California; San Francisco Low Impact Design Toolkit for Stormwater

8/3/2019 California; San Francisco Low Impact Design Toolkit for Stormwater

1/52LOW I MPACT DESIGN TOOLKIT

Low Impact Design Toolk itW 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 ?


2/52i i URBAN STORMWATER PLANNI NG CHARRETTE September 2007


3/52LOW I MPACT DESIGN TOOLKI T i i


4/52i v URBAN STORMWATER PLANNI NG CHARRETTE September 2007

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


5/52LOW I MPACT DESIGN TOOLKIT 1LOW I MPACT DESIGN TOOLKIT 1

Introduction 2

1. Eco-R oofs 6

2. Downspout Disconnection 10

3. Ciste rns 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 Daylighting 38

10. Const ructed Wetlands 42

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


6/52

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

2 URBAN STORMWATER PLANNI NG CHARRETTE September 2007

Thank you for participating in todays Urban Watershed Planning

Charrette. A charrette is a collaborative session in which a group ofdesigners, 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 Franciscos 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 flows

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

potential to increase the systems treatment efficiency by delaying

and/or reducing the volumes of runoff flowing to the combined

sewer, providing stormwater treatment, enhancing environmental

protection of receiving waters, and reducing the volume and

frequency of combined sewer overflows (CSOs). These technologies,if properly designed can also provide auxiliary benefits that include,

beautification, 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.


7/52LOW I MPACT DESIGN TOOLKIT 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 flow 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 flows

into surrounding water bodies and floods 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 infiltration can occur and groundwater is depleted.

Pre-development conditions in SanFrancisco

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 ?


8/524 URBAN STORMWATER PLANNI NG CHARRETTE September 2007


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

hydrologic processes by increasing retention, detention, infiltration, 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 overflows and localized flooding 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

Bioretentionplanters

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 filtered and infiltrated. 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 efficiency of the sewer system and treatment facilities, reduce the

likelihood of flooding and sewer overflows, and recharge our local groundwater reserves.

To d a y s G a m e

For the purposes of the Urban Watershed Planning Charrette each team will be asked to apply appropriate

stormwater BMPs within the boundaries of San Franciscos four eastern catchments.

Each BMP performs specific functions such as delaying peak flows that reduce flooding and reducing

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

Francisco. This booklet introduces and describes the benefits and limitations of each BMP used in todays

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

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

management goals in your basin. Your team then calculates the benefits 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 benefits 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 specific details on the benefits and limitations

design details, and the costs of implementation and maintenance.


10/52

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

as they provide multiple environmental benefits. Eco-roofs improve

water quality by filtering contaminants as the runoff flows 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 influenced 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 flows 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 industrialstructures, 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 retrofit must have sufficient

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

PHOTO

BYROSEYJENC

KS



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

c osts for the build ing

Extend s the life o f the roo f a g reen roof c an

last twice as long as a conventional roof,

saving replac em ent c osts and m ate rials

Provides noise red uc tionRed uc es the urban he at island e ffect

Lowers the temperature of stormwater run-

off, which maintains cool stream and lake

tem pe ra tures for fish and othe r aqua tic life

Crea tes ha b itat a nd increa ses b iod iversity in

the c ity

Provides aesthetic and recreational ameni-

ties

Poor design or installation can lead to po-

tential lea kage and / or roo f failure

Limited to roof slopes less than 20 degrees

(40 perce nt or a 5 in 12 pitc h)

Requires additional structural support to

bea r the adde d weight

Potentially increased seismic hazards with

inc rea sed roo f weight

Long payback time for installation costs

ba sed on ene rgy savings

May a ttrac t unwa nted wildlife

Inadequate drainage can result in mosqui

to b reed ing

Irrigation may be necessary to establish

plants and ma intain them d uring e xtende d

dry period s

Vegeta tion req uires ma intenanc e a nd c an

loo k overgrown o r weedy, sea sona lly it ca n

app ear dead

Extensive eco-roof and detention basin in Germany

Extensive eco-roof in Seattle, WA

The C ity of Toronto initiate d a g ree n roof d em onstration p rojec t in 2000 to find solutions to

overco me te c hnica l, financ ial and informa tion ba rriers to the wide sprea d a do pt ion of green

roo f infrastructu re in the m a rketp lac e. In Feb rua ry 2006, the Toronto City Co unc il a p p rove d

the Green Roo f Pilot Prog ram , alloc at ing $200,000 from Toronto wa ters bud ge t to enc ourage

gree n roo f c onstruct ion. Sub sidies of $10 p er sq ua re m et er ($0.93 p er sq ua re fo ot ) an d up to

a ma ximum o f $20,000 will be ava ilab le to privat e p rop erty owne rs for new and retrofit g ree nroo f project s. Add itionally, the Green Roo f Strat eg y rec om me nde d the fo llow ing ac tions:

use green roofs for all new and rep la c em ent roo fs on c ity-owned buildings; use zoning a nd

financ ial inc entives to m ake g reen roofs mo re e c ono mica lly de sirab le; initiate a n ed uc at ion

and pub licity program for green roofs; provide tec hnic al a nd de sign a ssista nc e to those in-

terested in g ree n roo f building; iden tify a g ree n roo fs resourc e p erson for ea c h c ity division;

de velop a da tab ase o f green roofs in the c ity; c onduc t a nd supp ort ong oing m onitoring a nd

resea rc h on g ree n roo fs; ad d a green roof c at eg ory to the G reen Toronto Aw a rds; and es-

ta b lish p a rtnerships w ith ot he r institut ions.

PHOTO

BYROSEYJENCKS



E c o - R o o f s

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

An 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 findings 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 filter 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 finally there is the roof structure.

Growing medium(>2)

Extensive eco-roof

Roof structure

Leaf screen GravelFilter fabric

Drainage andstorage

Root barrierand waterproofmembrane

Layers:

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

Most suitable slope of 5to 20 degrees

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

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 roofing systems. In the first 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, flow 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 s

City of C hica go . 2007 [c ited 2007 Jun]. Chica go Green Roo fs. Chica go , IL: Offic e o f the Environm ent. Ava ilab lefrom: http://www.artic.edu/webspaces/greeninit iatives/greenroofs/main.htm

City and County of San Franc isc o. 2006. Low Imp ac t Deve lopm ent Literature Review. Prep ared by Ca rollo Engineers [Unpub lished Me mo ].

