HomeMy WebLinkAbout; Agua Hedionda Watershed BMP Study; Agua Hedionda Watershed Regional Treatment BMP Feasibility Study; 2004-03-018.6.11 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 of 19% commercial, 65% residential, and 15% undeveloped. Exhibit 8-11A shows
the existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-1 IB 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 regardless of how it ranks amongst the other Regional Planning BMPs.
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
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Subwatershed boundaries
/Sy Potential BMP location boundaries
Date of Aerial Photograph: February 2002
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i:ilifrn....800 0 800 1600 Feet
Exhibit 8-11 A:
Agua Hedionda Watershed
Potential BMP Location
Basin 44 Exisiting Land Use
Legend:
Subwatershed boundaries
/\/ Potential BMP location boundaries
ACT*
AGR
AUT
COM
HEA
HIG
LIG
LOW
MED
OPE
PAR
PAS
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
N
A RICK ENGINEERING COMPANY
C.ilifm-in..800 0 800 1600 Feet
Exhibit 8-11B:
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 20% commercial, 57% 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
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Rick Engineering Company - Water Resources Division 125 3-1 -04
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Legend:
^WSubwatershed boundary
/\/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
RICK ENGINEERING COMPANY
800 0
NA
800 1600 Feet
Exhibit 8-12A:
Agua Hedionda Watershed
Potential BMP Location
Basin 45 Existing Land Use
Legend:
Sub watershed boundary
/\/ Potential BMP location boundary
AGR
AUT
COM
HEA
HIG
LIG
LOW
MED
OPE
PAR
PAS
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
N
A RICK ENGINEERING COMPANY
•800 0 800 1600 Feet
Exhibit 8-12B:
Agua Hedionda Watershed
Potential BMP Location
Basin 45 Planned Land Use
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8.6.13 Basin 90
Basin 90, also known as Cannon Lake, is located between El Arbul and Avenida Encinas and is
south of Cannon Road. Cannon Lake is enclosed by a residential area. Residents utilize Cannon Lake
recreationally and have 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 52% commercial, 13% industrial, 5% residential, and 29% 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 1st out of 6 LEAD BMPs.
Recommended modifications to Basin 90 include establishment of native wetland vegetation and the
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,
would treat a large subwatershed area, and would remove the most pollutants.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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Legend:
Subwatershed boundaries
/\y Potential BMP location boundaries
Date of Aerial Photograph: February 2002
A RICK ENGINEERING COMPANY
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NA 1000 2000 Feet
Exhibits-ISA:
Agua Hedionda Watershed
Potential BMP Location
Basin 90 Existing Land Use
Legend:
Subwatershed boundaries
y\y Potential BMP location boundaries
ACT *
AGR
AUT
HEA
HIG
LIG
LOW
MED
OPE
PAR
PAS
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
A RICK ENGINEERING COMPANY
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C ihfnriii i 1000 0
NA 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 corner of the Carlsbad Company Stores,
near Car Country Drive. This basin was not recorded in the Desiltation Basin Inventory (Carlsbad,
2000).
The subwatershed area (23 acres) comprises 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 8-14A 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: : KH:RC:jc/Report/140? 1 -A.602
Rick Engineering Company-Water Resources Division 133 3-1-04
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Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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Rick Engineering Company - Water Resources Division 134 3-1-04
Legend:
Subwatershed boundary
/\y Potential BMP location boundary
Date of Aerial Photograph: February 2002
A RICK ENGINEERING COMPANY
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800 o A
800 1600 Feet
Exhibit 8-14A:
Agua Hedionda Watershed
Potential BMP Location
Basin 96 Existing Land Use
a
Legend:
Subwatershed boundary
f\/ Potential BMP location boundary
ACT*
AGR
HEA
HIG
LIG
LOW
MED
OPE
PAR
PAS
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 ENGINEERING COMBXKY
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'800 0
NA 800 1600 Feet
Exhibit 8-14B:
Agua Hedionda 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. Hiis 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 18% commercial, 69% residential, and 12% undeveloped. Basin 97 would treat the
largest subwatershed of all the potential BMP locations in this study. Exhibit 8-15A shows the
existing land use conditions based on a 2002 aerial photograph of the basin. Exhibit 8-15B 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 10%,
and the optimal pollutant removal efficiency is 68%. The pollutant load removed ranked 5th out of
6 LEAD BMPs.
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.
Since this location requires further study, it was ranked 6th out of 6 LEAD BMPs.
Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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Legend:
Subwatershed boundaries
/\/ Potential BMP location boundaries
Date of Aerial Photograph: February &^>$p-
A RICK ENGINEERING COMPANY
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1000 0
NA 1000 2000 Feet
ExhibitS-ISA:
Agua Hedionda Watershed
Potential BMP Location
Basin 97 Existing Land Use
Source: City of Carlsbad General Plan Land
as of May 2003
Key to land use abbreviations is provided
in Appendix A
A RICK ENGINEERING COMPANY
1000 o
N
A 1000 2000 Feet
Exhibit 8-15B:
Agua Hedionda Watershed
Potential BMP Location
Basin 97 Planned Land Use
8.6.16 Basin98
Basin 98 is located along Tamarack Avenue 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 16% commercial, 46% residential, and 38% 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
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Rick Engineering Company - Water Resources Division 141 3-1 -04
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Subwatershed boundary
Potential BMP location boundary
Date of Aerial Photograph: February 2002
Exhibit 8-16A:
Agua Hedionda Watershed
Potential BMP Location
Basin 98 Existing Land Use
RICK ENGINEERING COMPANY
1600 Feet
Legend;
Subwatershed boundary
/\/ Potential BMP location boundary
ACT
AGR
AUT
COW
HEA
HIG
LIG
LOW
MED
OPE
PAR
PAS
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
N Exhibit 8-16B:
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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 (274 acres) is primarily undeveloped in the existing condition. The planned
land use comprises of 16% commercial, 69% residential, and 14% undeveloped. Exhibit 8-17A
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. The Regional Board does not
allow modifications to natural channels without extensive environmental permitting, 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
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Rick Engineering Company - Water Resources Division 145 3-1-04
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Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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Rick Engineering Company - Water Resources Division 146 3-1-04
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^^Subwatershed boundary
/V/ Potential BMP location boundary
Date of Aerial Photograph: February 2002
Exhibit 8-17A:
Agua Hedionda Watershed
Potential BMP Location
Basin 99 Existing Land Use
RICK ENGINEERING COMPANY
1600 Feet
Subwatershed boundary
Potential BMP location boundary
ACT*
AGR
AUT
COM
HEA
HIG
LIG
LOW
MED
OPE
PAR
PAS
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
N
RICK ENGINEERING COMPANY
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i.l", >'I|J1 V 800 o 800 1600 Feet
Exhibit 8-17B:
Agua Hedionda Watershed
Potential BMP Location
Basin 99 Planned Land Use
CHAPTER 9
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 2 1 , 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 Hydro logic 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: KH:RC:jc/Report/14071-A.002
Rick Engineering Company - Water Resources Division 1 49 3- 1 -04
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
Preparedly: KH:RC:jc/Report/l 4071 -A.002
Rick Engineering Company - Water Resources Division 150 3-1-04
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APPENDIX A
DEFINITIONS OF LAND USE CATEGORIES
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c Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
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Rick Engineering Company - Water Resources Division 3-1-04
Table A.1
Key to Land Use Category Abbreviations
See attached support material for descriptions of the land use within each category
Land Use Category
Open Space Reserves and Preserves
Passive Parks
Agriculture
Water
Low Density Residential
Medium Density Residential
High Density Residential
Commercial
Storefront Commercial
Auto Dealerships
Parking
Active Parks
Freeway
Other Transportation and Maintenance
Light Industry
Heavy Industry
Military
Category
Abbreviation
OPE
PAS
AGR
WAT
LOW
MED
HIG
COM
STO
AUT
PAR
ACT
FRE
TRA
LIG
HEA
MIL
Estimated Percent
Impervious
0
40
20
100
25
45
65
90
95
95
95
50
95
90
90
95
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.
HIG - High Density Residential
Multi-family 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
Olympic 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.
Iof5
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 Industry - Shipbuilding, airframe, and aircraft manufacturing. Usually located
close to transportation facilities and commercial areas. Parcels are typically large, 20-50
acres.
Extractive Industry - Mining, sand and gravel extraction, salt evaporation.
2 of 5
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 Industry-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.
Military Airports - Airports owned and operated by the military. Found on military
bases.
General Aviation Airports - 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 of 5
seaport terminals (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 10th 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 - Surface -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.
Surface Street Right-of-Ways - All street ROWs.
Regional Shopping Centers - Contain 1 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 10 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
Military 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 of 5
Military Training - Academic, operational and combat training facilities, training ranges,
and special purpose training ranges.
