HomeMy WebLinkAboutSDP 2019-0014; CARLSBAD OAKS NORTH LOT 2; SWQMP - STORM WATER QUALITY MANAGEMENT PLAN STUDY; 2020-03-18TABLE OF CONTENTS
Certification Page
Project Vicinity Map
FORM E-34 Storm Water Standard Questionnaire
Site Information
FORM E-36 Standard Project Requirement Checklist
Summary of PDP Structural BMPs
Attachment 1: Backup for PDP Pollutant Control BMPs
Attachment 1 a: OMA Exhibit
Attachment 1 b: Tabular Summary of DMAs and Design Capture Volume Calculations
Attachment 1c: Harvest and Use Feasibility Screening (when applicable)
Attachment 1d: Categorization of Infiltration Feasibility Condition (when applicable)
Attachment 1 e: Pollutant Control BMP Design Worksheets/ Calculations
Attachment 2: Backup for PDP Hydromodification Control Measures
Attachment 2a: Hydromodification Management Exhibit
Attachment 2b: Management of Critical Coarse Sediment Yield Areas
Attachment 2c: Geomorphic Assessment of Receiving Channels
Attachment 2d: Flow Control Facility Design
Attachment 3: Structural BMP Maintenance Thresholds and Actions
Attachment 4: Single Sheet BMP (SSBMP) Exhibit
STEP1
TO BE COMPLETED FOR ALL PROJECTS
To determine if your project is a udevelopment project", please answer the following question:
YES NO
Is your project LIMITED TO routine maintenance activity and/or repair/improvements to an existing ~ building or structure that do not alter the size {See Section 1.3 of the BMP Design Manual for guidance)?
If you answered "yes" to the above question, provide justification below then Go to step 5, mark the third box stating "my
project is not a 'development project' and not subject to the requirements of the BMP manual" and complete applicant
information.
Justification/discussion: (e.g. the project includes only interior remodels within an existing building):
If you answered "no" to the above question, the project is a 'development project', go to Step 2.
STEP2
TO BE COMPLETED FOR ALL DEVELOPMENT PROJECTS
To determine if your project is exempt from PDP requirements pursuant to MS4 Permit Provision E.3.b.(3), please answer
the following questions:
Is your project LIMITED to one or more of the following:
YES NO
1. Constructing new or retrofitting paved sidewalks, bicycle lanes or trails that meet the following criteria:
a) Designed and constructed to direct storm water runoff to adjacent vegetated areas, or other non-
erodible permeable areas;
b) Designed and constructed to be hydraulically disconnected from paved streets or roads; -; c) Designed and constructed with permeable pavements or surfaces in accordance with USEPA
Green Streets guidance?
2. Retrofitting or redeveloping existing paved alleys, streets, or roads that are designed and constructed ~ in accordance with the USEPA Green Streets guidance?
3. Ground Mounted Solar Array that meets the criteria provided in section 1.4.2 of the BMP manual? ~
If you answered ·yes~ to one or more of the above questions, provide discussionfjustification below, then Go to step 5,
mark the second box stating "my project is EXEMPT from PDP ... " and complete applicantinformation.
Discussion to justify exemption ( e.g. the project redeveloping existing road designed and constructed in accordance with
the USE PA Green Street guidance):
If you answered "no" to the above questions, your project is not exempt from PDP, go to Step 3.
E-34 Page 2 or 4 REV.02/16
STEP3
TO BE COMPLETED FOR ALL NEW OR REDEVELOPMENT PROJECTS
To determine if your project is a POP, please answer the following questions
(MS4 Permit Provision E.3.b.(1 )):
1. Is your project a new development that creates 10,000 square feet or more of impervious surfaces
collectively over the entire project site? This includes commercial, industrial, residential, mixed-use,
and public development projects on public or private land.
2. Is your project a redevelopment project creating and/or replacing 5,000 square feet or more of
impervious surface collectively over the entire project site on an existing site of 10,000 square feet or
more of impervious surface? This includes commercial, industrial, residential, mixed-use, and public
development proiects on public or private land.
3. Is your project a new or redevelopment project that creates and/or replaces 5,000 square feet or more
of impervious surface collectively over the entire project site and supports a restaurant? A restaurant
is a facility that sells prepared foods and drinks for consumption, including stationary lunch counters
and refreshment stands selling prepared foods and drinks for immediate consumption (Standard
Industrial Classification (SIC) code 5812).
4. Is your project a new or redevelopment project that creates 5,000 square feet or more of impervious
surface collectively over the entire project site and supports a hillside development project? A hillside
development project includes development on anv natural slope that is twenty-five percent or Qreater.
5. Is your project a new or redevelopment project that creates and/or replaces 5,000 square feet or more
of impervious surface collectively over the entire project site and supports a parking lot? A parking lot
is a land area or facility for the temporary parking or storage of motor vehicles used personally for
business or for commerce.
6. Is your project a new or redevelopment project that creates and/or replaces 5,000 square feet or more
of impervious surface collectively over the entire project site and supports a street, road , highway
freeway or driveway? A street, road, highway, freeway or driveway is any paved impervious surface
used for the transportation of automobiles, trucks, motorcycles, and other vehicles.
7. Is your project a new or redevelopment project that creates and/or replaces 2,500 square feet or more
of impervious surface collectively over the entire site, and discharges directly to an Environmentally
Sensitive Area (ESA)? "Discharging Directly to" includes flow that is conveyed overland a distance of
200 feet or less from the project to the ESA, or conveyed in a pipe or open channel any distance as
an isolated flow from the project to the ESA (i.e. not commingled with flows from adjacent/ands).*
8. Is your project a new development or redevelopment project that creates and/or replaces 5,000
square feet or more of impervious surface that supports an automotive repair shop? An automotive
repair shop is a facility that is categorized in any one of the following Standard Industrial Classification
(SIC) codes: 5013, 5014, 5541, 7532-7534, or 7536-7539.
9. Is your project a new development or redevelopment project that creates and/or replaces 5,000 square
feet or more of impervious area that supports a retail gasoline outlet (RGO)? This category includes
RGO's that meet the following criteria: (a) 5,000 square feet or more or (b) a project Average Daily
Traffic (ADT) of 100 or more vehicles per day.
10. Is your project a new or redevelopment project that results in the disturbance of one or more acres of
land and are expected to generate pollutants post construction?
11. Is your project located within 200 feet of the Pacific Ocean and (1) creates 2,500 square feet or more
of impervious surface or (2) increases impervious surface on the property by more than 10%? (CMC
21.203.040)
YES NO
If you answered "yes" to one or more of the above questions, your project is a PDP. If your project is a redevelopment
project, Go to step 4. If your project is a new project, Go to step 5, check the first box stating "My project is a PDP ... "
and complete applicant information.
If you answered "no" to all of the above questions, your project is a 'STANDARD PROJECT', "Go to step 5, check the
second box stating "My project is a 'STANDARD PROJECT' ... " and complete aoolicant information.
E-34 Page 3 of 4 REV. 02/16
STEP4'
TO BE COMPLETED FOR REDEVELOPMENT PROJECTS THAT ARE PRIORITY DEYELOPIIENTPROJECTS
(PDP)ONLY
Complete the questions below regarding your redevelopment project {MS4 Permit Provision E.3.b.(2)):
YES NO
Does the redevelopment project result in the creation or replacement of impervious surface in an amount
of less than 50% of the surface area of the previously existing development? Complete the percent
impervious calculation below:
Existing impervious area {A) = N/A sq. ft.
Total proposed newly created or replaced impervious area (B) = N/A sq. ft.
Percent impervious area created or replaced (B/A)*100 = N/A %
If you answered "yes·, the structural BMP's required for PDP apply only to the creation or replacement of impervious
surface and not the entire development. Go to step 5, check the first box stating "My project is a PDP ... " and complete
applicant information.
If you answered "no,• the structural BM P's required for PDP apply to the entire development. Go to etep 5, check the
check the first box stating "My project is a PDP ... • and complete applicant information.
STEPS
~ CHECK THE APPROPRIATE BOX AND COMPLETE APPLICANT INFORMATION
¥ My project is a PDP and must comply with PDP stonnwater requirements of the BMP Manual. I understand t must
prepare a Storm Water Quality Management Plan (SWQMP) for submittal at time of application.
+ My project le a 'STANDARD PROJECT' OR EXEMPT from PDP and must only comply with 'STANDARD PROJECT'
stormwater requirements of the BMP Manual. As part of these requirements, I will submit a • Standard Project
Requirement Checklist Form E~3fr and Incorporate low impact development strategies throughout my project.
Note: For projects that are close to meeting the PDP threshold, staff may require detailed impervious area calculations and
exhibits to verify if 'STANDARD PROJECT' stormwater requirements apply.
+ My Project Is NOT a 'development project' and is not subject to the requirements of the BMP Manual.
Applicant Information and Signature Box Assessor's
Parcel Number(s): 209-121-01-00
J\l'IETCJt:lN,_J ~71.e; REllY.. &S-r.k1EI /,:'k:;.'
Ap~c:~~~
I Applicant Title: ~rt:::eJ,
Date: ll-l'o -/Cf. Applicant ~===
• Envlronmentally Sensitive Areas Include but are not limited to all Clean Water Act Section 303(d) Impaired water bodies; areas designated as Areas of
Special B ologlcal Significance by the State Water Resources Control Board (Water Quality Control Plan for the San Diego Basin (1994) and
amendmen19}: water bodies designated with the RARE beneficial use by the S1ate Water Reaources Control Board (Water Quality Control Plan for the San
Diego Basin (1994) and amendments); areas designated as preserves or their equivalent under the Multi Species Conservation Program within the Cities
and County of San Diego; Habitat Management Plan; and any other equivalent environmentally sensitive areas which have been Identified by the City.
This Box for Cftv Use Onlv
City Concurrence: I vi=~ I tJ()
I I
By:
Date:
Project ID:
E-34 Page 4 of4 REV. 02/16
SITE INFORMATION CHECKLIST
Project Summary lnfonnatlon
Proiect Name Carlsbad Oaks North Lot 2 ,
Project ID SDP 2019-0014
Project Address Carlsbad Oaks North
Lot 2
Assessor's Parcel Number(s) (APN(s)) 209-121-01-00
Project Watershed (Hydrologic Unit) Carlsbad 904
Parcel Area
7 .5238 Acres ( 327,736 Square Feet)
Existing Impervious Area
<subset of Parcel Area) 0 Acres ( 0 Square Feet)
Area to be disturbed by the project
(Project Area) 6.00 Acres ( 261,360 Square Feet)
Project Proposed Impervious Area
(subset of Proiect Area) 4.65 Acres ( 202,554 Square Feet)
Project Proposed Pervious Area
(subset of Proiect Area) 1.35 Acres ( 58,806 Square Feet)
Note: Proposed Impervious Area + Proposed Pervious Area = Area to be Disturbed by the
Project.
This mav be less than the Parcel Area.
Description of Existing SHe CondHlon and Dralnaae Pattems
Current Status of the Site (select all that apply):
J Existing development
J v Previously graded but not built out
J Agricultural or other non-impervious use
J Vacant, undeveloped/natural
Description/Additional Information:
Existing Land Cover Includes (select all that apply):
J Vegetative Cover
J v Non-Vegetated Pervious Areas
J Impervious Areas
Description/ Additional Information:
Existing land cover is exposed soil with scattered natural vegetation that has grown in the area.
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Underlying Soil belongs to Hydrologic Soil Group (select all that apply):
J NRCS Type A
J NRCS Type B
J NRCS Type C
J V NRCS Type D
Approximate Depth to Groundwater (GW):
J GW Depth < 5 feet
J 5 feet < GW Depth < 1 0 feet
J 10 feet < GW Depth < 20 feet
J v GW Depth > 20 feet
Existing Natural Hydrologic Features (select all that apply):
J Watercourses
J Seeps
J Springs
J Wetlands
J V None
Description/ Additional Information:
...
Description of Existing Site Topography and Drainage [How is storm water runoff conveyed from
the site? At a minimum, this description should answer (1) whether existing drainage
conveyance is natural or urban; (2) describe existing constructed storm water conveyance
systems, if applicable; and (3) is runoff from offsite conveyed through the site? if so, describe]:
1. The existing drainage is composed of both, natural and urban, conveyance systems. The
site storm runoff first drains to the El Fuerte Street and then enters the branch of Aqua
Hedionda creek that drains to the Agua Hedionda lagoon. The Aqua Hedionda lagoon
discharges directly into the Pacific Ocean.
2. Existing conditions include the inlet located at El Fuerte Street.
3. Yes, the existing slope along the south of the site located downslope of the existing brow
ditch is currently being directed onto the empty lot. This will be accounted for in post
development with a brow ditch .
Description of Proposed Site Development and Drainage Patterns
Project Descri ption / Proposed Land Use and/or Activities:
Lot2
rrhe project is proposing to build 347 parking spaces (approximately 194,446 square feet of
~sphalt pavement) and 10% of the site will be landscaped throughout the parking areas and
frontages.
~s part of this project, one main driveway entrance will be provided at the connection to El Fuerte
Street.
!All necessary utilities (storm, water, dry, etc.) will be installed as part of the project and tie into
~xisting stubs provided for the site by City of Carlsbad DWG No. 415-9.
Normal uses of such a development will generate storm water runoff with the potential to carry
pollutants to off-site tributaries . Bio Filtration ponds are planned to be incorporated throughout the
site to treat and detain runoff from impervious and landscaped areas.
List/describe proposed impervious features of the project (e.g., buildings, roadways, parking
lots, courtyards, athletic courts, other impervious features):
The impervious area of the proposed project will include a parking lot.
List/describe proposed pervious features of the project (e.g., landscape areas):
The pervious area of the proposed project will include some landscaping areas, and bio filtration
ponds.
Identification of Receiving Water Pollutants of Concern
Describe path of storm water from the project site to the Pacific Ocean (or bay, lagoon, lake or
reservoir, as applicable):
rThe project site drains into the branch of Agua Hedionda creek that drains to Agua Hedionda
lagoon. The Aqua Hedionda lagoon discharges directly to the Pacific Ocean.
