CA: San Francisco: Low Impact Design Toolkit for Stormwater

L O W I M P A C T D E S I G N T O O L K I T i

Low Impact Design ToolkitW h a t w i l l y o u d o w i t h S a n F r a n c i s c o ’ s S t o r m w a t e r ?

i i U R B A N S T O R M W A T E R P L A N N I N G C H A R R E T T E ▪ S e p t e m b e r 2 0 0 7

L O W I M P A C T D E S I G N T O O L K I T i i i

i v U R B A N S T O R M W A T E R P L A N N I N G C H A R R E T T E ▪ S e p t e m b e r 2 0 0 7

Urban Watershed Planning Charrette

September 27, 2007

Bayside Conference Rooms, Pier 1

San Francisco, CA

Project Team:

San Francisco Public Utilities Commission

Arleen Navarret: Program Manager, WWPRD

Rosey Jencks: Project Manager

Leslie Webster: Design, Layout, and Illustrations

With research and editorial assistance from:

EDAW

Kerry McWalter

Megan Walker

Mark Winsor

Metcalf & Eddy

Scott Durbin

Kimberly Shorter

David Wood

Cover image:

Map of San Francisco drainage basins and historic hydrology

San Francisco Public Utilities Commission

Stormwater Management and Planning

1145 Market Street, 5th Floor

San Francisco, CA 94103

http://stormwater.sfwater.org

L O W I M P A C T D E S I G N T O O L K I T 1L O W I M P A C T D E S I G N T O O L K I T 1

Introduction 2

1. Eco-Roofs 6

2. Downspout Disconnection 10

3. Cisterns 14

4. Rain Gardens 18

5. Bioretention Planter s 22

6. Permeable Paving 26

7. Detention Basins 30

8. The Urban Forest 34

9. Stream Dayl ighting 38

10. Constructed Wetlands 42

Ta b l e o f C o n t e n t s

I n t r o d u c t i o nS u m m a r y

2 U R B A N S T O R M W A T E R P L A N N I N G C H A R R E T T E ▪ S e p t e m b e r 2 0 0 7

Thank you for participating in today’s Urban Watershed Planning

Charrette. A charrette is a collaborative session in which a group of

designers, planners or engineers draft a solution to a design problem.

Charrettes often take place in sessions in which larger groups divide

into sub-groups and then present their work to the full group as

material for future dialogue and planning. Charrettes serve as a way

of quickly drafting design solutions while integrating the aptitudes

and interests of a diverse group of people.

While there are many planning challenges facing San Francisco, this

charette will focus on integrating San Francisco’s urban stormwater

into its built environment using green stormwater management

technologies collectively known as “Best Management Practices”

(BMPs), “Low Impact Design” (LID) or “Green Infrastructure.”

The goal is to identify LID techniques that reduce the peak fl ows

and volumes of runoff entering the combined sewers. LID has the

potential to increase the system’s treatment effi ciency by delaying

and/or reducing the volumes of runoff fl owing to the combined

sewer, providing stormwater treatment, enhancing environmental

protection of receiving waters, and reducing the volume and

frequency of combined sewer overfl ows (CSOs). These technologies,

if properly designed can also provide auxiliary benefi ts that include,

beautifi cation, groundwater recharge, and habitat enhancement.

They can be placed into the existing urban fabric to give streets,

parks, plazas, medians and tree wells multiple functions.

L O W I M P A C T D E S I G N T O O L K I T 3

I n t r o d u c t i o n

Before San Francisco developed into the thriving city it is today, it consisted of a diverse range of habitats

including of oak woodlands, native grasslands, creeks, riparian areas, wetlands, and sand dunes. These

habitats provided food and forage for a wide range of plants, animals and insects. The natural hydrologic

cycle, working its way through each of these ecosystems, kept the air and water clean and recharged the

groundwater.

Today, much of the city is paved or built upon and plumbed with a combined sewer to convey stormwater

and wastewater. Former creeks have been diverted to the sewers and wastewater from homes and runoff

from rain events fl ow to treatment facilities where it is treated and discharged into the bay and the ocean.

During large storm events, the combined sewer system occasionally discharges partially treated fl ows

into surrounding water bodies and fl oods neighborhoods. In areas not served by the combined sewer,

stormwater discharges directly into water bodies untreated. A large quantity of impervious surfaces means

that there are very few places where infi ltration can occur and groundwater is depleted.

Pre-development conditions in San Francisco

Existing conditions in San Francisco

W h a t i s L o w I m p a c t D e s i g n ?



LID is a stormwater management approach that aims to re-create and mimic these pre-development

hydrologic processes by increasing retention, detention, infi ltration, and treatment of stormwater runoff at

its source. LID is a distinct management strategy that emphasizes on-site source control and multi-functional

design, rather than conventional pipes and gutters. Whereas BMPs are the individual, discrete water quality

controls, LID is a comprehensive, watershed- or catchment-based approach. These decentralized, small-

scale stormwater controls allow greater adaptability to changing environmental and economic conditions

than centralized systems.

LID has the potential to prevent the volume of combined sewer overfl ows and localized fl ooding in San

Francisco by slowing or intercepting stormwater before it reaches the sewer pipes. Roof runoff from buildings

can be intercepted by eco-roofs. The downspouts from roofs can be redirected to landscaped areas or cisterns

where the water can be stored and used during the dry seasons for irrigation or other non-potable uses.

Cisterns

Constructed wetlands

Eco-roofs

Street tree planting

Downspout disconnection

Stream daylighting

Bioretention planters

Rain gardens

Permeable paving

Detention basins

Potential LID additions to urban hydrology



Runoff from streets, parking lots and other paved areas can be directed to detention basins, or bioretention

planters where it is fi ltered and infi ltrated. An expanded urban forest, can also intercept and uptake excess

water. Historic creeks can be returned to the surface and diverted away from the sewer system. Together,

these approaches decrease increase the effi ciency of the sewer system and treatment facilities, reduce the

likelihood of fl ooding and sewer overfl ows, and recharge our local groundwater reserves.

To d a y ’ s G a m eFor the purposes of the Urban Watershed Planning Charrette each team will be asked to apply appropriate

stormwater BMPs within the boundaries of San Francisco’s four eastern catchments.

Each BMP performs specifi c functions such as delaying peak fl ows that reduce fl ooding and reducing

stormwater volumes that can be quantifi ed based on studies and modeling that has been calibrated for San

Francisco. This booklet introduces and describes the benefi ts and limitations of each BMP used in today’s

charrette. Each basin has a set of stormwater management goals for peak fl ow and volume reduction. Your

job is to identify appropriate locations for the BMPs described in this booklet to address surface water

management goals in your basin. Your team then calculates the benefi ts and costs and determines how

closely you meet your stormwater management goals and stay within your budget. Each turn will consist

of placing your BMP in the landscape and tallying the benefi ts and costs. Be sure to look for opportunities

for partnerships, multi-purpose projects and synergies between adjacent or nearby developments within the

neighborhood.

The following toolkit describes each BMP and provides specifi c details on the benefi ts and limitations,

design details, and the costs of implementation and maintenance.

E c o - R o o f sS u m m a r y


Green roofs, or eco-roofs, are roofs that are entirely or partially

covered with vegetation and soils. Eco-roofs have been popular in

Europe for decades and have grown in popularity in the U.S. recently

as they provide multiple environmental benefi ts. Eco-roofs improve

water quality by fi ltering contaminants as the runoff fl ows through

the growing medium or through direct plant uptake. Studies have

shown reduced concentrations of suspended solids, copper, zinc,

and PAHs (polycyclic aromatic hydrocarbons) from eco-roof runoff.

The engineered soils absorb rainfall and release it slowly, thereby

reducing the runoff volumes and delaying peak. Rainfall retention

and detention volumes are infl uenced by the storage capacity of the

engineered soils, antecedent moisture conditions, rainfall intensity,

and duration. A typical eco-roof has been found to retain 50 to 65

percent of annual rainfall and reduce peak fl ows for large rain events

(those exceeding 1.5 inches) by approximately 50 percent.

Eco-roofs fall under two categories: intensive or extensive. Intensive

roofs, or rooftop gardens, are heavier, support larger vegetation

and can usually designed for use by people. Extensive eco-roofs are

lightweight, uninhabitable, and use smaller plants. Eco-roofs can be

installed on most types of commercial, multifamily, and industrial

structures, as well as on single-family homes, garages, and sheds.

Eco-roofs can be used for new construction or to re-roof an existing

building. Candidate roofs for a “green” retrofi t must have suffi cient

structural support to hold the additional weight of the eco-roof, which

is generally 10 to 25 pounds per square foot saturated for extensive

roofs and more for intensive roofs.