Military 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, flower 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 of 5
c APPENDIX B
SUPPORTING DOCUMENTATION FOR BENEFICIAL USES OF SURFACE WATERS
FOR THE AGUA HEDIONDA WATERSHED
c
c Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by: KH:RC:jc/Report/14071-A.002
Rick Engineering Company - Water Resources Division 3-1-04
WATER QUALITY CONTROL PLAN
FOR THE SAN DIEGO BASIN (9)
SEPTEMBERS, 1994
CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD
SAN DIEGO REGION
naturally occurring pollutant concentrations
prevent the attainment of the use; or
^atural, ephemeral, irifermittent or low flow
clfeditions or water revels prevent the
attainment of the use; or V
r tJhumanlfeaused conditions or sources of;
pollution prevent the attainment qiLthe use"n *<3?l' Yif
and cannot^be remedied or wou^ cause
more environmental damage to correct than
to leave in plafie; or f
dams, diversionsT^-or other types o|f:
hydrologic modifications preclude th|/
^attainment of the use, W$ it is not feasibl^;
restore the water its origin!*' %body\to
condition or to operate such
a waf vthat would result in the*"i£.the use; or
physical conditions related to the natural
features of the^ water body, such as the lack'
of a proper su&|trate, cover, flow, depth,
pools, riffles,andfne like, unrelated to water';;;
quality, preclude attainment of aquatic life
protection uses; or v ( £
% '\< fcontrols more stringe.nl thanihe controls forl^
effluerft limitations in Clean 5feWater Acft
Section!; 301 (b) and 306 would result in;
substantial-,and widespread economic and;-
social
(7) States may not reni'qye designated uses if (a)
they are existing uses»* unless a use requiring
more stringent criteria is ad^ded, or (b) such uses
"\will be attained by implementing effluent limits
"under Clean Water Act Sections 301 (b) and
306 and by implementing be^fcjrianagement
practices for nonpotnt source comf.pl [40 CFR
(8) If existing uses are higher than those specified in
water qualityh-tandards, a state must revise its
standards to reflect the uses actually being
attained [40
If the designated uses;%o not include the uses
specified in Section 10i{a) (2) of the Clean
Vaster Act, or if the state wa|ts to remove a use
speWied in Section 101 (a) T^ the state must
conduc^.a "use attainability ariatysis" [40 CFR
131.101^ A use attainability Analysis is
defined iri%) CFR 131.3(g| as a fts^»jcturedvijfc " T®scientific assessment of the factors affecting the
attainment of^^fae use which may include
physftal, chemical, bio^jjcal, and economic
factol&j£ The uses listed^^ection 10f8|)(2)
are proifejion and propagatra^of fish, sheft'sh,
and wil^e, and recreation (i.e., fishable/
swimmabfe uses).
USE
DEFINITIONS
In 1972, the State 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 (AGR) - 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 (PROC) - 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.
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.
Freshwater Replenishment (FRSH) - Ipcludes uses of
water for natural or artificial maintenance of surface
water quantity or quality (e.g., salinity).
Navigation (NAV) - Includes uses
of water for shipping, travel, or
other transportation by private,
military, or commercial vessels.
BENEFICIAL USES -3 September 8, 1994
630). A legal description of the boundaries of each
ecological reserve is on file at the California
Department of Fish and Game headquarters, 1416
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
The following are designated Natural Preserves by
the State Park and Recreation Commission (Public
Resources Code, Division 5, Chapter 1, Article 1).
A legal description of each natural preserve is on file
at the California Department of Parks and Recreation
headquarters, 1416 Ninth Street, Sacramento:
• San Mateo Creek Wetland Natural Preserve, San v
Diego County
• Los Penasquitos Marsh Natural Preserve, San J
Diego County
The following area is designated a National Estuarine v
Research Reserve by the National Oceanic and '*
Atmospheric Administration (NOAA) (Coastal Zone
Management Act of 1972 as amended Section 315, &
16 USC 1461). A legal description of the
boundaries of the national estuarine research reserve
is on file at the NOAA headquarters, Office of Ocean
and Coastal Resource Management, NOAA, i
Washington, D.C., 20235: ;
• Tijuana River National Estuarine Research
Reserve, San Diego County
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
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 (M/GR) - 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 Ear/y Development
(SPWN) - 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
that support habitats suitable for the collection of
filter-feeding shellfish (e.g., clams, oysters and
mussels) for human consumption, commercial, or
sport purposes.
<*«9iw»s«iBS?i$!»^^
EXISTj4lG AMD
POTENmL BENEFMIAL
USEl
Tb(f Water resources of the jS^R Diego Region have
Jen extensively develogH over the years and
'"today's existing beneficial uses will probjply
continue into the fu$0'e. Since the adoptioj^r the
Basin Plan in 197pf%hanges in land use pafipfrns and
resultant chanJiS in water quality havjHTO to someJ^P* mSrsubsequent^ modifications of beneficial use
designates. Minor modificatiooThave also been
also TppUe to clarify the defintfron of some of the
ben^ncial use designation;
Fisig, swmmng, o
occurred since No
The beneficial use designations describ
chapter are cateraffced as "existing"
beneficial usejMn existing benefy
established jjy demonstrating t]
ier uses have actually
er 28, 1975; or
- 5
t• The water qjjSlity and quantity is suit
allow the tile to be attained.
*'Existing beneficial uses were originy determined as
part of a use survey of wg^F resources in the
Region described in ChapteTl, History of Basin
September 8, 1994
c APPENDIX C
CIS PROCESSING PROGRAM CONSTANTS, VARIABLES, AND EQUATIONS
c
c Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by: KH:RC:jc/Report/14071-A.002
Rick Engineering Company- Water Resources Division 3-1-04
r
ESTIMATED PERCENT IMPERVIOUS AND RUNOFF COEFFICIENT BY SOIL TYPE FOR EACH LAND USE CATEGORY
LU Cat
Active Parks
Passive Parks
Open Space Reserves and Preserves
Agriculture
Low Density Residential
Medium Density Residential
High Density Residential
Commercial
Storefront Commercial
Auto Dealerships
Parking
Freeway
Other Transportation and Maintenance
Light Industry
Heavy Industry
Military
Water
Vacant and Undeveloped Land
LU Abr
ACT
PAS
OPE
AGR
LOW
MED
H1G
COM
STO
AUT
PAR
FRE
TRA
LIG
HEA
MIL
WAT
VAC
LU Num
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
LU Percent Impervious
50
40
0
20
25
50
80
90
95
95
95
95
90
-90
95
90
100
0
C SoilA
0.55
0.48
0.20
0.34
0.38
0.55
0.76
0.83
0.95
0.95
0.95
0.95
0.83
0.83
0.95
0.83
0.95
0.20
C SoilB
0.58
0.51
0.25
0.38
0.41
0.58
0.77
0.84
0.95
0.95
0.95
0.95
0.84
0.84
0.95
0.84
0.95
0.25
C SoilC
0.60
0.54
0.30
0.42
0.45
0.60
0.78
0.84
0.95
0.95
0.95
0.95
0.84
0.84
0.95
0.84
0.95
0.30
C SoilD
0.63
0.57
0.35
0.46
0.49
0.63
0.79
0.85
0.95
0.95
0.95
0.95
0.85
