path Modification on Water Quality Constituent Retention
in an Urban Stormwater Detention Pond and Wetland System. Water Resources
Investigations Report 95-4297. U.S. Geological Survey, Tallahassee, FL.
Martin, E. 1988. Effectiveness Of An Urban Runoff Detention Pond/Wetland System. Journal
of Environmental Engineering 114(4):810-827.
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design Manual.
http://www.mde.state.md. us/ environment/wma/ stormwatermanual.
McLean, J. 2000. Mosquitoes In Constructed Wetlands: A Management Bugaboo? In T.R.
Schueler and H.K. Holland [eds.], The Practice of Watershed Protection. pp. 29-33. Center for
Watershed Protection, Ellicott City, MD
Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side
of Storm water Runoff Management: Disease Vectors Associated with Structural BMPs.
Stormwater 3(2): 24-39.
Oberts, G.L. 1994. Performance Of Stormwater Ponds And Wetlands In Winter. Watershed
Protection Techniques 1(2):64-68.
Oberts, G.L., and L. Wotzka. 1988. The Water Quality Performance Of A Detention Basin
Wetland Treatment System In An Urban Area. In Nonpoint Source Pollution: Economy, Policy,
Management and Appropriate Technology. American Water Resources Association,
Middleburg, VA.
Santana, F.J., J.R. Wood, R.E. Parsons, and S.K. Chamberlain. 1994. Control Of Mosquito
Breeding In Permitted Stormwater Systems. Sarasota County Mosquito Control and Southwest
Florida Water Management District, Brooksville, FL., 46 pp .
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
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TC-21 Constructed Wetlands
Saunders, G. and M. Gilroy, 1997. Treatment ofNonpoint Source Pollution with
Wetland/Aquatic Ecosystem Best Management Practices. Texas Water Development Board,
Lower Colorado River Authority, Austin, TX.
Schueler, T. 1997a. Comparative Pollutant Removal Capability Of Urban BMPs: A Reanalysis.
Watershed Protection Techniques 2(4):515-520.
Urbonas, B., J. Carlson, and B. Vang. 1994. Joint Pond-Wetland System in Colorado. Denver
Urban J?rainage and Flood Control District, Denver, CO.
Water Environment Federation and ASCE, 1998, Urban Runoff Quality Management, WEF
Manual of Practice No. 23 and ASCE Manual and Report on Engineering Practice No. 87.
Wu, J. 1989. Evaluation of Detention Basin Performance in the Piedmont Region of North
Carolina. Report No. 89-248. North Carolina Water Resources Research Institute, Raleigh, NC.
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January 2003
WEl\.ANOS
HIGH MARSH
FILTER DIAPHRAGM
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TC-21
RISER IN
EMBANKMENT
PLAN VIEW
PROFILE
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•
Extended Detention Basin
Description
Dry extended detention ponds (a.k.a. dry ponds, extended
detention basins, detention ponds, extended detention ponds)
are basins whose outlets have been designed to detain the
storm water runoff from a water quality design storm for some
minimum time (e.g., 48 hours) to allow particles and associated
pollutants to settle. Unlike wet ponds, these facilities do not have
a large permanent pool. They can also be used to provide flood
control by including additional flood detention storage.
California Experience
Caltrans constructed and monitored 5 extended detention basins
in southern California with design drain times of 72 hours. Four
of the basins were earthen, less costly and had substantially
better load reduction because of infiltration that occurred, than
the concrete basin. The Caltrans study reaffirmed the flexibility
and performance of this conventional technology. The small
headloss and few siting constraints suggest that these devices are
one of the most applicable technologies for stormwater
treatment.
Advantages
■ Due to the simplicity of design, extended detention basins are
relatively easy and inexpensive to construct and operate.
■ Extended detention basins can provide substantial capture of
sediment and the toxics fraction associated with particulates.
■ Widespread application with sufficient capture volume can
provide significant control of channel erosion and enlargement
caused by changes to flow frequency relationships resulting
· from the increase of impervious cover in a watershed.
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TC-22
Design Considerations
■ Tributary Area
■ Area Requ ired
• Hydraulic Head
Targeted Constituents
✓ Sediment A
✓ Nutrients •
✓ Trash ■
✓ Metals • ✓ Bacteria • ✓ Oil and Grease • ✓ Organics • Legend (Removal Effectiveness}
• Low
• Medium
■ High
Stormwater
Ouallty
Association
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TC-22 Extended Detention Basin
Limitations
■ Limitation of the diameter of the orifice may not allow use of extended detention in
watersheds ofless than 5 acres (would require an orifice with a diameter ofless than 0.5
inches that would be prone to clogging).
■ Dry extended detention ponds have only moderate pollutant removal when compared to
some other structural stormwater practices, and they are relatively ineffective at removing
soluble pollutants.
■ Although wet ponds can increase property values, dry ponds can actually detract from the
value of a home due to the adverse aesthetics of dry, bare areas and inlet and outlet
structures.
Design and Sizing Guidelines
■ Capture volume determined by local requirements or sized to treat 85% of the annual runoff
volume.
■ Outlet designed to discharge the capture volume over a period of hours.
■ Length to width ratio of at least 1.5:1 where feasible.
■ Basin depths optimally range from 2 to 5 feet.
■ Include energy dissipation in the inlet design to reduce resuspension of accumulated
sediment.
■ A maintenance ramp and perimeter access should be included in the design to facilitate
access to the basin for maintenance activities and for vector surveillance and control.
■ Use a draw down time of 48 hours in most areas of California. Draw down times in excess of
48 hours may result in vector breeding, and should be used only after coordination with
local vector control authorities. Draw down times ofless than 48 hours should be limited to
BMP drainage areas with coarse soils that readily settle and to watersheds where warming
may be determined to downstream fisheries.
Construction/Inspection Considerations
■ Inspect facility after first large to storm to determine whether the desired residence time has
been achieved.
■ When constructed with small tributary area, orifice sizing is critical and inspection should
verify that flow through additional openings such as bolt holes does not occur.
1 Performance
One objective of stormwater management practices can be to reduce the flood hazard associated
with large storm events by reducing the peak flow associated with these storms. Dry extended
detention basins can easily be designed for flood control, and this is actually the primary
purpose of most detention ponds.
Dry extended detention basins provide moderate pollutant removal, provided that the
recommended design features are incorporated. Although they can be effective at removing
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Extended Detention Basin TC-22
some pollutants through settling, they are less effective at removing soluble pollutants because
of the absence of a permanent pool. Several studies are available on the effectiveness of dry
extended detention ponds including one recently concluded by Caltrans (2002).
The load reduction is greater than the concentration reduction because of the substantial
infiltration that occurs. Although the infiltration of stormwater is clearly beneficial to surface
receiving waters, there is the potential for groundwater contamination. Previous research on the
effects of incidental infiltration on groundwater quality indicated that the risk of contamination
is minimal.
There were substantial differences in the amount of infiltration that were observed in the
earthen basins during the Caltrans study. On average, approximately 40 percent of the runoff
entering the unlined basins infiltrated and was not discharged. The percentage ranged from a
high of about 60 percent to a low of only about 8 percent for the different facilities. Climatic
conditions and local water table elevation are likely the principal causes of this difference. The
least infiltration occurred at a site located on the coast where humidity is higher and the basin
invert is within a few meters of sea level. Conversely, the most infiltration occurred at a facility
located well inland in Los Angeles County where the climate is much warmer and the humidity
is less, resulting in lower soil moisture content in the basin floor at the beginning of storms.
Vegetated detention basins appear to have greater pollutant removal than concrete basins. In
the Caltrans study, the concrete basin exported sediment and associated pollutants during a
number of storms. Export was not as common in the earthen basins, where the vegetation
appeared to help stabilize the retained sediment.
Siting Criteria
Dry extended detention ponds are among the most widely applicable stormwater management
practices and are especially useful in retrofit situations where their low hydraulic head
requirements allow them to be sited within the constraints of the existing storm drain system. In
addition, many communities have detention basins designed for flood control. It is possible to
modify these facilities to incorporate features that provide water quality treatment and/or
channel protection. Although dry extended detention ponds can be applied rather broadly,
designers need to ensure that they are feasible at the site in question. This section provides
basic guidelines for siting dry extended detention ponds.