Intensive eco-roof in Zurich, Switzerland

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E c o - R o o f s

C a s e S t u d y : To r o n t o , O n t a r i o

L i m i t a t i o n s

B e n e f i t sProvides insulation and can lower cooling costs for the building Extends the life of the roof – a green roof can last twice as long as a conventional roof, saving replacement costs and materials Provides noise reductionReduces the urban heat island effectLowers the temperature of stormwater run-off, which maintains cool stream and lake temperatures for fi sh and other aquatic lifeCreates habitat and increases biodiversity in the cityProvides aesthetic and recreational ameni-ties

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•Poor design or installation can lead to po-tential leakage and/or roof failureLimited to roof slopes less than 20 degrees (40 percent or a 5 in 12 pitch) Requires additional structural support to bear the added weight Potentially increased seismic hazards with increased roof weightLong payback time for installation costs based on energy savings May attract unwanted wildlifeInadequate drainage can result in mosqui-to breeding Irrigation may be necessary to establish plants and maintain them during extended dry periods Vegetation requires maintenance and can look overgrown or weedy, seasonally it can appear dead

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•Extensive eco-roof and detention basin in Germany

Extensive eco-roof in Seattle, WA

The City of Toronto initiated a green roof demonstration project in 2000 to “find solutions to overcome technical, financial and information barriers to the widespread adoption of green roof infrastructure in the marketplace.” In February 2006, the Toronto City Council approved the Green Roof Pilot Program, allocating $200,000 from Toronto water’s budget to encourage green roof construction. Subsidies of $10 per square meter ($0.93 per square foot) and up to a maximum of $20,000 will be available to private property owners for new and retrofit green roof projects. Additionally, the Green Roof Strategy recommended the following actions: use green roofs for all new and replacement roofs on city-owned buildings; use zoning and financial incentives to make green roofs more economically desirable; initiate an education and publicity program for green roofs; provide technical and design assistance to those in-terested in green roof building; identify a ‘green roofs resource person’ for each city division; develop a database of green roofs in the city; conduct and support ongoing monitoring and research on green roofs; add a green roof category to the Green Toronto Awards; and es-tablish partnerships with other institutions.

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E c o - R o o f s

D e s i g n D e t a i l sAn intensive eco-roof may consist of shrubs and small trees planted in deep soil (more than 6 inches)

arranged with walking paths and seating areas and often provide access for people. In contrast, an extensive

eco-roof includes shallow layers (less than 6 inches) of low-growing vegetation and is more appropriate

for roofs with structural limitations. Both categories of eco-roofs include engineered soils as a growing

medium, subsurface drainage piping, and a waterproof membrane to protect the roof structure.

Based on fi ndings from the City of Portland (2006) and the Puget Sound Action Team (2005), roofs with

slopes up to 40 degrees are appropriate for extensive eco-roofs, though slopes between 5 and 20 degrees are

most suitable (slope ration of 1:12 and 5:12). All eco-roofs are assembled in layers. The top layer includes the

engineered soils and the plants. The soil is a lightweight mix that includes some organic material. Under the

soil is a drainage layer that includes fi lter fabric to keep sediment from the soil in place and a core material

that stores water and allows it to drain off the roof surface. Next is the root barrier, which prevents the roots

from puncturing the waterproof membrane that lies below it, and fi nally there is the roof structure.

Growing medium (>2”)

Extensive eco-roof

Roof structure

Leaf screen GravelFilter fabric

Drainage and storage

Root barrier and waterproof

membrane

Layers:

C o s t a n d M a i n t e n a n c e

Most suitable slope of 5 to 20 degrees

A typical roof size of a single-family home in San Francisco is estimated at 1,500 square feet, while commercial

developments are closer to 10,000 square feet. The costs of eco-roofs vary widely depending on the size

and the type of roof but average $18 per square foot to install. Each eco-roof installation will have specifi c

operation and maintenance guidelines provided by the manufacturer or installer. Once an eco-roof is mature,

maintenance is limited to the vegetation. Intensive eco-roofs generally require more continued maintenance

than extensive roofi ng systems. In the fi rst few years watering, light weeding, and occasional plant feeding

will ensure that the roof becomes established. Routine inspection of the waterproof membrane and the

drainage systems are important to the roof longevity. Annual maintenance costs are estimated at $5.49 per

square foot, which includes aeration, plant and soil inspection, fl ow monitoring and reporting.

Drought tolerant plants

Overflow enters the gutter system


E c o - R o o f s

R e f e r e n c e sCity of Chicago. 2007 [cited 2007 Jun]. Chicago Green Roofs. Chicago, IL: Office of the Environment. Available from: http://www.artic.edu/webspaces/greeninitiatives/greenroofs/main.htm

City and County of San Francisco. 2006. Low Impact Development Literature Review. Prepared by Carollo En-gineers [Unpublished Memo].

City of Portland. 2007 [cited 2007 Jun]. Ecoroofs. Portland, OR: Office of Sustainable Development. Available from: http://www.portlandonline.com/osd/index.cfm?a=bbehci&c=ecbbd, (June 2007).

City of Portland. 2006 [cited 2007 Jul]. Ecoroof Questions and Answers. Portland, OR: Bureau of Environmental Services. Available from: http://www.portlandonline.com/shared/cfm/image.cfm?id=153098

City of Toronto. 2007 [cited 2007 Jun]. Greenroofs. Toronto, Canada. Available from: www.toronto.ca/greenroofs/ Hopper LJ (Editor). 2006. Living Green Roofs and Landscapes Over Structure. In Time Saver Standards for Land-scape Architecture, 2nd Edition, Hoboken. NJ: John Wiley and Sons, p. 367

Low Impact Development Center, Inc. 2007 [cited 2007 Jun]. Maintenance of Greenroofs. Available from: www.lid-stormwater.net/greenroofs/greenroofs_maintain.htm

Puget Sound Action Team (PSAT). 2005 [cited 2007 Jul]. Low Impact Development: Technical Guidance Manual for Puget Sound. Olympia, WA: Puget Sound Action Team and Washington State University Pierce County Exten-sion. Publication No. PSAT 05-03. Available from: www.psat.wa.gov/Publications/LID_tech_manual05/LID_man-ual2005.pdf

Portland’s Green Roof Initiative began in the mid 1990s, when the Bureau of Environmental Services (BES) started investigating the use of eco-roofs to control stormwater in their over-burdened combined sewer system. In 1999, the Housing Authority of Portland, in cooperation with BES, built a full-scale green roof on the Hamilton Apartments Building. The eco-roof cost $127,500 (unit cost of $15 per square foot of impervious area managed), with $90,000 of that granted by BES. Portland currently has about 80 eco-roofs built (roughly 8 acres) and another 40 in design or construction phases (roughly 10 acres).

C a s e S t u d y : C h i c a g o , I L

Chicago’s first green roof was a 20,000 square foot roof on the City Hall that was constructed in 2000. In 2005, the city launched its Green Roof Grant Program, awarding $5,000 each to 20 selected residential and small commercial buildings green roof projects (each with a footprint of less than 10,000 square feet). As of October 2006, more than 250 public and private green roofs were under design and construction in Chicago, totaling more than 1 million square feet of green roofs. The city also developed policies that encourage green roof development in Chicago. For example, all new and retrofit roofs in the city must meet a 0.25 solar reflectance, which green roofs are effective in meeting but traditional roofs are not. Also, the city offers a density bonus for roofs that have a minimum of 50 percent vegetative cover.

C a s e S t u d y : S a n F r a n c i s c o , C A

San Francisco has several completed and in-process eco-roof projects including: the new Academy of Sciences eco-roof which will be 2.5 acres or approximately 100,000 square feet; the Environmental Living Center in Hunter’s Point; 2 acre intensive eco-roof on North Beach Place; the Yerba Buena Gardens downtown which is mostly located above a parking ga-rage; and Portsmouth Square another public open space over a garage in Chinatown.

C a s e S t u d y : P o r t l a n d , O R

D o w n s p o u t D i s c o n n e c t i o nS u m m a r y

1 0 U R B A N S T O R M W A T E R P L A N N I N G C H A R R E T T E ▪ S e p t e m b e r 2 0 0 7

Downspout disconnection, also called roof drain diversion, involves

diverting rooftop drainage directly into infi ltration, detention, or

storage facilities instead of into the sewer. Rainwater can be harvested

from most types of rooftops. In areas where site conditions allow

infi ltration, roof drainage can be conveyed to drainless bioretention

planters, dry wells, or can be simply dispersed onto a rain garden,

lawn, or landscaped area. On sites that are not amenable to infi ltration,

roof drains can be routed into cisterns which are available in a range

of materials, sizes, and models, or under drained bioretention planters

that discharge to the sewer (see sections on Cisterns, Bioretention

Planters, and Rain Gardens). Roof rainwater harvesting can retain up

to 100 percent of roof runoff on site, discharging water in excess of

storage capacity fl owing to the combined sewer.

Downspouts on DaVinci Middle School in Portland, OR are directed to cisterns and a water garden

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L O W I M P A C T D E S I G N T O O L K I T 1 1

D o w n s p o u t D i s c o n n e c t i o n

B e n e f i t s L i m i t a t i o n s

Reduces runoff volume and attenuates peak fl owsMay decrease water usage through low-ered irrigation requirements Low installation costsLow maintenance requirementsLarge variety of implementation locations and scales

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Pre-fi ltration (such as a fi rst-fl ush diverter) is required if water is to be storedAdded complexity for buildings with inter-nally plumbed stormwater drainsSecondary system is required to deal with water after it leaves the downspout, such as a cistern or a rain garden

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The cost of roof downspout disconnection for existing buildings varies depending on how the roof is plumbed.