City of Portla nd . 2007 [c ited 2007 Jun]. Ec oroo fs. Portland , OR: Office o f Susta inab le Deve lop me nt. Ava ila b lefrom: ht tp: / / www .portland onl ine.com /o sd/ index.cfm?a=bb ehc i&c =ecb bd , (June 2007).

City o f Portland . 2006 [cite d 2007 Jul]. Ec oroo f Que stions a nd Answe rs. Portland , OR: Burea u o f Environm ent aServic es. Ava ilab le from : http:/ / ww w.po rtland online.co m/ shared / c fm/ imag e.cfm ?id=153098

City of Toront o. 2007 [c ited 2007 Jun]. Greenroo fs. Toront o, Ca na d a . Availab le from :www.toronto.ca/greenroofs/ Hopp er LJ (Ed itor). 2006. Living Gree n Roo fs a nd La nd sc a p es Ove r Struct ure. In Time Sa ver Sta nd a rds for La ndsc a p e Arc hitec ture, 2nd Ed ition, Hob oke n. NJ: John Wiley an d Son s, p. 367

Low Imp ac t Develop me nt Ce nter, Inc . 2007 [cited 2007 Jun]. Ma intenanc e o f Greenroofs. Availab le from :www.lid-stormwater.net/greenroofs/greenroofs_maintain.htm

Puge t Sound Ac tion Tea m (PSAT). 2005 [cited 2007 Jul]. Low Imp ac t Deve lopm ent: Tec hnica l Guidan c e Ma nuafor Pug et Soun d . Olymp ia, WA: Pug et Soun d A c tion Tea m a nd Wa shingto n Sta te University Pierce C oun ty Extension. Pub lic a tion No . PSAT 05-03. Ava ila b le from: w ww .psa t.wa .go v/ Pub lic a tions/ LID_tec h_ma nua l05/LID_ma nual2005.pdf

Portlands Green Roof Initiative began in the mid 1990s, when the Bureau of Environmental

Servic es (BES) sta rted investiga ting the use of ec o-roofs to c ont rol sto rmw a te r in t heir ove r-

b urdene d c om b ined sew er syste m. In 1999, the Housing Auth ority of Portland , in c oo p eration

with BES, bu ilt a full-sc a le g ree n roof on the Ha milton A p a rtm ent s Build ing. The ec o-roo f c ost

$127,500 (unit co st o f $15 pe r sq ua re fo ot of imp ervious a rea ma na ge d ), with $90,000 of tha t

gran te d b y BES. Portland c urrent ly ha s a b out 80 ec o-roo fs b uilt (roug hly 8 ac res) and a not her

40 in d esign or c onstruct ion p ha ses (roug hly 10 ac res).

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

Chic a go s first gree n roo f wa s a 20,000 sq ua re fo ot roo f on the City Ha ll tha t wa s c onstruct ed

in 2000. In 2005, the c ity la unc hed its Green Roo f Gran t Prog ra m, a wa rd ing $5,000 ea c h to 20

selec ted resid ential and sma ll com me rc ial b uildings green roof p rojec ts (ea c h with a foot print

of less tha n 10,000 sq ua re fe et ). As of O c to b er 2006, mo re th a n 250 pub lic a nd p rivate gree n

roo fs we re und er design a nd c onstruc tion in Chic ag o, tot aling mo re tha n 1 million squa re fe et

of green roofs. The c ity a lso d evelop ed po licies tha t enc ourage green roof de velopm ent in

Chica go . For examp le, all new and retrofit roofs in the c ity must m eet a 0.25 solar reflect anc e,

which green roofs are e ffec tive in m eet ing but trad itiona l roo fs are no t. Also, the c ity offe rs a

de nsity bo nus for roo fs that have a minimum of 50 pe rc ent ve ge ta tive co ver.

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

Sa n Fra nc isc o ha s seve ra l c om p leted a nd in-proc ess ec o-roo f projec ts includ ing: the new

Ac ad em y of Sc ience s ec o-roo f w hich w ill be 2.5 ac res or ap proxima tely 100,000 squa re feet;

the Environmental Living Center in Hunters Point; 2 acre intensive eco-roof on North Beach

Place; the Yerba Buena Gardens downtown which is mostly located above a parking ga-

rag e; and Portsmo uth Squa re ano ther pub lic op en spa c e over a ga rag e in Chinato wn.

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


14/52

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


Downspout disconnection, also called roof drain diversion, involves

diverting rooftop drainage directly into infiltration, detention, orstorage facilities instead of into the sewer. Rainwater can be harvested

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

infiltration, 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 infiltration,

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 flowing to the combined sewer.

Downspouts on DaVinci MiddleSchool in Portland, OR are directedto cisterns and a water garden

PHOTO

BYROSEYJENCKS



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 flows

May decrease water usage through low-

ered irrigation requirements

Low insta lla tion c ostsLow ma intenanc e req uireme nts

Large variety of implementation locations

and sca les

Pre-filtration (such as a first-flush diverter) is

req uired if wa ter is to b e sto red

Added complexity for buildings with inter

nally plumb ed stormwa ter drains

Sec ond ary system is req uired to d ea l withwa ter after it leave s the d ow nspo ut, suc h as

a c istern or a rain ga rden

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 efficiency 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




Current conditions

Disconnection options

Houses can be plumbed internallyor externally

All roof water goes to the sewer

Cisterns can be placed aboveground, below ground, or insidethe house

Roof water can also bedirected to a rain gardenor other landscaped areawhere infiltration is feasible

Overflow goes to the sewer




R e f e r e n c e s



City of Portland . 2007 [c ited 2007 Jun]. Do wn sp out Disc onn ec tion Burea u of Environm ent a l Service s, Availab lefrom: ht tp: / / www .portland onl ine.com /b es/ index.c fm?c=43081


Texa s Wat er Deve lop me nt Board . 2005 [c ited 2007 Jun]. The Texa s Ma nua l on Ra inwa ter Harvesting, ThirdEd ition . Austin, Texa s. Ava ila b le from: http :// ww w.tw d b .sta te.tx.us/ p ub lic a tions/ rep orts/ Ra inwa terHarvestingManual_3rdedit ion.pdf

TreePeop le. 2007 [c ited 2007 Jun]. O p en C ha rter Cistern, A va ila b le from :http:/ / ww w.treepe op le.org/ vfp.dll?Oa kTree~getPag e~&PNPK=150

The C ity of Portland includ ed d ow nsp out d isc onn ec tion in its Co rnersto ne Projec ts for red uc -

ing the Co mb ined Sew er Overflow s (CSOs). The p rog ra m b eg a n in 1995 and shou ld me et itsgo a ls of red uc ing C SOs b y 94% b y 2011. Househo lds a nd sma ll c om me rc ial bu ild ings within

targeted neighborhoods voluntarily disconnect their roof drains from the sewer system and

red irec t the flow to e ither a rain ga rd en o r a c istern. Som e a rea s of the c ity are e xc lud ed from

the p rog ram b ec ause o f inap prop riate slope s and soils.