0.85
0.95
0.85
0.95
0.35
Ltot of Equation* tiHd wtthhi OtS pracenlng routine to calculate *com tor each treatment devk* at each location
FIELD IN TABLE Constant or variable m Qts orocessinc; cod« and shown In final output data tar each potential treatment location
TABLE Indicate* whether the constant or variable applies to the pctvoon fapresentlnfl the area dratnlna bo the potential treatment location (BASIN) or to the polvaon reprasenllno the potential treatment location (BMP)
TYPE Indicates whether the fleW b a user entered constant (USER) or a variable that to cafcuMad by the QIS proces*fn<i (CALCULATED)
SAMPLE Sample showing (he type of data contained In Ihe field. For fields a TYPE • USER, lha sample shown Is ttie actual user entered constant
DESCRIPTION Description of lr* constant or variable field
EQUATION
FIELD IN TABLE
BASIN C
BASIN AC
LOW AC
MED AC
HIS AC
BMP AC
BMP SLOPE
BMP PIPE
BMP RIPARIAN AC
BMP BOGMAR AC
BMP SCRUBCHAP AC
BASIN OU
BASIN DLU
BMP SOIL
BIO DU RES
BIO AC RES
BIO SLOPE RES
BIO SOIL RES
BIO VEG RES
3IO DU WT
SIO AC WT
JIO SLOPE WT
SIO SOIL WT
3IO VEG WT
BIO TOTAL
WET DU RES
WET AC RES
WET SLOPE RES
WET SOIL RES
TABLE
BASIN
BASIN
BASIN
BASIN
BASIN
BMP
BMP
BMP
BMP
BMP
BMP
BASIN
BASIN
BMP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
TYPE
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
JSER
JSER
JSER
JSER
JSER
CALCULATED
CALCULATED
CALCULATED
CALCULATED
CALCULATED
SAMPLE
0.87
364.4
54.5
54.S
54.5
0.37
0.05
Y
0.09
0.00
0.09
67
LOW
1
5
5
5
5
5
0.30
0.10
0.50
0.05
0.05
7.7
5
5
5
5
UNITS
none
acres
acres
acres
acres
acres
foot/foot
none
acres
acres
acre*
none
none
none
none
none
none
none
none
none
non*
none
none
none
none
none
none
nor*
none
DESCRIPTION
Runoff coefficient for area draining to the potential treatment location based on land use and
soD type (additional back up attached shows runoff coefficients for each land use/ sol type
combination)
Total ares drainlno to the potential treatment location
Total area of LOW land use within BASIN
Total area of MED torrt u»* within BASIN
Total anM of HK3 land use within BASIN
Total area of potential treatment location
Slope across potential treatment location
Y or N: Indicates whether an axistina storm drain pipe Intersects the potential treatment location
Total area of riparian vegetation community wHhin BMP
Total area of boo/marsh vMetatfon community w*hln BMP
Total area of •crub/chaparral vaoeMton community within BMP
Estimated number of dweHIno units within Ihe area draining to the potenllal treatment location
Dominant lend use within the area dmbilrw to Ihe DotanWI treatment location
Dominant hydrotooto sol group within the potential treatment location (1 =>A.2»B. 3»C. 4«
1 to 10 result- now wel the potential treatment location meets dwaflina unit criterion for
Bloflten
1 to 10 result -how well the potential treatment location meets available area criteria for
BMffltars
1 to 10 result - how we« the potential treatment location meets slope criteria for Boflltera
1 to 10 result - how well the potential treatment location meets SOB croup criteria for Bioffflers
1 to 10 result- tow we* the potential treatment location meets vegetation group criteria for
Bttffltera
Weight assigned to dweflina unit criterion for Bkjffiters
iVetant assigned to rotative area criterion for Biofflters
Weiaht •Hioned to stooe criterion for Btoflttora
Height annned to soH criterion forBfcfirter*
Walaht assigned to vegetation criterion for Btofllters
W«iOht*d total score for the potential treatment location for a BJofllter
1 » 10 result - how weH the potential treatment location meets dwelling unit criterion for
Wetlands
1 to 10 resufl- how well the potentM traatment location meets avafaMe area criteria for
Wetlands
1 to 10 result - how wan the potential treatment location moots slope criteria for Wetlands
to 10 r«*ult • how wefl Ihe potential treatment location meets soH arouo criteria for Wetlands
EQUATION
=(2.9*LOW ACW14.6-MED ACVH43^IIO AC)
-Lend use cateoorv wWi oreatest acreaoe wKhln BASIN
-Hvdrolalc soil orouo with creates! acrmoa within BASIN
IF BASIN DU » 250 THEN BIO DU RES < 10
IF 200 <- BASIN DU < 250 THEN BIO DU RES = 5
IF BASIN DU< 200 THEN BIO DU RES-0
IF BMP_AC >• (0.02-BASIN AC) THEN BIO_AC_RES = 10
IF (0.01 S-BASIN AC) <• BMP AC < (0.02-BASIN AC) THEN BIO AC RES * 8
IF(0.01-BASIN AC)<-BMP AC < (0.01S-BASIN AC) THEN BIO AC RES • 6
IF BMP AC < (0.01*BASIN AC1THENB10 AC RES = 4
IF BMP SLOPE <- 0.005 THEN BIO SLOPE RES "10
IF 0.005 < BMP SLOPE <= 0.02 THEN BIO SLOPE RES * S
IF 0.02 < BMP_SLOPE <= 0.10 THEN BIO_SLOPE_RES •= 4
IF 0.10 < BMP SLOPE <• 0.20 THEN BIO SLOPE RES -2
IF BMP SLOPE > 0.2 THEN BIO SLOPE "RES = 0
IF BMP SOIL - 1 THEN BIO SOIL RES • 10
IF BMP_SO)L = 2 THEN BrO_SOIL_RES « 9
IF BMP SOIL • 3 THEN BIO SOIL RES * 5
IF BMP SOIL = 4 THEN BIO~SOIL~RES • 1
IF BMP SCRUBCHAP = 0 AND (BMP BOGMAR > 0 OR BMP RIPARIAN >0)
THEN BIO_VEG_RES » 10
IF BMP SCRUBCHAP - 0 AND (BMP BOGMAR * 0 AND BMP RIPARIAN = 0)
THEN BIO VEG RES = 5
IF BMP SCRUBCHAP > 0 THEN BIO VEG RES = 1
D.3
D.1
D.G
3.05
5.05
BIO TOTAL i (BIO DU WTBIO DU RES)
*(BIO AC WT*BIO AC" RES) + (BKT SLOPE VfTBtO SLOPE RES)
•KBIO SOIL WT-BIO SOIL RES) -HBIO VEG WTBIO VEG RES)
F BASIN DU " 250 THEN WET DU RES "10
F 200 <• BASIN DU-J250THENWET DU RES = S
F BASIN DU < 200 THEN WET DU RES • 0
F BMP_AC >* (0.02-BAS1NJ«:) THEN WET_AC_RES - !0
F(0.015*BASIN_AC)<-BMP AC < (0.02-BASIN AC) THEN WET AC RES - B
IF(0.01*BASIN ACJoBMP AC* (0.01 S-fiASIN^AC) THEN WET~AC~RES = B
FBMP AC<(0.01-BASIN ACITHENWET AC RES = 4
FBMP SLOPE •« 0.005 THEN WET SLOPE RES = 10
F 0.005 < BMP SLOPE « 0.02 THEN WET.SLOPE RES * a
F0.02<BMP SLOPE <- 0.10 THEN WET SLOPE RES-4
F 0.10 < BMP_SLOPE <• 030 THEN WET_SLOPE_RES - 2
F BMP SLOPE > 0.2 THEN WET SLOPE ~RES = 0
F BMP SOIL - 1 THEN WET SOIL RES « 10
F BMP_SO1L * 2 THEN WET SOIL RES = 9
FBMP SOIL- 3 THEN WET SOIL RES- 5
FBMP SOIL*4THENWET SOIL~RES = t
Cart»badWQMP_BMPEquallonsjds: Sheer!; 8/29/03
r
WET VEG RES
WET DU WT
WET AC WT
WET SLOPE WT
WET SOB. WT
WET VEQ WT
WET TOTAL
DET AC RES
DET SLOPE RES
DET SOIL RES
DET AC WT
DET SLOPE WT
DET SOIL WT
DET TOTAL
INF AC RES
INF SLOPE RES
INF SOIL RES
NF AC WT
NF SLOPE WT
INF SOIL WT
INF TOTAL
HYD AC RES
HYD SLOPE RES
•IYD AC WT
•(YD SLOPE WT
HYD TOTAL
FIL AC RES
FIL SLOPE RES
=1L AC WT
1L SLOPE WT
FIL TOTAL
BMP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
3MP
BMP
BMP
BMP
BMP
BMP
BMP
BMP
CALCULATED
USER
USER
USER
USER
USER
CALCULATED
CALCULATED
CALCULATED
CALCULATED
USER
USER
USER
CALCULATED
CALCULATED
CALCULATED
CALCULATED
USER
JSER
USER
CALCULATED
CALCULATED
CALCULATED
JSER
JSER
CALCULATED
CALCULATED
CALCULATED
JSER
JSER
CALCULATED
5
0.30
0.25
050
0.05
0.20
7.7
5
5
5
0.60
036
0.05
7.7
5
5
5
0.20
0.10
0.70
7.7
S
5
0.30
0.70
7.7
S
5
030
0.70
7.7
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
none
1 lo 10 res*- how well th* potential treatment location meets vegetation group crtWrta for
Weflandt
Wetaht SM toned to dweffino unit crtterton for Wetlands
Wetaht ***loned to relative tree criterion for Wetlands
Weight aukmed to slooe criterion for Wetland!