Professional installation of new gutters that direct water to another BMP can cost approximately $2,000 per

household. In addition to these plumbing costs, the cost of the paired BMP (rain garden, cistern, etc.) also

needs to be incorporated and is often the most important element in the system.

Maintenance of disconnected downspouts is relatively light. Regular monitoring should check for litter

in the gutter system to prevent clogs to the connected BMP that would reduce effi ciency of stormwater

capture. Checking to ensure that all parts of the system are operating properly is important. Additionally,

maintenance should be performed for the associated BMP as required.


Rainwater harvesting in Australia

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Current conditions

Disconnection options

Houses can be plumbed internally or externally

All roof water goes to the sewer

Cisterns can be placed above ground, below ground, or inside the house

Roof water can also be directed to a rain garden or other landscaped area where infiltration is feasible

Overflow goes to the sewer



R e f e r e n c e s

D e s i g n D e t a i l s


City of Portland. 2007 [cited 2007 Jun]. “Downspout Disconnection” Bureau of Environmental Services, Available from: http://www.portlandonline.com/bes/index.cfm?c=43081


Texas Water Development Board. 2005 [cited 2007 Jun]. “The Texas Manual on Rainwater Harvesting,” Third Edition. Austin, Texas. Available from: http://www.twdb.state.tx.us/publications/reports/RainwaterHarvesting-Manual_3rdedition.pdf

TreePeople. 2007 [cited 2007 Jun]. “Open Charter Cistern,” Available from:http://www.treepeople.org/vfp.dll?OakTree~getPage~&PNPK=150

The City of Portland included downspout disconnection in its Cornerstone Projects for reduc-ing the Combined Sewer Overflows (CSOs). The program began in 1995 and should meet its goals of reducing CSOs by 94% by 2011. Households and small commercial buildings within targeted neighborhoods voluntarily disconnect their roof drains from the sewer system and redirect the flow to either a rain garden or a cistern. Some areas of the city are excluded from the program because of inappropriate slopes and soils.

The city pays participants $53 per disconnection, or pays for a contractor to do the work. Community groups earn $13 for each downspout they disconnect. The program currently has 49,000 homeowners participating (about 4,400 disconnections per year from 1995 to 2006), and has removed approximately 1 billion gallons of stormwater per year from the combined sewer system. Disconnection costs around $0.01 per gallon of stormwater permanently re-moved from the sewer system. The new Clean River Rewards program offers stormwater dis-counts for property owners who control stormwater on site. This is expanding roof disconnec-tion to other parts of the city.


Downspout disconnection consists of diverting roof runoff to a storage or infi ltration BMP. In San Francisco,

many residential properties are plumbed directly to the sewer. Disconnecting a downspout either to collect

water requires installing a diverter that directs water from the pipes into the catchment system. Roof runoff

water is diverted to a storage or infi ltration system. Some pretreatment is required before the stormwater

can be stored to prevent clogging from leaf litter. The main considerations for designing downspout

disconnection and rainwater harvesting systems are: roof drainage confi guration, site conditions for a

storage tank, construction of new laterals, and desired rainwater uses.

C i s t e r n sS u m m a r y


Cisterns are a traditional technology employed in arid climates

to capture and store rainwater. Cisterns reduce the stormwater

volume by capturing rainwater for non-potable uses, such as

irrigation or fl ushing toilets. Suitable for a single house or an entire

neighborhood, cisterns range in size and may be placed above ground

or underground. Smaller, above ground cisterns, also called rain

barrels, are appropriate for single homes. Underground cisterns save

valuable space in urban locations and are more aesthetically pleasing

than surface cisterns but require pumps and other infrastructure in

order to reuse the water, making their maintenance and installation

more expensive. Large underground cisterns can be placed below

various types of open spaces such as parks or athletic fi elds.

The TreePeople Open Charter Elementary School Project retrofitted a paved schoolyard with stormwater treatment train to slow the flow of water, decrease local flooding events, and decrease the pollutant load. The treatment train consists of three components: a water treat-ment device; a 110,000 gallon cistern that stores rainwater and feeds the irrigation system; and a system of trees, vegetation and mulched swales that slow, filter and safely channel rainwater through the campus. The water capture and treatment project cost $500,000.

TreePeople also completed a project that installed a 250,000 gallon underground cistern in Coldwater Canyon Park, a 2,700 acre watershed retrofit in Sun Valley, in collaboration with the County Department of Public Works.

C a s e S t u d y : L o s A n g e l e s , C A


C i s t e r n s

C a s e S t u d y : C a m b r i a , C A

Cambia Elementary School captures and stores run-off water from the entire school site in a cistern lo-cated underneath ath-letic fields and uses the stored water to irrigate the fields year round. All of the stormwater on the 12 acre campus is captured and stored in large pipes that are located under 130,000 square feet of new ath-letic fields. Up to 2 million gallons of water can be stored.

L i m i t a t i o n sB e n e f i t s

Reduces runoff volume and attenuates peak fl owsMay decrease water usage if retained for irrigation purposes or toilet fl ushing Low installation costsLow maintenance requirements (for above ground cisterns)Low space requirements (for underground cisterns)Good for sites where infi ltration is not an op-tion

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Poor design, sizing, and siting can lead to potential leakage and/or failureStorage capacity is limited Provides no water quality improvementsLower aesthetic appeal (for above ground cisterns)Water reuse options limited to non-potable usesRequires infrastructure (pumps or valves) to use the stored water Inadequate maintenance can result in mos-quito breeding and/or algae production

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C o s t a n d M a i n t e n a n c eThe cost of cisterns varies depending on the size and type of cistern. According to the Low Impact Development

Center (2007), small residential rain barrels that connect to the existing gutters can be as inexpensive as

$225-$300 for 200-300 gallons of roof storage. A large scaled surface system costs approximately $40,000

for storage of 20,000 gallons of stormwater. Cisterns installed underground tend to have higher installation

and maintenance costs. Twice annual inspection is advisable to confi rm that all the parts are operable and

not leaking. Regular use of the water stored in cisterns between rain events is critical to ensure storage

is available for the next storm event. During the rainy season, it can be diffi cult to use the stored water if

because irrigation is generally not necessary. The stored water can be used during the rainy season for

other non-potable uses such as toilet fl ushing or fi re suppression.

Cistern at Cambria Elementary School

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C i s t e r n s


Water can be reused for non-potable uses

Leaf screens on gutters prevent clogging

First flush diverter

Overflow enters the combined sewer

Maintenance opening has screen to pre-vent mosquito and litter ac-cumulation

Sewer backflow pre-vention device

Pump

Proper design, siting, and sizing of cisterns are critical to ensure their full peak fl ow benefi ts. Stormwater

from roof downspouts is stored in the cistern until it is pumped out for use, or it reaches capacity and

exits through an overfl ow valve. Cisterns should be designed to outfl ow away from building foundations.

Above ground cisterns without a pumping mechanism must be elevated to allow proper water fl ow. Some

pretreatment is required to prevent clogging (e.g. leaf screens and fi rst-fl ush diverters) before the stormwater

can be stored to prevent clogging from leaf litter. Cisterns need to have access to air and light to avoid the

production of algae. Generally, cisterns have a raised manhole opening on the top that allows access for

maintenance and monitoring, which should be screened to prevent litter and mosquitoes from entering.

Options for rainwater reuse with a small-scale cistern


C i s t e r n s

R e f e r e n c e sLos Angeles County. 2002 [cited 2007 Jun]. Development Planning for Stormwater Management: A Manual For the Standard Urban Stormwater Mitigation Plan (SUSMP). Los Angeles, CA: Department of Public Works. Avail-able from: http://ladpw.org/wmd/NPDES/SUSMP_MANUAL.pdf

Low Impact Development Center, Inc. 2007 [cited 2007 May]. Cost of Rain Barrels and Cisterns. Sizing of Rain Barrels and Cisterns. Available from: http://www.lid-stormwater.net/raincist/raincist_cost.htm and http://www.lid-stormwater.net/raincist/raincist_sizing.htm

Rehbein Environmental Solutions, Inc. 2007 [cited 2007 May]. Cambria Elementary School. Available from: http://www.rehbeinsolutions.com/projects/cambria.html

Tom Richmond and Associates. 1999 [cited 2007 Jun]. Start at the Source: Design Guidance Manual for Storm-water Protection. San Francisco, CA: Bay Area Stormwater Management Agencies Association. Available from: http://scvurppp-w2k.com/pdfs/0203/c3_related_info/startatthesource/Start_At_The_Source_Full.pdf

TreeHugger. 2007 [cited 2007 Jun]. Seattle RainCatcher Pilot Program. Available from: http://www.treehugger.com/files/2005/03/seattle_raincat_1.php

Seattle Public Utilities (SPU) recently began their RainCatcher Pilot Program, which consists of three different types of rainwater collection systems. First is tight-line, which directs rainwater outflow to a pipe that flows under the yard, through weep holes in the sidewalk reducing volumes deposited in the storm drain via the curb. The second type, the tight-lined cistern, includes a cistern at the point of initial outflow that collects water during the storm event and releases it slowly into the underground pipes. Third, orifice cisterns include an operable valve, which can be opened during the wet season, discharging a small amount of water onto an adjacent permeable surface such as a lawn or rain garden to slow down flow, or closed to store up to 500 gallons of roof runoff, which can be used later for irrigation.