The c ity pa ys pa rticipa nts $53 per disc onne c tion, or p ays for a c ontrac tor to d o t he w ork.

Co mm unity groups ea rn $13 for ea c h do wnspo ut they d isc onnec t. The p rog ram c urrently has

49,000 homeowners participating (about 4,400 disconnections per year from 1995 to 2006),

and has rem ove d a pp roxima tely 1 b il lion ga llons of stormwa ter per year from the c om bined

sewer system. Disconnection costs around $0.01 per gallon of stormwater permanently re-

mo ved from the sew er syste m. The n ew Clea n River Rew a rd s p rog ra m offe rs sto rmw a te r dis-c oun ts for prop erty ow ners who c ont rol sto rmw a te r on site. This is expa nd ing roof d isc onne c -

tion to o ther pa rts of the c ity.


Downspout disconnection consists of diverting roof runoff to a storage or infiltration 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 infiltration system. Some pretreatment is required before the stormwater

can be stored to prevent clogging from leaf litter. The main considerations for designing downspoutdisconnection and rainwater harvesting systems are: roof drainage configuration, site conditions for a

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


18/52

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 flushing 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 fields.

The Tree Peo p le Op en C ha rte r Eleme nta ry Sc hoo l Projec t ret rofitte d a p a ved sc hoo lyard with

stormwater treatment train to slow the flow of water, decrease local flooding events, andd ec rea se the po lluta nt load . The trea tme nt train co nsists of three c om po nents: a w at er trea t-

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, fi lter and safely channel

ra inwa ter throug h the c am pus. The w at er ca pt ure a nd t rea tme nt p rojec t c ost $500,000.

Tree Peo p le also c om p leted a p rojec t tha t insta lled a 250,000 ga llon und erground c iste rn in

Co ldw a te r Ca nyon Park, a 2,700 ac re w a te rshed retrofit in Sun Va lley, in c ollab orat ion with

the Co unty Dep artme nt o f 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

Ca mb ia Elementa ry Sc hoo l

captures and stores run-

off water from the entire

school site in a cistern lo-

cated underneath ath-

letic fields and uses the

stored wa ter to irriga te the

field s yea r round . All of t he

stormwa ter on the 12 ac recampus is captured and

stored in large pipes that

are loc a ted unde r 130,000

square feet of new ath-

letic fields. Up to 2 million

gal lons of water can be

stored.

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


peak flows

May decrease water usage if retained for

irrigation purposes or toilet flushing

Low insta lla tion c osts

Low maintenance requirements (for above

ground c isterns)

Low spa ce req uirem ents (for unde rground

c iste rns)

Go od for sites where infiltra tion is not a n op -

tion

Poor design, sizing, and siting can lead to

po tential leakage and / or failure

Storage c apac ity is limited

Provide s no w ate r qua lity imp rovements

Lowe r aesthetic ap pe al (for ab ove ground

c iste rns)

Water reuse o p tions limited to non-po tab le

uses

Requires infrastructure (pumps or valves) to

use the stored wa ter

Inade qua te ma intenanc e c an result in mos-

quito b reeding a nd/ or alga e produc tion


The 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 confirm 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 difficult 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 flushing or fire suppression.

Cistern at Cambria Elementary Schoo



C i s t e r n s


Water can be reusedfor non-potable uses

Leaf screens ongutters preventclogging

First flushdiverter

Overflow enters thecombined sewer

Maintenanceopening hasscreen to pre-vent mosquitoand litter ac-cumulation

Sewer backflow pre-vention device

Pump

Proper design, siting, and sizing of cisterns are critical to ensure their full peak flow benefits. Stormwater

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

exits through an overflow valve. Cisterns should be designed to outflow away from building foundations.

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

pretreatment is required to prevent clogging (e.g. leaf screens and first-flush diverters) before the stormwatercan 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 s

Los Angeles Co unty. 2002 [c ited 2007 Jun]. Develop me nt Planning for Stormw ate r Mana ge me nt: A M anua l Fothe Sta nd a rd Urb a n Stormw a ter M itiga tion Pla n (SUSMP). Los Ange les, CA: De p a rtmen t o f Pub lic Works. Ava il

a b le from: http :// lad p w.o rg/ wm d / NPDES/ SUSMP_MA NUAL.pd fLow Imp a c t Dev elop me nt C ent er, Inc . 2007 [cite d 2007 Ma y]. Co st o f Ra in Ba rrels a nd Cisterns. Sizing o f Ra inBa rrels a nd Cisterns. Ava ila b le from: http:/ / ww w.lid -storm wa ter.net/ rainc ist/ rainc ist_co st.htm a ndhttp :// ww w.lid -storm wa ter.net/ rainc ist/ rainc ist_sizing.htm

Rehb ein Environm ent a l Solutions, Inc . 2007 [c ited 2007 Ma y]. Ca mb ria Eleme nta ry Sc hoo l. Ava ila b le from : http:/ /www.rehbeinsolutions.com/projects/cambria.html

Tom Richm ond an d A ssoc iate s. 1999 [c ited 2007 Jun]. Sta rt at the Sourc e: Design Gu ida nc e M a nua l for Storm-wa ter Protec tion. San Franc isc o, CA : Bay Area Stormw ate r Mana ge me nt Ag enc ies Assoc iation. Availab le fromhttp :// sc vurpp p -w2k.co m/ p d fs/ 0203/c 3_relate d _info/ sta rtatth esourc e/ Sta rt_At_The_Sourc e_Full.pd f

