HomeMy WebLinkAboutSDP 09-04A; Westfield Carlsbad Phase 2; Site Development Plan (SDP) (3)STORM WATER MANAGEMENT PLAN
FOR
WESTFIELD CARLSBAD PHASE 2
SDP 09-04 (A), Drawing XXX XX
May 1,2014
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CITY OF CARLBB \r3
PLANNING DfVI'^"
Wayne W. Chang, MS, PE 46548
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Civil Engineering ° Hydrology»Hydraulics»Sedimentation
P.O. Box 9496
Rancho Santa Fe, CA 92067
(858) 692-0760
-TABLE OF CONTENTS -
1.0 Introduction 1
1.1 Vicinity Map 1
1.2 Project Description 2
1.3 Site Map 2
1.4 Constraints and Opportunities 2
2.0 Water Quality Environment 3
2.1 Beneficial Uses 3
2.1.1 Inland Surface Waters 4
2.1.2 Groundwater 4
3.0 Pollutants and Conditions of Concem 4
3.1 Pollutants from Project Area 4
3.2 Pollutants of Concem in Receiving Waters 5
4.0 Permanent Storm Water Best Management Practices 6
4.1 Standard Site Design BMPs 6
4.2 Source Control BMPs 7
4.3 Low Impact Development Site Design BMPs 9
4.4 Treatment Control BMPs 10
4.5 Hydromodification 11
5.0 Storm Water BMP Maintenance 11
6.0 Summary/Conclusions 12
7.0 Certification 13
APPENDIX
A. Storm Water Standards Questionnaire, E-34
B. Single Sheet BMP Plan
C. 2010 303(d) List
D. Exemption Flow Chart
E. BMP Sizing Calculations
1.0 INTRODUCTION
This Storm Water Management Plan (SWMP) addresses water quality requirements
associated with the Westfield Carlsbad Phase 2 project in the city of Carlsbad, which
proposes transformation of the indoor mall between the easterly and westerly anchor stores to
an open air shopping corridor, expansion of some perimeter buildings and roofs, and parking
lot improvements. Phase 1 of the project has been approved. This SWMP accompanies the
final engineering plans by the project's civil engineer, Hofman Planning & Engineering, and
follows the criteria outlined in the City of Carlsbad's January 14, 2011, Standard Urban
Storm Water Management Plan (SUSMP).
According to the City's Storm Water Standards Questionnaire E-34 (see Appendix A), the
development is in the following five priority project categories: Commercial - greater than 1-
acre; Environmentally Sensitive Area; Parking lot; Streets, roads, highways, and freeways;
and More than 1-acre of disturbance. The SUSMP outlines the SWMP objectives, which are
to identify site opportunities and constraints, identify pollutants and conditions of concem,
follow low impact development design objectives, describe best management practices
(BMPs), and outline maintenance requirements. BMPs will be utilized to the maximum
extent practicable to provide a long-term solution for addressing runoff water quality. BMPs
were selected by Hofman Planning & Engineering to meet the objectives.
1.1 Vicinity Map
NOT TO SCALE
VICINITY MAP
CITY OF OCEANSIDE
HIGHWAYj^^
CITY OF VISTA
CITY OF SAN MARCOS
PACIFIC
OCEAN
CITY OF ENCINITAS
1.2 Project Description
The Westfield Carlsbad Phase 1 project has been approved and construction has begun.
Under Phase 2 covered by this report, the indoor mall between the easterly and westerly
anchor stores will be transformed to an open air shopping corridor. This will be
accomplished by removing a large portion of the central roof area between the anchor stores.
Phase 2 will also expand the existing roofs and buildings along some of the perimeter mall
areas. Finally, Phase 2 will reconstruct some of the landscape islands and parking lot along
the southerly parking area. The landscape island and parking lot modifications are primarily
being done to accommodate proposed vegetated bioswales along Marron Road, which are the
project's treatment control BMPs (see the Site Map in Appendix B).
Under pre-project conditions, the site is mostly impervious and supports the existing indoor
shopping mall and surrounding parking lots. There are landscaping islands and landscaping
areas spread throughout the exterior areas and parking lots. There is no significant off-site
run-on to the project area. Storm runoff generally flows away from the indoor mall and
towards the outer perimeter of the parking lots. Existing storm drain systems collect the on-
site runoff and convey it northerly to Buena Vista Creek, which is adjacent to the northerly
edge of the mall. There are several discharge points into the creek for the Phase 2 project area
flows.
Under post-project conditions, the on-site runoff directions will generally be maintained.
However, direct precipitation into the proposed open air mall area will be captured by new
storm drain systems within this area. Vegetated bioswales will be used to meet requirements
for treating the project runoff (the project is exempt from hydromodification as explained in
Section 4.5). New drainage infrastructure will be installed, as needed, but the storm runoff
will ultimately still be conveyed to Buena Vista Creek at the current discharge locations.
The project's grading, drainage, and BMP design were developed entirely by Hofman
Planning & Engineering and are consistent with the project entitlements.
1.3 Site Map
A BMP Plan showing the site plan is included in Appendix B.
1.4 Constraints and Opportunities
The development will occur within an existing major shopping mall. Therefore, the site is
currently mostly impervious and has established drainage pattems and drainage systems.
The project does not propose to adversely alter the existing conditions. The pre-project
drainage pattems are generally being maintained by the project and the impervious area will
not be significantly altered. The proposed landscaping islands and open air corridor will yield
a small reduction in impervious area. The building and roof expansions will primarily occur
over areas that are currently impervious. The project runoff will be treated by proposed
vegetated bioswales, whereas the existing mall was constmcted prior to the current water
quality requirements.
2.0 WATER QUALITY ENVIRONMENT
2.1 Beneficial Uses
The beneficial uses for the hydrologic unit (see Section 3.1) are included in Tables 1 and 2.
These tables were obtained from the Water Quality Control Plan for the San Diego Basin (9)
compiled on August 28, 2012. The following contains definitions of the beneficial uses in the
tables:
MUN - Municipal and Domestic Supply: Includes uses of water for community,
military, or individual water supply systems including, but not limited to, drinking
water supply.
AGR - Agricultural Supply (AGR): Includes uses of water for farming,
horticulture, or ranching including, but not limited to, irrigation, stock watering, or
support of vegetation for range grazing.
IND - Industrial Services Supply: Includes uses of water for industrial activities
that do not depend primarily on water quality including, but not limited to, mining,
cooling water supply, hydraulic conveyance, gravel washing, fire protection, or oil
well re-pressurization.
RECl - Contact Recreation: Includes uses of water for recreational activities
involving body contact with water, where ingestion of water is reasonably possible.
These uses include, but are not limited to, swimming, wading, water-skiing, skin and
SCUBA diving, surfing, white water activities, fishing, or use of natural hot springs.
REC2 - Non-Contact Recreation: Includes the uses of water for recreational
involving proximity to water, but not normally involving body contact with water,
where ingestion of water is reasonably possible. These uses include, but are not
limited to, picnicking, sunbathing, hiking, camping, boating, tide pool and marine life
study, hunting, sightseeing, or aesthetic enjoyment in conjunction with the above
activities.
WARM - Warm Freshwater Habitat: Includes uses of water that support warm
water ecosystems including, but not limited to, preservation or enhancement of
aquatic habitats, vegetation, fish or wildlife, including invertebrates.
WILD - Wildlife Habitat: Includes uses of water that support terrestrial ecosystems
including, but not limited to, preservation and enhancement of terrestrial habitats,
vegetation, wildlife, (e.g., mammals, birds, reptiles, amphibians, invertebrates), or
wildlife water and food sources.
RARE - Rare: Bodies of water where the protection of a threatened or endangered
species depends on the water either directly, or to support its habitat.
2.1.1 Inland Surface Waters
Inland surface waters for the Buena Vista Creek Hydrologic Area have the beneficial uses
shown in Table 1:
Table 1. Beneficial Uses for Inland Surface Waters
Hydrologic
Unit fN O
<a
p
Code c
3 -a o o t/1 o o fN O
<a cd "o OH < (X oi Oi U Oi
904.21 + • • • • • • •
-I- Exempted by the Regional Board from the municipal used designation.
• Existing Beneficial Use
2.1.2 Groundwater
Groundwater beneficial uses for the El Salto Hydrologic Subarea are shown in Table 2:
Table 2. Beneficial Uses for Groundwater
Hydrologic
Unit
Code c o ail < T3 C 2
fin
V)
904.21 • • o
• Existing Beneficial Use
° Potential Beneficial Use
3.0 POLLUTANTS AND CONDITIONS OF CONCERN
3.1 Pollutants from Project Area
The project is located within the El Salto Hydrologic Subarea (904.21) of the Buena Vista
Creek Hydrologic Area (904.20), which is within the Carlsbad Hydrologic Unit (904.00).