List any 303(d) impaired water bodies within the path of storm water from the project site to the
Pacific Ocean (or bay, lagoon, lake or reservoir, as applicable), identify the
pollutant(s)/stressor(s) causing impairment, and identify any TMDLs for the impaired water
bodies:
303(d) Impaired Water Body Pollutant(s)IStressor(s) TMDLs
None listed None listed None listed
Agua Hedionda Creek Pathogens
Agua Hedionda Creek Toxicity
Agua Hedionda Creek Metals/Metalloids
Agua Hedionda Creek Nutrients
Agua Hedionda Creek Salinity
Identification of Project Site Pollutants
Identify pollutants anticipated from the project site based on all proposed use(s) of the site (see
BMP Desiiw Manual Appendix B.6):
Also a Receiving
Not Applicable to Anticipated from the Water Pollutant of
Pollutant the Project Site Project Site Concern
Sediment -I
Nutrients -I -I
Heavv Metals Iii Iii
Oraanic Compounds Iii
Trash & Debris Iii
Oxygen Demanding -I Substances
Oil & Grease Iii
Bacteria & Viruses Iii
Pesticides -I
Other Site Requirements and Constraints
When applicable, list other site requirements or constraints that will influence storm water
management design, such as zoning requirements including setbacks and open space, or City
codes governing minimum street width, sidewalk construction, allowable pavement types, and
drainage requirements.
The existing site has been raised with fill about from the native soil, therefore the infiltration rate
of the soil is very low. However, the soil engineer's recommendation is to provide impervious
liner underneath the biofilter regardless the location of the BMP.
Optional Addltlonal lnfonnatlon or Continuation of Previous Sections As Needed
This space provided for additional information or continuation of information from previous
sections as needed.
Source Control Reaulrement Applled?
SC-6 Additional BMPs based on Potential Sources of Runoff Pollutants must
answer for each source listed below and identify additional BMPs. (See
Table In Appendix E.1 of BMP Manual for guidance).
J On-site storm drain inlets J v Yes J No J NIA
J Interior floor drains and elevator shaft sump pumps J Yes J No j V N/A
J Interior parking garages J Yes J No J V N/A
J Need for future indoor & structural pest control J Yes . No J Iii NIA
Landscape/Outdoor Pesticide Use J t,I Yes No J N/A
J Pools, spas, ponds, decorative fountains and other water features J Yes J No J V NIA
Food service J Yes J No J V NIA
J Refuse areas J Iii Yes J No J N/A
J Industrial processes J Yes J No j V NIA
J Outdoor storage of equipment or materials J Yes J No J til N/A
J Vehicle and Equipment Cleaning J Yes j No j til N/A
J Vehicle/Equipment Repair and Maintenance J Yes J No j til NIA
J Fuel Dispensing Areas j Yes No J til NIA
J Loading Docks J Yes J No j V N/A
J Fire Sprinkler Test Water J Yes j No j til N/A
J Miscellaneous Drain or Wash Water J Yes J No J til N/A
J Plazas, sidewalks, an d parking lots J t,I Yes j No J NIA
For "Yes" answers, identify the additional BMP per Appendix E.1. Provide justification for "No" answers.
YES RESPONSES:
On-site storm drain inlets: Stenciling "No Dumping! Flows to Creek"
Landscape/Outdoor Pesticide Use: Selected plants appropriate to site conditions
Refuse areas: Signs "Do not dump hazardous materials here"
Plazas, sidewalks, and parking lots: Drains to BMP
N/A RESPONSE:
NIA response above indicates that the feature is not a proposed part of the project.
E-36 Page 2 or 3 REV. 02/16
Site Deskin BMPa
All development projects must implement site design BMPs SD-1 through SD-8 where applicable and feasible. See
Chapter 4 and Appendix E.2 thru E.6 of the BMP Design Manual for information to implement site design BMPs
shown in this checklist.
Answer each category below pursuant to the following.
I "Yes" means the project will implement the site design BMPs as described in Chapter 4 and/or Appendix E.2
thru E.6 of the Model BMP Design Manual. Discussion / justification is not required.
I "No" means the BMPs is applicable to the project but it is not feasible to implement. Discussion/justification must
be provided.
! "N/A" means the BMPs is not applicable at the project site because the project does not include the feature that
is addressed by the BMPs (e.g., the project site has no existing natural areas to conserve).
Discussion/justification may be provided.
Site Dulan Reaulrernent I ADDHed?
SD-1 Maintain Natural Drainage Pathways and Hydrologic Features I J Yes I J No I J ~ N/A
Discussion/justification if SD-1 not implemented:
No natural drainage paths are present on this site.
SD-2 Conserve Natural Areas, Soils, and Vegetation I ~ Yes I J No I J NIA
Discussion/justification if SD-2 not implemented:
This site is a previously mass graded pad. All areas outside of the
project footprint limitations will be conserved to the current "natural"
layout left by the mass grading of the site.
SD-3 Minimize Impervious Area I J ~ Yesl J No I J N/A
Discussion/justification if SD-3 not implemented:
SD-4 Minimize Soil Compaction I J ., Yes! J No I J NIA
Discussion/justification if SO-4 not implemented:
SD-5 Impervious Area Dispersion I ., Yes I J No I J NIA
Discussion/justification if SD-5 not implemented:
SD-6 Runoff Collection I J ~ Yesl J No I J NIA
Discussion/justification if SD-6 not implemented:
SD-7 Landscaping with Native or Drought Tolerant Species I J ., Yes I J No I J NIA
Discussion/justification if SD-7 not implemented:
SD-8 Harvesting and Using Precipitation I J Yes I J ., Nol J N/A
Discussion/justification if SD-8 not implemented:
The 36 hour demand is less than the DCV and 0.25DCV, making Harvesting and Using to be infeasible per Harvest
and Use Feasibility Checklist (Form 1-7).
E-36 Page 3 of 3 REV. 02/16
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Does the project include grading and changes to site topography?
J v Yes
J No
Description/ Additional Information:
The proposed grading will utilize the pad that was pre-graded before to put a proposed site.
BMPs will be added, but no change to the overall site topography will be needed .
Does the project include changes to site drainage (e.g., installation of new storm water
conveyance systems)?
J v Yes
j No
Description/ Additional Information:
The project includes the installations of a new storm water conveyance system that will obtain,
treat and release storm water from the project site to an existing tie in on EL Fuerte Street and
then enters the branch of Aqua Hedionda creek that drains to the Agua Hedionda lagoon. The
Aqua Hedionda lagoon discharges directly into the Pacific Ocean .
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Identify whether any of the following features, activities, and/or pollutant source areas will be
present (select all that apply):
J Ii/ On-site storm drain inlets
J Interior floor drains and elevator shaft sump pumps
J Interior parking garages
J Need for future indoor & structural pest control
J Ii/ Landscape/Outdoor Pesticide Use
J Pools, spas, ponds, decorative fountains, and other water features
J Food service
J Refuse areas
J Industrial processes
J Outdoor storage of equipment or materials
J Vehicle and Equipment Cleaning
J Vehicle/Equipment Repair and Maintenance
J Fuel Dispensing Areas
J Loading Docks
J Fire Sprinkler Test Water
J Miscellaneous Drain or Wash Water
J Ii/ Plazas, sidewalks, and parking lots
SUMMARY OF PDP STRUCTURAL BMPS
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PDP Structural BMPs
AH PDPs must implement structural BMPs for storm water pollutant control (see Chapter 5 of
the BMP Design Manual). Selection of PDP structural BMPs for storm water pollutant control
must be based on the selection process described in Chapter 5. PDPs subject to
hydromodification management requirements must also implement structural BMPs for flow
control for hydromodification management (see Chapter 6 of the BMP Design Manual). Both
storm water pollutant control and flow control for hydromodification management can be
achieved within the same structural BMP(s).
PDP structural BMPs must be verified by the City at the completion of construction. This may
include requiring the project owner or project owner's representative to certify construction of
the structural BMPs (see Section 1.12 of the BMP Design Manual). PDP structural BMPs must
be maintained into perpetuity, and the City must confirm the maintenance (see Section 7 of the
BMP Design Manual).
Use this form to provide narrative description of the general strategy for structural BMP
implementation at the project site in the box below. Then complete the POP structural BMP
summary information sheet for each structural BMP within the project (copy the BMP summary
information page as many times as needed to provide summary information for each individual
structural BMP).
Describe the general strategy for structural BMP implementation at the site. This information
must describe how the steps for selecting and designing storm water pollutant control BMPs
presented in Section 5.1 of the BMP Design Manual were followed, and the results (type of
BMPs selected). For projects requiring hydromodification flow control BMPs, indicate whether
pollutant control and flow control BMPs are integrated together or separate.
This project is not "self-retaining" nor ''self-retaining", Runoff factor was adjusted to estimate DCV
Harvest and Use is not feasible since Reclaimed water is available near by the location and the
0.25 DCV is greater than the 36 hour demand per form 1-7.
Infiltration is not feasible due to low percolation test conducted by the soil engineer.
Based on the locations for storm water pollutant control BMP and the OMA delineations were
developed during the site planning phase. The DCV was calculated .
,. Sizing requirements was computed referred to Appendix 8.5
'"BMP was designed for the remaining DCV, therefore design BMP for the required size, per
design criteria and considerations listed in the BMP manual and comply with pollutant control
BMP sizing requirements.
Based on pollutants generated by the type of the project and the 303(d) list at the receiving body,
Biofiltration is selected to treat all the pollutants in the project before releasing the storm water to
the public water body.
The calculated footprints fit the site design and the constraints.
The selected BMPs were sized and designed accordingly using design criteria and
considerations from BMP manual fact sheets in Appendix E.
The project has met the pollutant control performance standards.
Structural BMP Summary Information
[Copy this page as needed to provide Information for each lndlvldual proposed
structural BMPl
Structural BMP ID No. For Lot 2; BMP A -B
DWG Sheet No.C-3
Type of structural BMP:
J Retention by harvest and use (HU-1)
J Retention by infiltration basin (INF-1)
J Retention by bioretention (INF-2)
J Retention by permeable pavement (INF-3)
J Partial retention by biofiltration with partial retention (PR-1)
J ~ Biofiltration (BF-1)
J Flow-thru treatment control included as pre-treatment'forebay for an onsite retention or
biofiltration BMP (provide BMP type/description and indicate which onsite retention or
biofiltration BMP it serves in discussion section below)
J Ii/ Detention pond or vault for hydromodification management
J Ii/ Other (describe in discussion section below)
Purpose:
J Pollutant control only
J Hydromodification control only
J ti! Combined pollutant control and hydromodification control
J Pre-treatment/forebay for another structural BMP
J Other (describe in discussion section below)
Discussion (as needed):
All of the BMPs used on this project are biofiltration units that are designed per worksheet B.5-1
of the COC BMP Design Manual and modeled using continuous simulation modeling with
SWMM. Each pond is designed with a typical detail and sized according the hydromodification
mentioned above. Since each pond is designed per a typical detail, it is intended that each pond
will be constructed and maintained using the same general methods and materials.
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ATTACHMENT 1
BACKUP FOR PDP POLLUTANT CONTROL BMPS
This is the cover sheet for Attachment 1.
Check which Items are Included behind this cover sheet:
Attachment Contents Checklist
Seauence
Attachment 1a OMA Exhibit (Required)
Attachment 1 b
Attachment 1 c
Attachment 1 d
See DMA Exhibit Checklist on the back
of this Attachment cover sheet.
(24"x36" Exhibit typically required)
Tabular Summary of DMAs Showing
OMA ID matching OMA Exhibit, OMA
Area, and OMA Type (Required)*
*Provide table in this Attachment OR
on DMA Exhibit in Attachment 1 a
Form 1-7, Harvest and Use Feasibility
Screening Checklist (Required unless
the entire project will use infiltration
BMPs)
Refer to Appendix B.3-1 of the BMP
Design Manual to complete Form 1-7.
Form 1-8, Categorization of Infiltration
Feasibility Condition (Required unless
the project will use harvest and use
BMPs)
Refer to Appendices C and D of the
BMP Design Manual to complete Form
1-8.
J Iii Included
J Iii Included on OMA
Exhibit in Attachment 1 a
J Iii Included as Attachment 1b,
separate from OMA Exhibit
J Iii Included
J Not included because the entire
project will use infiltration BMPs
J Iii Included
J Not included because the entire
project will use harvest and use
BMPs
Attachment 1 e Pollutant Control BMP Design J Iii Included
Worksheets/ Calculations (Required)
Refer to Appendices B and E of the
BMP Design Manual for structural
pollutant control BMP design
guidelines
ATTACHMENT 1a
Use this checklist to ensure the required information has been included on the OMA
Exhibit:
The DMA Exhibit must identify:
Ill Underlying hydrologic soil group
Ill Approximate depth to groundwater
V Existing natural hydrologic features (watercourses, seeps, springs, wetlands)
V Critical coarse sediment yield areas to be protected (if present)
V Existing topography and impervious areas
V Existing and proposed site drainage network and connections to drainage offsite
V Proposed grading
V Proposed impervious features
V Proposed design features and surface treatments used to minimize imperviousness
V Drainage management area (OMA) boundaries, OMA 10 numbers, and OMA areas
(square footage or acreage), and OMA type (i.e., drains to BMP, self-retaining, or self-
mitigating)
., Structural BMPs (identify location and type of BMP)
•·
-ATTACHMENT 1b
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ATTACHMENT1c
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-ATTACHMENT 1d
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Ca1cgoriz.11inn of Infiltration Feasibility Co11didon Form 1~8
Part 1 -Full Jnfiluarlon Feasibility Screening Criteria
Would infiltration of the full design volume be feasible from a physical perspective without any
undesirable consequences that cannot be reasonably mitigated]
Criteria Screening Question Yes No
1s the estlmaced re.liable infiltration race be.low proposed facility locations greater than
1 0.5 inches per hour? The response to this Screening Questioo shall be based on a X
compreheo ive evaluation of the factors presented in Appendix C.2 and Appendix D.