In general, dry extended detention ponds should be used on sites with a minimum area of s
acres. With this size catchment area, the orifice size can be on the order of 0.5 inches. On
smaller sites, it can be challenging to provide channel or water quality control becaus·e the
orifice diameter at the outlet needed to control relatively small storms becomes very small and
thus prone to clogging. In addition, it is generally more cost-effective to control larger drainage
areas due to the economies of scale.
I
Extended detention basins can be used with almost all soils and geology, with minor design
adjustments for regions of rapidly percolating soils such as sand. In these areas, extended
detention ponds may need an impermeable liner to prevent ground water contamination.
The base of the extended detention facility should not intersect the water table. A permanently
wet bottom may become a mosquito breeding ground. Research in Southwest Florida (Santana
et al., 1994) demonstrated that intermittently flooded systems, such as dry extended detention
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TC-22 Extended Detention Basin
ponds, produce more mosquitoes than other pond systems, particularly when the facilities
remained wet for more than 3 days following heavy rainfall.
A study in Prince George's County, Maryland, found that stormwater management practices can
increase stream temperatures (Galli, 1990). Overall, dry extended detention ponds increased
temperature by about 5°F. In cold water streams, dry ponds should be designed to detain
stormwater for a relatively short time (i.e., 24 hours) to minimize the amount of warming that
occurs in the basin.
Additional Design Guidelines
In order to enhance the effectiveness of extended detention basins, the dimensions of the basin
must be sized appropriately. Merely providing the required storage volume will not ensure
maximum constituent removal. By effectively configuring the basin, the designer will create a
long flow path, promote the establishment oflow velocities, and avoid having stagnant areas of
the basin. To promote settling and to attain an appealing environment, the design of the basin
should consider the length to width ratio, cross-sectional areas, basin slopes and pond
configuration, and aesthetics (Young et al., 1996).
Energy dissipation structures should be included for the basin inlet to prevent resuspension of
accumulated sediment. The use of stilling basins for this purpose should be avoided because the
standing water provides a breeding area for mosquitoes.
Extended detention facilities should be sized to completely capture the water quality volume. A
micropool is often-recommended for inclusion in the design and one is shown in the schematic
diagram. These small permanent pools greatly increase the potential for mosquito breeding and
complicate maintenance activities; consequently, they are not recommended for use in
California.
A large aspect ratio may improve the performance of detention basins; consequently, the outlets
should be placed to maximize the flowpath through the facility. The ratio of flowpath length to
width from the inlet to the outlet
should be at least 1.5:1 (L:W)
where feasible. Basin depths
optimally range from 2 to 5 feet.
The facility's drawdown time
should be regulated by an orifice
or weir. In general, the outflow
structure should have a trash
rack or other acceptable means
of preventing clogging at the
entrance to the outflow pipes.
The outlet design implemented
by Caltrans in the facilities
constructed in San Diego County
used an outlet riser with orifices
sized to discharge the water
quality volume, and the riser
Figure 1
Example of Extended Detention Outlet Structure
overflow height was set to the design storm elevation. A stainless steel screen was placed
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Extended Detention Basin TC-22
around the outlet riser to ensure that the orifices would not become clogged with debris. Sites
either used a separate riser or broad crested weir for overflow of runoff for the 25 and greater
year storms. A picture of a typical outlet is presented in Figure 1.
The outflow structure should be sized to allow for complete drawdown of the water quality
volume in 72 hours. No more than 50% of the water quality volume should drain from the
facility within the first 24 hours. The outflow structure can be fitted with a valve so that
discharge from the basin can be halted in case of an accidental spill in the watershed.
Summary of Design Recommendations
(1) Facility Sizing -The required water quality volume is determined by local regulations
or the basin should be sized to capture and treat 85% of the annual runoff volume.
See Section 5.5.1 of the handbook for a discussion of volume-based design.
Basin Configuration -A high aspect ratio may improve the performance of detention
basins; consequently, the outlets should be placed to maximize the flowpath through
the facility. The ratio of flowpath length to width from the inlet to the outlet should
be at least 1.5:1 (L:W). The flowpath length is defined as the distance from the inlet.
to the outlet as measured at the surface. The width is defined as the mean width of
the basin. Basin depths optimally range from 2 to 5 feet. The basin may include a
sediment forebay to provide the opportunity for larger particles to settle out.
A micropool should not be incorporated in the design because of vector concerns. For
online facilities, the principal and emergency spillways must be sized to provide 1.0
foot of freeboard during the 25-year event and to safely pass the flow from 100-year
storm.
(2) Pond Side Slopes -Side slopes of the pond should be 3:1 (H:V) or flatter for grass
stabilized slopes. Slopes steeper than 3:1 (H:V) must be stabilized with an
appropriate slope stabilization practice.
(3) Basin Lining -Basins must be constructed to prevent possible contamination of
groundwater below the facility.
(4) Basin Inlet -Energy dissipation is required at the basin inlet to reduce resuspension
. of accumulated sediment and to reduce the tendency for short-circuiting.
(5) Outflow Structure -The facility's drawdown time should be regulated by a gate valve
or orifice plate. In general, the outflow structure should have a trash rack or other
acceptable means of preventing clogging at the entrance to the outflow pipes.
The outflow structure should be sized to allow for complete drawdown of the water
quality volume in 72 hours. No more than 50% of the water quality volume should
drain from the facility within the first 24 hours. The outflow structure should be
fitted with a valve so that discharge from the basin can be halted in case of an
accidental spill in the watershed. This same valve also can be used to regulate the
rate of discharge from the basin .
The discharge through a control orifice is calculated from:
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TC-22 Extended Detention Basin
Q = CA(2gH-H0 )0-s
where: Q = discharge (ft3/s)
C = orifice coefficient
A = area of the orifice (ft2)
g = gravitational constant (32.2)
H = water surface elevation (ft)
Ha= orifice elevation (ft)
Recommended values for Care o.66 for thin materials and 0.80 when the material is
thicker than the orifice diameter. This equation can be implemented in spreadsheet
form with the pond stage/volume relationship to calculate drain time. To do this, use
the initial height of the water above the orifice for the water quality volume. Calculate
the discharge and assume that it remains constant for approximately 10 minutes.
Based on that discharge, estimate the total discharge during that interval and the
new elevation based on the stage volume relationship. Continue to iterate until H is
approximately equal to Ha. When using multiple orifices the discharge from each is
summed.
(6) Splitter Box -When the pond is designed as an offline facility, a splitter structure is
used to isolate the water quality volume. The splitter box, or other flow diverting
approach, should be designed to convey the 25-year storm event while providing at
least 1.0 foot of free board along pond side slopes.
(7) Erosion Protection at the Outfall -For online facilities, special consideration should
be given to the facility's outfall location. Flared pipe end sections that discharge at or
near the stream invert are preferred. The channel immediately below the pond
outfall should be modified to conform to natural dimensions, and lined with large
stone riprap placed over filter cloth. Energy dissipation may be required to reduce
flow velocities from the primary spillway to non-erosive velocities.
(8) Safety Considerations -Safety is provided either by fencing of the facility or by
managing the contours of the pond to eliminate dropoffs and other hazards. Earthen
side slopes should not exceed 3:1 (H:V) and should terminate on a flat safety bench
area. Landscaping can be used to impede access to the facility. The primary spillway
opening must not permit access by small children. Outfall pipes above 48 inches in
diameter should be fenced.
Maintenance
Routine maintenance activity is often thought to consist mostly of sediment and trash and
debris removal; however, these activities oft-en constitute only a small fraction of the
maintenance hours. During a recent study by Cal trans, 72 hours of maintenance was performed
annually, but only a little over 7 hours was spent on sediment and trash removal. The largest
recurring activity was vegetation management, routine mowing. The largest absolute number of
hours was associated with vector control because of mosquito breeding that occurred in the
stilling basins (example of standing water to be avoided) installed as energy dissipaters. In most
cases, basic housekeeping practices such as removal of debris accumulations and vegetation
management to ensure that the basin dewaters completely in 48-72 hours is sufficient to prevent
creating mosquito and other vector habitats.