Each cistern costs the SPU a total of $1000 with $325 of that sum paying for the wholesale purchase of the cistern and $675 to installation and the SPU overhead. The SPU also sells rain barrels to households in the SPU’s direct service areas. The rain barrels cost $59 each for the SPU customers and $69 for non-customers. SPU is currently analyzing the impact of cisterns on the combined sewer system as part of a grant. SPU installs the RainCatcher at no cost to the participant, provides maintenance and support, and evaluates the performance over time.

C a s e S t u d y : S e a t t l e , W A

Mosaic above ground cistern in TennesseePH

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R a i n G a r d e n sS u m m a r y


Rain gardens are stormwater facilities integrated into depressed

landscape areas. They are designed to capture and infi ltrate stormwater

runoff. Rain gardens include water-tolerant plants in permeable soils

with high organic contents that absorb stormwater and transpire it

back into the atmosphere. Rain gardens slow and detain the fl ow of

stormwater thereby decreasing peak fl ow volumes. They also fi lter

stormwater before it either recharges into groundwater reserves

or is returned to the combined sewer system. The are also easily

customizable and provide both habitat and aesthetic benefi ts. Rain

gardens are a subset of bioretention planters except that they do

not typically include engineered soils or an under-drain connection.

Their form is regionally variable - in the south and mid-west they

are often less formal, whereas in the west they often take a more

formal shape (see photos to right) Therefore, rain gardens are more

appropriate for residential landscaping or low impervious areas with

well draining soils.

Rain gardens are often small and can be implemented by private

landowners in small yards. They function like larger scaled

bioretention projects with many of the same benefi ts and limitations.

Stormwater from downspouts can be directed through an energy

dissipater to rain gardens to store and treat water before it makes it

to the sewer system or a receiving water body.


R a i n G a r d e n s


Reduces runoff volume and attenuates peak fl owsImproves water qualityImproves air qualityImproves urban hydrology and facilitates groundwater recharge Low installation costsLow maintenance requirementsLow space requirementsCreates habitat and increases biodiversity in the cityProvides aesthetic amenityEasily customizable

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Depth to bedrock must be over 10 feet for infi ltration based systemsLimited to slopes less than 5 percent, slopes greater than 5 percent require check damsSeasonal fl uctuation in water quality ben-efi ts based on the plants’ ability to fi lter pol-lutants Vegetation requires maintenance and can look overgrown or weedy, seasonally it may appear deadSite conditions must be conducive to partial or full infi ltration and the growing of vegeta-tion or an underdrain is needed10 foot minimum separation from ground-water is required to allow for infi ltration, unless the Regional Water Quality Control Board approves otherwiseNon-underdrained systems must have mini-mum soil infi ltration rates, no contaminated soils, no risk of land slippage if soils are heav-ily saturated, and a suffi cient distance from existing foundations, roads, subsurface in-frastructure

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Formal rain garden in Portland, OR

Residential rain garden in Maplewood, MN

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2-6” Ponding depth

Optional 12” sand bed

Dense vegetation tolerant of wet and dry conditions

Water from 1 acre or less of roof, paved or landscaped surfaces

Berm

Native soils suitable for infiltration

Rain gardens should be placed at least 10 feet from building foundations and typically collect stormwater

from roofs, small paved surfaces, or landscaped surfaces. The shallow depression fi lls with a few inches

of water during a rain event. Either the soils must be suitable to infi ltrate the collected water or a more

intensive bioretention planter is recommended. Dense vegetation assists with the uptake of pollutants and

the absorption of the stormwater. Rain gardens require a minimum of a 5 percent slope and well-drained

soils to function correctly. Rain gardens are more appropriate for drainage areas less than 1 acre in size.

C o s t a n d M a i n t e n a n c eRain gardens are a relatively low cost and low maintenance stormwater management solution. A resident can

build and install their own rain garden in their front or back yard for very little money. The more elaborate

the garden, the more expensive installation becomes. The cost averages $8 per square foot and are typically

about 600 square feet, making the total cost approximately $5,000. Some level of annual maintenance is

required and is most intensive soon after construction until the garden matures. In the early spring and fall

the garden needs to be weeded and the mulch refreshed bi-annually to encourage healthy vegetation and

pollutant uptake. Mulch and compost improve the soil’s ability to capture water. In the fi rst season irrigation

may be necessary to establish the plants.

2-3” MulchMin. 10’ from downspout

Min. 4’ width

Typical rain garden



R e f e r e n c e sCity of Portland. 2007 [cited 2007 Jun]. Design Report: Rain Garden at Glencoe Elementary School. Portland, OR: Bureau of Environmental Services. Available from: http://www.portlandonline.com/shared/cfm/image.cfm?id=147510

Rain Garden Network. 2007 [cited 2007 Jun]. Local, On-Site Solutions for your Local Stormwater Issues. Available from: http://www.raingardennetwork.com/

Rain Gardens of West Michigan. 2007 [cited 2007 Jun]. Raingardens: Qualities and Benefits. Available from: www.Raingardens.org

City of Maplewood. 2007 [cited 2007 Aug]. Rain Water Gardens. Available from: http://www.ci.maplewood.mn.us/index.asp?Type=B_BASIC&SEC=%7BF2C03470-D6B5-4572-98F0-F79819643C2A%7D


Glencoe Elementary School in SE Portland installed a rain garden in their school grounds in 2003 to prevent neighborhood-wide combined sewer overflow problems by reducing runoff volumes while providing aesthetic and educational amenities to the schoolyard. The com-pleted rain garden is a 2,000 square foot infiltration and detention system that manages run-off from 35,000 square feet of impermeable surfaces with a total cost of $98,000.

Rain garden at Glencoe Elementary School

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B i o r e t e n t i o n P l a n t e r sS u m m a r y


Bioretention is the use of plants, engineered soils, and a rock sub-

base to slow, store, and remove pollutants from stormwater runoff.

Bioretention planters improve stormwater quality, reduce overall

volumes, and delay and reduce stormwater runoff peak fl ows.

Bioretention planters can vary in size from small, vegetated swales to

multi-acre parks; however, there are limits to the size of the drainage

area that can be handled. System designs can be adapted to a variety

of physical conditions including parking lots, roadway median strips

and right-of-ways, parks, residential yards, and other landscaped

areas and can also be included in the retrofi ts of existing sites.

Bioretention in Vancouver, BC


Portland’s Green Streets Program has successfully implemented many bioretention projects since it began in 2003 including bioretention curb-side planters constructed in the parking zone on either side of a street, just up stream form the storm drain inlets. One such project, NE Siskiyou Street, captures runoff from approximately 9,300 square feet of paved surfaces. Total project cost (excluding street and sidewalk repairs) was $17,000, or $1.83 per square foot of impervious area managed.

Mississippi Commons, a mixed-use development project incorporates an internal “Rain Drain” system, which collects stormwater from the 20,000 square foot roof area, which was previously connected to the combined sewer, and directs it to a courtyard planter. The planter removes an average of 500,000 gallons of stormwater annually from the combined sewer system and was designed as an architectural feature for the internal courtyard of the development.

New Columbia, an 82 acre redevelopment area, is Portland’s largest Green Streets site, with 101 vegetated pocket swales for biofiltration, 31 flow-through planter boxes and 40 infiltration dry wells. It used 80 percent less underground stormwater piping than a comparable tradi-tional development and 98 percent of the stormwater is retained on the site.

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B i o r e t e n t i o n P l a n t e r s

L i m i t a t i o n s

B e n e f i t s

Bioretention planter in Vancouver, BC

Reduces runoff volume and attenuates peak fl owsImproves water qualityImproves air qualityImproves urban hydrology and facilitates groundwater recharge Lowers the temperature of stormwater run-off, which maintains cool stream tempera-tures for fi sh and other aquatic life Reduces the heat island effectCreates habitat and increases biodiversity in the cityProvides aesthetic amenity

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Depth to bedrock must be more than 10 feet for infi ltration based systemsLimited to slopes less than 5 percent Seasonal fl uctuation in water quality ben-efi ts based on the plants’ ability to fi lter pol-lutants Vegetation requires maintenance and can look overgrown or weedy, seasonally it may appear deadSite conditions must be conducive to partial or full infi ltration and the growing of vegeta-tion10 foot minimum separation from ground-water is required to allow for infi ltration, unless the Regional Water Quality Control Board approves otherwiseMust have minimum soil infi ltration rates, no contaminated soils, no risk of land slippage if soils are heavily saturated, and a suffi cient distance from existing foundations, roads, subsurface infrastructure, drinking water wells, septic tanks, drain fi elds, or other ele-ments.