Provide basis: Based on the results of permeability testing in three locations at the site, the unfactored infiltration
rates were measured to be 0.045 inches/hour (iph), 0.069 iph and 0.001 iph using a constant head borehole
permeameter placed inside a ~inch diameter boring between 2 and 4 feet below existing grades. If applying a
feasibility factor of safety of 2.0, the infiltration rates would be 0.022 iph, .0345 and 0.0005 iph. Based on the
USDA Web Soil Survey website, the underlying soils are classified as Huerhuero loam and belong to Hydrologic
Soil Group D, which are generally not considered suitable for infiltration BMP s. The existing compacted fill
should be classified as Hydtologic Soil Group D, which is not suitable for infiltration BMP's. Information
collected from the USDA website is attached. The Aardvark Permeameter test resu1ts are attached. In accordance
with the Riverside County ston11 water procedures, which reference the United States Bureau of Reclamation
Well Permeameter Method (USBR 7300), the saturated hydraulic conductivity is equal to lbe unfactored
infiltration rate.
2
Can infiltration greater than 0.5 inch.es per bour be allowed without increasing risk of
geotechnical hazards (slope stability groundwater mounding, utilities, or other factors)
char cannot be micigntcd to an acceptable level? The response to this Screening Question
shall be based on a comprehensive evaluation of the facrors presented in Appendix
C.2.
X
Provide basis: The onsite soils are moderately to highly expansive. Infiltration BM P's supported on expansive soils
will most likely result in heaving and distress to surrounding public and private improvements. The potential for
lateral water migration and distress to the public and private roadway improvements is high.
Fm m 1-8 P.1g-c 4 nf 4
Criteria Screening Question
7
Can Infiltration in any appreciable quantity be allowed without posing significant risk
for groundwater related concerns (shallow water table, storm water pollutants or other
factors)? The response to this Screening Question shall be based on a comprehensive
evaluation of the factor presented in Appendix C.3.
Yes No
X
Provide basis: Groundwater is not located within approximately l O feet from the bottom of the proposed basins.
ummarize findings of studies; provide reference to studies, calculations, maps, data sources, etc. Provide narrative
discussion of study/ data source applicability and why it was not feasible to mitigate low infiltration rates.
8
Can infiltration be allowed without violating downstream watet rights? The. respon e to
this Screening Question shall be based on a comprehensive evaluation of the factors
presenred in Appendix. C.3.
X
Provide basis: Geocon is not aware of any downstream water rights that would be affected by incidental infiltration
of storm water. Researching downstream water rights is beyond the scope of the geotechnical consultant.
Summarize findings of srudles; provide reference to studies, calculations, maps, data sources, etc. Provide n:u:rative
discussion of study/ data source applicability and why .it was not feasible to mitigate low infilcration rares.
Part 2
Result"'
If all answers from row 1-4 are yes then partial in.filtt:ation design is potentially feasibJe.
The feasibility screening category is Partial Infiltration
Tf any answer from row 5-8 is no then infiltration of any volume is considered to be
infeasible within the drainage area. The feasibility screening category js No Infiltration.
No
Infiltration
~o be completed using gathered site information and best ptofess.ional Judgment cons1denng the definition of MEP Jn
the MS4 Perm.it. Additional testing and/or studies may be requlred by City Engineer ro substantiate findings
ATTACHMENT1e
•
◄
ATTACHMENT 2
BACKUP FOR PDP HYDROMODIFICATION CONTROL MEASURES
[This is the cover sheet for Attachment 2.]
Indicate which Items are Included behind this cover sheet:
Attachment Contents Checklist
Sequence
Attachment 2a Hydro modification Management j v Included
Exhibit (Required)
See Hydromodification Management
Exhibit Checklist on the back of this
Attachment cover sheet.
....
Attachment 2b Management of Critical Coarse j v Exhibit showing project Sediment Yield Areas (WMM Exhibit drainage boundaries marked on is required, additional analyses are WMMCritical Coarse Sediment optional) Yield Area Map (Required)
... See Section 6.2 of the BMP Design Optional analyses for Critical Coarse Manual. Sediment Yield Area Determination .. J 6.2.1 Verification of Geomorphic
... Landscape Units Onsite
J 6.2.2 Downstream Systems
Sensitivity to Coarse Sediment
J 6.2.3 Optional Additional Analysis
of Potential Critical Coarse
Sediment Yield Areas Onsite
Attachment 2c Geomorphic Assessment of Receiving j v Not performed
Channels (Optional) J Included
See Section 6.3.4 of the BMP Design
Manual. .. Attachment 2d Flow Control Facility Design and j II Included .. Structural BMP Drawdown
Calculations (Required)
See Chapter 6 and Appendix G of the
BMP Desion Manual
-ATTACHMENT 2a -----
-
•
•
•
•
•
•
-
-
Use this checklist to ensure the required infonnation has been included on the
Hydromodification Management Exhibit:
The Hydromodification Management Exhibit must identify:
J ., Underlying hydrologic soil group
J It/ Approximate depth to groundwater
J Iii Existing natural hydrologic features ( watercourses, seeps, springs, wetlands)
J V Critical coarse sediment yield areas to be protected (if present)
J ., Existing topography
J V Existing and proposed site drainage network and connections to drainage offsite
J ., Proposed grading
J V Proposed impervious features
j V Proposed design features and surface treatments used to minimize imperviousness
J ., Point(s) of Compliance (POC) for Hydromodification Management
J Iii Existing and proposed drainage boundary and drainage area to each POC (when
necessary, create separate exhibits for pre-development and post-project conditions)
1J Structural BMPs for hydromodification management (identify location, type of BMP,
and size/detail)
ATTACHMENT 2b
-
•
•
Appendix I: Forms and Checklists
Downstream Systems Rec1uircmems for Fnrm f-10
Preservation of Coarse Scd imeut Supply
When it has been determined that potential critical coarse sediment yield areas exist within the
project site, the next step is to determine whether downstream systems would be sensitive to
reduction of coarse sediment yield from the project site. se this form to document the evaluation
of downstream systems requirements for preservation of coarse sediment supply.
Project Name: Carlsbad Oaks Lot 2
Project Tracking Number / Permit Application Number:
1 Will the project discharge runoff to a hardened J Iii Hardened MS4 Go to2
MS4 system (pipe or lined channel) or an un-system
lined channel? J Un-lined channel Goto4
2 Will the hardened MS4 system convey sediment J Convey Go to 3
(e.g., a concrete-lined channel with steep slope
and cleansing velocity) or sink sediment (e.g.,
flat slopes, constrictions, treatment BMPs, or
ponds with restricted outlets within the system
will trap sediment and not allow conveyance of J Iii Sink Go to7
coarse sediment from the project site to an un-
lined system).
3 What kind of receiving water will the hardened J Un-lined channel Go to4
MS4 system convey the sediment to?
J Lake Go to 7
J Reservoir
J Bay
j Lagoon Go to6
J Ocean
4 ls the un-lined channel impacted by deposition J Yes Go to 7
of sediment? This condition must be
documented by the local agency. J No Goto 5
1-32 February 2016
Appendix I: Forms and Checklists
Form I-JO Page 2 of 2
5 End -Preserve coarse sediment supply to protect un-lined channels from accderated erosion
due to reduction of coarse sediment yield &om the project site unless further investigation
determines the serument is not critical to the receiving stream. Sediment that is critical to
receiving streams is the sediment that is a significant source of bed material to the receiving
stream (bed sediment supply) (see Section 6.2.3 and Appendix H.2 of the manual).
6 End -Provide management measures for preservation of coarse sediment supply (protect
beach sand supply).
7 End -Downstream systetn does not warrant preservation of coarse sediment supply, no
measures for protection of critical coarse sedin1ent yield areas onsite are necessary. Use the
space below to describe the basis for this finding for the project.
Lot 2 is currently a mass graded pad being served by Faraday Avenue and El Fuerte Street,
served by utilities (sewer, water, recycled water, storm drain, and dry utilities) based on City of
Carlsbad approved drawing numbers 415-9, 415-9A, 415-9), and 415-91 (Carlsbad Oaks Phase
1 and Phase 2). The mass grading that took place involved placing engineered fill on the
southwestern portion of the site to create a pad on top of the granitic bedrock and level the site
for development Per Geocon Inc Soils report Project number 06442-42-26 Dated June 23 2016.
The critical course sediment that was potentially in place at the southwestern portion of the ite
has been displaced with the engineered fill.
Lot 2 is proposing a lined bio-6.Jtratioo system to be installed in several locations and treat water
on-site. Sediment that travels on site will settle in the proposed bio-filtration basins and sink at
those locations. BMP A-located at the northeastern side of the site connects directly into the
existing storm drain structure. BMP-B storm water flows are piped to a proposed storm drain
outlet on El Fuerte Street, and surface flows north to the same existing storm drain structure.
This existing storm drain structure outlets to an existing storm drainage detention basin formed
by the intersection of Faraday A venue and El Fuerte Street (as referenced and designed in the
Rancho Carlsbad Channel & Basin Project Hydrology Study by Rick Engineering -circa 1985).
Once released from the detention basin (installed and sized to detain the future Carlsbad Oaks
Business Park 100-year flows as weU as runoff from the construction of Faraday Avenue) the
flows are clischarged into Agua Hedionda Creek back to the north of Faraday Avenue and
ultimately Agua Hedionda Lagoon and the Pacific Ocean. This represents the Carlsbad
Hydrologic Unit, Aqua Hedionda HA, Los Monos HSA (904.31).
1-33 February 2016
•• .,, • storm. Therefore, additional analyses were performed in order to study detention scenarios. The
HBC-1 analysis containing the most desirable detention scenario is included in this report and is
..
based on the existing and four proposed detention facilities and ultimate development within the
entire watershed. The HBC. I input and methodology are discussed below. The HBC 1 results are
discussed in the following section.
Prior to preparing the JIBC .. t input, prtViou3 studies (listed in "Referen0es") for RCMHP
were reviC\Wd and site visits were performed. The site visit objectives wme to verify 1be watershed
boundary and major flow paths of both Apa Hedionda and Calaveras Creeks, detenninc existing
detention locations, and review proposed ~n locatioa.l. Prior to the si~viaits, the watershed
boundary and now paths were delineated on the United States Geological Survcy's (USGS)
quadrangle ma~. The watr:ribcd was divided into sub-basins in. order to obtain peak tlowa at
: r : • existing and proposed demltion facility locatiom and at locations listed in the cumm.t Flood
•
Insunmce·Study. The watershed boundary, flow paths, 8Dd sub-basin boundaries were varified
during the site visits and adjusted. appropriately. See Map Pocket 2 for the RCMHP watcrshcd
boundazymap.
During the site visits, existing detention facilities such u dams and toad anbaoJanents were
noted. Two dams exist within the RCMHP watcrshod: Calavcms and Squires. Of these two, only
Calaveras dam provides significant detention. It is located within Calaveras Creek and detains the
upstream grcek flows. On the other band, Squires Dam is loeatecl at the upper end of a dramage
basin and provides minimal detention. The plans for Calaveras Dam were obtained from the
Division of Safety of Dams (DSOD) and the outlet works and storage capacity were modeled in the
hydrologic analyses .
Prcpllffd B )':
Ride Enain11ering COll'lf'Oirl)'. Wow iwsOIIRCS Division 3 DCB:MDL :cmn.'Rcpon/ J, I J l 82.001
07101/98
• ,.... RCMHP. The side slopes were 2:1 (horizontal:vertical) tmd the approximate bed slopes were 0.1 s
and 0.30 percent in Agua Hedionda Creek and Calaveras ~respectively. The bottom width of
Agua Hcdionda Creek varied from S8 feet at the El Csrnino R.ca1 bridge to 44 ~ upstream of the
coofluencc. 'Ibo approximate dwmd depth was 11.5 feet The bottom width and channel depth of
... Calaveras Creek were four feet and Dino feet, impcdively.
• c•
' ..
...
..
A HEC-2 analysis was pcafonmd based on the original dosign, Tho HBC-2 results showed
that a large portion ofRCMHP remained uumdatod by 1he 100..year flood. In order to increase
eb•onel capacity, additional cbaonel improvements were mode1od in 1he HBC-2 analyai, far the
downs1ream scctlons of both creeb. At the Bl~ hal bridge. the bottom width was widcmcd
to 87 feet Witbin the next 1,400 feet upsb:eam of the mdse, the bottom width then tapered down
to tho original design bottom width of 44 feat in Agua Hedionda Cteck and fom feet in Calavenu
Creok.
. .
The rcswts oftbe hydraulic study aro comained in Appendix 3. Tbe zesults are also depicted
on the RCMHP 100-yea-Floodplain Map in Map Pocket 7. 1bc map shows that with the proposed
dctmtion facilities and channel improvements discusacd above, a majority of RCMHP will be
outside of the 100-year tloodplaio.
Malatenance Plan
nu.. Miwomaoce Plan coDWDS maintenenca ,:-equircm.mts for Aqua Hcdiondaand Calaveras
cn:et within RCMHP, 'Ibis plan also contains requirements for the four upstream detention basins..
It is vital that the creeks and detention buins be maintained on a replar basis to cnsurc an
.. • acceptable level of fl.ood protection for RCMHP. It is recommended that the maintenance described
PrtpiredBy:
R1o11: Eapldfirb& CompaD1 -Wdrlr R.esoun:a Dl\llsica 14
OCB:Mbl:mii,Jllcpori/J•I J 11U6I 07101/ff,
•
;; .
•
Appendix 1
I
100-year, 24-hour HEC-1 AnalysiJ for Rancho Carlsbad Mobile Home Park
Ultimate Development with Existing Detention Basins
(File Name: rcmh24r.hcl)
!J/.'\J . .\-Ill! .. ,in1: ll,;p••rt. l-l? I~~ .,1,:1
,1· 1)1. •)~
RUNOFF SOM4ARY • """ IR CU8IC: f'£E'f HR SEOOt'!O
TIMI IN """""· AREA 1V SQ\11,RB HlLBS
PE.a,: TIM! OF .'-.VBP.AGJ,: FLOW FOlt !"~!MUM PO.JOO !!Mil! :-V.XtmJH Tl"111 or
OPDA.TIOll' aTA1'lc»I """ , ... ....... 24·110UR 72-HOUI. .... .,.... IWIST>OI
IM>~ ,._T ,....,, 27-U. 10.51 1•s1. 591, 5"7'. ol,H
.,.,,.,, TO ,me, :nu. 10,SI 115]. 5'7, 575 . 4 . 3"4 404 .02 10.SI _ ..