The total drainage area of the hydrologic unit is approximately 210 square miles. Runoff
from the hydrologic area ultimately drains to Buena Vista Creek, which is along the north
perimeter of the project site. All of the project runoff will enter Buena Vista Creek. The
project site represents less than one percent of the Buena Vista Creek watershed.
The following table lists pollutants of concem that are anticipated or can potentially exist at
proposed priority development project sites. The pollutants are from the city of Carlsbad's
SUSMP. The project falls within the Commercial - greater than 1-acre; Environmentally
Sensitive Area; Parking lot; Streets, roads, highways, and freeways; and More than 1-acre of
disturbance priority project categories (highlighted yellow in the table). All of the listed
pollutants are either anticipated or can potentially exist at the developed site.
Table 3. Priority Project Pollutants
Priority
Project
Categories
Sediments Nutrients Heavy
Metals
Organic
Compounds
Trash
&
Debris
Oxygen
Demanding
Substances
Oil
&
Grease
Bacteria
&
Viruses
Pesticides
Detached
Residential
Development
X X X X X X X
Attached
Residential
Development
X X X pd) p(2) P X
Commercial
Development
> one acre
p(i) p(i) X p(2) X p(5) X p(3) p(5)
Heavy
Industry X X X X X X
Automotive
Repair Shops X xl'')!') X X
Restaurants X X X X p(l)
Hillside
Development
>5,000 ft^
X X X X X X
Parking Lots pd) pd) X X pd) X pd)
Retail
Gasoline
Outlets
X X X X X
Streets,
Highways &
Freeways
X p(l) X X(^) X p(5) X X p(l)
X = Anticipated
P = Potential
(1) A potential pollutant if landscaping exists on-site
(2) A potential pollutant if the project includes uncovered parking areas
(3) A potential pollutant if land use involves food or animal waste products
(4) Including petroleum hydrocarbons
(5) Including solvents
3.2 Pollutants of Concern in Receiving Waters
According to the 2010 303(d) list approved by the US Environmental Protection Agency (see
Appendix C), the receiving waterbody closest to the project, Buena Vista Creek, is 303(d)
listed for sediment toxicity and selenium. In addition, Buena Vista Lagoon is listed for
indicator bacteria, nutrients, and sedimentation/siltation. Both of these waterbodies is subject
to total maximum daily loads (TMDLs), but the TMDLs have not been completed. Based on
this information, the project generates pollutants of concern in the receiving waters for
sediments, nutrients, and bacteria & viruses.
4.0 PERMANENT STORM WATER BEST MANAGEMENT PRACTICES
To address water quality for the project, best management practices (BMPs) will be
implemented. The following discusses the Standard Site Design, Source Control, and Low
Impact Development design BMPs for the project.
4.1 Standard Site Design BMPs
The City of Carlsbad's standard objectives are required for all projects. The project will
accomplish these goals through the following standard site design BMPs, which are from the
Carlsbad SUSMP:
Standard Stormwater Requirements
Minimize Impervious Surfaces. The project will increase pervious surfaces through
landscaping within the development area. Many of the existing landscape areas will be
maintained.
Disconnect Discharges. Roof drains will discharge to adjacent landscape areas, where
feasible. The majority of the roof runoff will ultimately be treated by the vegetated
bioswales.
Conserve Natural Areas. There are no existing natural areas within the project footprint.
Stenciling Inlets and Signage. The curb cuts and inlets within the project will be stenciled
with prohibitive language such as "No Dumping -1 live downstream" or approved similar.
Landscape Design. A landscape plan will be prepared that uses drought-tolerant species in
accordance with the City's landscape manual. The project will only use water as needed to
support the landscaping.
Water Efficient Irrigation. The irrigation systems will be designed to each landscaped areas
water requirements to avoid over irrigation. Rain shutoff devices will be used to prevent
irrigation after rain events.
Protect Slopes And Channels. The project does not propose large slopes. The flow rate into
the receiving existing Buena Vista Creek channel will not be significantly altered by the
project.
Vegetate slopes with native or drought tolerant vegetation. The project does not propose
appreciable slopes. Native and drought tolerant vegetation will be used to the extent feasible.
Trash Receptacles. Exterior trash receptacles and dumpsters shall be routinely collected to
prevent overflow. Dumpsters shall have covers to prevent rain intrusion and be placed in
designated gated areas.
Material Storage Areas. The project does not propose outdoor material storage areas. Any
required material storage shall be kept under cover.
4.2 Source Control BMPs
Source control BMPs will consist of measures to prevent polluted runoff. The following
addresses the source control BMPs from Appendix 1 of the Carlsbad SUSMP:
Table 4. Pollutant Sources and Source Control Checklist
Potential Source
of Runoff Pollutants
Permanent Source
Control BMPs
Operational Source
Control BMPs
On-site storm drain
inlets
Mark all inlets with "No
Dumping -1 live downstream"
Maintain and periodically repaint
inlet markings
Provide stormwater pollution
information to owners, lessees, and
operators (Fact sheet SC-44 from
the CASQA Stormwater Quality
Handbook at
www.cabmphandbooks.com)
Owner/lessee agreements shall
state "Tenant shall not allow
anyone to discharge anything to
storm drains or to store or deposit
materials so as to create a potential
discharge to storm drains.
Interior floor drains
and elevator shaft
sump pumps
Interior floor drains and
elevator shaft sump pumps will
be plumbed to sanitary sewer.
Inspect and maintain drains to
prevent blockages and overflow.
Need for future
indoor & structural
pest control
Buildings shall be designed to
avoid openings that would
encourage entry of pests.
Integrated Pest Management (e.g.,
the EPA's Citizen's Guide to Pest
Control and Pesticide Safety)
information shall be provided to
owners, lessees, and operators.
Landscape/Outdoor
Pesticide Use
Final landscape plans will
accomplish all of the
following.
• Preserve existing native trees,
shrubs, and ground cover to
the maximum extent possible.
• Design landscaping to
minimize irrigation and
runoff, to promote surface
infiltration where
Maintain landscaping using
minimum or no pesticides.
See applicable operational BMPs
in Fact Sheet SC-41, "Building and
Grounds Maintenance," and TC-
30, "Vegetated Swale," in the
CASQA Stormwater Quality
Handbooks at
www.cabmohandbooks.com
Landscape/Outdoor
Pesticide Use
Final landscape plans will
accomplish all of the
following.
• Preserve existing native trees,
shrubs, and ground cover to
the maximum extent possible.
• Design landscaping to
minimize irrigation and
runoff, to promote surface
infiltration where
Integrated Pest Management (e.g.,
the EPA's Citizen's Guide to Pest
appropriate, and to minimize
the use of fertilizers and
pesticides that can contribute
to stormwater pollution.
• Where landscaped areas can
retain or detain stormwater,
specify plants that are
tolerant of saturated soil
conditions.
• Consider using pest-resistant
plants, especially adjacent to
hardscape.
• To ensure successful
establishment, select plants
appropriate to site soils,
slopes, climate, sun, wind,
rain, land use, air movement,
ecological consistency, and
plant interactions.
Control and Pesticide Safety)
information shall be provided to
owners, lessees, and operators.
Refuse areas • The shopping mall shall be
under contract with a refuse
company for regular trash
removal from the proposed
trash compactors.
• Signs will be posted on or
near the compactors and
receptacles with the words
"Do not dump hazardous
materials here" or similar.
Provide adequate number of
receptacles. Inspect receptacles
regularly; repair or replace leaky
receptacles. Keep receptacles
covered. Prohibit/prevent dumping
of liquid or hazardous wastes. Post
"no hazardous materials" signs.
Inspect and pick up litter daily and
clean up spills immediately. Keep
spill control materials available on-
site. See Fact Sheet SC-34, "Waste
Handling and Disposal" in the
CASQA Stormwater Quality
Handbooks at
www.cabmphandbooks.com
Fire Sprinkler Test
Water
Provide a means to drain fire
sprinkler test water to the
sanitary sewer.
See the note in Fact Sheet SC-41,
"Building and Grounds
Maintenance," in the CASQA
Stormwater Quality Handbooks at
www.cabmphandbooks.com
Miscellaneous Drain
or Wash Water
Boiler drain lines Boiler drain lines shall be directly
or indirectly connected to the
Condensate drain
lines
Rooftop equipment
Drainage sumps
Roofing, gutters, and
trim.
sanitary sewer system and may not
discharge to the storm drain
system.