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C o s t a n d M a i n t e n a n c eThe installation costs for a bioretention planter in

San Francisco that would be capable of managing

stormwater from a half acre of land is $65,000. Such

a system would be approximately 2,200 square feet

making the cost $39 per square foot. Operations and

maintenance costs are estimated at $1,168 per acre

per year based on data from the City of Seattle and

adjusted for local factors. Like any landscape feature,

bioretention planters must be pruned, mulched and

watered until the pants are established. Semi-annual

plant maintenance is recommended including

the replacement of diseased or dead plants.

Other regular maintenance requirements include

trash removal and weeding. Because some of the

sediment that enters bioretention planters have the

propensity to crust on the soil surface, which limits

the porosity of the soils, some raking of the mulch

and soil surface may also necessary to maintain

high infi ltration rates.

Bioretention planter in Portland, OR

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Typical bioretention planter


Gravel curtain drain protects building foun-dation

Building

Stone used to dissipate energy

1% Min. Slope

During a storm event, runoff may temporarily pond in a bioretention depression as it percolates through the

mulch layer and engineered soil mix. Plant material provides water quality benefi ts as the roots and soils

uptake some pollutants from stormwater. Bioretention areas can either infi ltrate a portion of or all of the

stormwater runoff depending on site and soil conditions. A perforated underdrain pipe is recommended,

in areas with poorly drained native soils. In areas where infi ltration is facilitated by well-drained soils,

bioretention planters can be designed without the underdrain, much like rain gardens, to infi ltrate the

stormwater. The primary considerations in siting a bioretention planter are space availability, suitability of

the soils for infi ltration, rates, depth to groundwater, depth to bedrock, and slope.

Bioretention planters should be designed with a maximum of 6 inches of ponding on the top surface, which

includes mulch and wet-tolerant vegetation. A minimum of 4 feet of engineered soils and a gravel drainage

layer beneath the vegetation allow for proper infi ltration. To ensure proper functioning, the maximum

drainage area for a single bioretention cell is 5 acres with a minimum of 5 feet of head to ensure drainage.

Installing an energy dissipater (i.e. grass channel, rip rap, etc.) to slow the water velocity at the entrance to

the bioretention area will minimize the potential for erosion or vegetation damage.

Infiltration where feasiblePerforated pipe in gravel jacket

Optional sand filter layerMin. 4’ engineered soils

2-3” Mulch

Max. 6” ponding depth

Curb cut




Bioretention.com. 2007 [cited 2007 May]. Components. Design Details. Maintenance. Retrieved at www.biore-tention.com

City of Portland. 2007 [cited 2007 May]. Sustainable Stormwater Management Green Solutions: Stormwater Swales and Planters. Portland, OR: Bureau of Environmental Services. Available from: http://www.portlandon-line.com/shared/cfm/image.cfm?id=123781


City of Seattle. 2007 [cited 2007 May]. High Point Development: Healthy Environment. Seattle, WA: Seattle Hous-ing Authority. Available from: http://www.seattlehousing.org/Development/highpoint/healthyenviro.html


R e f e r e n c e s

2-3” Mulch

Max. 6” ponding depth

Infiltration where feasible Street-side bioretention planter based on Portland’s Green Streets

‘Parking egress zone:’ concrete pav-ers over sand

Perforated pipe in gravel jacket

Optional sand filter layerMin. 4’ engineered soils

Curb cut



Seattle Public Utilities’ (SPU) Natural Drainage Program was established in 1999. Street Edge Alternatives (“SEA Streets”) was SPU’s pilot natural drainage systems project. A residential block was retrofitted with a narrower, meandering street with flat curbs, lined with vegetated swales and amended soils on both sides. The swales detain stormwater from the street right-of-way and properties along the east side of the street, totaling 2.3 acres. The project cost was $850,000, making the cost per square foot of drainage area managed, not including the replacement of sidewalks or streets, between $3 and $5.

The second project, the High Point Redevelopment Project, used swales, permeable pave-ment, downspout disconnection, rain gardens, tree preservation, and bioretention to man-age runoff from 129 acres of mixed income housing. Construction began in 2003 and will be complete in 2009.

P e r m e a b l e P a v i n gS u m m a r y


Permeable pavement refers to any porous, load-bearing surface that

allows for temporary rainwater storage prior to infi ltration or drainage

to a controlled outlet. The stormwater is stored in the underlying

aggregate layer until it infi ltrates into the soil below or is routed to the

conventional conveyance system. Research and monitoring projects

have shown that permeable pavement is effective at reducing runoff

volumes, delaying peak fl ows, and improving water quality. Several

types of paving surfaces are available to match site conditions,

intended use, and aesthetic preferences. Permeable pavement

systems are most appropriate in areas with low-speed travel and light-

to medium-duty loads, such as parking lots, low-traffi c streets, street-

side parking areas, driveways, bike paths, patios, and sidewalks.

Infi ltration rates of permeable surfaces decline over time to varying

degrees depending on design and installation, sediment loads, and

consistency of maintenance.

Top: Permeable pavers a county lane in Vancouver, BCBottom: Permeable pavers in Germany

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P e r m e a b l e P a v i n g

L i m i t a t i o n sB e n e f i t sReduces runoff volume and attenuates peak fl owsImproves water quality by reducing fi ne grain sediments, nutrients, organic matter, and trace metalsReduces the heat island effectImproves urban hydrology and facilitates groundwater recharge Provides noise reduction

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Limited to paved areas with slow and low traffi c volumes Require periodic maintenance to maintain effi ciencyEasily clogged by sediment if not correctly installed and maintainedMore expensive than traditional paving sur-faces (although these costs can be offset by not needing to install a curb and gutter drainage system)Depth to bedrock must be greater than 10 feet for infi ltration based systemsDiffi cult to use where soil is compacted: infi l-tration rates must be at least 0.5 inches per hour

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The estimated installation costs of permeable paving

average $10 per square foot. One of the biggest

maintenance concerns is sediment clogging the

pores in the paving. For this reason, sediment should

be diverted from the surface and the surface needs

to be cleaned regularly to ensure proper porosity.

Once a year, the paving needs to be inspected and

tested to determine if it is clogged, which can be

done in 5 minutes with a stopwatch and a sprinkler.

Also, broken or damaged pavers need to be removed

and replaced. Maintenance consisting of vacuum

sweeping and pressure washing (as long as water

supply is not limited) has an estimated cost, based

on local labor costs, of $6,985 per acre per year.


The Seattle High Point Project showcases the first “porous pavement” street in Washington and serves as a testing ground for its use elsewhere. Porous concrete pavement was used on two city street sections, half of the public sidewalks, and for parking and access on many of the private properties. Porous pavement sidewalks and gravel-paved driveways are em-ployed at key sites to help reduce paved or impervious surfaces and infiltrate stormwater.

Load-bearing turf block in Vancouver, BC

Porous asphalt in Portland, OR

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Optional geotextile fabric


Permeable pavers

Perforated pipe flows to sewer

Permeable paving consists of a series of layered elements that allows stormwater to penetrate through the

paved surface, be stored, and then either infi ltrate into the soils or be slowed and conducted to the sewer

system. The top layer is the permeable paving material, below which is a gravel or sand bedding that fi lters

large particulates. If a storm event exceeds the capacity of the storage layer, a perforated overfl ow pipe

directs excess water to the storm sewer.

Common permeable paving systems include the following:

Permeable hot-mix asphalt: Similar to standard hot-mix asphalt but with reduced aggregate fi nes

Open-graded concrete: Similar to standard pavement, but without the fi ne aggregate (sand and fi ner) and with

special admixtures incorporated (optional)

Concrete or plastic block pavers: Either cast-in-place or pre-cast blocks have small joints or openings that can

be fi lled with soil and grass or gravel

Plastic grid systems: Grid of plastic rings that interlock and are covered with soil and grass or gravel

Permeable pavements are best suited for runoff from impervious areas. If non-paved areas will drain to

pervious pavements, it is important to provide a fi ltering mechanism to prevent soil from clogging the

pervious pavement. Soil infi ltration rates must also be at least 0.5 inches per hour to function properly.

Site conditions (including soil type, depth to bedrock, slope, and adjacent land uses) should be assessed to

determine whether infi ltration is appropriate, and to ensure that excessive sediment and pollutants are not

directed onto the permeable surfaces.