·"""" ]!1'1. 111.oa 169, ... ... ·"
2 CCNBIHKD AT '°'""' ]OU. 10.50 1451', "'· , .. 2. ....
..maD TO ane, JOU. 111.51 lllilf. "·· HO . 4.U ns.o, 10.11 ............ 8SIIICl ,.,. 10.00 ]5]. us. 140, 1.11
2 CD11IIQID AT ac,uo HH, 10,50 1H!II. IO!J. 11,. ,.n
,. """"'TO ..,.,. 1,u. 111.51 UH. .... 7-,, . . '·'" 3151.74 10.!II
.....,..... .. .. ...,. 114, 10.00 ... "· "· ·"
2 CQMBJnD AT aouc-11 )191. 10.50 21152, "'· '°'· ,.11 • -·· .. , 1102. 10.17 Hl. JO. JO . 2.H
,o,na,ro ... m: nu. 10.u 111. 352. ]fit . 2.13 3'1:1,U Ul.25
2 CONlllllBD AT .,,..., ssa,. 10.50 2!1111. U02. un . ,.21
.....,, TO ..... sus. 10.,s 21,;i. 1185, 1111, ,.21 JU.!Jt 10.15
' HYllaoaRAl'll AT .., 516.
'
10.00 24], 100. ... ·" • ,.,mo ,. .. ......, HO. 111,1'1 2U. 100. "· ·" 351,ts 10.17
• -TO aTNU 4157, 10.50 2U, 100. ... ·" 121.21 10.so
HYDROOAA.Pil AT .. , ,.., . 10.00 ]67. 150. 1u. 1.41
l COIG1NBD AT JUll-lUC 6111, 10.u )48'. 14h. un. u.,s
ROUT&D TO ~-Nn UH. 10.n HU. U2~. u1,. ll ,45 211,01 10.6'1
l-l'tllli.:luAAPl:I AT ;:,.it.; ::G. 10.CC 1%. "· "· ·"
:s.o'JTED TC Mt-1-1\HS HO 10.0Q l'.Hi. "· "· . 70 l60.2'1 l•l. 00
.1·1-;R,:-~;:;,f.,_ ;,·,_· :M ., ,c. ; ~. ·••J ~ ~~. ,n. ~---• . •·'•• .,. __ '., le : ,r,
-,;
2 OONIIHE:D A.'r --1::190. 10.01 U4. 274, 26'. 2 .35
r~ """"""' ,..,.1 u,,. 10.25 "'· 271. an. 2.15 161.7' 10.:as
HYmOIJRAIIII AT ... 177. 10.111 "· "· 33. ·" ..,.,,., .. .... , 1'7', 10.00 ... ... "· ... Ui0.24 10.00
,.,,,......,. .. .., !112, 10.0t HO. ... ... 1.u
t O:IMHIISD U' --HK. 11.n HSS. -llll, n, •. 15.:11 ......... U'l·AR9 HH. 10.ll uu. llU. 115', 11.u 1n. tt 10,IJ ............ ... 500. 10,0I us. "· "· 1.00
:I OOIIIJ:DD A't. --7Nf. 11,71 41'11. uu. 1U.4i. u.u ........ NU-10 'fl'H, 10.'2 ""· 1H7, lMl. H.U ............. .... JH . 10.00 HI. .. . .,, ...
:a OQlanmJ ,.,. --10:H. 10.9:11 4115-:I060, ::ioo:a. . .... ., ......... UlO·kCJI. IOU. 11.00 411■, ;ao51. 1H7. u.u n.u 11,DO
..... ocnua AT .... ... 10., • ... 10, , .. .u
c• 2 0:IIGllllm AT _, .. ... ,,. 11.00 4131. 2061. 2007. 17,00 -·· "' su. 10.D0 20. 102. ... ,17 ........ ,,._,.. 1iH, 10.0D u,. 102. .. . .17 JJS,95 10. ao
"""""'"' c,.c, JU. 10 .• , u,. ... ... .17 20.02 10.n ............. "' l!HS, 10,25 'ffil. JU • . ... 2,'1'2
3 COGDID A'1' --UH. 10.21 H2. 411. , ... l,H
...,,...., ....,.,,. lHl, 11.00 , ... n1. H2, l,59 211.12 11,00
"""""'"" c,.c, U'fJ, U.17 .,.,. 291. 281. J .s, 100,2!1 11.1? ............. C3 , ... 10.ao :ao,. "· ... ·"
2 COMIIWKD AT ""'"" .. 1560. 11.0I 171, J?7. Hl. fi ,41
-·· "' "'· 10.01 )15. 12,. 126. 1.2,
2 CCMIIKlll AT o,, ..... UH, 10.c, USJ. sos. '87. 5,155
"'"""' 'l'O
Cli<•IIX 111'-11.aa llSJ. SOL US, 5,65 H.n U,OI • HYDROCU.i'H AT '°' "· 10.00 Jl. "· u. ·"
' COMBINED AT CONB!HI 1906. ll .O! uu. 511. 491. 5.60
2 COMBIJIKD AT """''"' ,, ... 11,00 6011. 2585. 2505. 22.10
ATTACHMENT 2d
~
---
Table of Contents
INTRODUCTION
Section I
Section II
Section Ill
Section IV
Section V
Section VI
Section VII
Pre-and Post-Development Model Setup ........................................................................... 3
System Representation ........................................................................................................... 6
Continuous Simulation Options ............................................................................................. 9
Biofiltration As LID Control .................................................................................................... 10
Running the Simulation .......................................................................................................... 16
Result Analysis ......................................................................................................................... 16
Summary and Conclusion ....................................................................................................... 27
ATTACHEMENTS
Attachment A
Attachment B
Attachment C
Attachment D
Attachment E
SWMM Drainage Management Area Map
SWMM Statistics Analysis, Flow Duration Curve and Pass/Fail Table
SWMM Input Data Summary and Detail
SWMM Drawdown Calculations and Summary
SWMM Hydrologic Soil Classification Attachment of Web Soi\ Survey
1 I Page
INTRODUCTION
This report provides Hydromodification and Water Quality design based on LID (Low Impact Development)
principles for a proposed Industrial site development located adjacent at the corner of Faraday Avenue and EL
Fuerte Street, Carlsbad Oaks Lot 2, Carlsbad, California.
The Hydromodification and Water Quality calculations were performed utilizing continuous simulation
analysis to size the storm water treatment and control facilities. Storm Water Management Model (SWMM)
version 5.0 distributed by USEPA is the basis of all calculations within this report. SWMM generates peak flow
recurrence frequencies and flow duration series statistics based on an assigned rain gauge for pre-
development, unmitigated post-development flows and post-development mitigated flows to determine
compliance with the State Water Resources Control Board Order No.R9-2015-001 and Hydromodification
Management Plan (HMP) requirements.
Total area is 6.0 acres for Lot 2 with a developed tributary area of approximately 6.0 for Lot 2. This tributary
area includes DMA-1 and DMA-2 which make up the main development of the site. DMA-3 is "self-mitigating"
and is not taken into account for the tributary area of Lot 2. There is one point of compliance (POC) for each
of the projects in the analysis; POC receives flows from basins and drains into an existing public storm drain at
El Fuerte Street, Carlsbad, CA.
The Hydromodification and Water Quality system proposed for this project consists of 2 biofiltration basins
with one point of compliance located at the northeast corner of the project. This system detains storm water
in the basin surface and also in the underdrain reservoir. Bio-filtration filters storm water through plant roots
and a biologically active soil mix, and then releases it into the existing storm drain system which currently
collects the sites storm flows. The resulting mitigated outflows are shown to be equal to or less than all
continuously simulated storms based on the historical data collected from the Oceanside rain gage.
Low Flow Threshold
A downstream channel assessment has not been completed for this project and therefore the low flow
threshold utilized for the system analysis is 10% of 2-year storm event (0.1Q2). This will be used as the low
flow threshold to meet peak flow frequency and flow duration controls.
2 I Page
SECTION I. MODEL SETUP
Pre-development Model Setup
The SWMM model for this projects pre-development site is analyzed using historical rain gauge data. The
Oceanside gauge is utilized for this project. That data provides continuous precipitation input to a sub-
catchment with its outfall based on the contributing basins imperviousness.
The imperviousness parameter in SWMM is the amount of effective or directly connected impervious area.
The effective impervious area is the impervious area that drains directly to the Stormwater conveyance
system. The pre-development condition is a vacant land with poor cover of grass and some shrubs with no
trees. For the purpose of this study, the site is assumed to have 0% of impervious surface in the existing
condition.
The site is currently a mass graded pad being served by a Faraday Avenue and El Fuerte Street and also is
served by utilities (sewer, water, recycled water, storm drain, and dry utilities) based on City of Carlsbad
approved drawing numbers 415-9, 415-9A, 415-9J, and 415-91 (Carlsbad Oaks Phase 1 and Phase 2). Existing
mass graded industrial pads sit to the west, east, and north. Drainage flows from southwest to northeast as
sheet flow and is collected in one existing desiltation basin located at the northeast corner of the site
{installed as part of the Carlsbad Oaks mass grading operations).
Once collected in this desiltation basin, the runoff flows through an existing storm drainage pipe across the
eastern property line into an existing storm drain structure located in El Fuerte Street where the mainline
storm drain system runs northeasterly across El Fuerte Street, and into an existing storm drainage detention
basin formed by the intersection of Faraday Avenue and El Fuerte Street (as referenced and designed in the
Rancho Carlsbad Channel & Basin Project Hydrology Study, by Rick Engineering -circa 1985). Once released
from the detention basin (installed and sized to detain the future Carlsbad Oaks Business Park 100-year flows
as well as runoff from the construction of Faraday Avenue) the flows are discharged into Agua Hedionda Creek
back to the north of Faraday Avenue and ultimately Agua Hedionda Lagoon and the Pacific Ocean. This
represents the Carlsbad Hydrologic Unit, Aqua Hedionda HA, Los Monos HSA (904.31). For SWMM model
illustration see figure 3, or Pre-development map in Attachment A of this SWMM report.
Post-Development Model Setup
Figure 3 illustrates each contributing basin discharging its overland flow directly into the biofiltration system.
Each biofiltration layer section has a similar configuration as seen as in the detail drawing below. There is no
actual elevation entered in the program. The bottom elevation of the biofiltration surface storage is assumed
at Oft. Storm drain pipe is also utilized as a detention by having an orifice small flow restrictor at lower invert
elevation of the downstream cleanout box and a bypass orifice/pipe to convey the bigger flow.
The Carlsbad Oaks lots 2 Industrial project layout proposes to construct a parking lot across the majority of
the property, with drainage to be directed to the 2 biofiltration systems on the site. Once within the water
quality treatment systems, the stormwater infiltrates through the treatment medium into underdrains that
route the flows to the private on site storm drainage system. This system uses new piping to direct the flows
to the existing storm drain stub installed as part of the Carlsbad Oaks Business Park project and ties into the
existing storm drainage system within El Fuerete Street draining northeast toward its outfall location.
3IPage
BMPID
BMP-A
BMP-B
....
"'
BIO-BASIN SUMMARY TABLE
BOX RISER/ ORIFICES
DIAMETER EFFECTIVE Al A2 A3 C D OVERFLOW
AREA {INCH) E STRUCTURE (INCH) (INCH) (INCH) (INCH) (FEET) LOWER
(SQFT) RISER SIZE TOP OF CLEAN MEDIA GRAVEL {INCHES) (INCH) BASIN OUT
8734.98 6 12.0 6.0 21.0 24 1.5 48x48 2.0
1354.12 6 12.0 6.0 21.0 24 1.5 36x36 1.0
Post-Development Drainage Management Areas {DMAs)
The DMAs provide an important framework for feasibility screening, BMP prioritization and storm water
management system configuration. DMAs are defined based on drainage patterns of the site and the
BMPs to which they drain. The Bio-Basin Summary Table above, references a gravel depth of 24" which
does not include the 3" minimum of gravel below the perforated pipe (see Figure-1 Typical Biofiltration
Basin). Implying that the total gravel depth for this project is 27" (24" + 3" minimum). This 27" value is
used in the SWMM model calculations the as the total storage depth.
In this project Lot 2 DMAs drain to BMPs A and B. The self-mitigating areas are bypassed to the POC
designated for the project site (see hydromodification exhibit) to keep pre development flows DMA
Table for Post-Development Lot 2. In the SWMM model and table below note that the total areas of
each OMA are equal to the combination of the DMA area and its respective BMP area. For example, in
this project the total area of DMA-1 = (DMA-1 Area)+ (BMP-A Area) OR 4.95ac = (4.75ac) + {0.20ac).
[SUBCATCHMENTS]
Name Outlet Area %1mperv Width %Slope
DMA-1 BMP-A 4.75 82 214.3536 0.9
DMA-2 BMP-B 0.80 58 252.834 0.5
BMP-A POC-1 0.20 0 45.95 0
BMP-B POC-1 0.03 0 5.979 0
Total 5.78
OMA Table for Pre-Development lot 2
DMAID DMA TOTAL %IMP TYPE (ACRE)
DMA-1 Drains to POC 5.78 0%
Total AREA 5.78
71Page
IMP
LINER?
YES
YES
...
The rate of stormwater runoff and volume depends directly on the precipitation magnitude and its
spatial and temporal distribution over the catchment. Each sub-catchment in SWMM is linked to a rain
gauge object that describes the format and source of the rainfall input for the sub-catchment.
Area
This area is bounded by the sub-catchment boundary. Its value is determined directly from maps or field
surveys of the site or by using SWM M's Auto-length too I when the sub-catchment is drawn to sea le on
SWMM's study area map. This Project is divided into several sub-catchments based on its outfall.
Width
Width can be defined as the sub-catchment's area divided by the length of the longest overland flow
path that water can travel. When there are several such paths, one would use an average of their
lengths to compute a width. If overland flow is visualized as running down -slope off an idealized,
re eta ngu la r catchment, then the width oft he sub-catchment is the physica I width of overland flow.