Condensate drain lines may
discharge to landscaped areas if
the flow is small enough that
runoff will not occur. Condensate
drain lines may not discharge to
the storm drain system.
Rooftop mounted equipment with
potential to produce pollutants
shall be roofed and/or have
secondary containment.
Any drainage sumps on-site shall
feature a sediment sump to reduce
the quantity of sediment in
pumped water.
Avoid roofing, gutters, and trim
made of copper or other
unprotected metals that may leach
into runoff.
Plazas, sidewalks,
and parking lots.
Plazas, sidewalks, and parking lots
shall be swept regularly to prevent
the accumulation of litter and
debris. Debris from pressure
washing shall be collected to
prevent entry into the storm drain
system. Wash water containing
any cleaning agent or degreaser
shall be collected and discharged
to the sanitary sewer and not
discharged to a storm drain.
4.3 Low Impact Development Site Design BMPs
Low Impact Development (LID) BMPs must be incorporated into the site design to meet the
City of Carlsbad's January 14, 2011 SUSMP requirements. The integrated LID outlines the
following strategies:
1. Optimize the site layout by preserving natural drainage features and designing
buildings and circulation to minimize the amount of roofs and paving.
2. Use pervious surfaces such as turf, gravel, or pervious pavement—or use surfaces that
retain rainfall. All drainage from these surfaces is considered to be "self-retained".
3. Disperse runoff from impervious surfaces onto adjacent pervious surfaces (e.g., direct
a roof downspout to disperse runoff onto a lawn).
4. Drain impervious surfaces to engineered Integrated Management Practices (IMPs),
such as bioretention facilities. IMPs infiltrate runoff to groundwater and/or percolate
runoff through engineered soil and allow it to drain away slowly.
The project design is in compliance with these strategies. The site layout has been designed
to preserve natural areas and maintain current drainage directions to Buena Vista Creek. The
building/roof expansion areas will be within the footprint of existing impervious areas to
minimize flow rate impacts. The circulation will generally be similar to current circulation
pattems.
Runoff from the roofs and parking lots will flow towards pervious landscape areas and
ultimately enter a vegetated bioswales, where possible.
Vegetated bioswales will be used to treat the on-site runoff and were approved during the
entitlement process. Vegetated bioswales provide high to medium removal effectiveness for
the pollutants generated by the project (per Table 2-2 and 2-3 of the Carlsbad SUSMP),
which are listed in Table 3. Sizing is included in Appendix E of this report.
4.4 Treatment Control BMPs
Treatment control BMPs were selected to treat the project's pollutants of concem identified
in Table 3. Vegetated bioswales will be used because they have a medium to high pollutant
removal efficiency for the project's pollutants of concern. For treatment control, a vegetated
bioswale is sized according to the flow-based approach in the Carlsbad SUSMP, which is
based on the rational method. The sizing is included in Appendix E.
Runoff within the new open air corridor will be captured by proposed drainage systems that
connect to existing drainage systems that discharge directly to Buena Vista Creek. As a
result, treatment control BMPs are not proposed for the open air corridor runoff. This will be
mitigated by directing portions of the existing untreated parking areas and roofs to the
proposed bioswales. The amount of existing parking areas and roofs to be treated will exceed
the open air corridor area by over two times.
The project proposes building/roof expansions at various locations around the mall perimeter.
The new roof areas will be designed to convey runoff to the surrounding parking lot. The
building/roof expansion areas will be within the footprint of areas that currently are mostly
impervious, so the expansion will not significantly alter the flow rates. Some of the
building/roof expansion areas direct runoff to the bioswales within Phase 1. Therefore, the
bioswales in Phase 1 will adequately treat this runoff A couple of the smaller expansion
areas along the north side are not tributary to a bioswale. The treatment requirement for these
areas will be met by the excess treatment mentioned in the prior paragraph.
10
Furthermore, retail development within a portion of the existing parking lot originally
proposed under Phase 1 is being eliminated. As a result, excess treatment control is being
provided by Phase 1, which serves as credit for future development.
4.5 Hydromodification
The January 14, 2011 SUSMP requires hydromodification (flow control) for priority
development projects to ensure that post-development peak flows do not exceed pre-
development peak flows. The SUSMP does provide for exemptions to hydromodification.
Westfield Carlsbad Phase 2 is a priority development project, but meets an exemption criteria
so is not subject to the hydromodification requirement (see Figure 2-1 from the SUSMP
included in Appendix D, which provides the exemption criteria flow chart).
The exemption criteria is met by Nodes 7 and 8. The project runoff discharges to Buena
Vista Creek, which flows into Buena Vista Lagoon, and then the Pacific Ocean. Buena Vista
Creek along the project site is an engineered trapezoidal channel. In an October 7, 2012,
Hydraulic Analyses for Buena Vista Creek Channel Maintenance Project report by Chang
Consultants prepared for the City of Carlsbad, the channel was stated to have capacity for the
20-year flow before overtopping. Furthermore, in a June 10, 2013, Hydromodification
Exemption Analyses for Select Carlsbad Watersheds report by Chang Consultants prepared
for the City of Carlsbad, Buena Vista Lagoon was determined to be a stabilized conveyance
to the Pacific Ocean with capacity for the 10-year flow. Since the streams that convey the
project runoff to an exempt system (Pacific Oceans) are stabilized conveyances with at least
10-year capacity, the project is exempt from hydromodification.
5.0 STORM WATER BMP MAINTENANCE
The developer will be responsible for funding and implementing the operations and
maintenance of the project BMPs. Provisions will be made to transfer operations and
maintenance to the new owner in the event of a change in ownership. The shopping mall
(Christopher Holman, Assistant General Manager; Westfield Plaza Camino Real; 2525 El
Camino Real, Suite 100, Carlsbad, CA 92008; Phone: (760) 729-6183; E-mail:
Cfholman@westfield.com) will ultimately be responsible for ongoing operations and
maintenance. The following describes the specific BMP maintenance.
Landscaping and Vegetated Bioswales
Maintenance will be performed by landscaping personnel. The vegetation will be maintained
and inspected on a monthly basis by landscape maintenance staff and will be replaced or
replanted, as necessary, to maintain a dense, healthy cover. The vegetation will also be
inspected after major storm events. Maintenance shall include periodic mowing, weed
control, irrigation, reseeding/replanting of bare areas, and clearing of debris. A design grass
height of 6 inches is recommended. Grass clippings shall not be left in grass swales. The
private drainage system shall be kept clear of debris and inspected prior to and during the
rainy season to ensure it is free-flowing.
11
Efficient Irrigation
The landscaping personnel shall inspect and maintain the irrigation system on a regular basis.
This will occur during the routine maintenance activities. All valves, heads, shutoff devices,
lines, etc. shall be kept in a properly functioning condition. Any defective parts shall be
replaced immediately. The irrigation system shall be adjusted to prevent excessive mnoff
from landscape areas. The irrigation schedule shall be adjusted based on seasonal needs.
Inlet Stenciling
Any stenciling shall be inspected at the beginning and end of each rainy season and repaired
or replaced, as needed.
Hazardous Wastes
Suspected hazardous wastes will be analyzed to determine disposal options. Hazardous
materials are not expected to be generated on-site; however, if discovered, hazardous
materials will be handled and disposed of according to local, state, and federal regulations. A
solid or liquid waste is considered a hazardous waste if it exceeds the criteria listed in the
Califomia Code of Federal Regulations, Title 22, Article 11 (State of Califomia, 1985).
6.0 SUMMARY/CONCLUSIONS
This final SWMP has been prepared in accordance with the City of Carlsbad's January 14,
2011, Standard Urban Storm Water Management Plan, and has evaluated and addressed
potential pollutants associated with the Westfield Carlsbad Phase 2 project and its effects on
water quality. This SWMP has been based on the final engineering plans by Hofman
Planning & Engineering. A summary of the facts and findings associated with the project and
the measures addressed by this SWMP are as follows:
• The beneficial uses for the receiving waters have been identified. BMPs will be used
to protect the beneficial uses as outlined by the SUSMP.
• The project will not significantly alter drainage pattems and will meet
hydromodification requirements.
• A Storm Water Pollution Prevention Plan for construction activities will be prepared
to address construction-related water quality objectives.
• Permanent BMPs will be incorporated into the project design in the form of site
design, source control, and LID treatment control.
• The proposed BMPs address mitigation measures to protect water quality and
beneficial uses to the maximum extent practicable.