TreeHugg er. 2007 [c ited 2007 Jun]. Sea ttle RainCa tc her Pilot Program. Ava ilab le from: http :// ww w.treehugg erc om / files/ 2005/ 03/ sea ttle_rainca t_1.php

Sea tt le Pub lic Utilities (SPU) rec en tly beg a n the ir Ra inCa tc he r Pilot Prog ram , whic h c on sists o f

three d ifferent typ es of ra inwa te r co llec tion syste ms. First is tight -line, whic h d irec ts ra inwa te r

outflow to a pipe that flows under the yard, through weep holes in the sidewalk reducing

volum es d ep osited in the storm d ra in via the c urb. The sec ond typ e, the tigh t-lined c iste rn,

inc lude s a c istern at the po int of initial outflow tha t c ollec ts wa ter during t he storm eve nt a nd

relea ses it slowly into t he u nd erground p ipes. Third , orifice c isterns includ e a n op erab le va lve,

which c an b e o pe ned dur ing the wet sea son, discha rging a sma ll amount o f wa ter onto an

ad jac ent p ermea ble surfac e suc h as a law n or rain ga rde n to slow do wn flow, or closed to

sto re up to 500 ga llons of roo f runoff, w hich c a n b e used late r for irriga tion.

Ea c h c istern c osts the SPU a to ta l of $1000 with $325 of tha t sum p a ying fo r the w holesa lep urch a se o f the c iste rn and $675 to insta lla tion a nd the SPU ov erhea d . The SPU a lso sells rain

b a rrels to ho useh old s in the SPU s d irec t service a rea s. The ra in ba rrels c ost $59 ea c h fo r the

SPU c usto mers a nd $69 fo r no n-c usto mers. SPU is c urren tly ana lyzing t he imp a c t o f c iste rns on

the c om b ined sew er syste m a s p a rt o f a g ra nt. SPU insta lls the Ra inCa tc her at no c ost to the

pa rt ic ipa nt, provide s ma intenanc e a nd supp ort, and evaluates the p erforma nce over t ime.

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

Mosaic above ground cistern in Tennessee

PHOTO

BYLESLIEWEBSTER


22/52

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 infiltrate stormwaterrunoff. 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 flow of

stormwater thereby decreasing peak flow volumes. They also filter

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 benefits. 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 benefits and limitations.

Stormwater from downspouts can be directed through an energydissipater 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



peak flows

Imp roves wa ter quality

Imp rove s a ir qua lity

Improves urban hydrology and facilitatesgroundwa ter rec harge

Low insta lla tion costs

Low ma intenanc e req uireme nts

Low spa c e requirem ents

Creates habitat and increases biodiversity

in the city

Provides aesthetic amenity

Easily c ustomizab le

Depth to be drock must b e o ver 10 feet fo

infiltra tion b ased system s

Limited to slopes less tha n 5 p erce nt, slopes

greater than 5 percent require check

dams

Sea sona l fluctuation in water quality ben-

efits ba sed on the plants ab ility to filter pol-

lutants


loo k overgrow n or we ed y, sea sona lly it may

app ear dead

Site co nd itions must be c ond uc ive to pa rtia

or full infiltration and the growing o f vegeta -

tion o r an und erdra in is need ed

10 foot minimum separation from ground-

water is required to allow for infiltration

unless the Regional Water Quality Contro

Board approves otherwise

Non-und erdrained system s must ha ve mini

mum soil infiltra tion ra tes, no c onta minated

soils, no risk of la nd slippage if so ils a re heav-

ily sa turated , and a suffic ient d istanc e from

existing foundations, roads, subsurface in-

frastructure

Formal rain garden in Portland, OR

Residential rain garden in Maplewood, MN

PHOTO

FROMw

ww.c

i.maplewood.m

n.us





2-6 Ponding depth

Optional 12sand bed

Dense vegetation tolerantof wet and dry conditions

Water from 1 acre orless of roof, paved or

landscaped surfaces

Berm

Native soils suitablefor 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 fills with a few inches

of water during a rain event. Either the soils must be suitable to infiltrate 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-drainedsoils to function correctly. Rain gardens are more appropriate for drainage areas less than 1 acre in size.


Rain 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 soils ability to capture water. In the first 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 Portla nd . 2007 [c ited 2007 Jun]. Design Rep ort: Ra in Gard en a t Glenc oe Eleme nta ry Sc hoo l. PortlandOR: Burea u of Environm enta l Servic es. Ava ilab le from : http:// ww w.po rtland online.co m/ sha red / c fm/ imag ecfm?id=147510

Ra in Ga rden Netw ork. 2007 [c ited 2007 Jun]. Loc a l, On-Site Solutions for your Loc a l Sto rmwa ter Issues. Ava ilab lefrom: ht tp: / / www .raingardennetwo rk.c om/

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

City of Maplewood. 2007 [cited 2007 Aug]. Rain Water Gardens. Available from: http://www.ci.maplewood.mn.us/ ind ex.asp ?Typ e=B_BASIC& SEC=%7BF2C03470-D6B5-4572-98F0-F79819643C 2A%7D


Glenc oe Eleme nta ry Sc hoo l in SE Portland insta lled a ra in ga rd en in th eir sc hoo l ground s in

2003 to p revent ne ighb orhood -wide c om bined sew er ove rflow p rob lem s by reduc ing runoff

volumes while p roviding a esthetic a nd e d uc at iona l ame nities to the sc hoo lya rd. The c om -

plete d rain g arde n is a 2,000 sq uare foo t infiltra tion a nd d ete ntion system that ma nag es run-

off from 35,000 sq ua re fe et o f imp erme a b le surfa c es with a to ta l c ost o f $98,000.

Rain garden at Glencoe Elementary Schoo


26/52

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 flows.

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 retrofits of existing sites.

Bioretention in Vancouver, BCC a s e S t u d y : P o r t l a n d , O R

Portland s Gree n Streets Prog ram ha s suc c essfully imp leme nte d m a ny biorete ntion p rojec ts

since it began in 2003 including bioretention curb-side planters constructed in the parking

zone on eithe r side of a street, just up strea m form t he sto rm d ra in inlets. One suc h p rojec t, NE

Siskiyou Street, c a p tures runo ff from a p p roxima te ly 9,300 sq ua re fee t o f p a ved surfa c es. Tot a l

p rojec t c ost (exc luding street a nd side wa lk rep a irs) w a s $17,000, or $1.83 pe r sq ua re fo ot of

imp ervious area m ana ged .