WeWit aotonad Do son criterion for W«tand»
WefcWa**g^ to vewtaflon criterion for Wetlands
Wefarrted total score lot the ootenttal treatment location for a Wetland
1 lo 10 r»«ult- how v^ the potenlia* trsatn>en( toe«ioo mw^»v*ll»brt»fes criteria for
Detention Basins
1 to 10 result • how well the potentM treatment location meets slope criteria for Detention
Basing
1 to 10 result -how well the potential treatment location meets sop group criteria for Detention
Basins
WettM Mitonad to relative area criterion lor Detention Basins
Wetoht asiianed to slooe criterion for Detention Basins
WeWitasskined to soil criterion tor Detention Basins
Wetahted total score for the potential treatment location for a Detention Basin
1 to 10 result - how well the potential treatment location moots aveftable area criteria tor
Infiltration
1 to 10 result- how well theootential treatment location meets stooe criteria for Infiltration
1 to 1 0 rent! • how well the ootenlial treatment location meets soil orouo criteria for Infiltration
Weight asiianed to relative area criterion for Infiltration
Wetotit assigned to slooe criterion for Infiltration
Weight assigned to soil criterion for InTiHration
Wetahtad total score for the ootentlal treatment location for Infiltration
1 to 1 0 result - how vnfl the potential treatment location meets available area criteria for
HyrJrodynamlc Seoaretora
1 to lOrBtuK-howwall the potential treatment location meets slope criteria for Hydrodynamle
Separators
Wetoht esskmed to relative area criterion for Hydrodynamic Separators
Wetofrt assloned to slooe criterion for Hvdrodvnarnic Separators
Wetohted total score for the ootentlal treatment location for a Hvdrodvnarnlc Separator
1 to 10 rwult- how w«i the potential treatment location meets avatable area criteria for
FItratton
1 to 10 reeult - how we* the DotonHal treatment location meets stooe crtterta for Filtration
/vetaht assianed to relative area criterion for Filtration
Vetoht Mstanad to slope criterion for Filtration
Weighted total score for the potential treatment location for Fttratfon
IF BMP SCRUBCHAP « 0 AND {BMP_BOOMAR > 0 OR BMP_RIPARIAN > 0)
THEN WET_VEO_RES « 10
IF BMP SCRUBCHAP • 0 AND (BMP BOOMAR = 0 AND BMP_RIPARIAN = 0)
THEN WET VEO RES " S
IF BMP SCRUBCHAP >0 THEN WET VEG RES-1
5,3
3.25
1.2
J.05
3.2
WET TOTAL "(WET DU WTWET DU RES)
+ (WET AC WTWET AC" RES) + (WET SLOPE WT*WET_SLOPE_RES)•KWET'SOIL WT-WET SOIL RESI-KWET VEQ WPWET VEG RESI
IF BMP AC r- (BASIN AC"BAS!N C-O.S/25) THEN DET AC RES • 10
IF{BASTN AC-BASIN (TO*!5)<"BMP AC < <BA$IN_AC-BASIN_C-O.O25)
THEN DET AC RES - S
IF BMP AC"* (BASIN AC-BASIN C-0.4/2Et THEN DET AC RES « 5
IF BMP SLOPE <* O.OS THEN OET SLOPE RES = 1 0
IF 0.05 < BMP_SLOPE <» 0.10 THEN OET_SLOPE_RES - 5
IF 0.10 < BMP SLOPE « 0.20 THEN DET SLOPE RES - 2
IF BMP SLOPE > 02 THEN DET SLOPE "fiES = 0~
IF BMP SOIL • 1 THEN DET SOIL_RES « 10
IF BMP SOIL " 2 THEN DET~SOIL RES - 9
IF BMP~SOIL « 3 THEN DET SOIL RES " 5
IF BMP SOIL « 4 THEN DET SOIL RES = 1
O.S
0.35
0.05
IF BMP PIPE " Y THEN DET TOTAL = 0
IF BMP"PIPE - N THEN DET TOTAL = + (DET AC WTDET AC RES)
"(DET~SLOPE WT-DET SLOPE RES)*{DET SOIL WTT3ET SOIL RES)
IF BMP AC >• (BASIN ACTBASIN C*0.6/2S> THEN INF AC RES = 10
IF (BASIN AC-BASIN_C-0.4/25) <- BMP AC < (BASIN_AC'BASIN_C-0.6/25}THENINF'AC RES -a
IF BMP AC < (BASIN AC*BASIN C*0.4/25) THEN INF AC RES = 5
IF BMP SLOPE <- 0.05 THEN INF_SLOPE_RES - 1 0
IF 0.05 < BMP_SLOPE <= 0.10 THEN INF_SLOPE_RES - 5
IF 0.10 < BMP SLOPE <• 0.20 THEN INF SLOPE RES = 2
tFBMP SLOPE > 02 THEN INF SLOPE RES = 0
IF BMP SOIL = 1 THEN INF SOIL RES HO
IF BMP SOIL " 2 THEN INF_SOIL RES = 8
IF BMP SOIL • 3 THEN INF SOIL RES = 0
IF BMP SOIL « 4 THEN INF SOIL RES - 0
D.2
3.1
J.7
INF TOTAL * + (INF AC WTINF AC RES)
+ (INF SLOPE WPINF SLOPE RES) + (INF SOIL WPINF SOIL RES)
IF BMP AC >- 0.1 THEN HYD AC RES = 10
IF 0.05 <• BMP AC < 0.1 THEN HYD AC RES • a
IF 0.02 <* BMP AC < 0.05 THEN HYD AC RES = 5
IF BMP AC < 0.02 THEN HYD AC RES-2
F BMP_SLOPE >= O.OS THEN HYD_SLOPE_RES •= 10
IF 0.05 > BMP SLOPE >" 0.02 THEN HYD SLOPE RES = 5
IF 0.02 > BMP SLOPE >- 0.01 THEN HYD~SLOPE RES - 2
IF BMP SLOPE < 0.01 THEN HYO SLOPE RES-0
).3
}.7
THEN HYD TOTAL = + (HYD AC WTHYD AC RES)
+ (HYD SLOPE WTHYD SLOPE RES)
F BMP AC >• 03 THEN FIL AC RES - 10
F 02 <* BMP_AC < 0.3 THEN FIL AC RES • 8
F 0.1 <= BMP AC < 02 THEN FIL AC RES - 5
F BMP AC < 0.1 THEN FIL AC RES « 2
F BMP SLOPE >=• 0.05 THEN FIL SLOPE RES - 10
F 0.05 > BMP SLOPE >- 0.02 THEN FIL SLOPE RES « 5
f 0.02 > BMP_SLOPE >= 0.01 THEN FIL SLOPE RES = 2
FBMP SLOPE < 0.01 THEN FIL SLOPE RES-0
1.3
).7
FIL TOTAL - + {FIL AC WTFIL AC RES)
+ (FIL SLOPE WTFIL SLOPE RES)
CaH3badWQMP_BMPEquanons.xls: Sheetl; &29/03
c APPENDIX D
CASQA HANDBOOK BMP SIZING GUIDELINES
c Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by: KH:RC:jc/Report/]4071-A.002
Rick Engineering Company - Water Resources Division 3-1-04
Californi a Stormwater Quality Association
Storn water Best Management Practice
H andbook
New Development and Redevelopment
L---H*fl
Of
c
Vegetated Swale 30
Design Considerations
• Tributary Area
• Area Required
• Slope
• Water Availability
BEST ORIGi
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.
Advantages
• 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.
Targeted Constituents
/ Sediment A
/ Nutrients •
•/ Trash •
/ Metals A
J Bacteria •
/ Oil and Grease A
V Organics A
Legend (Removal Effectiveness)
• Low • High
A Medium
altfornla
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
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1 of 13
- 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 \o
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.
2 of 13 California Stormwater BMP Handbook January 2003
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c
Vegetated Swale TC-30
Construction/Inspection Considerations
• 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 eifective
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 i). 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 9 studies have been conducted on all grassed channels designed for water quality (Table i).
The data suggest relatively high removal rates for some pollutants, but negative removals for
some bacteria, and fair performance for phosphorus.
January 2003 California Stormwater BMP Handbook 3 of 13
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TC-30 Vegetated Swale
Table 1 Grassed swale pollutant removal efficiency data
Removal Efficiencies (% Removal)
Study
Caltrans 2002
Goldberg 1993
Seattle Metro and Washington
Department of Ecology 1992
Seattle Metro and Washington
Department of Ecology, 1992
Wang etal., 1981
Dormanetal., 1989
Harper, 1988
Kercher etal. ,1983
Harper, 1988.
Koon, 1995
TSS
77
67.8
60
83
80
98
8?
99
8l
67
TP
8
4-5
45
29
-
18
83
99
17
39
TN
67
-
-
-
-
-
84
99
40
-
N03
66
31-4
-25
-25
-
45
80
99
52
9
Metals
83-90
42-62
2-16
46-73
70-80
37-8i
88-90
99
37-69
-35 to 6
Bacteria
-33
-100
-25
-25
-
-
-
-
-
-
Type
dry swales
Brassed channel
grassed channel
Brassed channel
dry swale
dry swale
dry swale
dry swale
wet swale
wet swale.
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 of less than 10 acres,
with slopes no greater than 5 %. Use of natural topographic lows is encouraged and natural
drainage courses should he regarded as significant local resources to be kept in use (Young et al.,
1996).
Selection Criteria (NCTCOG, 1993)
m Comparable performance to wet basins
• Limited to treating a few acres
• Availability 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.
4 of 13 California Stormwater BMP Handbook
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January 2003
v^^^'
Vegetated Swale TC-30
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 conveyance. 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 loo-year storm if it is
located "on-line." The side slopes should be no steeper than 3:1 (H:V).
6) Roadside ditches should be regarded as 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) 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
January 2003 California Stormwater BMP Handbook 5 of 13
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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. Topical 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.
6 of 13 California Stormwater BMP Handbook January 2003
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y~*
I
Vegetated Swale _ TC-30
Cost
Construction Cost
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.
January 2003 California Stormwater BMP Handbook 7 of 13
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TC-30 Vegetated Swale
Table 2 Swale Cost Estimate (SEWRPC, 1991)
Component
MoMteatfan/
UBRiODiUiUUuti-ugfn
Ste Pmpa rattan
Cteartrtf*...
GrubbEnff.
General^••iBin i^Tiai rt
LmolandTill1.
Sites Qawtopnient
Sriragfid TopsoP
Seed, and Mulch1..
Sod*
Subtotal
ConttngancfaB
Total
Unit
Swate
Aero
Yd"
Yd3
Yd3
Yip
-
Swale
-
Extent
1
O.S
372
1,210
1,210
1,210
-
1
-
tow
$107
9S,tBM
$2.10
$020
$0.40
$120
„
26%
-
Unit Cost
Moderate
$274
$5,200
$170
$0.35
$1.00
$2.40
-
25%
-
Htgti
$441
$5,400
SB (BOO
$6 JO
$0.50
$1.80saeo
_
26%
-
tow
$107
11 100
»BDU
$781
$242
$4B4
$1,462
*6,118
$1^9
•6J39S
Total Cort
Moderate
$274
$1 BOO
91,300
SI ,376
$424
$1,210
$2.004
$8,386
$2,347
$11.736
HW
$441
£2.700
WjteQ
$1,972
$605
$1,836
$4.356
$13,680
$3,415
$17X176
Source: (SEWRPC, 1991)
Note MobilfeHflonftJanK^fiEHtion refers to tliBOfginizHt^ a vogatsthre swate.