12
7.0 CERTIFICATION
The selection, sizing, and preliminary design of stormwater treatment and other control
measures in this plan meet the requirements of Regional Water Quality Control Board Order
R9-2013-0001 and subsequent amendments.
Wayne W. Chang, RCE 46548 Date
I certify that, as lessee of the property described herein, I have read and understand the
requirements of this Storm Water Management Plan (SWMP) and that I am responsible for
ensuring that all storm water treatment measures described within said SWMP will be
properly implemented, monitored, and maintained.
Name: Date
13
APPENDIX A
STORM WATER STANDARDS
QUESTIONNAIRE, E-34
STORM WATER Development Services
Land Development Engineering STANDARDS Development Services
Land Development Engineering
CITY OF QUESTIONNAIRE
E-34
1635 Faraday Avenue
760-602-2750
CARLSBAD
QUESTIONNAIRE
E-34 www.carlsbadca.gov
To address post-development pollutants that may be generated from development projects, the City requires that new development and
significant redevelopment priority projects incorporate Permanent Storm Water Best Management Practices (BMP's) into the project
design per the City's Standard Urban Stormwater Management Plan (SUSMP). To view the SUSMP, refer to the Engineering Standards
(Volume 4, Chapter 2) at www.carlsbadca.qov/standards.
Initially this questionnaire must be completed by the applicant in advance of submitting for a development application (subdivision,
discretionary permits and/or construction permits). The results of the questionnaire determine the level of stomn water standards that
must be applied to a proposed development or redevelopment project. Depending on the outcome, your project will either be subject to
'Standard Stonnwater Requirements' or be subject to additional criteria called 'Priority Development Project Requirements'. Many
aspects of project site design are dependent upon the storm water standards applied to a project.
Your responses to the questionnaire represent an initial assessment of the proposed project conditions and impacts. City staff has
responsibility for making the final assessment after submission of the development application. If staff determines that the questionnaire
was incorrectly filled out and is subject to more stringent stomn water standards than initially assessed by you, this will result in the return
of the development application as incomplete. In this case, please make the changes to the questionnaire and resubmit to the City.
If you are unsure about the meaning of a question or need help in detemiining how to respond to one or more of the questions, please
seek assistance from Land Development Engineering staff.
A separate completed and signed questionnaire must be submitted for each new development application submission. Only one
completed and signed questionnaire is required when multiple development applications forthe same project are submitted concurrently.
In addition to this questionnaire, you must also complete, sign and submit a Project Threat Assessment Form with construction permits
for the project.
Please start by completing Step 1 and follow the instructions. When completed, sign the form at the end and submit this with your
application to the city.
STEP1
TO BE CQMMM^W) FOR ALL PROJECTS
To determine if your project is a priority development project, please answer the following questions:
YES NO
1. Is your project LIMITED TO constructing new or retrofitting paved sidewalks, bicycle lanes or trails that meet
the following criteria: (1) Designed and constructed to direct storm water runoff to adjacent vegetated areas, or
other non-erodible permeable areas; OR (2) designed and constructed to be hydraulically disconnected from
paved streets or roads; OR (3) designed and constructed with permeable pavements or surfaces in
accxirdance with USEPA Green Streets guidance?
X
2. Is your project LIMITED TO retrofitting or redeveloping existing paved alleys, streets, or roads that are
designed and constructed in accordance with the USEPA Green Streets guidance?
X
If you answered "yes" to one or more of the above questions, then your project is NOT a priority development project and therefore is
NOT subject to the storm water criteria required for priority development projects. Go to step 4, mark the last box stating "my
project does not meet PDP requirements" and complete applicant information.
If you answered "no" to both questions, then go to Step 2.
E-34 Page 1 of 3 Effective 6/27/13
^ CITY OF
CARLSBAD
STORM WATER
STANDARDS
QUESTIONNAIRE
E-34
Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
STEP 2
TO^P^j^Q^j^^ETJ^fi^^^ ALL NEW OR REDEVELOPMENT PROJECTS
To determine if your project is a priority development project, please answer the following questions: YES NO
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.
X
2. Is your project creating 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 projects on public or private land.
X
3. 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 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.
X
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 any natural slope that is twenty-five percent or greater X
5. 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 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.
X
6. 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 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.
X
7. Is your project a new or redevelopment project that creates 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 commingles with flows from adjacent lands).*
X
8. Is your project a new development 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.
X
9. Is your project a new development that supports a retail gasoline outlet (RGO)? 777/s 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.
X
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? X
11.1s 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%? X
If you answered "yes" to one or more of the above questions, you ARE a priority development project and are therefore subject to
implementing structural Best Management Practices (BMP's) in addition to implementing Standard Storm Water Requirements such
as source control and low impact development BMP's. A Storm Water Management Plan (SWMP) must be submitted with your
application(s) for development Go to step 3 for redevelopment projects. For new projects, go to step 4 at the end of this
questionnaire, check the "my project meets PDP requirements" box and complete applicant information.
If you answered "no" to all of the above questions, you ARE NOT a priority development project and are therefore subject to
implementing only Standard Storm Water Requirements such as source control and low impact development BMP's required for all
development projects. A Storm Water Management Plan (SWMP) is not required with your application(s) for development. Go to step
4 at the end of this questionnaire, check the "my project does not meet PDP requirements" box and complete applicant
information.
E-34 Page 2 of 3 Effective 6/27/13
CITY OF
CARLSBAD
STORM WATER
STANDARDS
QUESTIONNAIRE
E-34
Development Services
Land Development Engineering
1635 Faraday Avenue
760-602-2750
www.carlsbadca.gov
TO BE COIMPLETED FOR REDEVELOPMENT PROJECTS THAT ARE PRIORITY DEVELOPEMENT PROJECTS ONLY tfl
Complete the questions below regarding your redevelopment project: 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?
If you answered "yes," the structural BMP's required for Priority Development Projects apply only to the creation or replacement of
impervious surface and not the entire development. Go to step 4, check the "my project meets PDP requirements" box and
complete applicant information.
If you answered "no," the structural BMP's required for Priority Development Projects apply to the entire development. Go to step 4,
check the "my project meets PDP requirements" box and complete applicant information.
CHECK THE APPROPRlj ilCOMPLETE APPLICANT INFORMATION
1^ My project meets PRIORITY DEVELOPMENT PROJECT (PDP) requirements and must comply with additional stormwater
criteria per the SUSMP and I understand I must prepare a Storm Water Management Plan for submittal at time of application.
I understand flow control (hydromodification) requirements may apply to my project Refer to SUSMP for details.
• My project does not meet PDP requirements and must only comply with STANDARD STORMWATER REQUIREMENTS per
the SUSMP. As part of these requirements, I will incorporate low impact development strategies throughout my project.
Applicant Information and Signature Box
Address: Westfield Plaza Camino Real
2525 El Camino Real. Suite 100. Carlsbad. CA 92008
Applicant Name:
Chnstopher Holman
Applicant Signature:
Accessor's Parcel Number(s)
156-302-08. -09. -24
Applicant Title: Assistant General Manager
Date:
This Box for City Use Only
City Concurrence: YES NO
By:
Date:
Project ID:
* Environmentally Sensitive Areas include but are not limited to all Clean Water Act Section 303(d) impaired water bodies; areas
designated as Areas of Special Biological Significance by the State Water Resources Control Board (Water Quality Control Plan for the
San Diego Basin (1994) and amendments); water bodies designated with the RARE beneficial use by the State Water Resources
Control Board (Water Quality Control Plan forthe San Diego Basin (1994) and amendments); areas designated as preserves or their
quivalent under the Multi Species Conservation Program within the Cities and County of San Diego; and any other equivalent
environmentally sensitive areas which have been identified by the Copermittees.
E-34 Page 3 of 3 Effective 6/27/13
APPENDIX B
BMP PLAN
APPENDIX C
2010 303(D) LIST
Page 423 of 481
REGION WATER BODY
NAME
WATER
TYPE
WATERSHED*
CALWATER /
USGS HUC
River & 90432000 /
Stream 18070303
POLLUTANT
o POTENTIAL SOURCES
Relevant Notes
Source Unknown
Nitrate and Nitrite
° Source Unknown
ESTIMATED FIRST TMDL
AREA YEAR REQUIREMENT DATE***
ASSESSED LISTED STATUS**
4.8 Miles 2006 5A 2019
Buena Vista Creek River &
Stream
90421000 /
18070303
Sediment Toxicity
° Unknown Nonpoint Source
° Unknown Point Source
11 Miles 2006 5A 2019
Selenium
Source Unknown 11 Miles 2010 5A 2019
Buena Vista Lagoon Estuary 90421000 /
18070303
Indicator Bacteria
° Nonpoint Source
° Point Source
202 Acres 1996 5A 2008
• Nutrients
Nonpoint Source
Point Source
202 Acres 1996 5A 2019
Estimated size of impairment is 150 acres located in upper portion of lagoon.