Mississipp i Co mm ons, a m ixed -use d eve lop me nt p rojec t inco rp orat es a n internal Ra in Dra in

system , whic h c ollec ts sto rmw a ter from the 20,000 sq ua re fo ot roo f a rea , which w a s p reviouslyc onnec ted to the co mb ined sewe r, and direc ts it to a c ourtyard planter. The p lanter remo ves

a n a verage of 500,000 ga llons of stormwa ter annua lly from the c om bined sew er system and

wa s d esigne d a s an a rc hitec tural feat ure for the internal c ourtyard o f the de velopm ent.

New Co lumb ia, an 82 ac re red eve lop me nt a rea , is Portland s largest Gree n Streets site, with

101 veg eta ted p oc ket swa les for biofiltration, 31 flow-throug h pla nte r b oxes a nd 40 infiltration

d ry we lls. It used 80 pe rc ent less unde rground stormwa ter piping tha n a c om pa rab le t rad i-

tional de velopm ent a nd 98 percent o f the stormwa ter is reta ined on the site.

PHOTO

BYROSEYJENCKS



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


B e n e f i t s

Bioretention planter in Vancouver, BC


peak flows


Imp roves a ir qua lity

Improves urban hydrology and facilitates

groundwa ter rec harge

Lowers the temperature of stormwater run-

off, which maintains cool stream tempera-

tures for fish and othe r aq uatic life

Red uc es the heat island effec t


in the city


Depth to bedrock must be more than 10

fee t for infiltra tion b ased system s

Limited to slopes less tha n 5 p ercentSea sona l fluctuation in water quality ben-

efits based on the plants ab ility to filter pol-

lutants


look ove rgrown or weed y, sea sona lly it may

appear dead

Site co nditions must be c ond uc ive to partial

or full infiltration and the growing of vege ta-

tion

10 foot minimum separation from ground-

water is required to allow for infiltration,unless the Regional Water Quality Control

Board approves otherwise

Must ha ve minimum soil infiltration rates, no

contaminated soils, no risk of land slippage

if soils a re hea vily sa turate d , and a sufficient

distance from existing foundations, roads,

subsurface infrastructure, drinking water

wells, septic tanks, drain fields, or othe r ele-

ments.


The 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 andmaintenance 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 infiltration rates.

Bioretention planter inPortland, OR

P

HOTO

BYROSEYJENCKS



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

Typical bioretention planter


Gravel curtain drainprotects building foun-dation

Building

Stone used todissipate 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 benefits as the roots and soils

uptake some pollutants from stormwater. Bioretention areas can either infiltrate 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 infiltration is facilitated by well-drained soils,bioretention planters can be designed without the underdrain, much like rain gardens, to infiltrate the

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

the soils for infiltration, 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 infiltration. 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 feasible

Perforated pipe ingravel jacket

Optional sand filter layer

Min. 4 engineered soils

2-3 Mulch

Max. 6 pondingdepth

Curb cut

Dense vegetation tolerant of wetand dry conditions


29/52


30/52

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


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

allows for temporary rainwater storage prior to infiltration or drainageto a controlled outlet. The stormwater is stored in the underlying

aggregate layer until it infiltrates 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 flows, 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-traffic streets, street-

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

Infiltration 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

PHOTOSBYROSEYJENCKS



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



peak flows

Improves water quality by reducing fine

grain sediments, nutrients, organic matter,

and trace me tals




Provides noise red uc tion

Limited to paved areas with slow and low

traffic volumes

Req uire pe riod ic ma intenanc e to ma intain

efficiency

Easily c logg ed by sed iment if not c orrec tly

installed a nd m aintained

More e xpensive tha n trad itiona l pa ving sur-

faces (although these costs can be offset

by not nee ding to install a c urb a nd g utte

drainage system)

Depth to b ed roc k must be greater than 10

fee t for infiltra tion b ased system s

Diffic ult to use w here soil is c om pac ted : infil

tration rate s must be a t least 0.5 inc hes per

hour


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 andtested 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 Sea ttle Hig h Point Projec t show c a ses the first p orous p a vem ent street in Washingto n

and serves as a testing ground for its use elsewhere. Porous concrete pavement was used

on tw o c ity street sec tions, half of the pub lic sidew alks, and for pa rking and ac c ess on m any

of the privat e p rop erties. Porous pa vem ent sid ew a lks and gravel-pave d drivew ays are em -

ployed at key sites to help red uc e pa ved or imp ervious surfac es and infiltrat e stormwa ter.

Load-bearing turf block in Vancouver, BC

Porous asphalt in Portland, OR

PHOTO

BYROSEYJENCKS

PHOTO

BYROSEYJENCKS




Optional geotextilefabric


Permeable pavers

Perforated pipeflows 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 infiltrate 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 filters

large particulates. If a storm event exceeds the capacity of the storage layer, a perforated overflow 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 fines

Open-graded concrete: Similar to standard pavement, but without the fine aggregate (sand and finer) 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 filled 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 filtering mechanism to prevent soil from clogging the

pervious pavement. Soil infiltration 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 infiltration is appropriate, and to ensure that excessive sediment and pollutants are not

directed onto the permeable surfaces.

Pavers with openspaces filled with

gravel or sand

Subgrade Infiltration where feasible

Storage layer:coarse gravel

Filter layer : finegravel or sand




Los Angeles Co unty. 2002 [cited 2007 Jun]. Develop me nt Planning For Stormwa ter Ma nag em ent: A Ma nual Fo

The Sta nd a rd Urb a n Storm wa ter M itiga tion Pla n (SUSMP). Los Ang eles, CA : Dep a rtmen t o f Public Works. Ava ila b le from: http :// lad p w.o rg/ wm d / NPDES/ SUSMP_MA NUAL.pd f

New York City. 2005 [c ited 2007 Jun]. High Performa nc e Infrastruct ure G uide lines: Best Pra c tice for the Pub licRight-of-Way. New York, NY: Dep artme nt o f Design a nd Co nstruc tion. Available from : http:/ / ww w.de signtrustorg/ p ub s/ 05_HPIG.p d f