• Susie has 0 bottom whtth of 1.0 toot, a top width of 10 feet with 1:3 sMestopes, and a 1,OQ(Mbot length.B Area cleared = (top width +10 feet) x swale length.e Area srubbed = {top wWthx swale length).
'Volume excavated = (0.67 x top width x swate depth) x swale length (parabolic cross-section).
0 Ares tilled = (top width + Bfswale depth2! x swale length (parabolta cross-section).
3(topwtdtn)
'Area seeded = area cleared x 0.5.
1 Area sodded = area cleared x 0,5.
8 of 13 California Stormwater BMP Handbook
New Development and Redevelopment
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January 2003
r
Vegetated Swale TC-30
Table 3 Estimated Maintenance Costs fSEWRPC 1991)
Component
Lawn Mowing
QanerstLawiCare
aaatoDBbifa and liter
nerrunl
Gran RuBaadjngwfth
Mulch and FartHzar
Praanrn Admhtetrabon and
Bmte ImpBcflon
ToW
UnttCost
$0.85 / 1.000 fF/ mowing
$9.00 / 1,000 fP/ year
$0.10/nroar foot/year
Saao/yiP
$0.1 B/Bnosr foot /year,
pkja$2S/trwpaclon
-
Swale Size
(Depth and Top VBdth)
14 Foot Depth, One-
Foot Bottom Whftfi,
10-Foot Top Whfth
30.14 /Iteoarftjot
$0.1B/linasrfoot
30.10 /ibioarfpot
$0.01 ntnoHrfoot
J0.1S/lfn«rfoot
^ « , «^ ,_ _^
3-Foot Depth, S^oot
Bottom WWth, 21-Foot
Top Width
1021 /flrraarfoct
«028/Imarfbet
«0.10/finoarfoot
$0.01 /Sraarfoot
$0.15 /n war toot
$07E/lli»«rfbo*
ConiRient
Lawn maintenance area-flop
w(dti + 10faotjxtengtti. Mow
algtrt times par joar
Lawn mairtotanco area - (top
wkflh-MOfeogxtengfi
-
AIM rowogettad oquata 1 %
of lawn ralntefHnco ana por
yaar
Inspect tour Bmos par y«r
™
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
9 of 13
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,
"Performance of vegetative controls for treating highway runoff," ASCE Journal of
Environmental Engineering, Vol. 124, No. n, pp. 1121-1128.
Brown, W., and T. Schueler. 1997. The Economics ofStormwater 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 Biofiltration 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 Biofiltration 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): 24-39.0akland, P.H. 1983. An evaluation of Stormwater pollutant removal
10 of 13 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www. cab m pha ndboo ks.com
Vegetated Swale TC-30
I!"-""-•»•
V^ 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)1379-383.
Seattle Metro and Washington Department of Ecology. 1992. Biqfiltration 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^-99-006
http://www.epa.gov/owm/mtb/vegswale.pdf. Office of Water, Washington DC.
,*«»"•"
V Wang, T., D. Spyridakis, B. Mar, and R. Horner. 1981. Transport, Deposition and Control of
Heavy Metals in Highway Runoff. FHWA-WA-RD-39-io. 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~Ri6. Virginia Transportation Research Council,
Charlottesville, VA.i
Information Resources
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual, www.mde.state.md.us/environment/wma/stormwatermanual. Accessed May 22,
2OO1.
Reeves, E. 1994. Performance and Condition of Biofilters in the Pacific Northwest. Watershed
>*-r Protection Techniques i(3):ii7-H9.
January 2003 California Stormwater BMP Handbook 11 of 13
New Development and Redevelopment
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TC-30 Vegetated Swale
Seattle Metro and Washington Department of Ecology. 1992. Biofiltration Swale Performance.
Recommendations and Design Considerations. Publication No. 657. Seattle Metro and
Washington Department of Ecology, Olympia, WA.
USEPA1993. Guidance Specifying Management Measures for Sources ofNonpoint Pollution in
Coastal Waters. EPA-840-B-92-OO2. 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.
12 of 13 California Stormwater BMP Handbook January 2003
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Vegetated Swale TC-30
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January 2003 California Stormwater BMP Handbook
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13 of 13
Wet Ponds TC-20
c Design Considerations
• Area Required
• Slope
• Water Availability
• Aesthetics
• Environmental Side-effects
5
!ST ORIGINAL
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 stormwater 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 stormwater 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 (1-5
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.
Targeted Constituents
J Sediment
S Nutrients
^ Trash
S Metals
<S Bacteria
J Oil and Grease
J Organics
Legend (Removal Effectiveness)
• Low • High
A Medium
CASQA
Ouatfty
Association
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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 and 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 of less 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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Wet Ponds TC-20
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 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.
i
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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TC-20 Wet Ponds
uses or other areas where high nutrient loads are considered to he 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: (i) 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 hi 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.
i
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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Wet Ponds TC-20
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 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 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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TC-20 Wet Ponds
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 aquatic 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 dram 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.
For on-line facilities, the principal and emergency spillways must be sized to provide i.o
foot of freeboard during the 25-year event and to safely pass the loo-year flood. The
embankment should be designed in accordance with all relevant specifications for small
dams.
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Wet Ponds TC-20
Overflow and Outlet Pipe Am
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(6) 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 i.o foot of
freeboard along pond side slopes.
(7) 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 Table i.
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TC-20 Wet Ponds
Table 1 California Wetland Vegetation
Botanical Name
BACCHARIS SALICIFOLIA
FRANKEN1A GRANDIFOLIA
SALIXGOODINGII
SALIX LASIOLEPIS
SAMUCUS MEXICANUS
HAPLOPAPPUS VENETUS
DISTICHIS SPICATA
LIMONIUM CALIFORNICUM
ATRIPLEX LENTIFORMIS
BACCHARIS PILULARIS
MIMULUS LONGIFLORUS
SCIRPUS CAUFORNICUS
SCIRPUS ROBUSTUS
TYPHALATIFOLIA
JUNCUS ACUTUS
Common Name
MULE FAT
HEATH
BLACK WILLOW
ARROYO WILLOW
MEXICAN ELDERBERRY
COAST GOLDENBRUSH
SALT GRASS
COASTAL STATICE
COASTAL QUAIL BUSH
CHAPARRAL BROOM
MONKEY FLOWER
BULRUSH
BULRUSH
BROADLEAF CATTAIL
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 NOs-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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Wet Ponds TC-20
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 of TSS 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
^^ a non"c^°SginS 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
thelevel 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.
• 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 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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TC-20 Wet Ponds
• 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 1O 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:
C = 24.5Vo-7°5
where:
C = Construction, design and permitting cost;
V = Volume in the pond to include the lo-year storm (fts).
Using this equation, typical construction costs are:
$45,700 for a l acre-foot facility
$232,000 for a lo 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 (0.8 ac.-ft.), while the City of Austin spent $584,000
(including design) for a pond with a permanent pool volume of 3,100 ms (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,OOO/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 of litter removal.
References and Sources of Additional Information
Amain, 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. Stilhnan, 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-o 1-050, 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. i 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.
January 2003 California Stormwater BMP Handbook 11 of 15
New Development and Redevelopment
www.cabmphandbooks.com
TC-20 Wet Ponds
Emmerling-Dinovo, C. 1995. Stormwater detention basins and residential locational decisions.
Water Resources Bulletin, 3i(3):5l5~52.
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(l):48-57-
Holler, J.D. 1990. Nonpoint Source Phosphorous Control By A Combination Wet Detention/
Filtration Facility In Kissimmee, FL. Florida Scientist 53(i):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 .1. and W. Woodham 1995. Efficiency of a Stormwater Detention Pond in Reducing
Loads of Chemical and Physical Constituents in Urban Stream flow, Pinettas 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 whiter. Watershed Protection
Techniques 1(23:64-68.
12 of 15 California Stormwater BMP Handbook
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January 2003
*•• i imi|Hl "M m u-pu '.mif™. E.
Wet Ponds TO20
Oberts, G.L., P.J. Wotzka, and J.A. Hartsoe. 1989. The Water Quality Performance of Select Urban
Runoff Treatment Systems. Publication No. 59O-89-o62a. Prepared for the Legislative Commission
on Minnesota Resources, Metropolitan Council, St. Paul, MN.
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.
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 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.
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. 19973. Comparative pollutant removal capability of urban BMPs: A reanalysis.
Watershed Protection Techniques 2(4):515~52O.
Schueler, T. I997b. Influence of groundwater on performance 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 Performance 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 LA
Roesner (Eds.). American Society of Civil Engineering, New York, New York. pp. 338-350.
January 2003 California Stormwater BMP Handbook 13 of 15
New Development and Redevelopment
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TC-20 Wet Ponds
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, Minneapolis, MN.