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Pavers with open spaces filled with gravel or sand

Subgrade Infiltration where feasible

Storage layer: coarse gravel

Filter layer: fine gravel or sand



Los Angeles County. 2002 [cited 2007 Jun]. Development Planning For Stormwater Management: A Manual For The Standard Urban Stormwater Mitigation Plan (SUSMP). Los Angeles, CA: Department of Public Works. Avail-able from: http://ladpw.org/wmd/NPDES/SUSMP_MANUAL.pdf

New York City. 2005 [cited 2007 Jun]. High Performance Infrastructure Guidelines: Best Practice for the Public Right-of-Way. New York, NY: Department of Design and Construction. Available from: http://www.designtrust.org/pubs/05_HPIG.pdf


Tom Richmond and Associates. 1999 [cited 2007 Jun]. Start at the Source: Design Guidance Manual for Storm-water Protection San Francisco, CA: Bay Area Stormwater Management Agencies Association. Available from: http://scvurppp-w2k.com/pdfs/0203/c3_related_info/startatthesource/Start_At_The_Source_Full.pdf

R e f e r e n c e s


In 2004, the Bureau of Environmental Services paved three blocks of streets in the Westmore-land neighborhood with permeable pavement that allows rainwater to infiltrate. They paved about 1,000 feet of street surface with interlocking concrete blocks. One block of SE Knapp Street was paved curb-to-curb with permeable blocks. The other streets – SE Rex Street and SE 21st Avenue – were paved with a center strip of standard asphalt and permeable pave-ment in both curb lanes. A fourth block was paved curb-to-curb with standard asphalt. New methods and equipment – like vacuum sweepers – will be used to clean the streets and keep them free of weeds and debris. The construction cost was $412,000.

In summer 2005, the City of Portland completed paving four blocks of North Gay Avenue. This is a pilot project to learn how well different pavement materials handle stormwater and hold up as a street surface. For this reason, the city installed four different pavement combinations on Gay including porous concrete curb-to-curb; porous concrete in both curb lanes, stan-dard concrete in the middle travel lanes; porous asphalt curb-to-curb; and porous asphalt in the curb lanes only. The results of this test are not yet available.

Permeable pavement

Storage layer: coarse gravel

Perforated pipe flows to sewer

Filter layer: fine gravel or sand

Porous asphalt

Optional geotextile fabric

Subgrade Infiltration where feasible

D e t e n t i o n B a s i n sS u m m a r y


Detention basins are temporary holding areas for stormwater that

store peak fl ows and slowly release them, lessening the demand on

treatment facilities during storm events and preventing fl ooding.

Generally, detention basins are designed to fi ll and empty within 24

to 48 hours of a storm event and therefore could reduce peak fl ows

and combined sewer overfl ows. If designed with vegetation, basins

can also create habitat and clean the air whereas underground basins

do not. Surface detention basins require relatively fl at slopes. Four

types of detention basins are detailed below.

1. Traditional dry detention basins simply store water and gradually

release it into the system. Dry detention basins do not provide water

quality benefi ts, as they only detain stormwater for a short period of

time. Maintenance requirements are limited to periodic removal of

sediment and maintenance of vegetation. Dry detention basins are

good solutions for areas with poorly draining soils, high liquefaction

rates during earthquakes, or a high groundwater table, which limit

infi ltration.

2. Extended dry detention basins are designed to hold the fi rst fl ush

of stormwater for a minimum of 24 hours. Extended dry detention

basins have a greater water quality benefi t than traditional detention

basins because the extended hold time allows the sediment particles

to settle to the bottom of the pond. Collected sediments must be

periodically removed from the basin to avoid re-suspension.

3. Underground detention basins are well suited to dense urban

Stormwater wet pond in Berlin, Germany (cont.)

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D e t e n t i o n B a s i n s


Reduces runoff volume and attenuates peak fl owsImproves water quality by removing some particulate matter, sediment and buoyant materials (extended dry detention only)Reduces fl oodingLow maintenance costs Low space requirements (underground only)Good for sites where infi ltration is not an op-tionMay create habitat and increases biodi-versity in the city (multi-purpose detention only)May provide open space and aesthetic amenity (multi-purpose detention only)

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locations where land costs make surface options unfeasible. Underground detention basins work best if

partnered with an ‘upstream’ BMP that provides water quality benefi ts, like bioretention planters, if water

is not returned to the combined sewer overfl ow. Underground detention basins need to be on a slight slope

to facilitate drainage but should not be placed on steep slopes because of the threat of erosion. They can

be placed under a roadway, parking lot, or open space and are easy to incorporate into other right-of-way

retrofi ts.

4. Multi-purpose detention basins are detention basins that have been paired with additional uses such as

large play areas, dog parks, athletic fi elds or other public spaces. Generally detention basins are only fi lled

with water during storm events and can act as open spaces during dry weather.

Big Creek multi-purpose detention basin in Roswell, GA

Detention basin in Seattle, WA

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Maintenance hatchParking lot

Surface detention basins generally consist of a depressed area of land, or an area that is surrounded by

built up berms, where stormwater is directed and stored during storm events. There is a spillway to allow

fl ows that exceed the designed capacity of the system to reenter the sewer system. Detentions basins

should not be constructed within 25 feet of existing structures and new structures cannot be built on top of

them. Detention basin sizing is important because if runoff exceeds the holding capacity, excess water is

discharged back into the normal conveyance system. Underground detention fi lls up during rain events and

stores the water until it can drain back into the combined system.

Sediment

Traditional dry detention basin

Extended Dry Detention Basin

Underground detention basin

Outflow

Overflow drains to sewer Trash racks

Designed storm elevation

Designed storm elevation

Sediment

Erosion protection

Berm

Min. 25’ from structuresOverflow spillway

Rip-rap, fabric sock, or trash rack filter sediment form outflow

Erosion Protection

Max. 4:1 slopeOutflow

Low-flow orifice



California Stormwater Quality Association. 2003 [cited 2007 Jun]. Extended Detention Basin. In Stormwater Best Management Practice Handbook. Available from: http://www.cabmphandbooks.com/Documents/Develop-ment/TC-22.pdf

City of Seattle. 2000 [cited 2007 Jun]. Flow Controls Technical Requirements Manual. Seattle, WA: Department of Planning and Development. Available from: http://www.seattle.gov/dclu/codes/Dr/DR2000-26.pdf

Frost-Kumpf, HA. 1995 [cited 2007 Jun]. Reclamation Art: Restoring and Commemorating Blighted Landscapes. Available from: http://slaggarden.cfa.cmu.edu/weblinks/frost/FrostTop.html

Los Angeles County. 2002 [cited 2007 Jun]. Development Planning For Stormwater Management: A Manual For The Standard Urban Stormwater Mitigation Plan (SUSMP). Los Angeles, CA: Department of Public Works. Avail-able from: http://ladpw.org/wmd/NPDES/SUSMP_MANUAL.pdf

New York City. 2005 [cited 2007 Jun]. High Performance Infrastructure Guidelines: Best Practice for the Public Right-of-Way. New York, NY: Department of Design and Construction. Available from: http://www.designtrust.org/pubs/05_HPIG.pdf

R e f e r e n c e s

C a s e S t u d y : R o s w e l l , G A

The Big Creek Park Demonstration Project includes a multi-purpose detention area to store and treat runoff from a suburban neighborhood to protect a downstream wetland. The multi-purpose pond is used for soccer and recreation during dry periods and fills with water during rain events. Under the sod surface, there is a layer of engineered soil and mixed rock to improve drainage. The feature includes an outlet structure that ensures drainage within 24 hours to prevent damage to the sod. The total storage volume provided in the 1.7 acre multi-purpose detention pond is 4.76 acre-feet of stormwater.

C o s t a n d M a i n t e n a n c eTypical construction, design and permitting costs for an above ground,

extended detention basin are estimated at $41,000 for a one-tenth of

an acre basin, which can manage stormwater from 2 acres of land.

Detention basins require periodic maintenance and monitoring of

conditions to make sure that sediment accumulation is not a problem.

Underground detention basins must have a maintenance access hatch

that allows system monitoring. Periodically, sediment may need to be

removed to maintain the continued effi ciency of the system.

C a s e S t u d y : K e n t , W A

Mill Creek Canyon Stormwater Detention Dam is a multi-purpose detention basin located in Kent, a suburb of Seattle. Built in 1982, this 2.5 acre portion of a larger park can store up to 18 acre-feet of stormwater from 2.2 square miles of pervious and impervious urban surfaces uphill of the site. A land artist, Herbert Bayer, participated in the design of the park and sculp-tural earthworks were used to capture the water in spirals and between mounds that park visitors can traverse using paths and bridges. The project was developed in collaboration between the King County Arts Council and the Kent Parks Department

Detention basin in Seattle, WA

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T h e U r b a n F o r e s tS u m m a r y


Urban forests made up of publicly and privately maintained street

and park trees offer a myriad of benefi ts to the urban environment,

including stormwater mitigation. Trees intercept rainfall before it

reaches the ground and uptake the water that does reach the ground,

thereby reducing runoff volume and peak fl ows. Also, their roots

and organic leaf litter help to increase soil permeability. In addition

to stormwater benefi ts, trees remove particulates, cool the air and

beautify the city.

In 2003, the City of San Francisco Street Tree Resource Analysis

completed by the Center for Urban Forest Research, reported that

approximately 56 percent of all street-tree planting sites (sidewalk

pavement cuts designated for street tree planting) in the city are

unplanted, ranging from 28 percent in affl uent districts to 74 percent

in under served districts (e.g., Bayview-Hunters Point). These

unplanted areas present an opportunity not only for signifi cant

stormwater reductions, but also for addressing environmental justice

issues. The analysis found that San Francisco’s street trees reduce

stormwater runoff by an estimated 13,270,050 cubic feet (99 million

gallons) annually, for a total value to the city of $467,000 per year. On

average, street trees in San Francisco intercept 1,006 gallons per tree

annually. Certain tree species were better at reducing stormwater

runoff than others. Those demonstrating the highest stormwater

reduction benefi ts were blackwood acacia, Monterey pine, Monterey

cypress, and Chinese elm.