Tom Richm ond an d A ssoc iate s. 1999 [c ited 2007 Jun]. Sta rt at the Sourc e: Design Gu ida nc e M a nua l for Storm-wa ter Protec tion San Franc isc o, CA: Bay Area Stormw ate r Mana ge me nt Ag enc ies Assoc iation. Availab le fromhttp :// sc vurpp p -w2k.co m/ p d fs/ 0203/c 3_relate d _info/ sta rtatth esourc e/ Sta rt_At_The_Sourc e_Full.pd f

R e f e r e n c e s


In 2004, the Burea u o f Environm ent a l Servic es p a ved three b loc ks of street s in the Westm ore-

land neighb orhood w ith pe rme a ble pa vem ent tha t allow s rainwa ter to infiltrat e. They pa ved

a b out 1,000 feet o f street surfa c e w ith inte rloc king c onc ret e b loc ks. One b loc k of SE Kna p p

Street wa s p a ved c urb-to-c urb w ith p erme a b le b loc ks. The ot her street s SE Rex Street a nd

SE 21st Avenue we re p ave d w ith a c ente r strip of sta nda rd a spha lt a nd p ermea ble p ave -

me nt in both c urb lane s. A fourth b loc k was pa ved c urb -to-c urb w ith sta nda rd a spha lt. New

me thod s and eq uipme nt like vac uum swe ep ers will be used to c lean the street s and keep

the m free of w ee d s a nd d eb ris. The c onstruct ion c ost w a s $412,000.

In sum me r 2005, the City of Portland c om p leted p a ving four bloc ks of North Ga y Avenu e. This

is a p ilot p rojec t to lea rn how w ell different p ave me nt ma teria ls hand le stormwa ter and hold

up a s a street surfa c e. For this rea son, the c ity insta lled four different p a vem ent c om b inations

on Gay including porous concrete curb-to-curb; porous concrete in both curb lanes, stan-

da rd c onc rete in the midd le trave l lane s; po rous aspha lt curb-to-curb; and po rous aspha lt in

the c urb lane s only. The results of this te st a re n ot yet a va ila b le.

Permeable pavemen

Storage layer:

coarse gravel

Perforated pipeflows to sewer

Filter layer: finegravel or sand

Porous asphalt

Optional geotextilefabric

Subgrade Infiltration where feasible


34/52

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 flows and slowly release them, lessening the demand ontreatment facilities during storm events and preventing flooding.

Generally, detention basins are designed to fill and empty within 24

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

and combined sewer overflows. If designed with vegetation, basins

can also create habitat and clean the air whereas underground basins

do not. Surface detention basins require relatively flat 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 benefits, 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

infiltration.

2. Extended dry detention basins are designed to hold the first flush

of stormwater for a minimum of 24 hours. Extended dry detentionbasins have a greater water quality benefit 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.)

PHOTO

BYROSEYJENCKS



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



peak flows

Improves water quality by removing some

pa rticulate ma tter, sed iment a nd buoya nt

ma terials (extended d ry de tention only)

Reduces flooding

Low ma intenanc e c ostsLow space requirements (underground

only)

Go od for sites where infiltra tion is not a n op -

tion

May create habitat and increases biodi-

versity in the city (multi-purpose detention

only)

May provide open space and aesthetic

amenity (multi-purpo se d etention only)

Limited po llution removal po tential

Inadequate drainage can result in mosqui

to b reed ing

Low aesthetic value (unless designed fo

multi-purpose)

Site limited by d ep th to bed roc k and slope

Must have no risk of land slippage if soils a rehea vily sa turate d, a nd a sufficient distance

from existing foundations, roads, and sub

surface infrastructure

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

partnered with an upstream BMP that provides water quality benefits, like bioretention planters, if water

is not returned to the combined sewer overflow. 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

retrofits.

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

large play areas, dog parks, athletic fields or other public spaces. Generally detention basins are only filled

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

Big Creek multi-purpose detentionbasin in Roswell, GA

Detention basin in Seattle, WA

PHOTO

BYROSEYJENCKS





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

flows 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 isdischarged back into the normal conveyance system. Underground detention fills up during rain events and

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

Sediment

Traditional dr y detention basin

Extended Dry Detention Basin

Underground detention basin

Outflow

Overflowdrains tosewer Trash racks

Designed storm elevation

Designed storm elevation

Sediment

Erosion protection

Berm

Min. 25 from structuresOverflow spillway

Rip-rap, fabric sock, ortrash rack filter sedimentform outflow

Erosion Protection

Max. 4:1 slopeOutflow

Low-flow orifice




Ca lifornia Storm wa ter Qu a lity A ssoc iation. 2003 [cited 2007 Jun]. Extend ed Dete ntion Basin. In Storm wa ter BesManagement Pract ice Handbook. Avai lable from: ht tp: / /www.cabmphandbooks.com/Documents/Develop

me nt/ TC-22.pd f

City of Sea ttle. 2000 [cited 2007 Jun]. Flow C ont rols Tec hnic a l Req uirem ent s Ma nua l. Sea ttle, WA: Depa rtme nof Planning and Development. Available from: http://www.seattle.gov/dclu/codes/Dr/DR2000-26.pdf

Frost-Kum pf, HA. 1995 [cite d 2007 Jun]. Rec lam a tion Art: Restoring a nd C om me mo rating Blighte d Land sc a p esAva ilab le from : http:// slagg arde n.cfa .cm u.edu/ we blinks/ frost/ FrostTop .html

Los Angeles Co unty. 2002 [cited 2007 Jun]. Develop me nt Planning For Stormwa ter Ma nag em ent: A Ma nual FoThe Sta nd a rd Urb a n Storm wa ter M itiga tion Pla n (SUSMP). Los Ang eles, CA : Dep a rtmen t o f Public Works. Ava ila b le from: http :// lad p w.o rg/ wm d / NPDES/ SUSMP_MA NUAL.pd f

New York City. 2005 [c ited 2007 Jun]. High Performa nc e Infrastruct ure G uide lines: Best Pra c tice for the Pub licRight-of-Way. New York, NY: Dep artme nt o f Design a nd Co nstruc tion. Available from : http:/ / ww w.de signtrustorg/ p ub s/ 05_HPIG.p d f

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 Pa rk Demo nstration Projec t inc lude s a multi-purpo se d ete ntion a rea to sto re

and trea t runoff from a suburba n neighb orhood to p rotec t a d ow nstrea m w etland. Themulti-purpose pond is used for soccer and recreation during dry periods and fills with water

d uring rain eve nts. Und er the sod surfa c e, the re is a la yer of eng ineered soil a nd m ixed roc k

to imp rove drainag e. The fea ture include s an outlet struc ture tha t ensures drainag e w ithin

24 hours to p revent d am ag e to the sod . The tot al storag e volume p rovide d in the 1.7 a c re

multi-purp ose de tention p ond is 4.76 a c re-feet of stormwa ter.