DIRECTION
OF OVER
FLOW
Figure-2-2 Irregular subcatchment
shape for width calculations
(DiGiano et al., 1977,p.165).
MAIN
DRAINAGE
CHANNEL
Figure-2-3 Idealized representation
of a subcatchment.
Source: STORM WATER MANAGEMENT MODEL REFERENCE MANUAL VOLUME 1-JANUARY 2016
The method of calculations used following Figure 2-2 involves an estimitation by Guo and Urbonas
(2007). As stated in the Storm Water Management Model Reference Manual Vol. 1
A more fundamental approach to estimating both subcatchment width and slope has recently been
developed by Guo and Urbonas (2007). The idea is to use "shape factors" to convert a natural
watershed as pictured in Figure 2-2 into the idealized overland flow plane of Figure 2-3. A shape factor
is an index that reflects how overland flows are collected in a watershed. The shape factor X for the
a ctua I watershed is defined as A/L 2 where A is the watershed area and L is the length of the watershed's
main drainage channel (not necessarily the length of overland flow). The shape factor Y for the idealized
watershed is W/L. Requiring that the areas of the actual and idealized watersheds be the same and
that the potential energy in terms of the vertica I fa 11 along the drainage channel be preserved, Guo and
9IPage
Urbonas (2007) derive the following expression for the shape factor Y of the idealized watershed:
Y = 2X(l.5 -Z)(2K -X)/(2K -1) (3-12)
where K is an upper limit on the watershed shape factor. Guo and Urbonas (2007) recommend that K be
between 4 and 6 and note that a value of 4 is used by Denver's Urban Drainage and Flood Control
District.
Once Y is determined, the equivalent width W for the idealized watershed is computed as Yl.
Applying this approach:
X =(A• 43,560 ft2/acre) / (L2)
Z = Am/A
Z = skew factor, 0.5 :<:;; Z :<:;; 1,
Am = larger of the two areas on each side of the channel A= total area.
This width value is considerably lower than those derived from direct estimates of either the
longest flow path length or the drainage channel length. As a result, it would most likely produce a
longer time to peak for the runoff hydrograph.
Slope
This is the slope of the land surface over which runoff flows and is the same for both the pervious and
impervious surfaces. It is the slope of what one considers being the overland flow path or its area-
weighted average if there are several paths in the sub-catchment.
Imperviousness
This is the percentage of sub-catchment area covered by impervious surfaces such as sidewalks and
roadways or whatever surfaces that rainfall cannot infiltrate.
Roughness Coefficient
The roughness coefficient reflects the amount of resistance that overland flow encounters as it runs off
of the sub-catchment surface. The value used for this project's predevelopment is a 0.12 as Shrubs and
Bushes. This was based on the figures in 2-4 and 2-4a and assuming to be the most accurate to the
predevelopment site before mass grading and the "pre-project" and conditions were created. The value
for the post development is 0.05 for an average close gut grass, closely clipped sod.
lOIPage
...
Table 3-S Estinaatrs of 1'tannln111 roughn,:s1 corfflcient for u,,,rland Row
Source Ground Cover 11 Ranae
Smooth asphalt 0.01
Crawford and Linsley Asphalt ofconcrcte oavintt 0,014
( 1966)8 J'acked clay 0,03
Lie:httuTf 0.20
Dense turf 0.35
Dense shrubben• and forest litter 0,4
Concrelc or asohalt 0.011 0,010-0.0] 3
Engman (1986 )t, Bare sand 0.010 0.0l-0.Ol6
Graveled surface 0.02 0.012-0.03
Bare clay-loam ( eroded) 0.02 0.012-0.033
Ranae (narural) 0.13 0.01-0.32
Bluegrass sod 0.45 0.39-0.63
Shon v:rass orairic 0.15 0.10-0.20
Bermuda 1m1ss 0.41 0.30-0.48
Yen (2001 )' Smooth asphalt navement 0.012 0.010-0.01 S
Smooth imoervious surface 0.013 0.01 1-0.015
Tar and sand oavemcn1 0.014 0.012-0.016
Concrete pavement 0.017 0.014-0.020
Rough impervious surf ace 0.019 0,015-0.023
Smooth bare oacked soil 0.021 0.017-0.025
Moderate bare packed soil 0.030 0.02S-0.03S
Rough bare packed soil 0.038 0.032-0.045
Gravel soil 0.032 0.025-0.045
Mowed poor erass 0.038 0.030•0.045
Avcra2c 2rass closely clinncd sod 0.050 0.040-0.060
Pasture 0.055 0,040-0.070
Timberland 0.090 0.060-0.120
Dense 2rass 0.090 0.060-0.120
Shrubs and btu,:hcs 0.120 0,080-0.180
Business land use 0.022 0.014-0.035
Semi-business l.a11d use 0.035 0.022-0.050
Industrial land use 0.035 0.020-0.050
Dense residential land use 0.040 0.025-0.060
Suburban r~idential land use o.oss 0.030-0.080
Parks and lawns 0.075 0,040·0. 120
"Obtained by calibration of Stanford Watershed Model.
hComputed by Engman ( 1986) by kinematic wave and storage analysis of measured
rainfall-runoff data .
'Compured on basis of kinematic wave analysis.
Source: Storm Water Management Model Reference Manual Volume I -Hydrology
IRP11icPnl ~ '"'""""' ,n1~
11 I Page
-
Infiltration Model
The pre-development condition is primarily empty land with moderate vegetation cover. In the model,
clay soil was used for the post-development condition and the pre-development condition for a
conservative approach {yield to a higher runoff). Infiltration of rainfall from the pervious area of a sub-
catchment into the unsaturated upper soil zone can be described using three different infiltration
models: Horton, Green-Ampt, and Curve Number. There is no general agreement on which method of
these three is the best.
The Green-Am pt method was chosen to calculate the infiltration of the pervious areas based on the
availability of data for this project. It is invoked when editing the infiltration property of a sub-
catchment.
The Hydrologic Soil Class identified for this project is a rating of D. This determination was from Web Soil
Survey and is provided as Attachment E of this projects SWMM report.
Bl Page
Table 1 -Soil Infiltration Parameter
S\'\/MM
Parnmeter Unit Range Use in San Diego
Name
Infiltration Method
Suction Head Inches
(Greeo-Ampt)
Conductivity Inches per hour
(Green-Ampt)
Initial Deficit
(Green-Am pt)
Groundwater
LID Controls
Snow Pack
Land Uses
Initial Buildup
Curb Length
yes/no
HORTON
GREEN_AMPT
CURVE NUMBER
1.93 -12.60presented
in Table A2 of SWMM
Manual
0.01 -4.74 presented
in Table A2 of SWMM
Manual by soil texture
class
0.00 -<;0.45 presented
in Table A.3 of SWMM
Manual by hydrologic
soil group
The d.iff erence between
soil porosity and initial
moisture content.
Based on the values
provided in Table A.2
of SWMM Manual, the
range for completely
dry soil would be 0.097
to 0.375
yes/no
GREEN_AMPT
H ydrologic Soil Group A: 1.5
Hydrologic Soil Group B: 3.0
Hydrologic Soil Group C: 6.0
Hydrologic Soil Group D: 9.0
Hydrologic Soil Group A; 0.3
Hydrologic Soil Group B: 0.2
Hydrologic Soil Group C: 0. 1
Hydrologic Soil Group D: 0.025
Note: reduce conductivity by 25%in
the post-project condition when
native soils will be compacted. For fill
soils in post-project condition, see
Section G.1.4.3.
Hydrologic Soil Group A: 0.30
Hydrologic Soil Group B: 0.31
Hydrologic Soil Group C: 0.32
Hydrologic Soil Group D: 0.33
Note: in long-term continuous
simulation, thi value is not important
as the soil will reach equilibrium after
a few storm events regardless of the
initial moisture content specified.
NO
Project Specilic
ot applicable to hydromodification
management studies
Source: Model BMP Design Manual San Diego Region Appendices, February 26, 2016
14 I Page
LID controls
Utilizing LID controls within a SWMM project is a two-step process that:
Creates a set of scale-independent LID controls that can be deployed throughout the study area,
Assign any desired mix and sizing of these controls to designated sub-catchments.
The LID control type that was selected was a biofiltration cell that contains vegetation grown in an
engineered soil mixture placed above a gravel drainage bed. Biofiltration provides storage,
infiltration (depending on the soil type) and evaporation of both direct rainfall and runoff captured
from surrounding areas. For this project, we do not allow infiltration to the existing/filled soil.
SECTION Ill. CONTINUED SIMULATION OPTIONS
Simulation Dates
These dates determine the starting and ending dates/times of a simulation and are chosen based on the
rain data availability.
Start analysis on Ol/03/19Sl
Start Reporting on 0l/03/19Sl
End Analysis on 05/23/2008
Time Steps
The Time Steps establish the length of the time steps used for runoff computation, routing computation
and results reporting. Time steps are specified in days and hours: minutes: seconds except for flow
routing which is entered as decimal seconds.
Climatology
-Evaporation Data
The available evaporation data for San Diego County that is similar to the Lot 5 project conditions is
taken Table G.1-1: Monthly Average Reference Evapotranspiration by Ho Zone for use in SWMM
Models for Hydromodification Management Studies in San Diego County CIMIS Zone 4 (in/day).
January February March April May June
0.060 0.080 0.110 0.150 0.170 0.190
July August September October November December
0.190 0.180 0.150 0.110 0.080 0.060
15 I Pa g c
SECTION IV. BIOFILTRATION AS LID CONTROL
LID controls are represented by a combination of vertical layers whose properties are defined on a per-
unit-area basis. This allows an LID of the same design but differing coverage area to easily be placed
within different sub-catchments of a study area. During a simulation, SWMM performs a moisture
balance that keeps track of how much water moves between and is stored within each LID layer. If the
biofiltration basin is full and water is leaving the upper weir, the flow is divided in two flows: the lower
flow discharging from the bottom orifice directly draining to the point of compliance and the upper flow
is routed at the top of the biofiltration basin and after routing, discharged to the point of compliance. In
this project, we used 100% of the area of this specific sub-catchment for biofiltration.
l. Surface
Storage Depth
When confining walls or berms are present, this is the maximum depth to which water can pond above
the surface of the unit before overflow occurs (in inches). In this project, storage depths vary. Table 3
shows depths of surface ponding.
Vegetation Volume Fraction
It ls the fraction of the volume within the storage depth that is filled with vegetation. This is the volume
occupied by stems and leaves, not their surface area coverage. Normally this volume can be ignored, but
may be as high as 0.1 to 0.2 for very dense vegetative growth. Based on our visual observation in the
field, the average type of vegetation for this site is a low-density vegetation type. Therefore, we used 0.1
for the vegetation volume fraction assuming type of vegetation used is a low-density type.
Surface Roughness
Manning's n value for overland flow over a vegetative surface.
Surface Slope
Slope of porous pavement surface or vegetative swale (percent).
Z. Soil
Thickness
The thickness of the soil layer in inches. We used a typical value of 21 inches soil thickness for a
biofiltration. This includes the 3" of mulch layer per Worksheet 8.5-1 in the Carlsbad BMP Manual.
The volume of pore space relative to total volume of soil (as a fraction). We designed it with a soil mix
porosity of 0.40 maximum for a good percolation rate (Countywide Model SUSMP Table Bl -Soil
Porosity Appendix A: Assumed Water Movement Hydraulics for Modeling BMPs).
Field Capacity
Volume of pore water relative to total volume after the soil has been allowed to drain fully (as a
fraction). We used 0.2 for this soil. Below this level, vertical drainage of water through the soil layer does
not occur. (See Table 1-Soil Infiltration Parameter).
161Page
•
Wilting Point
Volume of pore water relative to total volume for a well-dried soil where only bound water remains (as
a fraction). The moisture content of the soil cannot fall below this limit.
We assumed the minimum moisture content within this biofiltration soil is 0.1.
Conductivity
Hydraulic conductivity for the fully saturated soil is 5 inches/hour. This is a design minimum value for
percolation rate.
Conductivity Slope
Slope of the curve of log (conductivity) versus soil moisture content (dimensionless). Typical values
range from 5 for sands to 15 for silty clay. We designed this soil to have a very good percolation rate
therefore the conductivity slope is 5.
Suction Head
The average value of soil capillary suction along the wetting front (inches). This is the same parameter as
used in the Green-Ampt infiltration model. Table 1 was utilized to determine the capillary of the soil mix
top layer of a biofiltration system. The suction head will be 1.5 inches.
3. Storage Layer
The Storage Layer page of the LID Control Editor describes the properties of the crushed stone or gravel
layer used in biofiltration cells as a bottom storage/drainage layer. The following data fields are
displayed:
Height
this is the thickness of a gravel layer (inches). Crushed stone and gravel layers are vary ranging from 12
to 36 inches thick. A table is provided to summarized the BMP configurations.
Void Ratio
The volume of void space relative to the volume of solids in the layer. Typical values range from 0.5 to
0.75 for gravel beds. Note that porosity= void ratio/ (1 + void ratio). We designed this void ratio to have
a value of0.67.
Seepage Rate
The rate at which water infiltrates into the native soil below the layer (in inches/hour). This would
typically be the Saturated Hydraulic Conductivity of the surrounding sub-catchment if Green-Ampt
infiltration is used. Since the liner beneath the gravel layer is proposed, the seepage rate is assumed to
be O in/hr .
Clogging Factor
Total volume of treated runoff it takes to completely clog the bottom of the layer divided by the void
volume of the layer. For south east biofiltration, a value of O was used to ignore clogging since the
system does NOT consider infiltration to the native soils. Clogging progressively reduces the Infiltration
171Pagc
Rate in direct proportion to the cumulative volume of runoff treated and may only be of concern for
infiltration trenches with permeable bottoms and no under drains. We assumed zero for the clogging
factor since the infiltration rate is not considered.