Sedimentation/Siltation
Nonpoint Source
Point Source
202 Acres 1996 5A 2019
Chollas Creek River &
Stream
90822000 /
18070304
Copper
° Nonpoint Source
° Point Source
3.5 Miles 1996 5A 2004
Diazinon
Nonpoint Source 3.5 Miles 2002 5B 2003
9/25/2013
APPENDIX D
EXEMPTION FLOW CHART
SECTION 2: IDENTIFY POLLUTANTS, BMP SIZING AND SELECTION
HO 1. \s Projtct a
\Priorty D«vtlopm«rit^
1. \s Projtct a
\Priorty D«vtlopm«rit^
^y^^ Prop«r\^
Bicrgy Dissipation^^
ProvWed?
1 ES ot II i ^y^^ Prop«r\^
Bicrgy Dissipation^^
ProvWed?
HO R«-d«sign Entrgy ^y^^ Prop«r\^
Bicrgy Dissipation^^
ProvWed?
14 Hydromodlfteation Controls Required
Goto Figure 2.2 of Decision Matrix
I'KiliRI- 2-1. IIMl^ Applicability Dclcrmiiiaiioii*
'refer lo expandc'il I IMP c'M-m|iiiini criicn.i hilow for justifications required on each node
30 City of Carlsbad SUSMP - January 14, 2011
APPENDIX E
BMP SIZING CALCULATIONS
SUMMARY
The best management practices (BMPs) selected for the site will be vegetated bioswales. This
section contains sizing of these treatment control BMPs. Some of the proposed project areas
(open air corridor and two building expansion areas along north side of mall) will not be treated
by BMPs. This will be offset and mitigated for by directing more than two times the existing
parking lot and roof areas to a proposed bioswale. Other proposed project areas will be treated by
the Phase 1 bioswales, which have capacity for the areas. The Phase 1 SWMP can be reviewed
for the Phase 1 BMP sizing.
The majority of the Phase 1 project runoff from the proposed project areas will be conveyed
through vegetated bioswales prior to entering the public storm drain system. The vegetated
bioswales will be installed along the southerly (along Marron Road) Phase 2 site perimeter.
Runoff from the project footprint and existing parking lot flows to these areas, so vegetated
bioswales are well-suited to the proposed layout. The SUSMP states that projects not subject to
hydromodification and not using the unified LID approach can use the numeric sizing approach
for treatment control. This involves sizing vegetated bioswales using the flow-based approach,
which is based on the rational method equation and determined by multiplying the runoff
coefficient, rainfall intensity (0.2 inches per hour for water quality), and tributary area, or:
Q=CIA where Q is the water quality flow rate, cfs
C is the runoff coefficient = 0.87 for type A, C, and D soil and
95% impervious, or =0.34 for type A soil and 20% impervious
I is the rainfall intensity = 0.2 inches per hour
A is the tributary area (see the Site Map drainage basins)
The rational method results are as follows:
Rational Method
Node Number
Tributary
Area', ac C
Intensity,
in/hr
Flow Rate,
cfs
22 1.73 0.87 0.2 0.30
28 3.41 0.87 0.2 0.59
31 0.80 0.87 0.2 0.14
36 0.39 0.87 0.2 0.07
41 0.10 0.34 0.2 0.01
'See the BMP Plan for the Major Drainage Basin Locations.
Summary of Water Quality Flow Rates Tributary to Vegetated Bioswales
The vegetated bioswale sizing requirements are determined from the tabulated flow rates and the
CASQA guidelines (see attached TC-30 data sheet). CASQA states that vegetated bioswales
should be analyzed with a Manning's n of 0.25, side slopes no steeper than 3:1, a channel slope
less than 2.5 percent, a bottom width of less than 10 feet, and a minimum hydraulic residence
time of 10 minutes. From the above table, the maximum flow to be treated in a bioswale will be
0.59 cfs. FlowMaster was used to analyze a bioswale with this flow, n=0.25, 3:1 side slopes, a 6-
foot bottom width, and a 1 percent longitudinal slope. The results are attached and show a flow
velocity of 0.26 feet per second. The minimum required bioswale length is determined by
multiplying the flow velocity by 10 minutes and applying the required conversion factor (60
seconds per minute). The minimum length is 156 feet. All of the proposed bioswales exceed this
length. Since all of the bioswales are sufficient for the greatest flow rate, the bioswales are
adequately sized.
Worksheet for Bioswale
Project Description
Friction Method Manning Formula
Solve For Normal Depth
Input Data
Rougliness Coefficient 0.250
Channel Siope 0.01000 ft/ft
Left Side Slope 3.00 ft/ft (H:V)
Right Side Slope 3.00 ft/ft (H:V)
Bottom Width 6.00 ft
Discharge 0.59 ms
Results
Normal Depth 0.33 ft
Flow Area 2.30 ft^
Wetted Perimeter 8.08 ft
Hydraulic Radius 0.28 ft
Top Width 7.97 ft
Critical Depth 0.07 ft
Critical Slope 2.28318 ft/ft
Velocity 0.26 ft/s
Velocity Head 0.00 ft
Specific Energy 0.33 ft
Froude Number 0.08
Flow Type Subcritical
GVF Input Data
Downstream Depth 0.00 ft
Length 0.00 ft
Number Of Steps 0
GVF Output Data
Upstream Depth 0.00 ft
Profile Description
Profile Headloss 0.00 ft
Downstream Velocity Infinity ft/s
Upstream Velocity Infinity ft/s
Normal Depth 0.33 ft
Critical Depth 0.07 ft
Channel Slope 0.01000 ft/ft
5/1/2014 10:49:45 PM
Bentley Systems, Inc. Haestad Methods ScflaMtojCBkMVIaster VSi (SELECTseries 1) [08.11.01.03]
27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page lof 2
San Diego Cbuntj' Hydrology Manual
Date: June 2003
Section:
Page:
3
6 of 26
Table 3-1
RUNOFF COEFFICIENTS FOR URBAN AREAS
Land Use Runoff Coefficient "C
Soil Type
NRCS Elements County Elements % MPER. A C D
Undisturbed Natural Terrain (Natural)
Low Density Residential (LDR)
Low Density Residential (LDR)
Low Density Residential (LDR)
Medium Density' Residential (MDR)
Medium Density Residential (MDR)
Medium Density Residential (MDR)
Mediimi Density Residential (MDR)
High Density Residential (HDR)
High Density Residential (HDR)
Commercial/Industrial (N. Com)
Commercial/Indtistrial (G. Com)
CommerciaLTndustrial (O.R Com)
Commercial/Industrial (Limited L)
Commercial/Industrial (General L)
Permanent Open Space
Residential, 1.0 DU/A or less
Residential, 2.0 DU/A or less
Residential 2.9 DU/A or less
Residential, 4.3 DU/A or less
Residential, 7.3 DU/A or less
Residential, 10.9 DU/A or less
Residential, 14.5 DUA or less
Residential, 24.0 DU/A or less
Residential, 43.0 DU/A or less
Neighborhood Commercial
General Commercial
Office Professional/Commercial
Limited Industrial
General Industrial
0*
10
20
25
30
40
45
50
65
80
80
85
90
90
95
0.20
0.27
I 0.34
0.38
0.41
0.48
0.52
0.55
0.66
0.76
0.76
0.80
0.83
0.83
0.87
0.25
0.32
0.38
0.41
0.45
0.51
0.54
0.58
0.67
0.77
0.77
0.80
0.84
0.84
0.87
0.30
0.36
0.45
0.54
0.57
0.60
0.69
0.78
0.78
0.81
0.84
0.84
0.87
0.35
0.41
0.46
0.49
0.52
0.57
0.60
0.63
0.71
0.79
0.79
0.82
0.85
0.85
0.87
*The values associated with 0% impervious may be used for direct calculation of the rimofT coefficient as described in Section 3.1.2 (representing the pervious runoff
coefficient, Cp, for the soil type), or for areas that will remain undisturbed in perpetuity. Justification must be given that the area will remain natural forever (e.g., the area
is located in Cleveland National Forest).