I
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Consequently, maintenance costs should be estimated based primarily on the mowing frequency
and the time required. Mowing should be done at least annually to avoid establishment of
woody vegetation, but may need to be performed much more frequently if aesthetics are an
important consideration.
Typical activities and frequencies include:
■ Schedule semiannual inspection for the beginning and end of the wet season for standing
water, slope stability, sediment accumulation, trash and debris, and presence of burrows.
■ Remove accumulated trash and debris in the basin and around the riser pipe during the
semiannual inspections. The frequency of this activity may be altered to meet specific site
conditions.
■ Trim vegetation at the beginning and end of the wet season and inspect monthly to prevent
establishment of woody vegetation and for aesthetic and vector reasons.
■ Remove accumulated sediment and regrade about every 10 years or when the accumulated
sediment volume exceeds 10 percent of the basin volume. Inspect the basin each year for
accumulated sediment volume.
Cost
Construction Cost
The construction costs associated with extended detention basins vary considerably. One recent
study evaluated the cost of all pond systems (Brown and Schueler, 1997). Adjusting for
inflation, the cost of dry extended detention ponds can be estimated with the equation:
where: C = Construction, design, and permitting cost, and
V = Volume (ft3).
Using this equation, typical construction costs are:
$ 41,600 for a 1 acre-foot pond
$ 239,000 for a 10 acre-foot pond
$ 1,380,000 for a 100 acre-foot pond
Interestingly, these costs are generally slightly higher than the predicted cost of wet ponds
(according to Brown and Schueler, 1997) on a cost per total volume basis, which highlights the
difficulty of developing rea~onably accurate construction estimates. In addition, a typical facility
constructed by Caltrans cost about $160,000 with a capture volume of only 0.3 ac-ft.
An economic concern associated with dry ponds is that they might detract slightly from the
value of adjacent properties. One study found that dry ponds can actually detract from the
perceived value of homes adjacent to a dry pond by between 3 and 10 percent (Emmerling-
Dinovo, 1995) .
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TC-22 Extended Detention Basin
Maintenance Cost
For ponds, the annual cost of routine maintenance is typically estimated at about 3 to 5 percent
of the construction cost (EPA website). Alternatively, a community can estimate the cost of the
maintenance activities outlined in the maintenance section. Table 1 presents the maintenance
costs estimated by Caltrans based on their experience with five basins located in southern
California. Again, it should be emphasized that the vast majority of hours are related to
vegetation management (mowing).
Table 1 Estimated Average Annual Maintenance Effort
Activity Labor Hours Equipment& Cost Material($)
Inspections 4 7 183
Maintenance 49 126 2282
Vector Control 0 0 0
Administration 3 0 132
Materials 535 535
Total 56 $668 $3,132
References and Sources of Additional Information
Brown, W., and T. Schueler. 1997. The Economics of Stormwater BMPs in the Mid-Atlantic
Region. Prepared for Chesapeake Research Consortium. Edgewater, MD. Center for Watershed
Protection. Ellicott City, MD.
Denver Urban Drainage and Flood Control District. 1992. Urban Storm Drainage Criteria
Manual-Volume 3: Best Management Practices. Denver, CO.
Emmerling-Dinovo, C. 1995. Stormwater Detention Basins and Residential Locational
' Decisions. Water Resources Bulletin 31(3): 515-521
Galli, J. 1990. Thermal Impacts Associated with Urbanization and Stormwater Management
Best Management Practices. Metropolitan Washington Council of Governments. Prepared for
Maryland Department of the Environment, Baltimore, MD.
GKY, 1989, Outlet Hydraulics of Extended Detention Facilities for the Northern Virginia
Planning District Commission.
MacRae, C. 1996. Experience from Morphological Research on Canadian Streams: Is Control of
the Two-Year Frequency Runoff Event the Best Basis for Stream Channel Protection? In Effects
of Watershed Development and Management on Aquatic Ecosystems. American Society of
Civil Engineers. Edited by L. Roesner. Snowbird, UT. pp. 144-162.
Maryland Dept of the Environment, 2000, Maryland Stormwater Design Manual: Volumes 1 &
2, prepared by MDE and Center for Watershed Protection.
httP://www.mde.state.md.us/environment/wma/stormwatermanual/index.html
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Metzger, M. E., D. F. Messer, C. L. Beitia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side
Of Storm water Runoff Management: Disease Vectors Associated With Structural BMPs.
Stormwater 3(2): 24-39.
Santana, F., J. Wood, R. Parsons, and S. Chamberlain. 1994. Control of Mosquito Breeding in
Permitted Stormwater Systems. Prepared for Southwest Florida Water Management District,
Brooksville, FL.
Schueler, T. 1997. Influence of Ground Water on Performance of Stormwater Ponds in Florida.
Watershed Protection Techniques 2(4):525-528.
Watershed Management Institute (WMI). 1997. Operation, Maintenance, and Management of
Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency, Office
of Water. Washington, DC.
Young, G.K., et al., 1996, Evaluation and Management of Highway Runoff Water Quality,
Publication No. FHWA-PD-96-032, U.S. Department of Transportation, Federal Highway
Administration, Office of Environment and Planning.
Information Resources
Center for Watershed Protection (CWP), Environmental Quality Resources, and Loiederman
Associates. 1997. Maryland Stormwater Design Manual. Draft. Prepared for Maryland
Department of the Environment, Baltimore, MD.
Center for Watershed Protection (CWP). 1997. Stormwater BMP Design Supplement for Cold
Climates. Prepared for U.S. Environmental Protection Agency, Office of Wetlands, Oceans and
Watersheds. Washington, DC.
U.S. Environmental Protection Agency (USEPA). 1993. Guidance Specifying Management
Measures for Sources ofNonpoint Pollution in Coastal Waters. EPA-840-B-92-002. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
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ANTI-SEEP COLLAR or_/
FILTER DIAPHRAGM
Schematic of an Extended Detention Basin {MOE, 2000)
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PLAN VIEW
PROFILE
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J
Infiltration Basin
Description
An infiltration basin is a shallow impoundment that is designed
to infiltrate stormwater. Infiltration basins use the natural
filtering ability of the soil to remove pollutants in stormwater
runoff. Infiltration facilities store runoff until it gradually
exfiltrates through the soil and eventually into the water table.
This practice has high pollutant removal efficiency and can also
help recharge groundwater, thus helping to maintain low flows in
stream systems. Infiltration basins can be challenging to apply
on many sites, however, because of soils requirements. In
addition, some studies have shown relatively high failure rates
compared with other management practices.
California Experience
Infiltration basins have a long history of use in California,
especially in the Central Valley. Basins located in Fresno were
among those initially evaluated in the National Urban Runoff
Program and were found to be effective at reducing the volume of
runoff, while posing little long-term threat to groundwater
quality (EPA, 1983; Schroeder, 1995). Proper siting of these
devices is crucial as underscored by the experience of Caltrans in
siting two basins in Southern California. The basin with
marginal separation from groundwater and soil permeability
failed immediately and could never be rehabilitated.
Advantages
■ Provides 100% reduction in the load discharged to surface
waters.
■ The principal benefit of infiltration basins is the
approximation of pre-development hydrology during which a
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TC-11
Design Considerations
■ Soil for Infiltration
■ Slope
■ Aesthetics
Targeted Constituents
✓ Sediment
✓ Nutrients
✓ Trash
✓ Metals
✓ Bacteria
✓ Oil and Grease
✓ Organics
Legend (Removal Effectiveness)
• Low ■ High
A Medium
Stormwater
Ouallty
Association
■
■
■
■
■ • •
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TC-11 Infiltration Basin
significant portion of the average annual rainfall runoff is infiltrated and evaporated rather
than flushed directly to creeks.
■ If the water quality volume is adequately sized, infiltration basins can be useful for providing
control of channel forming (erosion) and high frequency (generally less than the 2-year)
flood events.