4. Underdrain Layer
LID storage I ayers can contain an optiona I u nderd rain system that co I lects stored water from the bottom
of the I ayer and conveys it to a co nventiona I storm drain. The U nderdra in page of the LID Contra I Editor
describes the properties of this system. It contains the following data entry fields:
Drain Coefficient and Drain Exponent
Coefficient C and exponent n that determines the rate of flow through the underdrain as a function of
height of stored water above the drain height. The following equation is used to compute this flow rate
(per unit area of the LID unit):
q= C(h-Hdr
where q is the outflow (in/hr), his the height of stored water (inches), and Hd is the drain height. A
typical value for n would be 0.5 (making the drain act like an orifice.
Drain Offset Height
Height of any underdrain piping above the bottom of a storage layer (inches). In this project, this value
was set to 3" as the underdrain piping is at the bottom of the 24" of the live gravel storage layer but
above the 3" of dead gravel storage.
Table 3-Summary of LID Drain/flow coefficient
EFFECTIVE
IMP AREA
NAME (SQFT)
BMP-A 8735.0
BMP-B 1354.1
Note:
q = C(h-Hdr
C= C0A0 ,/29 X 12°·5 X 3600 A
LID
Storage
ORIFICE Height
(IN) (IN)
2.0 6
1.0 6
UNDERDRAIN
SOil/SANO OFFSET
(IN) GRAVEL {IN)
(IN) C
21 27 3 0.1469
21 27 3 0.2466
18 I Page
•
SECTION V. RUNNING THE SIMULATION
In general, the Run time will depend on the complexity of the watershed being modeled, the routing
method used, and the size of the routing time step used. The larger the time steps, the faster the
simulation, but the less detailed the results.
Model Results
SWMM's Status Report summarizes overall results for the 58-yr simulation. The runoff continuity error is
-6.23% and the flow routing continuity error is 0.00%. When a run completes successfully, the mass
continuity errors for runoff, flow routing, and pollutant routing will be displayed in the Run Status
window. These errors represent the percent difference between initial storage+ total inflow and final
storage+ total outflow for the entire drainage system. If they exceed some reasonable level, such as 10
percent, then the validity of the analysis results must be questioned. The most common reasons for an
excessive continuity error are computational time steps that are too long or conduits that are too short.
In addition to the system continuity error, the Status Report produced by a run wil1 list those nodes of
the drainage network that have the largest flow continuity errors. If the error for a node is excessive,
then one should first consider if the node in question is of importance to the purpose of the simulation.
If it is, then further study is warranted to determine how the error might be reduced.
The SWMM program ranks the partial duration series, the exceedance frequency and the return period.
They are computed using the Weibull formula for plotting position. See the flow duration curve and
peak flow frequency on the following pages.
SECTION VI. RESULT ANALYSIS
Development of the Flow Duration Statistics
The flow duration statistics are also developed directly from the SWMM binary output file. It should be
noted right from the start that the "durations" that we are talking about in this section have nothing to
do with the "storm durations" presented in the peak flow statistics section. Other than using the same
sequence of letters for the word, the two concepts have nothing to do with each other and the reader is
cautioned not to confuse the two. The goal of the flow duration statistics is to determine, for the flow
rates that fall within the hydromorphologicaly significant range, the length of time that each of those
flow rates occur. Since the amount of sediment transported by a river or stream is proportional to the
velocity of the water flowing and the length of time that velocity of flow acts on the sediment, knowing
the velocity and length of time for each flow rate is very useful.
Methodology
The methodology for determining the flow duration curves comes from a document developed by the
U.S. Geological Survey (USGS). The first stop on the journey to find this document was a link to the
USGS water site (http://www.usgs.gov/water/). This link is found in Appendix E (SDHMP Continuous
19IPage
Simulation Modeling Primer), found in the County Hydromodification Management Plan 1. On this web
site a search for "Flow Duration Curves" leads to USGS Publication 1542-A, Flow-duration curves, by
James K. Searcy 1959 ( http://p u bs. er. u sgs.gov /p u bl icati o n/ws p 1542A). In th is pub Ii cation the
development of the flow duration curves is discussed in detail.
In Pub 1542-A, beginning on page 7 an example problem is used to illustrate the compilation of data
used to create the flow duration plots. A completed form 9-217-c form shows the monthly tabulation of
flow rates for Bowie Creek near Hattiesburg, Miss. For each flow range the number of readings is
tabulated and then the total number of each flow rate is totaled for the year. It should be noted that
while this example is for a stream with a minimum flow rate of lO0cfs, for the purposes of run-off
studies in Southern California the minimum flow rate of zero (0) cfs is the common low flow value. Once
each of the year's data has been compiled the summary numbers from each year are transferred to
form 9-217-d. On this form the total number of each flow rate is again totaled and the percentage of
time exceeded calculated {as will be explained later under the discussion of our calculations). Once the
data has been compiled a graph of Discharge Rate vs. Percent Time Exceeded is developed. As will be
explained in the next section, the use of these curves leads to the amount of time each particular flow
can be expected to occur {based on historical data).
How to Read the Graphs2
Figure 6-1 shows a flow duration curve for a hypothetical development. The three curves show what
percentage of the time a range of flow rates are exceeded for three different conditions: pre-project,
post-project and post-project with storm water mitigation. Under pre-project conditions the minimum
geomorphically significant flow rate is 0.l0cfs (assumed) and as read from the graph, flows would equal
or exceed this value about 0.14% of the time (or about 12 hours per year) (0.0014 x 36Sdays x 24
hour/day). For post-project conditions, this flow rate would occur more often -about 0.38% of the time
(or about 33 hours per year) (0.0038 x 36Sdays x 24 hour/day). This increase in the duration of the
geomorphically significant flow after development illustrates why duration control is closely linked to
1 FINAL HYDRO MODIFICATION MANAGEMENT PLAN, Prepared for County of San Diego, California, March 2011, by
Brown and caldwell Engineering of San Diego.
(http ://www. p roj ectclea nwater. org/i mages/sto ries/Docs/LDS/H MP /0311 SD HM P wAp pend ices. pdf)
2 The graph and the explanation were taken directly from Appendix E of the Hydromodification Pian
20 I Page
continually decrease as we move down the chart. If all the calculations are correct, then everything
should zero out on the last \ine of the calculations.
The final step in developing the flow duration curves is to make a plot of the Discharge Rate vs. the
Percent Time Exceeded. For the purposes of th is report, the first va I ue corresponding to the zero f I ow
rate is not plotted allowing the graph to be focused on the actual flow rate values.
The Flow Duration Analysis
The Peak Flow Statistics analysis is composed of the following series of files:
1. The Flow Duration Plot
2. Comparison of the Un-Mitigated Flow Duration Curve to the Pre-Development Curve (Pass/Fail)
3. Comparison of the Mitigated Flow Duration Curve to the Pre-Development Curve (Pass/Fail)
4. The calculations for the Pre-Development flow duration curve development (USGS9217d)
5. The calculations for the Post-Development flow duration curve development {USGS9217d)
6. The ca I cu I ati on s for the Mitigated flow du ration curve development (USG S9217 d)
The Flow Duration Plot
The Flow Duration Curves Plot is the plotting of all three (pre, un-mitigated and mitigated) sets of
Discharge Rate vs. the Percent Time Exceeded data point pair lists. In addition to these curves
horizontal lines are plotted corresponding to the 010 and 01f (low flow threshold) values. Within the
geomorphically significant range (010 -OJ,) one can see a visual representation of the relative positions
of the flow duration curves. The flow duration curves are compared in an East/West (horizontal)
direction to compare post development Discharge Rates to pre-development Discharge Rates. The pre-
development curve is plotted in blue and the mitigated curve is plotted in green. As long as the post
development curve lies to the left of the pre-development curve (mostly3), the project meets the peak
flow hydromodification requirements.
Pass/Fail comparison of the curves
The next two sets of data are the point by point comparison of the post-development curve(s) and the
pre-development curve. The Pass/Fail table is helpful in determining compliance since the plotted lines
can be difficult to see at the scales suitable for use in a report. Each point on the post-development
curve has a corresponding "Y" value (Flow Rate), and "X" value{% Time Exceeded). For each point on
the post development curve, the "Y" value is used to interpolate the corresponding Percent Time
Exceeded (X) value from the pre-development curve. Then the Post-development Percent Time
Exceeded value is compared to the pre-development Percent Time Exceeded value. Based on the
relative values of each point, pass/fail criteria are determined point by point.
For each set of data, the upper right hand header value shows the name of the file being displayed (ex.
flowDurationPassFailMitigated.TXT). The first line of the file shows the name of the SWMM output file
(*.out). The next Ii ne shows the time stamp of the SWM M file that is being analyzed. The ti me stamps
of a11 of the report files should be within a minute or two of each other, otherwise there may have been
3 See hydromodification limits for exceedance of pre-development values
22 I Page
tampering with the files. Each report run creates and prints all of the files and reports at one time so all
the time stamps should be very close.
The first column is the zero based number of the point. The next two columns show the post
development "X" and "Y" values. The next column shows the value interpolated between the two
bounding points on the pre-development curve. The next three columns show the true or false values
of the comparison of the two "X" values. The last column shows the resultant pass or fail status of the
point. There are three ways a point can pass. They are:
1. Qpost being outside of the geomorphically significant range Qirto Q10
2. Qpost being less than Q pre
3. Qpost being less than 110% of the value ofQpre if the point is between Qirand Q10
There are two ways that a point can fail. They are:
I. Qpost being greater than 110% of Qpre if the point is between Q1r and Qio
2. If more than 10% of the points are between 100% and 110% of Qpre for the points
between Q1r and Q10
A quick scan down the last column will quickly tell if there are any points that fail.
At the bottom of each set of data are the date stamp of the report to the left, and to the right is the
page number/number of pages for the specific set of data (not the pages of the report!). Each new set
of data has its own page numbering. Between the file name in the header row and the page numbering
in the footer row, the engineer can readily scan the document for the data of interest.
Plan Check Suggestions
As was described under the peak flow section, is the responsibility of the reviewing agency to confirm
that the data sets presented are valid results from consistent calculations, and that any and all results
can be duplicated by manual methods and achieve the same results. In light of these goals, the plan
checker is invited to consider the following tasks as part of the plan check process.
Compare the Data Stamps for Each of the Statistics Files Used In This Analysis.
As was described in the Peak Flows section, all report files should have time stamps that are nearly
identical. If the time values are more than a few minutes apart then the potential for inconsistent
results files should be investigated.
Verify the Flow Rate Counts
For each of the pre, and mitigated flow duration tables, a few randomly selected flow value counts
should be checked against the values taken directly from the SWMM file. This can be done by opening
the corresponding SWMM file, selecting the outfall node, selecting Report>Table>By Object, Setting the
time format to Date/Time, selecting the appropriate node value, and clicking the OK button to generate
a table of the date/time/Total Inflow values. Next step is to click in the left most header row of the
SWMM table which will select the entire table. Now from the main menu select Edit>Copy
To>Clipboard. Now open a new blank sheet in MS Excel (or suitable spread sheet program) select cell
231Page
Al and paste the results from the clipboard into the spread sheet. Now sort the values based on the
Total Inflow column. This will group all the flow values together enabling the number of occurrences of
each value to be counted. At this point the a few (or all) of the counts on the various USGS9217d.txt
files can be verified.
Manually Verify That the Percent Exceeded Values (form USGS9217d) are Correctly Calculated
The discharge rates and counts are confirmed as was described above. The top row should be the
smallest runoff value (O.OOcfs usually). Total Periods Exceeding of the first line should be the total
number of rainfall records in the study. The percentage of Time Exceeding should be the total periods
Exceeding divided by the total number of rainfall records in the study (100% for the first line). For each
successive discharge rate, the total periods exceeding for the current line should be the total periods
exceeding from the line above minus the number of periods from the line above. The number of
periods and the number of periods exceeding should zero out at the last line.
Compare Plotted Curves to Table Data
Randomly check a few of the plotted points against the values verified above.
Verify by Observation that the plotted values of 010and Oi1 are reasonable.
Verify that the correct values for each of these return periods are plotted correctly on the graph.
Development of the Peak Flow Statistics
The peak flow statistics are developed directly from the binary output file produced by the SWMM
program. The site is modeled three ways, Pre-Development, Post-Development-Unmitigated, and Post-
Development-Mitigated. For each of these files a specific time period differentiating distinct storms is
chosen. The SWMM results are extracted and each flow value is queried. The majority of the values for
Southern California sites are zero flow. As each successive record is read, as soon as a non-zero value is
read the time and flow value of that record are recorded as the beginning of an event. The first record is
automatically recorded as the "tentative" peak value. As each successive non-zero value is read and the
successive flow value is compared to the peak value and the greater value is retained as the peak value
of the storm. As soon as a successive number of zero values equal to the predetermined storm
separation value, then the time value of the last non-zero value is recorded as the end of the storm, the
duration of the storm is the difference between the end time and the start time, and the peak value is
recorded as the highest flow value between the start and end times.
Once the entire SWMM output file is read all of the distinct storm events will have been recorded in a
special list. The storms will be in the order of their occurrence. To develop the peak flow statistics table
the first step is to sort the storms in descending order of the peak flow value. Once the list is sorted
then the relative rank of each storm is assigned with the highest ranking storm being the storm with the
highest peak flow. There are several methods that can be used to determine which storm should be
ranked above another equally valued storm. For the purposes of these studies an Ordinal ranking is
used so that each storm has a unique rank number. Where two or more storms have equal flow values,
the earlier storm is assigned the higher rank. This is done consistently throughout the storm record.
Since we are only looking at peak flow statistics, it is assumed that the relative ranking of individual {but
equal) storms is irrelevant to the calculations.
24JPagc
For each set of data, the upper right hand header value shows the name of the file being displayed (ex.
peakFlowPassFailMitigated.TXT). The first line of the file also shows this value. The next line shows the
time stamp of the file that is being analyzed. The time stamps of all of the report files should be within a
minute or two of each other, otherwise there may have been tampering with the files. Each report run
creates and prints all of the files and reports at one time so all the time stamps should be very close. It
should be noted that the SWMM.out files will not have related time stamps since each file is developed
independently.