DU/A = dwelling units per acre
NRCS = National Resources (3onser^'ation Service
3-6
Soil Map—San Diego County Area, California
Map Scale: 1:6,040 if printed on A landscape (11" x 8.5") sheet
^—^— iMftprt;
N 0 50 100 SOIL GROUPS IN YELLOW 200 300
A a Feet
0 250 500 1000 1500
Map projection: Wfeb Mercator Comer coordinates: WCS84 Edge tics: LTTM Zone UN WGS84
USDA Natural Resources
Conservation Service
Web Soil Survey
National Cooperative Soil Sun/ey
5/1/2014
Page 1 of 3
Vegetated Swale TC-30
Design Considerations
• Tributary Area
• Area Required
• Slope
• Water Availability
Description
Vegetated swales are open, shallow channels with vegetation
covering the side slopes and bottom that collect and slowly
convey runoff flow to downstream discharge points. They are
designed to treat runoff through filtering bythe vegetation in the
channel, filtering through a subsoil matrix, and/or infiltration
into the underlying soils. Swales can be natural or manmade.
They trap particulate pollutants (suspended solids and trace
metals), promote infiltration, and reduce the flow velocity of
stormwater runoff. Vegetated swales can serve as part of a
stormwater drainage system and can replace curbs, gutters and
storm sewer systems.
California Experience
Caltrans constructed and monitored six vegetated swales in
southern California. These swales were generally effective in
reducing the volume and mass of pollutants in runoff. Even in
the areas where the annual rainfall was only about lo inches/yr,
the vegetation did not require additional irrigation. One factor
that strongly affected performance was the presence of large
numbers of gophers at most ofthe sites. The gophers created
earthen mounds, destroyed vegetation, and generally reduced the
effectiveness of the controls for TSS reduction.
Advantages
• If properly designed, vegetated, and operated, swales can
serve as an aesthetic, potentially inexpensive urban
development or roadway drainage conveyance measure with
significant collateral water quality benefits.
Targeted Constituents
Sediment •
0 Nutrients •
0 Trash •
0 Metals •
0 Bacteria •
0 Oil and Grease •
0 Organics
Legend (Removal Effectiveness)
• Low • High
• Medium
( AI IHIK.M \KIOK\nVAIH;
January 2003 California Stormwater BMP Handbook
New Development and Redevelopment
www.cabmphandbooks.com
1 of 13
TC-30 Vegetated Swale
• Roadside ditches should be regarded as significant potential swale/bufFer strip sites and
should be utilized for this purpose whenever possible.
Limitations
• Can be difficult to avoid channelization.
• May not be appropriate for industrial sites or locations where spills may occur
• Grassed swales cannot treat a very large drainage area. Large areas may be divided and
treated using multiple swales.
• A thick vegetative cover is needed for these practices to function properly.
• They are impractical in areas with steep topography.
• They are not effective and may even erode when flow velocities are high, if the grass cover is
not property maintained.
• In some places, their use is restricted by law: many local municipalities require curb and
gutter systans in residential areas.
• Swales are mores susceptible to failure if not properly maintained than other treatment
BMPs.
Design and Sizing Guideiines
• Flow rate based design determined by local requirements or sized so that 85% of the annual
runoff volume is discharged at less than the design rainfall intensity.
• Swale should be designed so that the water level does not exceed 2/3rds the height of the
grass or 4 inches, which ever is less, at the design treatment rate.
• Lon^tudinal slopes should not exceed 2.5%
• Trapezoidal channels are normally recommended but other configurations, such as
parabolic, can abo provide substantial water quality improvement and may be easier to mow
than designs with sharp breaks in slope.
• Swales constructed in cut are preferred, or in fill areas that are far enough from an adjacent
slope to minimize the potential for gopher damage. Do not use side slopes constructed of
fill, which are prone to structural damage by gophers and other burrowing animals.
• A diverse selection of low growing, plants that thrive under the specific site, climatic, and
watering conditions should be spedfied. Vegetation whose growing season corresponds to
the wet season are preferred. Drought tolerant vegetation should be considered especially
for swales that are not part of a regularly irrigated landscaped area.
• The width of the swale should be determined using Manning's Equation using a value of
0.25 for Manning's n.
2 of 13 California Stormwater BMP Handbook January 2003
New Development and Redevelopment
www.cabmphandbooks.com
Vegetated Swale TC-30
Construction/Inspection Considerations
m Include directions in the specifications for use of appropriate fertilizer and soil amendments
based on soil properties determined through testing and compared to the needs ofthe
vegetation requirements.
• Install swales at the time of the year when there is a reasonable chance of successful
establishment without irrigation; however, it is recognized that rainfall in a given year may
not be sufficient and temporary irrigation may be used.
• If sod tiles must be used, they should be placed so that there are no gaps between the tiles;
stagger the ends of the tiles to prevent the fonnation of channels along the swale or strip.
• Use a roller on the sod to ensure that no air pockets form between the sod and the soil.
• Wh«-e seeds are used, erosion controls will be necessary to protect seeds for at least 75 days
after the first rainfall of the season.
Performance
The Hterature suggests that vegetated swales represent a practical and potentiaUy effective
technique for controlling urban runoff quality. While limited quantitative performance data
exists for vegetated swales, it is known that check dams, slight slopes, permeaUe soils, dense
grass cover, increased contact time, and small storm events all contribute to successful pollutant
removal by the swale system. Factors deo^asing the effectiveness of swales indude compacted
soils, short runoff contact time, large storm events, fi-ozen ground, short grass heights, steep
slopes, and high runoff velocities and discharge rates.
Conventional vegetated swale designs have achieved mixed results in removing particulate
pollutants. A study performed by the Nationwide Urban Runoff Program (NURP) monitored
three grass swales in the Washington, D.C, area and found no significant improvement in urban
runoff quality for the pollutants analyzed. However, the weak performance of these swales was
attributed to the high flow velocities in the swales, soil compaction, steep slopes, and short grass
height.
Another project in Durham, NC, monitored the performance of a carefully designed artificial
swale that recdved runoff from a commerdal parking lot. The project tracked 11 storms and
concluded that particulate concentrations of heavy metals (Cu, Pb, Zn, and Cd) were reduced by
approximately 50 percent. However, the swale proved largely ineffective for removing soluble
nutrients.
The effectiveness of vegetated swales can be enhanced by adding chedc dams at approximately
17 meter (50 foot) increments along thdr length (See Figure 1). Hiese dams maximize the
retention time within the swale, decrease flow velodties, and promote particulate settling.
Finally, the incorporation of vegetated filter strips parallel to the top of the channel banks can
help to treat sheet flows entering the swale.
Only 9 studies have been conducted on all grassed channels designed for water quality (Table 1).
Hie data suggest relatively high removal rates for some pollutants, but negative removals for
some bacteria, and fair performance for phosphorus.
January 2003 California Stormwater BMP Handbook 3 of 13
New Developnnent and Redevelopment
www.cabmphandbooks.com
TC-30 Vegetated Swale
Table 1 Grassed swale pollutant removal efflclency data
Removal Efficiencies (% Removal)
Study TSS TP TN NO, Metals Bacteria Type
Caltrans 2002 77 8 67 66 83-90 -33 diy swales
Goldbei:g 1993 67.8 45 -31-4 42-62 -ICQ grassed chani^I
Seattle Metro and Washington
Department of Ecok^ 1992 60 45 --25 2-16 -25 grassed channel
Seattle Metro and Washington
Department of Eoobgy, 1992 83 29 --25 46-73 -25 grassed channel
Wangetal., 198X 80 ---70-80 diy swale
Donnan ^al., 1989 98 18 -45 37-81 -dry swale
Haiper, 1988 87 83 84 80 88-90 -diy swale
Kercher et aL, 1983 99 99 99 99 99 diy swak
Haiper, 1988. 81 17 40 52 37-69 -wetswak
Koon, 1995 67 39 -9 -35 to 6 wet swale
While it is difficult to distinguish between different designs based on the small amount of
avaiiable data, grassed channels generally have poorra- removal rates than wet and diy swales,
although some swales appear to export soluble phosphorus (Harper, 1988; Koon, 1995). It is not
clear why swales export bacteria. One explanation is that bacteria thrive in the warm swale
soils.
Siting Criteria
The suitability of a swale at a site will depend on land use, size of the area serviced, soil type,
slope, imperviousness ofthe contributing watershed, and dimensions and slope of the swale
system (Schuder et al., 1992). In general, swales can be used to serve areas of less than 10 acres,
with slopes no greater than 5 %. Use of natural topographic lows is encouraged and natural
drainage courses should be regarded as significant local resources to be kept in use (Young et al.,
1996).