T h e U r b a n F o r e s t

Reduces runoff volume and attenuates peak fl owsImproves water qualityImproves air qualityProvides shade and therefore may lower energy costs for buildings Decreases soil erosion in parks and open spaces Reduces the heat island effectCreates habitat and increases biodiversity in the cityProvides aesthetic amenityCan contribute to carbon sequestration

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L i m i t a t i o n sRequires adequate space for planting Moderate installation and maintenance costsIn some San Francisco neighborhoods, cul-tural preferences have lead to disagree-ment about aesthetic value of street treesPotential confl icts with overhead wires Potential to damage underground infra-structure with rootsNon-ideal growing conditions can cause stunting, disease or premature death

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C a s e S t u d y : L o s A n g e l e s , C A

Million Trees LA is a plan to plant 1 million trees in Los Angeles over the next several years. In the first year of the program, approximately 44,378 trees have been planted. The Los Angeles Department of Water and Power (LADWP) “Trees for a Green LA” program, in con-junction with Million Trees LA, offers free shade trees to residential electric customers who attend an online or neighborhood workshop on how to plant and care for their tree. Non-residential (Home Owners Associations or apartment owners) can receive free shade trees by completing the workshop or certifying that a profes-sional landscape contractor will plant and maintain the trees.

Trees lining a grassy swale in Germany

Trees lining a street and bioreten-tion planter in Portland, OR

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Street trees in San Francisco

A typical street tree planted in an urban location

helps manage stormwater in a number of ways.

First, water is stored in the canopy of the tree and

is later evaporated into the atmosphere. Second,

the tree pit provides a location in the paved

sidewalk for water to infiltrate or be stored in the

soil for later use by the tree or other vegetation.

The leaf litter and other organic material as

well as the roots contribute to the soil’s ability

to hold and infiltrate water. Trees also transpire

water from the soil into the atmosphere during

their process of photosynthesis. Tree selection

is important to maximize the benefits of each

tree as a part of the urban forest. Tree pits can

be integrated into a bioretention planter that

provides additional stormwater management

benefits. The City of Portland has successfully

implemented bioretention planters in conjunction

with street trees.

Rain is intercepted by the canopy and evapo-rates

Roots and organic mate-rial absorb water

Water is transpired back to the atmo-sphere

Tree grate

Tree pit

Compacted soil

Concrete sidewalk

Perforated pipe drains to sewer

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Street trees on Grove Street in San Francisco



R e f e r e n c e s

C a s e S t u d y : Wa s h i n g t o n , D C

Maintenance of street trees in San Francisco is carried

out by a combination of the city, private residents, and

non-profi t organizations such as Friends of the Urban

Forest. The cost for the city to maintain a street tree is

estimated to be $150 per tree per year. The fi rst three

years of the tree’s life are generally more expensive than

the years that follow because trees require irrigation

until established.

The cost to install trees in San Francisco varies

depending on the species but averages $750 to $1,000

for a 24 inch box tree, which is the most common size

of tree planted in San Francisco. In areas where risk

of damage to the young trees is high, such as Market

Street, 36 inch box trees are installed instead with costs

closer to $1,450 per tree.



City and County of San Francisco. 2007 [cited 2007 Jun]. The Benefits of an Urban Forest. San Francisco, CA: SF Environment. Available from: http://www.sfenvironment.com/aboutus/openspaces/urbanforest/benefits.htm

Friends of the Urban Forest. 2007 [cited 2007 Jun]. Available from: http://www.fuf.net/

Maco SE, McPheson EG, Simpson JR, Peper PJ, Xiao Q. 2003 [cited 2007 Jun]. City of San Francisco, California: Street Tree Resource Analysis. Davis, CA: Center for Urban Forest Research USDA Forest Service Pacific Southwest Research Station. Available from: http://www.fs.fed.us/psw/programs/cufr/products/cufr427_SFSTAFinal.pdf

Maryland Department of Natural Resources. 2007 [cited 2007 Jun]. The Benefits of Urban Trees. Available from: http://www.dnr.state.md.us/forests/publications/urban.html

Million Trees LA. 2007 [cited 2007 Jun]. Available from: http://www.milliontreesla.org/

South Carolina Forestry Commission. 2007 [cited 2007 Jun]. The Benefits of Urban Trees. Available from: http://www.state.sc.us/forest/urbben.htm

Since 1999, the Urban Forestry Administration (UFA) has planted 14,500 trees (or approximate-ly 2,400 trees per year). The UFA has developed relationships with local public/private partner organizations such as Green Spaces for DC, the Casey Trees Endowment Fund, Community Resources, and others, who are currently involved in tree-related work within DC’s neighbor-hoods. According to the Mayor’s office, over the last three years the tree budget of the UFA has been boosted to $7 million per year. The UFA is removing dead trees and old stumps, while every year trimming 15,000 to 17,000 trees and planting 4,000 new trees.

Trees near a grassy swale in Berlin, Germany

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S t r e a m D a y l i g h t i n gS u m m a r y


Stream daylighting refers to projects that uncover and restore

streams, and rivers that were previously buried in underground

pipes and culverts, covered by decks, or otherwise removed from

view. Stream diversion, more akin to sewer separation than to stream

restoration, involves re-routing an underground stream to discharge

directly into another water body rather than being added to the load

on the combined sewer system. The volume of infl ow that can be

diverted from the sewer system will be specifi c to the local hydrology

and therefore cannot be generalized. Several projects, however,

demonstrate that stream diversion can be effective at reducing wet-

weather fl ows to combined sewers.

The City of San Francisco has several historic creek channels that run

clean water through culverts to treatment plants and then to the bay

and ocean. Diverting these historical streams to a separate system

can decrease demand on the treatments facilities. Daylighting creeks

also has the additional benefi ts of partially repairing the natural

hydrologic cycle, increasing capacity in drainages with undersized

pipes, slowing the rate of peak fl ows, providing habitat, creating

recreational facilities, and providing a site for ongoing environmental

awareness and education.


Small, open runnel in Kolding, Denmark

The City of Portland is currently installing new pipelines to divert Tanner Creek directly into the Willamette River instead of into the combined sewer system. The finished project is expected to remove approximately 165 million gallons of stormwater annually from the combined sew-er system.

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S t r e a m D a y l i g h t i n g

Reduces runoff volume and attenuates peak fl owsImproves water quality Reduces fl oodingImproves urban hydrology and facilitates groundwater recharge Replaces deteriorating culverts with an open drainage system that can be more easily monitored and repairedCosts less, or marginally more, than replac-ing an existing culvertCreates habitat and increases biodiversity in the cityProvides recreational amenitiesProvides educational opportunities

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High installation costsMay have high maintenance costsMay have high land requirementsPoor design can lead to soil erosionPoor design can aggravate or create fl ood-ing problemsSome benefi ts are lost if only fragmented segments are daylit

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C a s e S t u d y : Z u r i c h

Diverted creek in Zurich, Switzerland

The City of Zurich, Switzerland, daylit and diverted over 14 miles of streams and brooks to reduce flows into the combined sewer system and wastewater treatment facilities. As a result, nearly 4.5 million gal-lons per day has been diverted from the city’s two wastewater treatment plants.

The average estimated cost of a stream daylighting project is

$500,000 per 5,000 square feet or $100 per square foot. However,

the width of the restoration can also be a major factor in the fi nal

cost of the project. Maintenance activities include general weeding

and monitoring for damage such as erosion of the banks as well

as continuously monitoring water quality, to ensure the habitat

health. Until vegetation is established, maintenance of the stream

and vegetation is critical. As with all open water, ponding that would

support mosquito habitat needs to be minimized, and safety must

be considered where public access to the stream is desired.

Diverted creek in Zurich, Switzerland

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100 year flood elevation

Culverted creek

Diverted creek

Bankful bench

Currently streams are sim-ply combined with the sewer mains

Creek water runs along the surface towards the Bay or Ocean and the total volume of wastewater flow is decreased - this can be implemented on all or part of the storm flow

Currently in San Francisco, creeks run in the sewer pipe under the surface of the city. Diversion creates

a separate conveyance system for the creek, bypassing the sewer treatment plants and instead heading

to natural bodies of water like the bay or the ocean. As is done in Zurich, Switzerland, diverted runoff is

conveyed on the surface in small channels and therefore provide an aesthetic amenity. Flooding is prevented

through upstream fl ow controls. Daylighting is well suited for creeks that lay within an existing open space

because of the land requirements may otherwise be prohibitive. The daylit creek can increase aesthetic and

recreational enjoyment to the visitors of the open space.