The first column is the zero based number of the point. The next two columns show the post
development "X" and "V" values. The next column shows the value interpolated between the two
bounding points on the pre-development curve. The next three columns show the true or false values
of the comparison of the two "V" values. The last column shows the resultant pass or fail status of the
point. There are three ways a point can pass. They are:
1. Point is outside of the geomorphically significant range 010 -O..t
2. Oi,011 being less than Q pre
3. 0.,,,,1 being less than 110% of the value of 0,pre if the point is between Os and Ui.06
There are four ways that a point can fail. They are:
1. Oi,o,t being greater than O,,re if the point is between 0..f and 0.s
2. 0.,0,1 being greater than 110% of Oi,re if the point is between Qi, and 010
3. If more than 10% of the points are between 100% and 110% of Uii,e for the points between Os
andQ10
4. If the frequency interval for points> 100% of O.,re is greater than 1 year for the points between
Us and 0.10
A quick scan down the last column will quickly tell if there are any points that fail.
At the bottom of each set of data are the date stamp of the report to the left, and to the right is the
page number/number of pages for the specific set of data (not the pages of the report!). Each new set
of data has its own page numbering. Between the file name in the header row and the page numbering
in the footer row, the engineer can readily scan the document for the data of interest.
The Peak Flow Statistics Calculations
There are three sets of data for the Peak Flow Statistics calculations (Pre-Development, Un-Mitigated,
and Mitigated). As was the case for the pass/fail data, the upper right hand corner of each sheet has the
file name. The first row of the data is the SWM M file name. The second row is the SW MM file time
stamp of the file being analyzed. The 4th, 5th, and 6th rows are the calculated values for Q10, Os, and Qi.
These values are derived by linear interpolation between the nearest bounding points in the listing.
While the relationship between the points in the peak flow analysis is not technically a linear
relationship, the error introduced in using linear interpolation between such relatively close data points
is assumed to be irrelevant. Finally, the footer row shows the report time and the page/number of
pages of the data set.
6 See section on how a point can fail point number 3 hereon
26 I Page
As was previously discussed, each storm listed was determined by reading the flow values directly from
the binary output file from the SWMM program. The storms were then sorted in descending order of
peak flow values. Then each storm was assigned a unique rank, then the Frequency and Return Period
were calculated using Weibull formulas. Every discharge value for the entire rainfall record is listed in
each of these lists. It should be noted that the derivation of these peak flow statistics values use full
precision (i.e. no rounding off) of the SWMM output values. Since the precision of the calculations may
not be the same as the SWMM program uses, and also the assignment of rank to values of equal peak
flow value may differ slightly from the way SWMM calculates the tables, minor variances in the data
values and/or the order of storms can be expected.
Finally, as was previously stated, the values of the Return Period were plotted vs. the peak flow values
to develop the peak flow frequency curves.
Plan Check Suggestions
As is the responsibility of the reviewing agency, any and all methods should be considered to verify that
the SWMM analysis adequately models the site as far as hydrologic discharge is concerned, and that the
data sets presented are valid results from consistent calculations, and that any and all results can be
duplicated by manual methods and achieve the same results. In light of these goals, the plan checker is
invited to consider the following tasks as part of the plan check process.
Compare the Data Stamps for Each of the Statistics Files Used In This Analysis.
For each set of calculations and report files, the first step of the process is to list out all the files in the
report folder and delete those files. The very first step leaves the reports folder completely empty.
Then as each successive step is performed, the results file is placed in the reports folder. Once all of the
results files are complete, then the report file is compiled using the data directly from the files placed in
the results folder. This means that the time stamps on each of the report files in the report should be
within a minute or two depending on the speed of the computer. If the time values are more than a few
minutes apart then the potential for inconsistent results files should be investigated.
Verify A Few Random Storm Statistics
For each of the Pre, Un-mitigate and Mitigated peak flow statics tables, a few randomly selected storms
should be checked against the values taken directly from the SWMM file. This can be done by opening
the corresponding SWMM file, selecting the outfall node, selecting Report> Table>By Object, Setting the
time format to Date/Time, selecting the appropriate node value, and dicking the OK button to generate
a table of the date/time/Total Inflow values. Now scroll down the list to the start date and time of the
randomly selected storm. Verify that the start date, end date, and the highest flow value between the
start and end date correspond to the values shown in the statistics table. Do this for a few storm to
verify that the data corresponds to the SWMM output file. Verify by hand a few of the frequency and
return period values.
Compare Plotted Curves to Table Data
Randomly check a few of the plotted points against the values found in the Peak Flow Frequency Tables.
27 I Page
Verify by Observation that the values ofQ10, Qs, Q2 and Qirare reasonable.
For each value shown on the reports, verify that the value shown for say QlO is in between the next
higher return period and the next lower period. Also verify that the correct values for each of these
return periods are plotted correctly on the peak flow frequency graph.
Manually Verify That the Pass Fail Table Is Correctly Calculated
Select at random several points on each of the pass/fail tables to verify that the values for post X/Y and
interpolated Y look reasonable. Also check that the various test results are shown accurately in the
chart and also the final pass/fail result looks accurate.
Drawdown Time of Bio-filtration Surface Ponding
The drawdown time for hydromodification flow control facilities was calculated by assuming a starting
water surface elevation coincident with the peak operating level in the bio-filtration facility such as the
elevation at the weir or the emergency spillway overflow.
The instruction from the county of San Diego Department of Environmental Health {DEH) limits the
drawdown time hydromodification flow control facilities to 96 hours. This restriction was implemented
as mitigation to potential vector breeding issues and the subsequent risk to human health. See
Attachment C for Drawdown time of each pond and derivations of drawdown times for BMPs.
Drawdown time and Calculations are included as Attachment D of this SWMM report.
VII. SUMMARY AND CONCLUSION
Hydromodification calculations were performed utilizing continuous simulation to size storm water
control facilities. SWMM (Storm Water Management Model) version 5.0 distributed by USEPA was used
to generate computed peak flow recurrence and flow duration series statistics.
There are several tributary areas planned as industrial use treated by 2 biofiltration basins (labeled as
BMP-# (Best Management Practices) with a total tributary area of approximately 6.00 acres. The areas
were grouped based on its outfall and were analyzed for pre-development and post-development
conditions; Whole Basin A and Basin B drains to one point of compliance (POC).
The analyzed SWMM runs attached show that the proposed biofiltration facilities provided with variety
of orifice flow control at the base of the gravel storage configured as shown in Figure 6-1 is in
compliance with the HMP and BMP Manual.
Lot 2
On POC, The flow duration curve on the following page shows the existing condition 17.5 hours
(0.200x365daysx24 hour/day= 17.5 hours).
With the proposed square footage of LID areas and orifices acting as the low flow restrictor configured
as shown in Figure 1 the duration of the flow is 17.6 hours (0.201x36Sdaysx24 hour/day =17.6 hours).
This flow duration is higher than.the existing but within the allowed 10% to meet compliance.
281Pagc
Excel Engineering U SGS9217 d Pre .csv
:J;-~0 .; /(:>°' 0/ Q:-'lf e,\ v7 ~""$-0 ~q_
:<Pf:$ #<o !{, !-0 ,<.~ qJ(:o . c; 1;-"<f q_0 ~ <:S·<,; ~,;j ~ ;..r:7' ..... ~ q_0 ..
52 2.98 3 60 _Q.012_
53 3.03 0 57 _Q,011
54 3.09 0 57 0.011
55 3.14 3 57 QJ)11
56 3.19 1 54 0.Q11
57 3.24 3 53 0.011
58 3.29 2 50 0.010
59 3.34 2 48 0.010
60 3.39 2 46 0.009
61 3M 1 44 0.009
62 i;fa 3 r 43 0.009
63 3.54 3 40 0.008
l59 l .. §4 1 37 0.007
_65 3.64 1
..
36 0.007
66 3.69 . j 1 35 0.007
_§7 3.74 0 .14 0.007
§_8 3.80 1 34 0.007
.filJ 3.85 1 33 0.007
70 3.90 , ]_ 32 0.006
71 3.95 1 I -31 o.oos".
72 4.00 1 30 0.006
73 4.05 : j 2 29 0.006
74 -,uo 1 27 0.005
75 4.15 _9 26 0.005
76 4.20 0 26 0.005
77 4.25 1 26 0.005
78 4.30 0 25 0.005
79 4.35 , 25 0.005
80 4.40 0 24 p.oof
_81 4.45 3 24 _Q_.005
§_2 4.50 _j 2 21 0.004
83 4.56 2 19 0.004
84 4.61 0 17 0.003
85 4.66 0 17 0.003
86 4.71 0 17 0.003
87 4.76 0 17 t 0.003
88 4.81 , 17 0.003
89 4.86 0 16 0.003
90 4.91 1 16 0.003
91 4.96 , 15 0.093
92 5.01 0 14 p.003
93 5.06 1 14 0.003
94 _§.11 0 13 0.003
95 5.16 1 13 O.Q_(_)_?
96 5.21 2 • i 12 o.o~
97 5.26 2 10 0.002
98 "5:32 , 8 0.002 ... 99 :1 5.37 1 7 0-:001 " foo 5.42 0 -6 j:001 .:---···End oToata~: _______ ::· ______ "
..
...
3/18/2020 6:29 PM 2/2
Excel Engineering
END OF STATISTICS ANALYSIS
Excel Engineering
Underdrain and Orawdown Results
The following table summarizes the underdrain coefficients used for each of the BMP units and translates
the C factor coefficient to an equivalent round orifice diameter based on l/16th inch increments. The
drawdown equations are based on standard falling head drawdown theory. The primary drawdown number of
interest is the surface drawdown based on vector concerns. The various soil and gravel storage layer
calculations consider the void ratio and porosity of the respective layer. It should be noted that these
drawdown calculations only consider the volume of water within the bioretention units. If the bioretention
unit utilizes any storage above the berm height, then that storage drawdown is in addition to the values
shown in the table below. Those calculations, if present, are shown elsewhere in the report. The
derivation and explanation of the equations used to determine the values displayed in the chart are
discussed in the following two sections of this portion of the report.
• -□ ~ --...
~ fll --Q) c:: c:: 4 c:: c:: ..c: .u ., Q) Q) c:: • Q) .---l 4 :,, Q) :,, ..c: :,, Q) 3 -fll ., 4 u •rl ... 4--< .---l ... .... 0 0 u 0 -0 0, 0 u • Q) -,: ~ ·n "" 0 ... . ·-< ~ 0 ~ 0 .u "O fll "O "O "' "O .---l ; u -.... rl u +-' ::, "2 0 -.u "2 "' "' :,, 4--< -:,, .---l :,, ... -:,, fll .0 0 0 0 4--< .... ....._ u "' "' c:: "' --"' 4 4 fl! •rl fll 0 ... fll .u
:;I H ... H "' 4 rl 0 fll •rl •rl •rl ... :, 6 .. 0 4 .u ..c: 4 0
"' :z ,-l ll< >---1 -o-=, 4--< ,... -,... -,... -c:: Q) 0 "' □ Ul 0 "' -0 .u
BMP-A BMP-A 8735.0 32 0.14699 6 21 24 0.4 0.67 6.1 10.3 25. 0 41. 4
BMP-B BMP-B 1354.1 16 0.24657 6 21 24 0.4 0.67 3.6 6.2 14.9 24.7
The character* in the column heading indicates that the values was read directly from the SWMM inp file.
Assume: orifice coefficient C, ~ 0.61, void ratio for surface -1.0, centroid of underdrain orifice is located at h~O
SWMM C Factor and Drawdown Results
Excel Engineering
Orawdown Equations
The drawdown equations presented in the chart are the drawdown times for the
respective layers within the bioretention unit {only). If the bioretention
unit includes storage ponding above the berm height, then the drawdown time
for the storage portion is in addition to the values shown in the chart.
Those calculations (if present) are shown elsewhere in the report. For most
cases the storage drawdown time will be comparatively short as compared to
the bioretention drawdown times.
To derive a general formula that relates drawdown time for each layer of the
bioretention unit in terms of the SWMM C factor, we set the change in water
volume with respect to time equal to the standard orifice equation (found in
the County Hydraulics manual):
dh q = -nAp = CoAo✓2gh dt
Where n = porosity of the layer, Ap = area of the BMP unit, Co= orifice
coefficient, Ao= area of the orifice, and g = gravity constant. The
porosity n for the surface layer is 1.0, and the values for the soil and
storage layers read from the SWMM LID definitions.
Solving the definite integral from hl to h2
Solving for T:
1h=h2 f t=T CoAo,ffg h-0•5dh = ---dt
h=hl t=O nAp
CoAo,Jfg
2(Vh2 -..Jiil.) = A (T) n p
Or
2n( ill -ill) = C (T)
where: C = CoAofig (in"112/hr)
Ap
T = zn(..fhi-JIT) (hr)
C
Where h2(in) is the total beginning head above the underdrain orifice at t=O
and hl(in) is the total ending head above the orifice at t=T. Ex: h2 for
surface= depth of gravel storage plus depth of soil layer plus berm height,
and hl for surface= depth of gravel storage plus depth of soil layer.
inp File Listing
ATTACHMENT 3
Structural BMP Maintenance Information
Use this checklist to ensure the required information has been included in the Structural
BMP Maintenance Information Attachment:
Preliminary DesignlPlanninglCEQA level submittal:
Attachment 3 must identify:
Typical maintenance indicators and actions for proposed structural BMP(s) based
on Section 7.7 of the BMP Design Manual
Final Design level submittal:
Attachment 3 must identify:
J Iii Specific maintenance indicators and actions for proposed structural BMP(s). This
shall be based on Section 7. 7 of the BMP Design Manual and enhanced to reflect
actual proposed components of the structural BMP(s)
J It/ How to access the structural BMP(s) to inspect and perform maintenance
J ..,; Features that are provided to facilitate inspection (e.g., observation ports,
cleanouts, silt posts, or other features that allow the inspector to view necessary
components of the structural BMP and compare to maintenance thresholds)
J ..,; Manufacturer and part number for proprietary parts of structural BMP(s)
when applicable
J ..,; Maintenance thresholds for BMPs subject to siltation or heavy trash(e.g., silt level
posts or other markings shall be included in all BMP components that will trap and
store sediment, trash, and/or debris, so that the inspector may determine how full
the BMP is, and the maintenance personnel may determine where the bottom of
the BMP is . If required, posts or other markings shall be indicated and described
on structural BMP plans.)