Typical 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 efficiency of the system.

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

Mill Creek C anyo n Stormwa ter Detention Dam is a multi-purpo se d ete ntion ba sin loc at ed in

Kent , a sub urb o f Sea ttle. Built in 1982, this 2.5 ac re p ortion o f a larger p a rk c a n sto re up to18 acre-feet of stormwater from 2.2 square miles of pervious and impervious urban surfaces

up hill of the site. A la nd a rtist, Herbe rt Ba yer, p a rticip a ted in the d esign of the p a rk and sc ulp-

tural earthworks were used to capture the water in spirals and between mounds that park

visitors c a n trave rse using p a ths a nd b ridg es. The p rojec t w a s d eve lop ed in co lla b orat ion

be twe en the King Co unty Arts Co unc il and the Kent Parks Dep artme nt

Detention basin in Seattle, WA


38/52

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 benefits 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 flows. Also, their roots

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

to stormwater benefits, 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 affluent districts to 74 percent

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

unplanted areas present an opportunity not only for significant

stormwater reductions, but also for addressing environmental justice

issues. The analysis found that San Franciscos 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 treeannually. Certain tree species were better at reducing stormwater

runoff than others. Those demonstrating the highest stormwater

reduction benefits were blackwood acacia, Monterey pine, Monterey

cypress, and Chinese elm.



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


peak flows


Imp roves a ir qua lity

Provides shade and therefore may lower

ene rgy costs for buildings

Decreases soil erosion in parks and open

spaces



in the city


Ca n co ntribute to c a rbo n seq uestration

B e n e f i t s


Req uires ad eq uate spa c e for plantingModerate installation and maintenance

costs

In som e San Franc isco neighborhoo ds, cu l-

tural preferences have lead to disagree-

ment ab out a esthetic va lue of stree t trees

Potential c onflicts with ove rhea d wires

Potential to damage underground infra-

structure w ith roo ts

Non-ideal growing conditions can cause

stunting, disease or premature death

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 p lan to p lan t 1 m illion t rees in Los

Ang eles ove r the next seve ra l yea rs. In t he first ye a r of

the program, approximately 44,378 trees have been

plante d. The Los Ang eles Dep artment of Wa ter and

Pow er (LADWP) Tree s for a Gree n LA p rog ra m, in c on-

junc tion w ith M illion Trees LA, o ffe rs free sha d e tree s to

resid ential elec tric c ustom ers who at tend an online o rneighb orhood workshop on how to p lant a nd c are for

their tree. Non-residential (Home Owners Associations

or apa rtme nt ow ners) ca n rec eive free shad e trees by

completing the workshop or certifying that a profes-

sional land sc ap e c ontrac tor will plant a nd m ainta in the

trees.

Trees lining a grassy swale in Germany

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

PHOTO

BYROSEYJENC

KS



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


Street trees in San Francisco

A typical street tree planted in an urban locationhelps manage stormwater in a number of ways.First, water is stored in the canopy of the tree andis later evaporated into the atmosphere. Second,

the tree pit provides a location in the paved

sidewalk for water to infiltrate or be stored in thesoil for later use by the tree or other vegetation. The leaf litter and other organic material as well as the roots contribute to the soils abilityto hold and infiltrate water. Trees also transpire

water from the soil into the atmosphere duringtheir process of photosynthesis. Tree selectionis important to maximize the benefits of eachtree as a part of the urban forest. Tree pits canbe integrated into a bioretention planter that

provides additional stormwater management

benefits. The City of Portland has successfullyimplemented bioretention planters in conjunctionwith street trees.

Rain is intercepted bythe canopy and evapo-rates

Roots and organic mate-rial absorb water

Water is transpiredback to the atmo-sphere

Tree grate

Tree pit

Compactedsoil

Concrete sidewalk

Perforated pipe drains to sewer

PHOTO

BYLESLIEWEBSTER

Street trees on Grove Street in San Francisco



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

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-profit 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 first three

years of the trees life are generally more expensive than

the years that follow because trees require irrigation

until established.

The cost to install trees in San Francisco varie

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 costscloser to $1,450 per tree.



City a nd Co unty of Sa n Franc isc o. 2007 [cite d 2007 Jun]. The Bene fits of a n Urb a n Forest. Sa n Franc isc o, C A: SFEnvironment. Available from: http://www.sfenvironment.com/aboutus/openspaces/urbanforest/benefits.htm

Friend s of the Urba n Forest. 2007 [c ited 2007 Jun]. Ava ilab le from : http :// ww w.fuf.net/

Ma c o SE, Mc Phe son EG, Simp son JR, Pep er PJ, Xia o Q . 2003 [c ited 2007 Jun]. C ity of Sa n Franc isc o, Ca liforniaStree t Tree Resourc e A na lysis. Dav is, CA : Ce nte r for Urba n Fore st Resea rch USDA Fore st Servic e Pac ific Sou thw esResea rch Sta tion. Ava ila b le from: http :// ww w.fs.fed .us/ p sw/ p rogra ms/c ufr/p rodu c ts/ c ufr427_SFSTAFinal.pd f

Ma ryla nd Dep a rtmen t o f Nat ural Resourc es. 2007 [c ited 2007 Jun]. The Bene fits of Urb a n Trees. Ava ila ble fromhttp://www.dnr.state.md.us/forests/publications/urban.html

Million Trees LA. 2007 [c ited 2007 Jun]. Ava ila ble from: htt p :// ww w.m illiont reesla.org/

Sou th Ca rolina Fo restry Comm ission. 2007 [c ited 2007 Jun]. The Bene fits of Urb a n Tree s. Ava ila b le from: htt p :/ /www.state.sc.us/forest/urbben.htm

Sinc e 1999, the Urb a n Forestry Ad ministrat ion (UFA) ha s p lan te d 14,500 tree s (or ap p roxima te -

ly 2,400 trees p er yea r). The UFA ha s d eve lope d relat ionships with loc a l pub lic / p rivate p a rtne r

orga niza tions suc h a s Green Sp a c es for DC, the Ca sey Tree s End ow me nt Fund , Co mm unity

Resourc es, and ot hers, who a re c urrent ly involved in tree -rela ted wo rk within DC s neig hb or-hoo ds. Acc ording to the M a yor s office, ove r the last three yea rs the tree b udg et o f the UFA

ha s b ee n b oo sted to $7 million p er yea r. The UFA is rem oving d ea d trees a nd old stum p s,

wh ile eve ry yea r trimm ing 15,000 to 17,000 tree s a nd p lanting 4,000 new trees.