U.S. Environmental Protection Agency (USEPA). 1993. Guidance Specifying Management Measures
for Sources ofNonpoint Pollution in Coastal Waters. EPA-84O-B-92-OO2. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
14 of 15 California Stormwater BMP Handbook January 2003
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Wet Ponds TC-20
POND BUFFER (25 FEET MINIMUM)
MAINTENANCE
ACCESS ROAD
MAXIMUM ED UMtT
MAXIMUM SAFETY STORM UMIT
SAFETY BENCH
EMBANKMENT-
RISER-
ANTI-SEEP COLLAR or-
FILTER DIAPHRAGM
RISER IN
EMBANKMENT
PLAN VIEW
EMERGENCY
SPILLWAY
PROFILE
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
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15 of 15
Constructed Wetlands TC-21
c Design Considerations
• Area Required
• Slope
• Water Availability
• Aesthetics
• Environmental Side-effects
ORIGINAL
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 flood control
benefits on a regional scale.
Wetlands are among the most effective stonnwater practices in
terms of pollutant removal and they also offer aesthetic value. As
stonnwater 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.
Targeted Constituents
/ .Sediment i
</ Nutrients t
•/ Trash
/ Metals
•/ Bacteria
V Oi! and Grease
V Organics
Legend {Removal Effectiveness)
• Low • High
A Medium
CASQA
Itfornla
Stormwater
Quality
Association
January 2003 California Stormwater BMP Handbook
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1 of 9
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 TO21
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: (i) 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 wetia'nds 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.
January 2003 California Stormwater BMP Handbook 3 of 9
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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 (<i8 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 forebay 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 more 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 pdnd 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
4 of 9 California Stormwater BMP Handbook January 2003
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Constructed Wetlands TO21
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 i.o
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 Utter 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
January 2003 California Stormwater BMP Handbook 5 of 9
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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:
C = 3O.6Vo-7°5
where:
C = Construction, design, and permitting cost;
V = Wetland volume needed to control the lo-year storm (fts).
Using this equation, typical construction costs are the following:
$ 57,100 for a i 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 relatively 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.
6 of 9 California Stormwater BMP Handbook January 2003
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Constructed Wetlands TO21
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
^f 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 i(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 7 of 9
New Development and Redevelopment
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TC-21 Constructed Wetlands
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. 19973. Comparative Pollutant Removal Capability Of Urban BMPs: AReanalysis.
Watershed Protection Techniques 2(4)1515-520.
Urbonas, B., J. Carlson, and B. Vang. 1994. Joint Pond- Wetland System in Colorado. Denver
Urban Drainage 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.
8 of 9 California Stormwater BMP Handbook January 2003
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Constructed Wetlands TC-21
s'sf*™'' -•
LIMIT 25% OF POND
PERIMETER OPEN GRASS
WETLAND BUFFER
(25 FEET MINIMUM) \
~~r<"x
MAINTENANCE _/ X
ACCESS ROAD \
25' WETLAND BUFFER LANDSCAPED WITH
NATIVE TREES / SHRUBS FOR HABITAT
,7-HIQH MARSH
(LESS THAN 6" WATER DEPTH)
LOW MARSH
(WATER DEPTH BETWEEN 6' and 16")
RISER/
BARREL
RISER IN
EMBANKMENT
PLAN VIEW
WETLANDS
HIGH MARSH EMBANKMENT-
RISER-
FOREBAY
GABION WALL
LOW MARSH
ANTl-SEEP COLLAR or -
FILTER DIAPHRAGM
EMERGENCY
SPILLWAY
PROFILE
January 2003 California Stormwater BMP Handbook
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9 of 9
Extended Detention Basin TC-22
Design Considerations
• Tributary Area
• Area Required
• Hydraulic Head
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
stormwater 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
headless 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.
Targeted Constituents
/
/
/
/
/
/
Sediment
Nutrients
Trash
Metals
Bacteria
Oil and Grease
A
•
•
A
A
A
/ Organics A
Legend (Removal Effectiveness)
• Low • High
A Medium
CASQA
Ifffornla
Stormwater
Quality
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 of less than 5 acres (would require an orifice with a diameter of less 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 of less 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.
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 5
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 because 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.
iExtended 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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TO 2 2 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 of low 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
overflow height was set to the design storm elevation. A stainless steel screen was placed
Figure 1
Example of Extended Detention Outlet Structure
2
e>
01o
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Extended Detention Basin TO 2 2
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 i.o
foot of freeboard during the 25-year event and to safely pass the flow from loo-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-Ho)°-5
where: Q = discharge (fta/s)
C = orifice coefficient
A = area of the orifice (ft2)
g = gravitational constant (32,2)
H = water surface elevation (ft)
H0= orifice elevation (ft)
Recommended values for C are 0.66 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 H0. 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 i.o foot of freeboard 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 often constitute only a small fraction of the
maintenance hours. During a recent study by Caltrans, 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.
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Extended Detention Basin TC-22
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:
C = 12.4V°-76°
where: C = Construction, design, and permitting cost, and
V = Volume (ft3).
Using this equation, typical construction costs are:
$ 41,600 for a i 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 reasonably accurate construction estimates. In addition, a typical facility
constructed by Caltrans cost about $160,000 with a capture volume of only 0.3 ac-ft.
An economic concern associated with dry ponds is that they might detract slightly from the
value of adjacent properties. One study found that dry ponds can actually detract from the
perceived value of homes adjacent to a dry pond by between 3 and 10 percent (Emmerling-
Dinovo, 1995)-
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TC-22 Extended Detention Basin
Maintenance Cost
For ponds, the annual cost of routine maintenance is typically estimated at about 3 to 5 percent
of the construction cost (EPA website). Alternatively, a community can estimate the cost of the
maintenance activities outlined in the maintenance section. Table i presents the maintenance
costs estimated by Caltrans based on their experience with five basins located in southern
California. Again, it should be emphasized that the vast majority of hours are related to
vegetation management (mowing).
Table 1
Activity
Inspections
Maintenance
Vector Control
Administration
Materials
Total
Estimated Average Annual
Labor Hours
4
49
0
3
.
56
Maintenance Effort
Equipment &
Material ($)
7
126
o
o
535
$668
Cost
183
2282
0
132
535
$3,132
References and Sources of Additional Information
Brown, W., and T. Schueler. 1997. The Economics ofStormwater 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 i &
2, prepared by MDE and Center for Watershed Protection.
http://www.mde.state.md.us/environment/wma/stonnwatermanual/index.html
8 of 10 California Stormwater BMP Handbook
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Extended Detention Basin TO22
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.
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, O.K., et al., 1996, Evaluation and Management of Highway Runoff Water Quality,
Publication No. FHWA-PD-96-O32, 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 of Nonpoint Pollution in Coastal Wafers. EPA-840-B-92-OO2. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
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TC-22 Extended Detention Basin
MAXIMUM ELEVATION
OF SAFETY STORM
MAXIMUM ELEVATION
OF ED POOL
SAFETY.
BENCH
EMERGENCY
SPILLWAY
PLAN VIEW
EMBANKMENT-
RISER-
FOREBAY
ANTI-SEEP COLLAR or •
FILTER DIAPHRAGM
EMERGENCY
SPILLWAY
PROFILE
Schematic of an Extended Detention Basin (MDE, 2000)
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Infiltration Basin TO 11
c Design Considerations
• Soil for Infiltration
• Slope
• Aesthetics
BEST ORIGINAL
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 hi the Central Valley. Basins located hi 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
Targeted Constituents
J Sediment i
S Nutrients i
S Trash I
S Metals i
S Bacteria i
/ Oil and Grease I
/ Organics I
Legend (Removal Effectiveness)
• Low • High
A Medium
IHornla
Stormwjrter
Quality
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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Infiltration Basin _ TO 11
( 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; i987a,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
I at sites with rates of less than 0.5 in/hr, basing siting on soil type rather than field infiltration
x»< 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.
• 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
m At least three in-hole conductivity tests shall be performed using USER 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:
kt
where A = 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
CFRi46.5(e)(4).
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Infiltration Basin TC-11
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 o.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 $i8/fts 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 5 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.
January 2003 California Stonnwater BMP Handbook 5 of 8
New Development and Redevelopment
www.cabmphandbooks.com
TC-11 Infiltration Basin
References and Sources of Additional Information
Caltrans, 2002, BMP Retrofit Pilot Program Proposed Final Report, Rpt. CTSW-RT-oi-oso,
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 of infiltration basins assessed in Puget Sound. Watershed Protection
Techniques i(3):i24~i25.
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual. htrp://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., 19873, "Water Quality beneath Urban Runoff Water Management Basins,"
Water Resources Bulletin, Vol. 23, p. 197-205.
Nightingale, H.I., 19870, "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., 19870, "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. i, 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/6oo/R-94/osi, 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 i - Final Report,
WH-554, Water Planning Division, Washington, DC.
6 of 8 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Infiltration Basin TC-11
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.
Irtfbrmation 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 Wafers. EPA-84O-B-92-OO2. U.S. Environmental Protection Agency, Office of Water,
Washington, DC.