J ..,; Recommended equipment to perform maintenance
J ..,; When applicable, necessary special training or certification requirements
for inspection and maintenance personnel such as confined space entry or
hazardous waste management
Chapter 7: Long Term Operation and Maintenance
• The sump area of a structural BMP should not exceed 20 feet in depth due to the loss of
efficiency of a vactor truck. The \Vater removal rate is three to four times longer when the depth
is greater than 20 feet. Deep structures may require additional equipment (stronger vactor trucks,
ladders, more vactor pipe segments).
• All manhole access points to underground structural BMPs must include a ladder or steps.
Measures to facilitate inspection of the structural BMP
• Structural BMPs shall include inspection ports for observing all underground components that
require inspection and maintenance.
• Silt level posts or other markings shall be included in all BMP components that will trap and
store sediment, trash, and/ or debris, so that the inspector may determine how full the BMP is,
and the maintenance personnel may determine where the bottom of the BMP is. Posts or other
markings shall be indicated and described on structural BMP plans.
• Vegetation requirements including plant type, coverage, and minimum height when applicable
shall be provided on the structural BMP and/ or landscaping plans as appropriate or as required
by the [City Engineer].
• Signage indicating the location and boundary of the structural BMP is recommended.
Wben designing a structural BMP, the engineer should review the typical structural BMP
maintenance actions listed in Section 7.7 to determine the potential maintenance equipment and
access needs.
When selecting permanent structural BMPs for a project, the engineer and project owner should
consider the long term cost of maintenance and what type of maintenance contracts a future
property owner, homeowners association or property owners association will need to manage. The
types of materials used (e.g. proprietary vs. non-proprietary parts), equipment used (e.g. landscape
equipment vs. vactor truck), actions/labor expected in the maintenance process and required
qualifications of maintenance personnel (e.g. confined space entry) affect the cost of long term
O&M of the structural BMPs presented in the manual.
7.7 Maintenance Indicators and Actions for
Structural BMPs
This Section presents typical maintenance indicators and expected maintenance actions
(routine and corrective) for typical structural BMPs.
There are many different variations of structural BMPs, and structural BMPs may include multiple
components. For the purpose of maintenance, the structural BMPs have been grouped into four
categories based on common maintenance requirements:
• Vegetated infiltration or filtration BMPs
• Non-vegetated infiltration BMPs
• Non-vegetated filtration BMPs
• Detention BMPs
February 2016
Appendix E: BMP Design Fact Sheet
I (These Source:-Will lk
nn the Project Site • • • Tl \' S'"'Q ~r p "l C • .1 Tl s c I BMP ••. lt:11 our. w l~ n ust 011s1u1.:r ll'SC nurcc 011tro s
1
Potential Sources of
Runoff PoUutant
[Z) A. n ite storm drain
inlets
□ ot pplicable
2
Permanent Controls-Show on
Drawings
IZ] Locati ns of inlet .
3
Permanent Control -List in Table
and arrative
IL] Mark all inlets with the words ' o
Dumping lows to Bay" or similar.
See stencil template pr vided in
App ndix I-4
E-4
4
Operational BMPs-lnclude in
Table and Narrative
12] Maintain and periodically repaint
or replace in1 t markings.
[Z] Provide storm water pollution
prevention infonn_ation to new
site owners lessees, or operators.
0 ee applicable ope.rational BMPs
in Fact She t C-44 'Drainage
System Maintenance," in the
C Q Storm ater Quality
Handbooks at
'-VWW.ca qa. rg/resou.rces/bmp,:
handb oks/municipal-brnp-
handbook.
[Z] nclud th following in lea e
agreements: "Tenant shall not
allow any ne t discharge
anything to storm drains r to
tore or dep sit materials s as to
create a p tenrial dischar e to
storm drains."
February 26, 2016
Appendix E: BMP Design Fact Sheets
If These $ource5 \~1i!I Jk·
on che Project Siic ·•• ... Then \'our S\VQl\lP must l'onsidcr These Sourl:c Control BJ\11':,;
1
Potential SoW'ces of
Runoff Pollutants
Ill D2. Landscape/
Outdoor Pe ticidc
e
D or Applicable
2
Permanent Controls-Show on
Drawings
0 how )ocati ns of existing
trees r areas of shrub and
ground cov r t be
u.oclisturbed and retained.
Show elf-retaining landscape
areas, if any.
how storm water u atment
f:acilitie .
3
Permanent Controls-List in Table and
arrati e
State that .finaJ Land cape plans \: ill
accompli h all of the following.
IZI Preserve e • sting drought tolerant
tree hrub , and growid co er t the
maximum extent po ible.
0 Design land capiog to minimize
irrigation and run ff, t promote
surface infiJcracion where appropriate,
and to minimize the use of fertilizers
and p sticide that can c ntribute to
storm wate r polluti n.
IZI Whcr land caped areas ar used to
retain or detain st rm water, specify
plants that are tolerant f peri die
saturated soil conditions.
121 Consider using pest-resi tant plants
especially adjacent t hardscape.
0To ensure uccessful establishm nt,
elect plants appropriate t ite soils,
slopes, climat , sun, wind, rain, land
use air movement, col ·cal
con isteocy, and plant in teraction s.
E-6
4
Operational BMPs-Include in
Table and auati: e
[21 Maintain landscaping u ing
minimum or no pe ticides.
IZI See appli able operati nal
BMP in Fact heet --4-1,
'Building and Grounds
Maintenance," in the CA Q
Storm ater Quality
Handbooks at
www.ca qa.t,rg/re • urces/brnp
-handbooks/municipal-hmp-
haodbook.
0 Provide IPM information to
new owners, lessees and
operators.
February 26, 2016
Appendix E: BMP Design Fact Sheets
IfThl·sc Sources Will Be
h P . •5. . .. Then Your S\X1QMP must con~idcr These Source Control Bl\1Ps on r e roiect 1te ...
1
Potential Sources of
Runoff Pollutants
2
Permanent Controls-Show on Drawings
DJ. Vehicle and O Show on drawings as appropriate:
Equipment Clearung
0 or Applicable
(1) Commercial/industrial facilities having
vehicle / equipment d eaning needs must
either provide a covered, benned area for
washing activities or discourage
vehicle/equipment washing by removing
hose bibs and installing signs prohibiting such
uses.
(2) Multi-dwelling complexes must have a
paved, bermed, and covered car wash area
(unless car washing i pr hibited onsite and
hoses are provided with an automatic shut-
off to discourage such use).
(3) Washing areas for cars, vehicles, and
equipment must be paved, designed to
prevent nill-on to or runoff from the area,
and plumbed to drain to the sanitary sewer.
(4) Commercial car wash facilities must be
designed such that no runoff from the facility
1s discharged to the stonn drain system.
Wastewater from the facility must discharge
to the sanitary sewer, or a wastewater
reclamation system must be installed.
3
Permanent Controls-List in
Table and Narrative
D If a car wash area is not
provided, describe measures
taken to discourage onsite
car washing and explain how
these will be enforced.
4
Operational BMPs-lnclude in
Table and Narrative
Describe operational measures to
implement the following (if
applicable):
D Washwater from vehicle and
equipment washing operations
must not be discharged to the
storm drain system.
D Car dealerships and similar
may rinse cars with water
only.
D See Fact Sheet SC-21,
"Vehicle and Equipment
Cleaning," m the CASQA
Storm Water Quality
Handbooks at
www.casqa.org/resources/bm
p-handbooks/municipal-bmp-
haudbook.
February 26, 2016
Appendix E: BMP Design Fact Sheets
If These Sources Will Be ... Then Your S\VQMP must consider These Source Control BMPs on the: Proj~t:t Site: ...
1
Potential Sources of
Runoff Pollutants
K.
D Vehicle/ quiprnent
Repair and
Maintenance
0 oc Applicable
2
Permanent Controls-Show on
Drawings
D Accommodate all vehicle
equipment repair and
maintenance indoors. Or
designate an outdoor work area
and design the area to protect
from rainfall, run-on runoff, and
wind dispersal.
D Show secondary containment for
exterior work areas where motor
oil, brake fluid, gasoline, diesel
fuel, radiator fluid, acid-
containing batteries or other
hazardous materials or hazardous
wastes are used or stored. Drains
must not be installed within the
secondary containment areas.
D Add a note on the plans that
states either (1) there are no floor
drains or (2) floor drains are
connected to wastewater
pretreatment systems prior to
discharge to the sanitary sewer
and an industrial waste discharge
permit will be obtained.
3
Permanent Controls-List in
Table and Narrative
4
Operational BMPs-Include in
Table and Narrative
D State that no vehicle repair or In the report, note that all of the following
maintenance will be done restrictions apply to use the site:
outdoors, or else describe the
required features of the
outdoor work area.
D State that there are no floor
drains or if there are floor
drains, note the agency from
which an industrial waste
discharge perm.it will be
obtained and that the design
meets that agency's
requirements.
D State that there are no tanks,
containers or sinks to be used
for parts cleaning or rinsing
or, if there are, note the
agency from which an
industrial waste discharge
permit will be obtained and
that the design meets that
agency's requirements.
E-11
D o person must dispose of, nor permit
the disposal, directly or indirectly of
vehicle fluids, hazardous materials, or
rinsewater from parts deaning into
storm drains.
D No vehicle fluid removal must be
performed outside a building, nor on
asphalt or ground su.rfaces, whether
inside or outside a building, except in
such a manner as to ensure that any
spilled fluid will be in an area of
secondary containment. Leaking
vehicle fluids must be contained or
drained from the vehicle immediately.
D No person must leave unattended drip
parts or other open containers
containing vehicle .fluid, unless such
containers are in use or in an area of
secondaty containment.
February 26, 2016
Appendix E : BMP Design Fact Sheet
lfThc::;c Sources \'X'ill Be . , . .
I l> . ~-• ..• Then\ nur SWQMP must i..:011'.-1<.kr These Source Control Bl\lPs 11n t 1C fOjC<.:t ~UC'. ...
1
Potential Sources of
Runoff Pollutant
D L. Fuel Dispensing
0 ot ppli~ ble
2
Perm.anent Conttols,......Show on
Drawings
D ueling areas16 must have
impermeabl £l r · (i.e., p rtland
cement concrete or equi aJent mooth
imp .rvi us surfac ) that ar (1) graded
at the minimum lope neces ary to
prevent p nding; and (2) separated
from the rest of the site by a grade
break that pr vent run-on of corm
wa ter to the MEP.
D Fueling area must be co ered by a
canopy that extends a minimum of ten
eet in each direction from each
pump. [Alt mati e: The fueling area
must be c vered and the covers
minimum dimen i o must be equal
to or greater than the area within the
grade break or fuel dispensing areal.]
□ The canopy [or cov rJ must not drain
nto the fueling area.
3
Perm.anent Controls-List
in Tabl and Narr-ative
4
Operational BMPs-lnclude in
Table and Nanative
□ The prope -own r must dry w ep
the fueling area routinely.
ee the Bu ines Guide h et,
"Automotive Service-Service
tations" in the C A torm
Water Quality Handbooks ac
hrtps://www. asqa.urg/ ·e ourc s/b
mp-handbooks.
16 The fueling areo must be defined a the area extending a minimum of 6.5 feet from the comer of each fuel di penser or the length at which the hose and nozzle as emb\y may be
op rated plus a minimum of on foot, whichever is greater.
E-12 February 26, 2016
Appendix E: BMP Design Fact Sheets
lfThcse Sources Will Be , , .
h I> . s· ... Then, our S\'\'Q:\lP mu•.:r consider Thest' Sl)lln.'C Comrol BMPs on l C mJCCI UC: ...
1
Potential Source of
Runoff Pollutants
D Fire prinkler
Test ater
0 ot pplicabl
0 . Miscellaneous Drain
or a h ter
□Boiler drain lines
□ ndensate drain
lines
OR oftop
eqwpmenc
□Drain sumps
DR ofi.n , gutter ,
and trim
D ot pplicablc
2
Permanent Control -
Show on Drawing
3
Permanent Contr ls-List in Table and
Narrative
□Pro ide a mea.os to drain fire sprinkler test water
to the sanitary ewer.
□ Boiler drain lines must be directl , or indirectly
connect d to the sanitary sewer sy tern and may
not discharge to the storm drain s em.
□Condensate drain line may discharge to
land cap d areas if the flow is small en ugh that
run ff will n t occur. Cond nsate drain Lin
ma not discharge to the storm drain sy t m.
D Ro oftop mounted quipment with p tential to
produce pollutants must be r ofed and/or have
sec ndary conrainment.
□Any drainage sumps oosit must feature a
sediment sump to r duce the quantity of
ediment in pumped water.
□ void r fing, gutters, and trim made f copper
or ther uoprotect d m tals that may 1 ach into
run ff.
E-14
4
Ope.rational BMPs-lnclude in
Table and Narrative
□ ee the note in Fact heet C-
41, ' Building and Gr unds
Maintenance " in the C Q
torm Water Quality
Handbooks at
,vww.casq .org/re iurces/bm
p-handbooks/municipal-bmp-
handbook
February 26, 2016
I
Appendix E: BMP Design Fact Sheets
lfThc!-e Sources Will Be :· p . 5. . .. Then Ynur SWQJ\1P mus, consider The~c Source Control BMPs on tne roiect He ...
1
Potential Sources of
Runoff Pollutants
0P.
sidewalks,
parking lots.
D ot Applicable
Plazas,
and
2
Permanent Controls-Show on
Drawings
3
Permanent Controls-List in
Table and Narrative
E-15
4
Operational BMPs-Include in
Table and Narrative
0 Plazas, sidewalks, and parking lots must
be swept regularly to prevent the
accumulation of litter and debris.
Debris from pressure washing must be
collected to prevent entry into the
storm drain system. Washwater
containing any cleaning agent or
degreaser must be collected and
discharged to the sanitary sewer and
not discharged to a storm drain.
February 26, 2016
ATTACHMENT 4
City standard Single Sheet BMP (SSBMP) Exhibit
[Use the City's standard Single Sheet BMP Plan.]