Selection Criteria (NCTCOG, 1993)
• Comparable performance to wet basins
• limited to treating a few acres
• Availability of water during dry periods to maintain vegetation
• Suffident available land area
Research in the Austin area indicates that vegetated controls are effective at removing pollutants
even when dormant. Therefore, irrigation is not required to maintain growth during dry
periods, but may be necessary only to prevent the vegetation from dying.
4 of 13 California Stormwater BMP Handbook
New Devek>pmentand Redevek>pment
www.cabmphandbooks.com
January 2003
Vegetated Swale TC-30
The topography of the site should permit the design of a channd with appropriate slope and
cross-sectional area. Site topography may also dictate a need for additional structural controls.
Recommendations for longitudinal slopes range between 2 and 6 percent. Hatter slopes can be
used, if suffident to provide adequate conveyance. Steep slopes increase flow veiodty, decrease
detention time, and may require energy dissipating and grade check. Steep slopes also can be
managed using a series of check dams to terrace the swale and reduce the slope to within
acceptable limits. TTie use of check dams with swales also promotes infihration.
Additional Design Guidelines
Most of the design guidelines adopted for swale design spedfy a minimum hydrauHc residence
time of 9 minutes. "Hiis criterion is based on the results of a single study conducted in Seattle,
Washington (Seattle Metro and Washington Department of Ecology, 1992), and is not well
supported. Analysis ofthe data collected in that study indicates that pollutant removal at a
residence time of 5 minutes was not significantiy different, although there is more variability in
that data. Therefore, additional research in the design criteria for swales is needed. Substantial
pollutant removal has also been observed for vegetated controls designed solely for conveyance
(Barr^ et al, 1998); consequently, some flexibility in the design is warranted.
Many design guidelines recommend that grass be frequentiy mowed to maintain dense coverage
near the ground surface. Recent research (Colwell et al., 2000) has shown mowing fi^quency or
grass height has little or no effect on pollutant removal.
Summttry of Design Recommendations
1) The swale should have a length that provides a minimum hydraulic residence time of
at least 10 minutes. The maximum bottom width shoukl not exceed 10 feet unless a
dividing berm is provided. The depth of flow should not exceed 2/3rds the hdght of
the grass at the peak of the water quality design storm intensity. The channel slope
should not exceed 2.5%.
2) A design grass hdght of 6 indies is recommended.
3) Regardless of the recommended detention time, the swale shoukl be not less than
100 feet in length.
4) The width ofthe swale should be determined using Manning's Equation, at the peak
of the design storm, using a Manning's n of 0.25.
5) Hie swale can be sized as both a treatment facility for the design storm and as a
conveyance system to pass the peak hydraulic flows of the 100-year storm if it is
located "on-line." The side slopes should be no steeper than 3:1 (H:V).
6) Roadside ditches should be regarded as significant potential swale/buffer strip sites
and should be utiHzed for this purpose whenever possible. If flow is to be introduced
through curb cuts, place pavement slightiy above the elevation of the vegetated areas.
Curb cuts should be at least 12 inches wide to prevent clog^ng.
7) Swales must be vegetated in order to provide adequate treatment of runoff. It is
important to maximize water contact with vegetation and the soil surface. For
general purposes, select fine, close-growing, water-resistant grasses. If possible,
divert runoff (other than necessary irrigation) during the period of vegetation
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TC-30 Vegetated Swale
establishment. Where runoff diversion is not possible, cover graded and seeded
areas with suitable erosion control materials.
Maintenance
The useful life of a vegetated swale system is directiy proportional to its maintenance frequency.
If properly designed and regularly maintained, vegetated swales can last indefinitely. The
maintenance objectives for v^etated swale systems include keeping up the hydraulic and
removal effidency of the channel and maintaining a dense, healthy grass covw.
Maintenance activities should include periodic mowing (with grass never cut shorter than the
design flow depth), weed control, watering during drought conditions, reseeding of bare areas,
and clearing of debris and blockages. Cuttings should be removed from the channel and
disposed in a local composting fadlity. Accumulated sediment should also be removed
manually to avoid concentrated flows in the swale. The apphcation of fertilizers and pestiddes
should be minimal.
Another aspect of a good maintenance plan is repairing damaged areas within a channel For
example, if the channel develops ruts or holes, it should be repaired utilizing a suitable soil that
is properly tamped and seeded. The grass cover should be thick; if it is not, reseed as necessary.
Any standing water removed during the maintenance operation must be disposed to a sanitary
sewer at an approved discharge location. Residuals (e.g., silt, grass cutting) must be disposed
in accordance with local or State requirements. Maintenance of grassed swales mostly involves
maintenance of the grass or wetland plant cover. Typical maintenance activities are
summarized bdow:
• Inspect swales at least twice annually for erosion, damage to vegetation, and sediment and
debris accumulation preferably at the end of the wet season to schedule summer
maintenance and before major fall runoff to be sure the swale is ready for winter. However,
additional inspedion after periods of heavy runoff is desirable. The swale should be checked
for debris and litter, and areas of sediment accumulation.
• Grass hdght and mowing frequency may not have a large impad on pollutant removal.
Consequently, mowing may only be necessary once or twic« a year for safety or aesthetics or
to suppress weeds and woody vegetation.
• Trash tends to accumulate in swale areas, particularly along highways. The need for litter
removal is determined through periodic inspection, but litter should always be removed
prior to mowing.
• Sediment accumulating near culverts and in channels should be removed when it builds up
to 75 mm (3 in.) at any spot, or covers vegetation.
• Regularly inspect swales for pools of standing water. Swales can become a nuisance due to
mosquito breeding in standing water if obstructions develop (e.g. debris accumulation,
invasive vegetation) and/or if proper drainage slopes are not implemented and maintained.
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Vegetated Swale TC-30
Cost
Construction Cost
littie data is available to estimate the difference in cost between various swale designs. One
study (SWRPC, 1991) estimated the construction cost of grassed channels at approHmately
$0.25 per ft^ This price does not include design costs or contingendes. Brown and Schueler
(1997) estimate these costs at approximately 32 percent of construction costs for most
stormwater management practices. For swales, however, these costs wouki probably be
significantiy higher since the construction costs are so low compared with otho" practices. A
more realistic estimate would be a total cost of approximately $0.50 per ft", which compares
favorably with other stonnwater management pradices.
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TC-30 Vegetated Swale
Table 2 Swale Cost Estimate (SEWRPC, 1991)
UiMCost Total Cost
Compomnt Unit Extent Low Modwat* Ffigh Low Modwate High
Moblizitlon /
Domobilzition-Light
Smie 1 $107 $274 $441 $107 $274 $441
Site Prapamtkn
Ctearinfl'
Grubbintf
Gsneral
Bcavatiorf.
Laval and Tl*
Acre
Acre
Yd'
Yd=
0.S
0.25
372
1,210
$2200
$3,aoo
$2.10
$020
$3300
$5200
$3.70
$0.35
$6,400
$6,600
$5.30
$0SO
$1,100
«)S0
$781
$242
$1,000
$1,300
$1,376
$424
$2,700
$1,650
$1,072
$605
Sites DevBlopmont Salvaged Topsol
Seed, and Muk:h'..
Sod".
Yd"
Yd*
1,210
1,210
$0.40
$120
$1.00
$2.40
$1.60
$3.60
$«4
$1,452
$1,210
$2,004
$1338
$4356
Subtotal - ----$5,116 $0,3SB $13360
Contingencies Swale 1 25% 25% 25% $1278 $2,347 $3,415
-----$6,395 $11,735 $17,075
Source: ^EWRPC, 1991)
Note: MobifaBlonMemoblizatkin relars to theor^nizatkn and pteming InwDlvad In sstabCshlng a vegetafva swMle.
' Swale has a bottom width of 1.0 foot, a top width of 10 feet wth 1:3 side slopes, and a 1,000-foot length.
"Area cleared = (top width 10 feet) x swale length.
' Area grubbed = (top width x swale length).
'Vdume excavated = (0.67 x top width x swale depVh) x swale lengtfl (parabolic cross-sectton).
* Area tilled = (top width -^ Stswale deotfi^ x swale length (parabolic cross-sectton).
3(top width)
' Area seeded = area deared x 0.5.
• Area sodded = area cleared x 0.5.
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Vegetated Swale TC-30
Tabie 3 Estimated Maintenance Costs (SEWRPC, 1991)
Swale Size
(Depth and Top WldHi)
Component Unit Cost 1.5 Foot Depth, One-
Foot Bottom Width.