Limitations
■ May not be appropriate for industrial sites or locations where spills may occur.
■ Infiltration basins require a minimum soil infiltration rate of 0.5 inches/hour, not
appropriate at sites with Hydrologic Soil Types C and D.
■ If infiltration rates exceed 2.4 inches/hour, then the runoff should be fully treated prior to
infiltration to protect groundwater quality.
■ Not suitable on fill sites or steep slopes.
■ Risk of groundwater contamination in very coarse soils.
■ Upstream drainage area must be completely stabilized before construction.
■ Difficult to restore functioning of infiltration basins once clogged.
Design and Sizing Guidelines
■ Water quality volume determined by local requirements or sized so that 85% of the annual
runoff volume is captured.
■ Basin sized so that the entire water quality volume is infiltrated within 48 hours.
■ Vegetation establishment on the basin floor may help reduce the clogging rate.
Construction/Inspection Considerations
■ Before construction begins, stabilize the entire area draining to the facility. If impossible,
place a diversion berm around the perimeter of the infiltration site to prevent sediment
entrance during construction or remove the top 2 inches of soil after the site is stabililized.
Stabilize the entire contributing drainage area, including the side slopes, before allowing any
runoff to enter once construction is complete.
■ Place excavated material such that it can not be washed back into the basin if a storm occurs
during construction of the facility.
■ Build the basin without driving heavy equipment over the infiltration surface. Any
equipment driven on the surface should have extra-wide ("low pressure") tires. Prior to any
construction, rope off the infiltration area to stop entrance by unwanted equipment.
■ After final grading, till the infiltration surface deeply.
■ Use appropriate erosion control seed mix for the specific project and location.
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Performance
As water migrates through porous soil and rock, pollutant attenuation mechanisms include
precipitation, sorption, physical filtration, and bacterial degradation. If functioning properly,
this approach is presumed to have high removal efficiencies for particulate pollutants and
moderate removal of soluble pollutants. Actual pollutant removal in the subsurface would be
expected to vary depending upon site-specific soil types. This technology eliminates discharge to
surface waters except for the very largest storms; consequently, complete removal of all
stormwater constituents can be assumed.
There remain some concerns about the potential for groundwater contamination despite the
findings of the NURP and Nightingale (1975; 1987a,b,c; 1989). For instance, a report by Pitt et
al. (1994) highlighted the potential for groundwater contamination from intentional and
unintentional stormwater infiltration. That report recommends that infiltration facilities not be
sited in areas where high concentrations are present or where there is a potential for spills of
toxic material. Conversely, Schroeder (1995) reported that there was no evidence of
groundwater impacts from an infiltration basin serving a large industrial catchment in Fresno,
CA. .
Siting Criteria
The key element in siting infiltration basins is identifying sites with appropriate soil and
hydrogeologic properties, which is critical for long term performance. In one study conducted in
Prince George's County, Maryland (Galli, 1992), all of the infiltration basins investigated clogged
within 2 years. It is believed that these failures were for the most part due to allowing infiltration
at sites with rates of less than 0.5 in/hr, basing siting on soil type rather than field infiltration
tests, and poor construction practices that resulted in soil compaction of the basin invert.
A study of 23 infiltration basins in the Pacific Northwest showed better long-term performance
in an area with highly permeable soils (Hilding, 1996). In this study, few of the infiltration
basins had failed after 10 years. Consequently, the following guidelines for identifying
appropriate soil and subsurface conditions should be rigorously adhered to.
■ Determine soil type (consider RCS soil type 'A, B or C' only) from mapping and consult
USDA soil survey tables to review other parameters such as the amount of silt and clay,
presence of a restrictive layer or seasonal high water table, and estimated permeability. The
soil should not have more than 30% clay or more than 40% of clay and silt combined.
Eliminate sites that are clearly unsuitable for infiltration.
■ Groundwater separation should be at least 3 m from the basin invert to the measured
ground water elevation. There is concern at the state and regional levels of the impact on
groundwater quality from infiltrated runoff, especially when the separation between
groundwater and the surface is small.
I
■ Location away from buildings, slopes and highway pavement (greater than 6 m) and wells
and bridge structures (greater than 30 m). Sites constructed of fill, having a base flow or
with a slope greater than 15% should not be considered.
■ Ensure that adequate head is available to operate flow splitter structures (to allow the basin
to be offline) without ponding in the splitter structure or creating backwater upstream of the
splitter.
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TC-11 Infiltration Basin
■ Base flow should not be present in the tributary watershed.
Secondary Screening Based on Site Geotechnical Investigation
■ At least three in-hole conductivity tests shall be perlormed using USBR 7300-89 or Bouwer-
Rice procedures (the latter if groundwater is encountered within the boring), two tests at
different locations within the proposed basin and the third down gradient by no more than
approximately 10 m. The tests shall measure permeability in the side slopes and the bed
within a depth of 3 m of the invert.
■ The minimum acceptable hydraulic conductivity as measured in any of the three required
test holes is 13 mm/hr. If any test hole shows less than the minimum value, the site should
be disqualified from further consideration.
■ Exclude from consideration sites constructed in fill or partially in fill unless no silts or clays
are present in the soil boring. Fill tends to be compacted, with clays in a dispersed rather
than flocculated state, greatly reducing permeability.
■ The geotechnical investigation should be such that a good understanding is gained as to how
the stormwater runoff will move in the soil (horizontally or vertically) and if there are any
geological conditions that could inhibit the movement of water.
Additional Design Guidelines
(1) Basin Sizing -The required water quality volume is determined by local regulations
or sufficient to capture 85% of the annual runoff.
(2) Provide pretreatment if sediment loading is a maintenance concern for the basin.
(3) Include energy dissipation in the inlet design for the basins. Avoid designs that
include a permanent pool to reduce opportunity for standing water and associated
vector problems ..
(4) Basin invert area should be determined by the equation:
where A=
A =WQV
kt
Basin invert area (m2)
WQV = water quality volume (m3)
k = 0.5 times the lowest field-measured hydraulic conductivity
(m/hr)
t = drawdown time ( 48 hr)
(5) The use of vertical piping, either for distribution or infiltration enhancement shall
not be allowed to avoid device classification as a Class V injection well per 40
CFR146.5(e)(4).
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Maintenance
Regular maintenance is critical to the successful operation of infiltration basins. Recommended
operation and maintenance guidelines include:
■ Inspections and maintenance to ensure.
■ Observe drain time for the design storm after completion or modification of the facility to
confirm that the desired drain time has been obtained.
■ Schedule semiannual inspections for beginning and end of the wet season to identify
potential problems such as erosion of the basin side slopes and invert, standing water, trash
and debris, and sediment accumulation.
■ Remove accumulated trash and debris in the basin at the start and end of the wet season.
■ Inspect for standing water at the end of the wet season.
■ Trim vegetation at the beginning and end of the wet season to prevent establishment of
woody vegetation and for aesthetic and vector reasons.
■ Remove accumulated sediment and regrade when the accumulated sediment volume
exceeds 10% of the basin.
■ If erosion is occurring within the basin, revegetate immediately and stabilize with an erosion
control mulch or mat until vegetation cover is established.
■ To avoid reversing soil development, scarification or other disturbance should only be
performed when there are actual signs of clogging, rather than on a routine basis. Always
remove deposited sediments before scarification, and use a hand-guided rotary tiller, if
possible, or a disc harrow pulled by a very light tractor.
Cost
Infiltration basins are relatively cost-effective practices because little infrastructure is needed
when constructing them. One study estimated the total construction cost at about $2 per ft
(adjusted for inflation) of storage for a 0.25-acre basin (SWRPC, 1991). As with other BMPs,
these published cost estimates may deviate greatly from what might be incurred at a specific
site. For instance, Caltrans spent about $18/ft3 for the two infiltration basins constructed in
southern California, each of which had a water quality volume of about 0.34 ac.-ft. Much of the
higher cost can be attributed to changes in the storm drain system necessary to route the runoff
to the basin locations.