R e f e r e n c e s


City of Berkeley. 2006 [cited 2007 Jun]. Strawberry Creek Park. Berkeley, CA: Department of Parks, Recreation and Waterfront. Available from: http://www.ci.berkeley.ca.us/parks/parkspages/StrawberryCreek.html


City of Seattle. 2007 [cited 2007 Jun]. Ravenna Creek Daylighting within Ravenna Park Pro Parks Project Informa-tion. Seattle, WA: Department of Parks and Recreation. Available from: http://www.seattle.gov/parks/proparks/projects/RavennaCreekatRavenna.htm

City of Portland. 2005. Combined Sewer Overflow Project: January 2005. Portland, OR: Bureau of Environmental Services.

City of Zurich. 2006 [cited 2007 Apr]. Clean Water in Our City. Available from: http://www3.stzh.ch/internet/erz/home/medien/broschueren.html

Sunset Magazine. 1991 [cited 2007 Jun]. How to Bring a Stream Back to Life: Berkeley and San Diego Show How it is Done, In Sunset Magazine, April 1991. Available from: http://findarticles.com/p/articles/mi_m1216/is_n4_v186/ai_10478671

Pinkham, R. 2000 [cited 2007 Jun]. Daylighting: A New Life for Buried Streams. Snowmass, Colorado: Rocky Mountain Institute. Available from: http://www.rmi.org/images/PDFs/Water/W00-32_Daylighting.pdf

Daylit creek

100 year flood elevationBankful bench

Where creeks run through parks or large open spaces, the riparian habitat can be restored - this can be imple-mented on all or part of the storm flow

The Ravenna Creek Daylighting Project included work in two existing parks to bring 650 linear feet of the historic creek out of a culvert and onto the surface, providing habitat, drainage, and aesthetic improvements. Upon leaving the parks, the creek water is diverted underground along its natural drainage path to a slough that drains to the Puget Sound instead of into the sewer system. The total cost of the project was $1,885,000 including planning and construction, community participation, and interpretive artwork. It was carried out through collaboration between Seattle Park and Recreation and the Department of Natural Resources.

C a s e S t u d y : B e r k e l e y , C A

Strawberry Creek Park was built in 1982 in place of a defunct railroad yard. During the planning and construction of the park, the designers identified the culverted Strawberry Creek under the site and recognized the opportunity to daylight the creek. Strawberry Creek is now restored and planted with California native plants. The creek is just one part of a larger park that pro-vides diverse recreational facilities for the neighborhood. Through the help of volunteers and the use of recycled materials, the project was completed within a $650,000 budget.

C o n s t r u c t e d W e t l a n d sS u m m a r y


Stormwater constructed wetlands are man-made wetlands designed

to collect and purify stormwater through microbial breakdown, plant

uptake, fi ltration, settling and adsorption. Water is stored in shallow

pools that are designed to support wetland plants. Constructed wetlands

have some of the same ecological functions as natural wetlands and

are benefi cial for fl ood control and water quality improvements.

Important site conditions include infi ltration rates, size of drainage

area, depth to bedrock, available area, soil characteristics, and depth

to groundwater. They can be used in conjunction with other BMPs.

There are two main types of constructed wetlands: surface and

subsurface. Surface wetlands are characterized by emergent

vegetation and open water. The water and plants create a habitat for

aquatic life along with water quality benefi ts. Subsurface wetlands

are less common than surface wetlands in the United States. Water

in these systems fl ows below the ground surface through a planted

substrate, such as gravel, sand, or rock. Subsurface wetlands generally

require less land area and take less time to cleanse runoff water.

Tanner Springs Park constructed wetlands in Portland, OR

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C o n s t r u c t e d W e t l a n d s

Reduces runoff volume and attenuates peak fl owsImproves water qualityImproves air qualityImproves urban hydrology and facilitates groundwater recharge Can function as a regional facility treating large volumes of waterLow maintenance costsCreates habitat and increases biodiversity in the cityMay provide open space, recreation, and aesthetic amenity

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High installation costsRequires continuous base fl ow or use of na-tive wetland plants adapted to seasonal dry periods Requires large land area which is more dif-fi cult in densely populated areasLimited to slopes less than 8 percent Vegetation may require maintenance May act as a heat sink that discharges warmer water to downstream water bod-ies10 foot minimum separation from ground-water is required to allow for infi ltration, unless the Regional Water Quality Control Board approves otherwiseMust be a minimum of 10 feet from adja-cent building foundations

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C o s t a n d M a i n t e n a n c eInstallation costs for constructed wetlands average

$57,000 for each acre of land managed, or $13 per

square foot of the completed system. Periodic

sediment removal is sometimes necessary. The

forebay area should be inspected biennially and

cleared as needed to avoid sediment build-up.

System should be carefully observed (twice a year

for the fi rst three years) over time to make sure that

the plants are growing properly and not dominated

by invasive species. The constructed wetland should

also be monitored for vector species.

Constructed wetlands in Tanner Springs Park in Portland, OR

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Tanner Springs Park is a 0.92 acre wetland and bioretention park that is built on the site of a former natural wetland. The park was designed with a constructed surface wetland and bio-filters. It collects the runoff from the adjacent sidewalks, treats it, and re-circulates it through permanent water features. None of the water from Tanner Springs Park reaches the Willa-mette River unless the flow of water exceeds the designed capacity of the system.

Another project in Portland, the Stormwater Park at the Water Pollution Control Laboratory (constructed in 1997), collects water from the entire uphill neighborhood community includ-ing 40 acres of impermeable surfaces and 10 acres of permeable surfaces and uses con-structed wetlands to adequately cleanse the water before it re-enters the Willamette River. Previously a 6 acre industrial site, 1.5 acres now consist of bio-swales, stormwater ponds and constructed wetlands.


Inflow

Berm

Variety of wetland vegetation and aquatic life filter water

For both surface and subsurface systems, stormwater fl ows into the system through an inlet pipe and enters

a forebay that allows settling of the large sediment. The forebay must be dredged and cleaned on a regular

basis to avoid clogging of the system. To mimic a natural wetland, the bottom of a constructed wetland

should have irregular heights to create pockets of both deep and shallow water. As water moves through

the system, the plant roots and the other microorganisms provide water quality treatment. Water leaves the

system after being retained for an adequate period of time for the desired pollutants to be removed. Surface

wetlands move water horizontally through the system and water is exposed to the surface. Subsurface

wetlands move water either horizontally or vertically and water is not exposed on the surface.

Surface wetland

Outflow

Maintenance opening

Irregular bottom surface

BermOpen water surface

Perforated pipe

Inlet pipe



R e f e r e n c e sCalifornia Stormwater Quality Association. 2003 [cited 2007 Jun]. Extended Detention Basin. In Stormwater Best Management Practice Handbook. Available from: http://www.cabmphandbooks.com/Documents/Develop-ment/TC-22.pdf

King County Wastewater Treatment Division. 2007 [cited 2007 Jun]. Waterworks Gardens in Renton, WA. Avail-able from: http://dnr.metrokc.gov/WTD/waterworks/

Liptan T, Murase RK. 2002 [cited 2007 Jun]. Watergardens as Stormwater Infrastructure in Portland, Oregon. In Handbook of Water Sensitive Planning and Design. Editor France R. Lewis Publishers. Available from: http://www.portlandonline.com/shared/cfm/image.cfm?id=41627

Los Angeles County. 2002 [cited 2007 Jun]. Development Planning For Stormwater Management: A Manual For the Standard Urban Stormwater Mitigation Plan (SUSMP). Los Angeles, CA: Department of Public Works. Avail-able from: http://ladpw.org/wmd/NPDES/SUSMP_MANUAL.pdf

State of Virginia. 2003 [cited 2007 Jun]. Chapter 3: Constructed Wetlands, Stormwater Wetlands. St. Paul, MN: Department of Conservation and Recreation, Metropolitan Council and Barr Engineering Co. Available from: http://www.dcr.virginia.gov/soil_&_water/documents/Chapter_3-09.pdf

University of Washington. 2007 [cited 2007 Jun]. Green Technology: Art and Water Infrastructure. Seattle, WA: Department of Landscape Architecture. Available from: http://online.caup.washington.edu/courses/larcwi01/larc433/ArtWater/Case.htm

Clayton County Water Authority. 2007 [cited 2007 Jun]. Melvin L. Newman Wetlands Center. Marrow, GA: Clay-ton County Water Authority. Available from: http://www.ccwa1.com/facilities/wetlands.center.aspx

C a s e S t u d y : H a m p t o n , G A

The Clayton County Water Authority created a constructed wetland as part of a mitigation requirement for a drinking water reservoir. The constructed wetland incorporates a board-walk and environmental education center into the unique wetland located in the heart of an urban/suburban community. The 32 acre surface wetland provides water quality treatment of urban runoff thereby protecting the downstream drinking water reservoir. Habitat and wa-ter quality monitoring have shown the wetland to be an effective water quality BMP.

Subsurface wetland

Mulch

Maintenance opening

Variety of wetland vegetation

Berm

Adjustable sand pipe controls water level

Inlet pipe

Outflow

Permanent water level

Medium and coarse gravel

Perforated pipe




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CA: San Francisco: Low Impact Design Toolkit for Stormwater

Documents

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