10-Foot Top WkRh
3-Foot Depth, 3-Foot
Bottom Width. 21-Foot
Top Width
Comment
Lawn McMfing $0.85/1,000 fp/mowing $0.14/linaarfoot $021/Inear foot Lawn malitanancB araaKtep
widtii-IOfeaQxtength. Mow
eight tln»s par yoar
General Lawn Cire $0.00/1,000 tP/year $0.18/Hnear foot $028/Inear foot Lawn maintaMnoa araa «(top
widtilOfeaQ xtongti
Swale tJebris and Litter
Removal
$0.10 / inear foot / year $0.10/Ineir foot $0.10/inear foot -
Gnas Raasedkig wlh
Mulch and FeiHizar
$0.30/yd* $031 /Unaarfoct $031 /Inear foot Araa rewagateted equate 1%
of lawn maintenance area per
year
PfOffnni AJii ii jatfHnn and
Swate Inspecfon
$ai5/lnaarft)at/yMr,
plus $25/ fwpocfon
$0.15/llnearfbot $0.15/Inav foot Inapact four timet per yaar
Total -$0.58/Hnear foot $0.75/Hnear foot -
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TC-30 Vegetated Swale
Maintenemce Cost
Caltrans (2002) estimated the expected annual maintenance cost for a swale with a tributary
area of approximate 2 ha at approximately $2,700. Since almost all maintaiance consists of
mowing, the cost is fundamentally a function of the mowing frequency. Unit costs developed by
SEWRPC are shown in Table 3. In many cases vegdated channels would be used to convey
runoff and would require periodic mowing as well, so there may be Httie additional cost for the
water quahty component. Since essentially all the adivities are related to vegetation
management, no spedal training is required for maintenance personnel.
References and Sources of Additional Information
Barrett, Michael E., Walsh, Patrick M., MaUna, Joseph F., Jr., Charbeneau, Randall J, 1998,
"Performance of vegdative controls for treating highway runoff," A^E Journal of
Environmental Engineering, Vol. 124, No. 11, pp. 1121-1128.
Brown, W., and T. Schueler. 1997. TTie Economics of Stormwater BMPs in the Mid-Atiantic
Region. Prepared for the Chesapeake Research Consortium, Edgewater, MD, by the Center for
Watershed Protection, EUicott City, MD.
Center for Watershed Protedion (CWP). 1996. Design of Stormwater Filtering Systems.
Prepared for the Chesapeake Research Consortium, Solomons, MD, and USEPA Region V,
Chicago, IL, by the Caiter for Watershed Protection, ElHcott City, MD.
Colwell, Shanti R., Horner, Richard R., and Booth, Derek B., 2000. Cftaraderizafion of
Performance Predictors and Evaluation of Mowing Practices in BiofUtration Swales. Report
to King County Land And Water Resources Division and others by Center for Urban Water
Resources Management, Department of Civil and Environmental Engineering, University of
Washington, Seattle, WA
Dorman, M.E., J. Hartigan, R.F. Steg, and T. Quasebarth. 1989. Retention, Detention and
Overland Mow for Pollutant Removal From Highway Stormwater Runoff. Vol. 1. FHWA/RD
89/202. Federal Highway Administration, Washington, DC.
Groldberg. 1993. Dayton Avenue Swale Biofiltration Study. Seattie Engineering Department,
Seattie, WA.
Harper, H. 1988. Effects of Stormwater Management Systems on Groundwater Quality.
Prepared for Florida Department of Environmental Regulation, Tallahassee, FL, by
Environmental Research and Design, Inc., Orlando, FL.
Kercher, W.C, J.C. Landon, and R. Massarelli. 1983. Grassy swales prove cost-effective for
water pollution control. Public Worics, 16: 53-55.
Koon, J. 1995. Evaluation of Water Quality Ponds and Swales in the Issaquah/East Lake
Sammamish Basins. King County Surface Water Management, Spittle, WA, and Washington
Department of Ecology, Olympia, WA.
Metzger, M. E., D. F. Messer, C. L. Bdtia, C. M. Myers, and V. L. Kramer. 2002. The Dark Side
Of Stormwater Runoff Management: Disease Vectors Assodated With Strudural BMPs.
Stormwater 3(2): 24-39.0akland, P.H. 1983. An evaluation of stormwater poUutant removal
10 of 13 Caiifomla Stomnwater BMP Handbook January 2003
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Vegetated Swale TC-30
through grassed swale treatment. In Proceedings of the International Symposium of Urban
Hydrology, Hydraulics and Sediment Control, Lexington, KY. pp. 173-182.
Occoquan Watershed Monitoring Laboratory. 1983. Final Report: Metropolitan Washington
Urban Runoff Project. Prepared for the Metropolitan Washington Coundl of Governments,
Washington, DC, by the Occoquan Watershed Monitoring Laboratory, Manassas, VA.
Pitt, R., and J. McLean. 1986. Toronto Area Watershed Management Strategy Study: Humber
River Pilot Watershed Project. Ontario Ministry of Environment, Toronto, ON.
Schueler, T. 1997. Comparative Pollutant Removal Capability of Urban BMPs: A reanalysis.
Watershed Protection Tediniques 2(2):379-383.
Seattie Metro and Washington Department of Ecology. 1992. Biofiltration Swale Performance:
Recommendations and Design Considerations. Publication No. 657. Water Pollution Control
Department, Seattle, WA.
Southeastern Wisconsin Regional Planning Commission (SWRPC). 1991. Costs of Urban
Nonpoint Source Water Pollution Control Measures. Technical report no. 31. Southeastern
Wisconsin Regional Planning (Commission, Waukesha, WI.
U.S. EPA, 1999, Stormwater Fad Sheet: Vegetated Swales, Report # 832-F-99-006
http://www.epa.f^ov/owm/mtb/vepwale.pdf. Office of Water, Washington DC.
Wang, T., D. Spyridakis, B. Mar, and R. Homer. 1981. Transport, Deposition and Control of
Heavy Metals in Highway Runoff. FHWA-WA-RD-39-10. University of Washington,
Department of Civil Engneering, Seattle, WA.
Washington State Department of Transportation, 1995, Highway Runoff Manual, Washington
State Department of Transportation, Olympia, Washington.
Welbom, C, and J. Veenhuis. 1987. Effects of Runoff Controls on the Quantity and Quality of
Urban Runoff in Two Locations in Austin, TX. USGS Water Resources Investigations Report
No. 87-4004. U.S. Geological Survey, Reston, VA.
Yousef, Y., M. Wanielista, H. Harper, D. Pearce, and R. Tolbert. 1985. Best Management
Practices: Removal of Highway Contaminants By Roadside Swales. University of Central
Florida and Florida Department of Transportation, Orlando, FL.
Yu, S., S. Barnes, and V. Gerde. 1993. Testing of Best Management Practices for Controlling
Highivay Runoff. FHWA/VA-93-R16. Virginia Transportation Research Council,
Charlottesville, VA.
Information Resoia-ces
Maryland Department of the Environment (MDE). 2000. Maryland Stormwater Design
Manual, www.mde.state.md.us/environment/wma/stormwatermanual. Accessed May 22,
2001.
Reeves, E. 1994. Performance and Condition of Biofilters in the Padfic Northwest. Watershed
Protection Techniques i(3):ii7-ii9.
January 2003 California Stormwater BMP Handbook 11 of 13
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TC-30 Vegetated Swale
Seattie Metro and Washington Department of Ecology. 1992. Biofiltration Sivale Performance.
Recommendatk)ns and Design Considerations. Publication No. 657. Seattle Metro and
Washington Department of Ecology, Olympia, WA.
USEPA 1993. Guidance Specifying Management Measures for Sources of Nonpoint Pollution in
Coastal Waters. EPA-840-B-92-002. U.S. Environmental Protection Agency, Office of Water.
Washington, DC.
Watershed Management Institute (WMI). 1997. Operation, Maintenance, and Management of
Stormwater Management Systems. Prepared for U.S. Environmental Protection Agency, Office
of Water. Washington, DC, bythe Watershed Management Institute, Ingleside, MD.
12 of 13 California Stormwater BMP Handbook January 2003
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Vegetated Swale TC-30
Provide for scour
proKctkm.
(a) Cro» section orswale with cluck dun.
Notation:
L sL«ngihol(wal«iinpoundnMntat»«p«rElwc)idanitft) lb) Dliii«niloa«l view ortwakimnoiiidmtBl art*.
DJ •D^efdwckdamdl)
Ss * BotlMn ttpt d swats (ft/fQ W •Teowldlhofcfcsc)idwi(ft) W, K Bottom wtdlh or ciMck dam (R)
2iu « Raio of liorizontal to VMUCSI Changs In swal* sMs slops (fVft)
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