Infiltration basins typically consume about 2 to 3% of the site draining to them, which is
relatively small. Additional space may be required for buffer, landscaping, access road, and '
fencing. Maintenance costs are estimated at s to 10% of construction costs.
One cost concern associated with infiltration practices is the maintenance burden and longevity.
If improperly maintained, infiltration basins have a high failure rate. Thus, it may be necessary
to replace the basin with a different technology after a relatively short period of time.
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TC-11 Infiltration Basin
References and Sources of Additional Information
Caltrans, 2002, BMP Retrofit Pilot Program Proposed Final Report, Rpt. CTSW-RT-01-050,
California Dept. of Transportation, Sacramento, _CA.
Galli, J. 1992. Analysis of Urban BMP Performance and Longevity in Prince George's County,
Maryland. Metropolitan Washington Council of Governments, Washington, DC.
Hilding, K. 1996. Longevity ofinfiltration basins assessed in Puget Sound. Watershed Protection
Techniques 1(3):124-125.
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual. htt:J>://www.mde.state.md.us/environment/wma/stormwatermanual. Accessed May
22, 2002.
Nightingale, H.I., 1975, "Lead, Zinc, and Copper in Soils of Urban Storm-Runoff Retention
Basins," American Water Works Assoc. Journal. Vol. 67, p. 443-446.
Nightingale, H.I., 1987a, "Water Quality beneath Urban Runoff Water Management Basins,"
Water Resources Bulletin, Vol. 23, p. 197-205.
Nightingale, H.l., 1987b, "Accumulation of As, Ni, Cu, and Pb in Retention and Recharge Basin
Soils from Urban Runoff," Water Resources Bulletin, Vol. 23, p. 663-672.
Nightingale, H.I., 1987c, "Organic Pollutants in Soils of Retention/Recharge Basins Receiving
Urban Runoff Water," Soil Science Vol. 148, pp. 39-45.
Nightingale, H.I., Harrison, D., and Salo, J.E., 1985, "An Evaluation Technique for Ground-
water Quality Beneath Urban Runoff Retention and Percolation Basins," Ground Water
Monitoring Review, Vol. 5, No.1, pp. 43-50.
Oberts, G. 1994. Performance of Stormwater Ponds and Wetlands in Winter. Watershed
Protection Techniques 1(2): 64-68.
Pitt, R., et al. 1994, Potential Groundwater Contamination from Intentional and
Nonintentional Stormwater Infiltration, EPA/600/R-94/051, Risk Reduction Engineering
Laboratory, U.S. EPA, Cincinnati, OH.
Schueler, T. 1987. Controlling Urban Runoff: A Practical Manual for Planning and Designing
Urban BMPs. Metropolitan Washington Council of Governments, Washington, DC.
Schroeder, R.A., 1995, Potential For Chemical Transport Beneath a Storm-Runoff Recharge
(Retention) Basin for an Industrial Catchment in Fresno, CA, USGS Water-Resource
Investigations Report 93-4140.
Southeastern Wisconsin Regional Planning Commission (SWRPC). 1991. Costs of Urban
Nonpoint Source Water Pollution Control Measures. Southeastern Wisconsin Regional
Planning Commission, Waukesha, WI.
U.S. EPA, 1983, Results of the Nationwide Urban Runoff Program: Volume 1 -Final Report,
WH-554, Water Planning Division, Washington, DC.
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Watershed Management Institute (WMI). 1997. Operation, Maintenance, and Management of
Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency Office
of Water, Washington, DC.
Information Resources
Center for Watershed Protection (CWP). 1997. Stormwater BMP Design Supplement for Cold
Climates. Prepared for U.S. Environmental Protection Agency Office of Wetlands, Oceans and
Watersheds. Washington, DC.
Ferguson, B.K., 1994. Stormwater Infiltration. CRC Press, Ann Arbor, MI.
USEPA. 1993. Guidance to Specify Management Measures for Sources ofNonpoint Pollution in
Coastal Waters. EPA-840-B-92-002. U.S. Environmental Protection Agency, Office of Water,
Washington, DC .
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TC-11 Infiltration Basin
INFLOW
8 of 8
/
CONCRETE
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EMERGENCY
SPILLWAY
PLAN VIEW
PROFILE
January 2003
APPENDIXE
CALCULATED BMP POLLUTANT REMOVAL EFFICIENCIES
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by:
Rick Engineering Company -Water Resources Division
KH:RC:nd/Report/14071-A.00I
09-19-03
CITY OF CARLSBAD
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY-14071A
CITY OF CARLSBAD -POLLUTANT REMOVAL LOADS FOR POTENTIAL BMPS BY BASIN
•:.-, h ·'."It ·:; -,r'K:'.r·· --.j.'
,,_.;;; lq r:i,::}~~ .:. A:IiliJ -~--'
--.. -.
• J
Biofilter 5.50 3.74 68% 0.54 0.37 69% 3 1.75
Wet Pond 5.50 0.44 8% 0.02 5% 0.12
Extended Detention 5.50 1.03 19% 0.05 9% 0.22
Infiltration 5.50 0.00 0% 0.00 0% 0.00
. ... . ." .·1 f _
Biofilter 26 4.18 16% 3.10 0.50 16% 14 2.22
Wet Pond 26 1.37 5% 0.09 3% 0.41
Extended Detention 26 3.18 12% 0.17 6% 0.76
Infiltration 26 0.00 0% 0.00 0% 0.00 ~-
-> , ·-~.
.,!, 'Ill .... 1:z _, •.\
Biofilter 10 6.42 66% 1.12 0.75 67% 5 3.28
Wet Pond 10 2.29 24% 0.15 13% 0.66
Extended Detention 10 5.31 55% 0.28 25% 1.23
Infiltration 10 0.00 0% 0.00 0% 0.00
I~• -r,'°1,-D .. !ill •. 0WJ -l,n li,111 ""' -II .
-ft
Biofilter 6 2.37 37% 0.70 0.26 37% 3 1.16
Wet Pond 6 0.85 13% 0.05 8% 0.23
Extended Detention 6 1.98 31% 0.10 14% 0.44
Infiltration 6 0.08 1% 0.01 1% 0.04
I .. ~ ~
II a .. 0 ... ·-Biofilter 0.5 0.32 61% 0.09 0.05 62% 0 0.24
Wet Pond 0.5 0.04 8% 0.00 5% 0.02
Extended Detention 0.5 0.10 19% 0.01 9% 0.03
Infiltration 0.5 0.10 20% 0.02 19% 0.07
Iii
0 -Biofilter 4 1.10 31% 0.51 0.16 31% 2 0.66
Wet Pond 4 0.15 4% 0.01 2% 0.05
Extended Detention 4 0.36 10% 0.02 5% 0.10
Infiltration 4 0.05 1% 0.01 1% 0.03
l°ft
Biofilter 2.8 0.43 15% 0.40 0.06 16% 2 0.25
Wet Pond 2.8 0.08 3% 0.01 2% 0.03
Extended Detention 2.8 0.18 7% 0.01 3% 0.05
Infiltration 2.8 0.01 0% 0.00 0% 0.00
9 '.iii, ...
ft ·-
n ' --Ill ·" I~ 1-~
Biofilter 0.5 0.19 39% 0.06 0.02 40% 0 0.09
Wet Pond 0.5 0.08 16% 0.01 9% 0.02
Extended Detention 0.5 0.18 37% 0.01 17% 0.04
Infiltration 0.5 0.01 1% 0.00 1% 0.00 ,. .
.. a El Cl
Biofilter 1 0.91 68% 0.14 0.09 69% 1 0.41
Wet Pond 1 0.82 61% 0.05 35% 0.21
Extended Detention 0.81 61% 0.04 28% 0.17
Infiltration 1 0.00 0% 0.00 0% 0.00
C:JobslCarlsbadlRemovalEfficiencyUlt.xls Basins
' -
Ill
laf~J~ ., ..... ., ... ,~,
-U~J--:n
~
.D I
69% 6 1.73 29% 20 7.82 40% 126
5% 0.30 5% 1.24 6%
9% 0.37 6% -0.66 -3%
0% 0.00 0% 0.00 0%
Iii' .., 1111 .-,
..