Trees near a grassy swale in Berlin, Germany

PH

OTO

BYROSEYJENCKS


42/52

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


Stream daylighting refers to projects that uncover and restore

streams, and rivers that were previously buried in undergroundpipes 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 inflow that can be

diverted from the sewer system will be specific to the local hydrology

and therefore cannot be generalized. Several projects, however,

demonstrate that stream diversion can be effective at reducing wet-

weather flows 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 benefits of partially repairing the natural

hydrologic cycle, increasing capacity in drainages with undersized

pipes, slowing the rate of peak flows, providing habitat, creating

recreational facilities, and providing a site for ongoing environmental

awareness and education.


Small, open runnel in Kolding,Denmark

The City o f Portland is c urrent ly insta lling ne w p ipelines to d ivert Ta nner Cree k d irec tly into t he

Willa me tte River inste a d of into the c om b ined sew er system . The finished p rojec t is expe c te d

to rem ove ap proxima tely 165 million ga llons of stormwa ter annua lly from the c om bined sew -

er system.

PHOTO

BYROSEYJENCKS



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


peak flows


Reduces flooding



Replaces deteriorating culverts with an

open drainage system that can be more

ea sily monitored and rep a ired

Co sts less, or ma rgina lly more, tha n rep lac -

ing a n existing c ulvert


in the city

Provides recreational amenities

Provides ed ucationa l opp ortunities

High insta lla tion c osts

May have high ma intenanc e c osts

May ha ve high land req uireme nts

Poo r design c an lead to soil erosion

Poor design c an a gg rava te or create flood-

ing problems

Som e b enefits are lost if only fragmented

seg me nts a re d aylit

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


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

Diverted creek in Zur ich, Switzerland

The City o f Zuric h, Sw itzerland , da ylit a nd

diverted over 14 miles of streams and

brooks to reduc e flows into the c om bined

sew er system and wa stew at er trea tme nt

fa c ilities. As a result, ne a rly 4.5 million g a l-

lons pe r da y has be en d iverted from the

c ity s two wa stew at er trea tme nt plants.

The average estimated cost of a stream daylighting project i

$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 final

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 Zur ich, Switzerland

PHOTO

BYROSEYJENCKS





100 year floodelevation

Culverted creek

Diverted creek

Bankful bench

Currently streams are sim-ply combined with the sewermains

Creek water runs along thesurface towards the Bay orOcean and the total volume ofwastewater flow is decreased- this can be implemented onall 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 flow controls. Daylighting is well suited for creeks that lay within an existing open spacebecause 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 o f Berkeley. 2006 [c ited 2007 Jun]. Straw b erry Creek Park. Berkeley, CA : Dep a rtmen t o f Pa rks, Rec reat ionand Waterfront. Available from : http :// ww w.c i.be rkeley.ca .us/ pa rks/ pa rkspa ge s/ Strawb erryCreek.html


City o f Sea ttle. 2007 [cite d 2007 Jun]. Ra ven na Cree k Daylighting within Ra ven na Pa rk Pro Pa rks Projec t Informa

tion. Sea ttle, WA: Depa rtment o f Parks and Rec reation. Available from: http :// ww w.sea ttle.go v/ pa rks/ prop arks/projects/RavennaCreekatRavenna.htm

City of Portla nd . 2005. Co mb ined Sew er Ove rflow Projec t: Janua ry 2005. Portland , OR: Burea u of Environm ent aServic es.

City of Zuric h. 2006 [cited 2007 Apr]. Clean Wa ter in Our City. Ava ila ble from : http:/ / ww w3.stzh.ch / internet/ erz/home/medien/broschueren.html

Sunset Ma ga zine. 1991 [cite d 2007 Jun]. How to Bring a Strea m Ba c k to Life: Berkeley a nd Sa n Diego Sho w How iis Done , In Sunset M a g a zine, Ap ril 1991. Availab le from : http :// finda rtic les.co m/ p / a rtic les/ mi_m1216/is_n4_v186/a i_10478671

Pinkham , R. 2000 [c ited 2007 Jun]. Daylighting : A New Life fo r Buried Strea ms. Snow ma ss, Co lorad o: Roc kyMo untain Institute. Av ailab le from : http :// ww w.rmi.org/ imag es/ PDFs/ Water/ W00-32_Daylighting.pd f

Daylit creek

100 year floodelevation

Bankful bench

Where creeks run throughparks or large open spaces,the riparian habitat can berestored - this can be imple-mented on all or part of thestorm flow

The Ra venn a Cree k Daylig hting Projec t inc lude d w ork in tw o e xisting p a rks to b ring 650 linea r

feet of the historic creek out of a culvert and onto the surface, providing habitat, drainage,

and ae sthetic imp rovem ents. Upo n leaving the pa rks, the c reek w at er is diverted und erground

along its nat ura l drainag e p at h to a slough tha t d rains to t he Puge t Sound instea d of into the

sew er system . The t ot a l co st o f the p rojec t w a s $1,885,000 includ ing p lanning a nd c onstruct ion,community participation, and interpretive artwork. It was carried out through collaboration

be twe en Sea ttle Park and Rec rea tion and the Dep artme nt of Na tural Resources.

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

Straw b erry Creek Pa rk wa s b uilt in 1982 in pla c e o f a d efunc t railroa d ya rd . During the p lanning

and c onstruc tion of t he p ark, the d esigners identified the c ulverted Straw be rry Creek unde r

the site and rec og nized the op po rtunity to da ylight the c reek. Straw be rry Creek is now restored

and plant ed with Ca lifornia n

California; San Francisco Low Impact Design Toolkit for Stormwater

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