January 2003 California Stormwater BMP Handbook 7 of 8
New Development and Redevelopment
www.cabmphandbooks.com
TC-11 Infiltration Basin
STILLING
BASIN
EMERGENCY
SPILLWAY
RISER/
BARREL
PLAN VIEW
INFLOW
BACKUP UNDERDRAIN PIPE IN CASE OF
STANDING WATER PROBLEMS ANT1-SEEP COLLAR or -
FILTER DIAPHRAGM
EMERGENCY
SPILLWAY
PROFILE
8 of 8 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
January 2003
c APPENDIX E
CALCULATED BMP POLLUTANT REMOVAL EFFICIENCIES
c
c Agua Hedionda Watershed Regional Treatment BMP Feasibility Study
Prepared by: KH:RC:jc/Report/14071-A.002
Rick Engineering Company- Water Resources Division 3-1-04
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY- 14071A
o TSS
Load Removed
(tons) (tons)
BASIN 1
BOD COD Total P Diss. P TKN
% Load Removed % Load Removed % Load Removed % Load Removed % Load Removed %
Removed (tons) (tons) Removed (tons) (tons) Removed (Ibs) (Ibs) Removed (Ibs) (Ibs) Removed (Ibs) (Ibs) Removed
Biofitter
Wet Pond
Extended Detention
Infiltration
BASIN 5
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 11
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 13
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 17
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 20
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 21
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 22
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 23
Biofilter
Wet Pond
Extended Detention
Infiltration
5.76
5.76
5.76
5.76
35
35
35
35
15
15
15
15
12
12
12
12
1.1
1.1
1.1
1.1
5
5
5
5
5.6
5.6
5.6
5.6
0.8
0.8
0.8
0.8
1
1
1
1
3.92
0.63
1.47
0.00
5.60
1.84
4.26
0.00
9.74
3.48
8.06
0.00
4.31
1.66
3.85
0.44
0.64
0.09
0.20
0.69
1.62
0.23
0.53
0.25
0.86
0.16
0.36
0.04
0.32
0.13
0.31
0.04
0.98
1.14
0.88
0.00
68%
11%
25%
0%
16%
5%
12%
0%
66%
24%
55% ,
0%
37%
14%
33% .
4%
61%
8%
19%
66%
31%
4%
10%
5%
15%
3%
7%
1%
39%
16%
37%
4%
68%
79%
61%
0%
0.57
4.24
1.69
1.28
0.18
0.76
0.80
0.11
0.15
0.39
0.04
0.07
0.00
0.69
0.13
0.24
0.00
1.13
0.23
0.42
0.00
0.48
0.10
0.19
0.04
0.11
0.01
0.02
0.11
0.24
0.02
0.04
0.03
0.13
0.01
0.02
0.00
0.04
0.01
0.02
0.00
0.10
0.07
0.04
0.00
69%
6%
12%
0%
16%
3%
6%
0%
67%
13%
25%
0%
37%
8%
15%
3%
62%
5%
9%
61%
31%
2%
5%
4%
16%
2%
3%
1%
40%
9%
17%
4%
69%
45%
28%
0%
3
19
7
6
1
3
3
0
1
1.83
0.17
0.31
0.00
3.05
0.56
1.05
0.00
4.98
1.00
1.86
0.00
2.11
0.46
0.85
0.20
0.48
0.04
0.07
0.48
0.98
0.08
0.14
0.14
0.50
0.05
0.10
0.02
0.15
0.03
0.06
0.02
0.45
0.29
0.18
0.00
69%
6%
12%
0%
16%
3%
6%
0%
67%
13%
25%
0%
37%
8%
15%
3%
62%
5%
9%
61%
31%
2%
5%
4%
16%
2%
3%
1%
40%
9%
17%
4%
69%
45%
28%
0%
28
289
120
79
9
43
45
6
7
8.15
1.92
2.35
0.00
19.65
9.38
11.49
0.00
33.61
17.47
21.39
0.00
12.42
6.96
8.52
3.13
2.41
0.48
0.58
6.43
5.65
1.16
1.42
2.11
2.94
0.78
0.96
0.30
1.02
0.62
0.75
0.28
2.02
3.41
1.39
0.00
29%
7%
8%
0%
7%
3%
4%
0%
28%
15%
18%
0%
16%
9%
11%
4%
26%
5%
6%
69%
13%
3%
3%
5%
7%
2%
2%
1%
17%
10%
12%
5%
29%
49%
20%
0%
20
193
81
55
5
27
28
4
5
8.20
1.77
-0.94
0.00
^^^|18.07
7.91
-4.21
0.00
31.49
15.01
-7.99
0.00
11.89
6.11
-3.25
2.17
1.94
0.35
-0.19
3.75
4.93
0.93
-0.49
1.34
2.58
0.63
-0.33
0.19
0.96
0.53
-0.28
0.19
2.03
3.14
-0.56
0.00
40%
9%
-5%
0%
•^•1 9%
4%
-2%
0%
39%
18%
-10%
0%
22%
11%
-6%
4%
36%
7%
-3%
69%
18%
3%
-2% :
5% :
9%
2%
-1%
1%
23%
13%
-7%
5%
40%
62%
-11%
0%
133
^^H986
397
296
38
162
169
22
33
N/A
N/A
N/A
N/A•Jj^H
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
•••N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
o
C:Jobs/Carlsbad/RemovaiEfficiencyUltDec.xls Basins 3-1-04
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY- 14071A
o TSS
Load Removed
(tons) (tons)
BOD COD Total P Diss, P TKN
% Load Removed % Load Removed % Load Removed % Load Removed % Load Removed %
Removed (tons) (tons) Removed (tons) (tons) Removed (Ibs) (ibs) Removed (Ibs) (Ibs) Removed (!bs) (Ibs) Removed
BASIN 26
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 44
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 45
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 90
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 96
Biofilter
Wet Pond
Extended Detention
Infiltration
BASIN 97
Biofitter
Wet Pond
Extended Detention
Infiltration
BASIN 98
Biofitter
Wet Pond
Extended Detention
Infiltration
BASIN 99
Biofilter
Wet Pond
Extended Detention
Infiltration
5
5
5
5
9
9
9
9
5
5
5
5
21
21
21
21
0.2
0.2
0.2
0.2
40
40
40
40
5
5
5
5
15
15
15
15
2.73
0.29
0.66
0.16
5.90
1.37
3.17
0.00
3.32
1.63
2.98
0.00
6.70
16.71
12.90
0.00
0.15
0.18
0.14
0.21
4.06
0.17
0.39
0.13
1.53
-
-
0.00
0.39
0.46
1.07
0.00
60%
6%
15%
3%
68%
16%
37%
0%
68%
33%
61%
0%
32%
79%
61%
0%
68%
79%
61%
95%
10%
0%
1%
0%
31%
-
-
0%
3%
3%
7%
0%
0.43
0.84
0.49
2.43
0.04
3.85
0.55
1.42
0.26
0.02
0.03
0.01
0.58
0.08
0.14
0.00
0.34
0.09
0.14
0.00
0.16
0.22
0.14
0.00
0.03
0.02
0.01
0.03
0.39
0.01
0.02
0.01
0.17
-
_
0.00
0.04
0.03
0.05
0.00
61%
4%
7%
3%
69%
9%
17%
0%
69%
19%
28%
0%
32%
45%
28%
0%
69%
45%
28%
88%
10%
0%
0%
0%
31%
_
—
0%
3%
2%
3%
0%
2
4
2
11
0
19
2
7
1.31
0.08
0.14
0.07
2.78
0.36
0.67
0.00
1.54
0.42
0.62
0.00
0.72
1.00
0.62
0.00
0.04
0.02
0.02
0.05
1.93
0.05
0.08
0.06
0.69
-
—
0.00
0.18
0.12
0.23
0.00
61%
4%
7%
3%
69%
9%
17%
0%
69%
19%
28%
0%
32%
45%
28%
0%
69%
45%
28%
88%
10% .