• r , •. -e:i. o•
16% 32 2.20 7% 144 13.50 9% 724
3% 1.05 3% 5.91 4%
6% 1.29 4% -3.15 -2%
0% 0.00 0% 0.00 0%
. J
• ••.,. ~ ·C
67% 12 3.25 28% 54 20.75 39% 262
13% 1.69 15% 9.89 18%
25% 2.07 18% -5.26 -10%
0% 0.00 0% 0.00 0%
a ':I, .. .Jlill ,, __ g
"'ii' -.. II 1111 la n j11., 11:i .
37% 7 1.15 16% 30 6.55 22% 163
8% 0.60 8% 3.14 10%
14% 0.74 10% -1.67 -6%
1% 0.10 1% 0.40 1%
~ II
62% 1 0.24 26% 3 0.96 . 36% 19
5% 0.05 5% 0.17 7%
9% 0.06 6% -0.09 -3%
19% 0.19 21% 0.56 21%.
31% 5_ 0.65 13% 18 3.34 18% 109
2% 0.13 3% 0.63 3%
5% 0.16 3% -0.33 -2%
1% 0.07 2% 0.28 2%
16% 4 0.25 7% 14 1.29 9% 84
2% 0.07 2% 0.31 2%
3% 0.08 2% -0.17 -1%
0% 0.01 0% 0.03 0%
40% 1 0.09 17% 2 0.56 23% .13
9% 0.05 10% 0.31 13%
17% 0.06 12% -0.16 -7%
1% 0.01 1% 0.03 1%
.,a, • li.1' •· /,i 1:i ..; 11 Q 11 .11. 1,,., Elin .· IP-~ iii. II ., .1!111 · -.tll' II
69% 1 0.41 29% 5 1.87 40% 31
35% 0.54 38% 2.25 48%
28% 0.28 20% -0.51 -11%
0% 0.00 0% 0.00 0%
8127103
, .. ,
•·
-"W -,nr.fflj °I\: • .. H".J':.11&
' -.. '" ·' !I
NIA NIA
NIA NIA
NIA NIA
NIA NIA
!Joi.Iii a
NIA NIA
NIA NIA
NIA NIA
NIA NIA
"'Ir., M ' .n ili :f'ir.11' -·
a
.Q
'
I -
NIA
NIA
NIA
NIA
..~..,
NIA
NIA
NIA
NIA ....
NIA
NIA
NIA
NIA
·~.'
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
If_ ii 11:b-.
NIA
NIA
NIA
NIA
·-11-. .. .;'
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA
NIA ·, .,._,, -~-'"'.{ _..., ..... . ·•< o<l.. 1.::--,, ........ '
NIA NIA
NIA NIA
NIA · NIA
NIA NIA ..
·111
NIA · NIA
NIA NIA
NIA NIA
NIA NIA
•
CITY OF CARLSBAD
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY-14071A
CITY OF CARLSBAD -POLLUTANT REMOVAL LOADS FOR POTENTIAL BMPS BY BASIN
Biofilter 6
Wet Pond 6
Extended Detention 6
Infiltration 6
Biofilter 5
Wet Pond 5
Extended Detention 5
Infiltration 5
Biofilter 3
Wet Pond 3
Extended Detention 3
Infiltration 3
Biofilter 21
Wet Pond 21
Extended Detention 21
Infiltration 21
Biofilter
Wet Pond
Extended Detention
Infiltration
Biofilter
Wet Pond
Extended Detention
Infiltration
Biofilter
Wet Pond
Extended Detention
Infiltration
Biofilter
Wet Pond
Extended Detention
Infiltration
a I
E ..
0.4
0.4
0.4
0.4 ..
48
48
48
48
7
7
7
7
.. "v.
20
20
20
20
,~.,:.,11,u•.1.:.i, #--·-fl CiTiJ:JJ
-~-oll'_I •l!!!f£9.
1• • ,1 .. .1=1,a .,.. •
' ·. 11:1 , J '"rf ·. ff .. ..
2.40 43% 0.53 0.23 43% 3
0.24 4% 0.01 2%
0.57 10% 0.02 5%
0.04 ·1% 0.00 1%
-. \ :'a I •• Ill,'.._ .... __::.._, C -' •• -• 7 •~ a....., _,_, . ' •• ~;_a ii_?_,!! _., in: ·• ·. • ,,.. 0 -• C ..j ... I< : -, .. .,.
3.25 68% 0.48 0.33 69%
0.69 14% 0.04 8%
1.59 33% 0.07 15%
0.00 0% 0.00 0%
1.81 68% 0.28 0.19 69%
0.81 30% 0.05 17%
1.63 61 % 0.08 28%
0.00 0%. 0.00 0%
Cl; 0
-" 11:1 D 'Ill I• ., ,. a . ,.
6.74 32% 2.45 0.09 32%
16.81 79% 0.13 45%
12.98 61% 0.08 28%
0.00 0% 0.00 0%
-, r .. -
0.26 68% 0.07 0.05 69%
0.30 79% 0.03 45%
0.23 61% 0.02 28%
0.12 32% 0.02 29%
Ill II\ Ill 11:1
..... Ill.' ....
3.45 7% 4.73 0.35 7%
0.14 0% 0.01 0%
0.33 1% 0.01 0%
0.03 0% 0.00 0% .
a .. .. ''...a 1, a
1.22 19% 0.77 0.15 19%
0.00 0% 0.00 0% .. ...
a t .-..
0.37 2% 1.86 0.04 2%
0.43 2% 0.02 1%
1.00 5% 0.04 2%
0.00 0% 0.00 0%
2
1
IIJ _ .. -.. ..
C ~-"'
1::1
11
0
II' a ..,
23
, r. -1ll ; a ..
4
a~ ..
9
C:JobslCarlsbadlRemovalEfficiencyUlt.xls Basins
'" . -ill .·. ( ' ·-~,:!"--:JI' .,.-·• ,-' --~-~-r:;::--,· = ·-· ,, -·111 ., " ..... .t i
1.15
0.07
0.12
0.02
aa·,,.
1.57
0.19
0.35
0.00
0.87
0.22
. 0.35
0.00
I~ Dn
0.41
0.57
0.35
0.00
Iii
0.06
0.04
0.03
0.03 , .... "'
1.72
0.04
0.07
0.01 --" ,. a
0.66
0.00
0.17
0.11
0.21
0.00
• 'A-1; -1£-1@1D>.tl :· !, •. mh~ . ~--< ...
a ~-_ ~ 1,l!'J• ,.,,:, • g4 ~=• t --.;,. li'J'J'IUn .mi.::;n II ~ .iii"""' -r:I• , .. ,. . .,,., 1• fll•NII, a .. (U!Ml • J:r,r,;,, ,.,,,, .. '/I •
1' 0 I' -,II_; 0: a :-n _ ~-, Cl
43% 6 1.14 18% 20
2% 0.17 3%
5% 0.21 3%
1% 0.05 1% r .. \ " .. . .,4. ..~ , II)
69% 5 1.56 29% 17
8% 0.48 9%
15% 0.58 11%
0% 0.00 0% -~r :: .. l
69% 3 0.86 29% 10
17% 0.56 19%
28% 0.60 20%
0% 0.00 0%
32% 27 0.40 14%
45% 1.46 49%
28% 0.60 20%
0% 0.00 0%
n
69% 0 0.06 29% 1
a
45%
28%
29%
7%
0%
0%
0%
19%
0%
2%
1%
2%
0%
II _,
8127103
.. a,
8
-a
21
0.11 49%
0.04 20%
0.07 33%
1.70 3% 173
0.10 0%
0.12 0%
0.04 0%
.,,. ..
0.66 8% 26
0.00 0%
... "b "' II ...,
0.17 1% 68
0.29 1%
0.36 2%
0.00 0%
, ,~
86
--~-~: . ..
5.01 25% 129
0.68 3%
-0.36 -2%
0.15 1% -, •. a -. .JI _ } , .. ,., C.
6.92 40% 112
1.95 11%
-1.04 -6%
0.00 0%
m.!'·
3.96 40% 64
2.35 24%
-1.09 -11%
0.00 0%
1.84 19% 555
6.13 62%
-1.09 -11%
0.00 0%
a Ii"' '" ... ,..,.
.,-• ._ <~' I!! -
0.49 40% 9
0.75 62%
-0.13 -11%
0.40 33%
7.36 4% 1136
0.40 0%
-0.21 0%
0.12 0% .. d\ a -
2.84 11% 173
0.00 0%
0.75 1% 445
1.17 2%
-0.62 -1%
0.00 0%
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA .,. a .. a,
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
NIA NIA
•
CITY OF CARLSB
! -"~ ·~•~'* -. ,:'. --~· --T.y~--' Ill
..., h
~"
I~ ~~~ .. ~
r .;L:': _':( '-Ill 11:• IB Jrli
lfi·--=· ,.,--~~ ~ -· ,Bf.a I!' '"111111'.l"!lt• .":i.,~ -•· I::,:,, ... 1•..-• ••
a -J!f·.1111 fm11Jl :• 11, " r:i ff llll ,:.:., ... ,.,.,.!J ••
:t'•~lWtF.!:"""' -• ••-• I• .. .
Biofilter 78 -19.40 -25% 2 1.15
Wet Pond 2.85 4% 0.13
Extended Detention -0.48 -1% 0.28
Infiltration 0.00 0% 0.00
:.-•~l~W."I !1g!i!~~._, ... ..... '"'·'.' ~ ill ~ -ii -[~ , ,
• ... , .. ·, ,· ·~· . ~-u -
Blofilter 452 -26.47 -6% 12 1.90
Wet Pond 10.77 2% 0.59
Extended Detention -1.79 0% 1.30
Infiltration 0.00 0% 0.00
:l'.!.l...~11.•111ffll~ t_;n,,'. .,.... if',-~:::. 'J...'--r~' :~-~t ~-" "!~;· ~
·• . . . -
Biofilter 167 -40.34 -24% 5 2.99
Wet Pond 17.87 11% 1.02
Extended Detention -2.98 -2% 2.23
Infiltration 0.00 0% 0.00
:f~\-'11~~ : ;J ,ff' 1 IC! II l! ... II i "' .. C a .. -'
Biofilter 104 -14.01 -14% 3 0.96
Wet Pond 6.24 6% 0.33
Extended Detention -1.04 -1% 0.72
Infiltration 1.12 1% 0.03
:,~l.1l~il:ir1a .. ~mr 1a II '" Cl .. e.. ... ... .. Da/1 l~,111 "" II -" Biofilter 11 -2.37 -22% 0 0.10
Wet Pond 0.40 4% 0.01
Extended Detention -0.07 . -1% 0.03
Infiltration 1.84 17% 0.04
:f~l:'tl~lf'.,tll ... /~ . .., ~if; . r ~. -:.a IJ a II 11,,,' a 'Ill
Biofilter 70 -7.96 -11% 2 0.46
Wet Pond 1.39 2% 0.06
Extended Detention -0.23 0% 0.13
Infiltration 0.86 1% 0.02
:f'•"="l~~~F' .l3"'.r.ll a ~ .. .. ,a aD., ,!'di, ...
a 1121 a .... --Biofilter 56 -3.18 -6% 1 0.19
Wet Pond 0.72 1% 0.03
Extended Detention -0.12 0% 0.07
Infiltration 0.09 0% 0.00
-'j .··•,-'-
l<c:a '
aw -·-~ l !'J. • • tr -.
~ ,:m
67% 2
8%
17%
0%
al u "" ; §... ... -·-.
16% 12
5%
11%
0%
,--,l • _,-... -· . lj '"'
65% 5
22%
48%
0%
36% 3
12%
27%
1% :, Ill 1a ...
60% 0
8%.
17%
21%
CITY OF CARLSBAD
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY-14071A
·----~·-~ -.,,,, ---•.--,-"'FT .
1hCib ., ·;JJ . .'. Ill 1 ~ ~Flil
,~#• ,,~1~,, .. fd ~tEfilj. • fl'.l"!Jt, _JI • • fm'1.fl YJ -({/JJj),a ·"~ ~ 1:. f 1•.a:..t&r -~ ' h
""' ... ..
0.87 42% 14 6.40
0.12 6% 0.94
0.18 9% 1.26
N/A N/A 0.00 . II ., ~ I•
"' . l!I
1.22 10% 61 6.48
0.48 4% 2.64
0.72 6% 3.54
N/A N/A 0.00 ... ·"" l · .. '• ... ·, _-;.
1.88 41% 21 9.27
0.80 17% 4.12
1.20 26% 5.51
N/A N/A 0.00
II ~ I) 1 a (la : .
"' .... ' 0.65 23% 15 3.67
0.28 10% 1.64
0.41 15% 2.19
N/A N/A 0.20
a_ Gill
.. 111""' a . P, .
0.10 38% 2 0.88
0.02 6% 0.15
0.02 9% 0.20
N/A N/A 0.46
----·
" -
11 ~ --f:J.J • .,, ......
QI_ ....
45%
7%
9%
0%
11%
4%
6%
0%
t--"~-··::
44%
19%
26%
0%
ID
24%
11%
15%
1%
1-1\1 ....
40%
7%
9%
21% , ~ ,o ... ~Iii ... Ill l' a -II I( ., l"".11 .. ~ aa -"""'" g, 0 -I:!,
30% 2 0.34 19% 11 2.20 20%
4% 0.06 3% 0.39 4%
9% 0.09 5% 0.52 5%
1% N/A N/A 0.16 1%
a I ~ .. .. ~ a . a .., ·~ .. °£,. 0 ctqi a . .. a " .
15% 1 0.13 10% 8 0.83 10%
3% 0.03 2% 0.19 2%
6% 0.04 3% 0.25 3%
0% N/A N/A 0.02 0%
..
~ ,. :, ...
I•~ .fmI.:11·
111
0.04
g a ..
0.29
ii
0.11
0.06
II
0.01
-0.04
IC!. II
0.03
:.-~~l~li'Jl' . .t'it 1f' Ell : I( II ~" IIJII -.. I! I I.~ ... ..,. ,a '. ~ ""' !J .. ~a:., Cl ---~· Ill "a ., oa.a.."" ,. .. 9, .,a .. 111.. .. 1111 ~
Biofilter 10 -1.39 -14% 0 0.09 38% 0 0.06 24% 1 0.25 26% 0.01
Wet Pond 0.71 7% 0.04 15% 0.03 12% 0.13 13%
Extended Detention -0.12 -1% 0.08 33% 0.04 18% 0.17 18%
Infiltration 0.11 1% 0.00 1% N/A N/A 0.01 1%
,:.,•.~"'IIDm~ } i..-,.. "" .. I • .. .. -·-. I., _;, I~ .. ... ·u. ' ~ .. Qi II! Cl a IP ,. " ~ r.-. .. " 1n, ... 1m .
Biofilter 20 -4.98 -25% 0 0.29 67% 1 0.21 42% 3 1.52 45% 0.01
Wet Pond 5.56 28% 0.25 57% 0.23 45% 1,70 50%
Extended Detention -0.40 -2% 0.23 54% 0.15 29% 0.98 29%
Infiltration 0.00 0% 0.00 0% N/A N/A 0.00 0%
C:Jobs/Carlsbad/RemovalEfficiencyUlt.xls Basins 8/27/03
~ f: -·-.. ~~~s ... _...., .
, •• f;ll ,llft ,. .. l
I::,. --~ ~ .... :.z,, -(1"1:f: ... ~ • _J
·•.·,, l :r;J';"; , .... :..,a -.... .• .::-,,"' 1,1 ' .. ~ -,.
0.018 42%
0.002 5%
0.004 10%
N/A N/A
a di a ~ _;.11 ~
0.028 10%
0.010 3%
0.018 6%
N/A N/A
" :J 1j~':.·:· I< f'-:c, , :-. '
0.043 41%
0.016 15%
0.030 29%
N/A N/A
C
11::1 . .