0%
0%
0%
31%
- •
-
0%
3%
2%
3%
0%
22
42
24
143
1
192
24
70
5.63
0.86
1.05
0.80
12.12
4.09
5.00
0.00
6.95
4.97
4.79
0.00
3.24
11.75
4.79
0.00
0.30
0.51
0.21
1.04
8.26
0.50
0.62
0.65
3.19
-
-
0.00
0.78
1.35
1.66
0.00
26%
4%
5%
4%
29%
10%
12%
0%
29%
21%
20%
0%
14%
49%
20%
0%
29%
49%
20%
100%
4%
0%
0%
0%
13%
_
-
0%
1%
2%
2%
0%
16
31
17
86
1
141
17
52
5.70
0.80
-0.42
0.59
12.23
3.78
-2.01
0.00
6.98
4.57
-1.92
0.00
3.25
10.81
-1.92
0.00
0.29
0.44
-0.08
0.71
8.35
0.47
-0.25
0.48
3.16
—
-
0.00
0.79
1.26
-0.67
0.00
35%
5%
-3%
4%
40%
12%
-7%
0%
40%
26%
-11%
0%
19%
62%
-11%
0%
40%
62%
-11%
100%
6%
0%
0%
0%
18%
_
-
0%
2%
2%
-1%
0%
105
199
^•i113
553
5
924
116
339
N/A
N/A
N/A
N/A
IHIH
N/A
N/A
N/A
N/A
^•HN/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
—
-
N/A
0
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
HHH
N/A
N/A
N/A
N/A•m
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
—
—
N/A
N/A
N/A
N/A
N/A
O
C:Jobs/Carlsbad/RemovalEfficiencyUltDec.xls Basins 3-1-04
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY- 14071A
O NO2 & NO3
Load Removed % Load
(Ibs) (Ibs) Removed (Ibs)
Total Pb
Removed %
(Ibs) Removed
Total Cu Total Zn
Removed % Load Removed %
(Ibs) Removed (Ibs) (Ibs) Removed
Total Cd
Load Removed %
(Ibs) fibs) Removed
BASIN 1
Biofilter
Wet Pond
Extended Detention
Infiltration
81 -20.32
4.07
-0.68
0.00
-25%
5%
-1%
0%
2 1.20
0.18
0.40
0.00
67%
10%
23%
0%
2 0.91
0.17
0.26
N/A
42%
8%
12%
N/A
15 6.70
1.35
1.80
0.00
45%
9%
12%
0%
0.05 0.019
0.003
0.006
N/A
42%
7%
13%
N/A
BASIN 5
Biofilter
Wet Pond
Extended Detention
Infiltration
608 -35.60
14.49
-2.41
0.00
-6%
2%
0%
0%
16 2.50
0.78
1.71
0.00
16%
5%
11%
0%
17 1.64
0.64
0.96
N/A
10%
4%
6%
N/A
86 9.04
3.69
4.94
0.00
11%
4%
6%
0%
0.39 0.038
0.013
0.025
N/A
10%
3%
6%
N/A
BASIN 11
Biofilter
Wet Pond
Extended Detention
Infiltration
253 -61.24
27.12
-4.52
0.00
-24%
11%
-2%
0%
7 4.54
1.54
3.38
0.00
65%
22%
48%
0%
7 2.85
1.21
1.81
N/A
41%
17%
26%
N/A
32 14.07
6.25
8.37
0.00
44%
19%
26%
0%
0.16 0.065
0.024
0.046
N/A
41%
15%
29% '
N/A
BASIN 13
Biofilter
Wet Pond
Extended Detention
Infiltration
188 -25.44
12.14
-2.02
6.10
-14%
6%
-1%
3%
5 1.74
0.64
1.40
0.19
36%
13%
29%
4%
5 1.17
0.54
0.80
N/A
23%
10%
16%
N/A
27 6.67
3.19
4.27
1.07
24%
12%
16%
4%
0.11 0.026
0.010
0.019
N/A
23%
9%
17%
N/A
BASIN 17
Biofilter
Wet Pond
Extended Detention
Infiltration
21 -4.80
0.81
-0.14
12.21
-22%
4%
-1%
57%
0 0.21
0.03
0.06
0.24
60%
8%
17%
68%
1 0.20
0.03
0.05
N/A
38%
6%
9%
N/A
4 1.78
0.30
0.40
3.03
40%
7%
9%
69%
0.01 0.005
0.001
0.001
N/A
38%
5%
10%
N/A
BASIN 20
Biofilter
Wet Pond
Extended Detention
Infiltration
104 -11.78
2.06
-0.34
4.18
-11%
2%
0%
4%
2 0.68
0.09
0.20
0.11
30%
4%
9%
5%
3 0.50
0.08
0.13
N/A
19%
3%
5%
N/A
16 3.26
0.57
0.76
0.78
20%
4%
5%
5%
0.06 0.012
0.002
0.003
N/A
19%
3%
5%
N/A
BASIN 21
Biofilter
Wet Pond
Extended Detention
Infiltration
112 -6.35
1.44
-0.24
0.62
-€%
1%
0%
1%
2 0.37
0.06
0.14
0.02
15%
3%
6%
1%
3 0.27
0.06
0.09
N/A
10%
2%
3%
N/A
16 1.66
0.38
0.50
0.11
10%
2%
3%
1%
0.07 0.006
0.001
0.002
N/A
10%
2%
3%
N/A
BASIN 22
Biofilter
Wet Pond
Extended Detention
Infiltration
17 -2.40
1.23
-0.21
0.63
-14%
7%
-1%
4%
0 0.16
0.06
0.14
0.02
38%
15%
33%
5%
0 0.10
0.05
0.07
N/A
24%
12%
18%
N/A
2 0.43
0.22
0.30
0.08
26%
13%
18%
5%
0.01 0.002
0.001
0.002
N/A
24%
10%
20%
N/A
BASIN 23
Biofilter
Wet Pond
Extended Detention
infiltration
22 -5.40
7.77
-0.43
0.00
-25%
36%
-2%
0%
0 0.32
0.35
0.25
0.00
67%
74%
54%
0%
1 0.23
0.32
0.16
N/A
42%
58%
29%
N/A
4 1.64
2.37
1.06
0.00
45%
65%
29%
0%
0.01 0.005
0.006
0.004
N/A
42%
50%
32%
N/A
C:Jobs/Carlsbad/RemovalEfficiencyUltDec.xls Basins 3-1-04
AGUA HEDIONDA WATERSHED
REGIONAL BMP FEASIBILITY STUDY- 14071A
n N02 & N03 Total Pb Total Cu Total Zn Tota| Cd
Load Removed % Load Removed % Load Removed % Load Removed % Load Removed %
(Ibs) (Ibs) Removed (Ibs) (Ibs) Removed (Ibs) (Ibs) Removed (Ibs) (ibs) Removed (Ibs) (Ibs) Removed
BASIN 26
Biofilter
Wet Pond
Extended Detention
Infiltration
59 -12.93
1.68
-0.28
1.75
-22%
3%
0%
3%
1 0.77
0.08
0.17
0.05
59%
6%
13%
4%
2 0.62
0.08
0.12
N/A
37%
5%
7%
N/A
12 4.83
0.63
0.84
0.44
40%
5%
7%
4%
0.03 0.013
0.001
0.003
N/A
37%
4%
8%
N/A
BASIN 44
Biofilter
Wet Pond
Extended Detention
Infiltration
118 -29.57
8.50
-1.42
0.00
-25%
7%
-1%
0%
3 1.74
0.38
0.84
0.00
67%
15%
32%
0%
3 1.38
0.38
0.57
N/A
42%
12%
17%
N/A
23 10.23
2.95
3.95
0.00
45%
13%
17%
0%
0.07 0.028
0.007
0.013
N/A
42%
10%
19%
N/A
BASIN 45
Biofilter
Wet Pond
Extended Detention
Infiltration
71 -17.74
10.80
-1.42
0.00
-25%
15%
-2%
0%
2 1.05
0.49
0.85
0.00
67%
31%
54%
0%
2 0.78
0.46
0.54
N/A
42%
25%
29%
N/A
12 5.61
3.43
3.62
0.00
45%
27%
29%
0%
0.04 0.016
0.008
0.012
N/A
42%
21%
32%
N/A
BASIN 90
Biofilter
Wet Pond
Extended Detention
Infiltration
379 -8.27
25.55
-1.42
0.00
-12%
36%
-2%
0%
9 0.49
1.16
0.85
0.00
31%
74%
54%
0%
12 0.37
1.08
0.54
N/A
20%
58%
29%
N/A
64 2.62
8.11
3.62
0.00
21%
65%
29%
0%
0.32 0.008
0.019
0.012
N/A
20%
50%
32%
N/A
BASIN 96
Biofilter
Wet Pond
Extended Detention
Infiltration
7 -1.77
2.54
-0.14
5.79
-25%
36%
-2%
82%
0.1 0.10
0.11
0.08
0.15
67%
74%
54%
98%
0.1 0.04
0.06
0.03
N/A
42%
58%
29%
N/A
0 0.13
0.19
0.09
0.30
45%
65%
29%
99%
0.002 0.001
0.001
0.001
N/A
42%
50%
32%
N/A
BASIN 97
Biofilter
Wet Pond
Extended Detention
Infiltration
536 -19.84
1.03
-0.17
1.48
-4%
0%
0%
0%
12 1.16
0.05
0.10
0.04
10%
0%
1%
0%
15 0.94
0.05
0.07
N/A
6%
0%
0%
N/A .
107 7.16
0.37
0.50
0.36
7%
0%
0%
0%
0.31 0.019
0.001
0.002
N/A
6%
0%
1%
N/A
BASIN 98
Biofilter
Wet Pond
Extended Detention
Infiltration
81 -9.15
~
-
0.00
-11%
-
-
0%
2 0.52
—_
0.00
30%
—
-
0%
2 0.35
-
~
N/A
19%_
-
N/A
12 2.54
-
-
0.00
20%
—
—
0%
0.04 0.008
-
-
N/A
19%
-
-
N/A
BASIN 99
Biofilter
Wet Pond
Extended Detention
Infiltration
199 -1.90
2.82
-0.47
0.00
-1%
1%
0%
0%
4 0.11
0.13
0.28
0.00
3%
3%
6%
0%
5 0.09
0.12
0.19
N/A
2%
2%
3%
N/A
39 0.68
1.01
1.35
0.00
2%
3%
3%
0%
0.11 0.002
0.002
0.004
N/A
2%
2%
4%
N/A
L C:Jobs/Cartsbad/RemovalEfficiencyUltDec.xls Basins 3-1-04