0.014 23%
0.005 8%
0.010 16%
N/A N/A
· ii:.a :'.:Q;; , ...
0.003 38%
0.000 5%
0.001 10%
N/A N/A
. --;.~_:'' ·~~-::.~I!_
0.008 19%
0.001 3%
0.002 5%
N/A N/A _,._ ~i-'~ -0.003 10%
0.001 2%
0.001 3%
N/A N/A
' -~;.,i,:~ ~-1h::11 ·...,.
0.001 24%
0.001 10%
0.001 20%
N/A N/A
1: .-< , .. :. ,,'f n,
: .• 11·.•
0.004 42%
0.004 39%
0.003 32%
N/A N/A
CITY OF CARLSB
~~ ·---.,_-~ ~ -•--: I , ... -... ~r"--i
.. 2?L -~' ': ~(3{m~ ~ ;
. ,_ --ci.:,·-·-!cr-,· ') '7
-~ 'f• • .1-.-.(:.lfl' "ra,·" .-. .. r~s ~--! (l}JJjj.. (IJMJ ~ •.. ;:.,;;
1:f•.'-"1l~l~~r •;i--,-,-..... o II , ., • ;. ~--·-., -11
Biofilter 72 -11,38 -16%
Wet Pond 1.43 2%
Extended Detention -0.24 0%
Infiltration 0.46 1%
:f.•.l:il~t~l. -,:;: ! ... .. ..
--.·,.' . ;: C •. -Jll
Biofilter 67 -16.70 -25%
Wet Pond 4.36 7%
Extended Detention -0.73 -1%
Infiltration 0.00 0%
:f !l:1 l ~ ~)l ~~::-11, ,,;_:; .,-; --·,:/~.;,--' p
l' .
Biofilter 40 -10.05 -25%
Wet Pond 5.54 14%
Extended Detention -0.80 -2%
Infiltration 0.00 0%
:1'•~"11~K!IO-re· .~ i •la \i -.
-----1..: --...
Biofilter 385 -4.68 -12%
Wet Pond 14.47 36%
Extended Detention -0.80 -2%
Infiltration 0.00 0%
:J~'il~Jlllif ,, ~-' II II
Biofilter 12 -3.00 -25%
Wet Pond 4.32 36%
Extended Detention -0.24 -2%
Infiltration 3.29 27%
:f~l~U!l'J ~ a, a .. Ir .. .. . -Biofilter 642 -17.07 -3%
Wet Pond 0.86 0%
Extended Detention -0.14 0%
Infiltration 0.38 0%
:f!~h.,u..•t:,: II Ill --~ ~-D"' ..,. a_
f rl 11 ...
Biofilter 102 -7.00 -7%
Wet Pond ---
Extended Detention --
Infiltration 0.00 0%
1111 ' 11:1
R 11'""' a :••~•~JID;I . . .,
Biofilter 261 -1.80 -1%
Wet Pond 2.63 1%
Extended Detention -0.44 0%
Infiltration 0.00 0%
C:JobslCarlsbadlRemovalEfficiencyUlt.xls Basins
r -;. .,:,,-"'! ... ,..,. --a . ., 'I!~ ,..,.,.,, ·11
-' --.Cl'-
CJl.El filIDti) =-,:~:JI ••"'.(!It• II ~ = ...
II ,'Y/J ':ffl ·• -·~, .. _, ...• , ....... , .. --~ ,,, .... .. ~
CITY OF CARLSBAD
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY-14071A
--·---....... --·"':.r II '~I!' ---; -~~ -
__,__.:c ---I\ 1JT• iF.11 IIRlf ' ., ~ ,_ .. • -~ ~---~ l:<fl:.,•.,•l"~;.11-... {j ffl m~. u•~!:.1;;_ .fml;J} -fmI:ifl a:, .
" ---B
' ~•" l.!Fml ·-t'mJ_:j] l ~J• • ..
!'.ll a .. .,.._ Ill ~ di.,, "' .. . D • a;?"
2 0.67 42% 2 0.54 26% 15 4.26 28% 0.04
0.07 4% 0.07 3% 0.54 4%
0.14 9% 0.10 5% 0.72 5%
0.01 1% NIA NIA 0.11 1%
l! ., -· ' . r fQ .. ·-['t1 1;11 .. .11 ... -.. .. " .. a . •.
J .: • Ill "' • ·, 1:11..,.,. ~ a;. --
1 0.97 67% 2 0.77 42% 13 5.77 45% 0.04
0.19 13% 0.19 11% 1.51 12%
0.43 29% 0.29 16% 2.02 16%
0.00 0% NIA NIA 0.00 0%
ill' ' • ,.'Q . II( .'II -D ~0. .... :~11"'. .• ill ri -• r -,i-'"· " ii ' ... 11,,, ,, m ... -,~ •.-~"· :, ~ a,;..., ...
1 0.58 67% 1 0.44 42% 7 3.17 45% 0.02
0.25 28% 0.23 22% 1.75 25%
0.47 54% 0.30 29% 2.04 29%
0.00 0% NIA NIA 0.00 0% ..... .. . a ~ i R --a Ill .II .. I~ .,, a ' --.
9 0.27 31% 12 0.20 20% 65 1.48 21% 0.32
0.65 74% 0.61 58% 4.58 65%
0.47 54% 0.30 29% 2.04 29%
0.00 0% NIA NIA 0.00 0%
"a.:'11,.
... ·_.,.p II ~a,c: aa .. m.11 di.Cl l: ... p/:1 .. g .. ... Ill Iii
I • ..
0.3 0.17 67% 0.2 0.07 42% 1 0.23 45% 0.004
0.19 74% 0.10 58% 0.33 65%
0.14 54% 0.05 29% 0.15 29%
0.08 33% NIA NIA 0.17 33% , ... .. a 13 '"a it'" .. I) , .. ,p • ... ill Jllia, -.. 1~, .. uo ""'9 a'+ d"q, a~ _ .. II ~
-.. o ..
14 0.98 7% 18 0.81 4% 133 .. 6.35 5% 0.38
0.04 0% 0.04 0% 0.32 0%
0.08 1% 0.06 0% 0.43 0%
0.01 0% NIA NIA 0.09 0%
If r,/' ·"• .,II 'ai 1 "Ii, J' "el ... _QI, "U .. ' 1a1~ ~ c_ a ~
"' .. .. ,,, . ,..,p 0 .. a..a ., "" . 9 • Ill
2 0.37 18% 3 0.30 12% 20 2.44 12% 0.06 -------
------
0.00 0% NIA NIA 0.00 0%
h~a I"• ~ .. n lb.,~
..,_ ' ---llli"' O I fl rf ~· Q ..
II ,till Ila ,n a II " -II Cl II ...
6 0.11 2% 7 0.08 1% 52 0.64 1% 0.15
0.12 2% 0.12 2% 0.94 2%
0.26 5% 0.17 2% 1.26 2%
0.00 0% NIA NIA 0.00 0%
8/27103
~ ---~ _, ..
'i.;f~~
~(el" -::-::: .,~ . .. ~ ... -. ---:~ ),°j ~ a .tm:t:J} ,:,-• ,.,,
'.' h'i I'll ' .. ...
0.011 26%
0.001 3%
0.002 5%
NIA NIA
a -l '~:.
0.016 42%
0.003 9%
0.007 17%
NIA NIA
a, ·,;a-Ir -,:f.•~~-:° n , •
0.009 42%
0.004 19%
0.007 32%
NIA NIA
. ,!'I iii
0.004 20%
0.011 50%
0.007 32%
NIA NIA
!1:1 11:11 a11I 1·; .. -· '!-1:1'-i ~-
0.002 42%
0.002 50%
0.001 32%
NIA NIA -iii, l1Jo 11 1~ I
0.017 4%
0.001 0%
0.001 0%
NIA NIA ·o . .. I )~--:D !~,
0.007 12% ----
NIA NIA ·---.. ~~., "" 0.002 1%
0.002 1%
0.004 3%
NIA NIA