portland stormwater solutions handbook

StormwaterSolutions

Handbook

AcknowledgementsThis document was prepared for the

City of Portland Environmental Services.

Contributors and Review Committee

Lisa Doolittle

Linda Dobson

Susan Garland

Emily Hauth

Nancy Jerrick

Diana Hinton

Dawn Uchiyama

Carolyn Sharp

Dawn Hottenroth

Tom Liptan

Linc Mann

More information onCity of Portland stormwater projects

is available onlinewww.cleanriverspdx.org

For a CD ofstormwater materials

or for information or to register for the Clean River Rewards program visit

www.CleanRiverRewards.comor call 503-823-1371

Graphic Design Leslie Winter-Gorsline

WS 0603 Printed on 100% recycled paper.

STORMWATER SOLUTIONS HANDBOOK - Environmental Services - City of Portland Oregon 3

Stormwater Solutions Handbook

Portland receives about 37 inches of rain a year. When it rains, stormwater runoff that isn’t man-aged properly washes over streets, roofs, parking lots and other hard surfaces and carries dirt,oil, metals and chemicals into our rivers and streams. How we manage runoff impacts ourstreams, our built environment and our pocketbooks. Up to 95% of Portland’s rain falls in small,frequent storms. Runoff from small storms can easily be managed at most sites by integrating

stormwater with site and building design. Managing stormwater at its source with natural systemsreduces the need to build storm sewers.

As Portland grows, the City works to accommodate growth and commerce while maintaining clean riversand streams, air quality and livability. Urban practices and the growing amount of paved areas, roof topsand other impervious surfaces pollute rivers and streams, increase flooding, and degrade fish and wildlifehabitat. Loss of vegetation increases air and water temperatures. The solution is to develop in a way thatrestores the function and value of trees, soil and open space in our communities. If we develop todaywith long-term sustainability in mind, future generations can enjoy a vibrant city and clean and healthyrivers, instead of bearing the burden of our actions.

The following stormwater solutions are for anyone interested in managing stormwater onsite, planningor designing new construction projects or making changes to existing development. Whether you arerepaving a driveway or adding a garage to your home, planning an apartment complex or town center,redeveloping a warehouse, or building a public road, these stormwater management techniques will help meet the City’s objectives for stormwater management, clean water, and healthy habitat for people,fish and wildlife.

This handbook is divided into three sections:1. When It Falls On The Roof2. When It Gets To The Ground3. Taking It Underground

Depending on your location, the site conditions, type of buildings on your site, and the complexity andexpense of the stormwater management system, examples from one or all sections of this guide may be useful. This handbook is not intended as a comprehensive or technical guide to the design ofstormwater management systems, but it is a starting point to give a context for consideration of different stormwater solutions. New innovations and improvements occur all the time. For more technicaland detailed information, refer to the Stormwater Management Manual or consult with a professional.The Stormwater Management Manual is available at portlandonline.com/bes.

STORMWATER SOLUTIONS HANDBOOK - Environmental Services - City of Portland Oregon

Table of contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . .5Facilities Illustration . . . . . . . . . . . . . . . . . . . . . . . . . . .6Factors Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

When it falls on the roof . . . . . . . . . . . . . . . . .9Downspout disconnection . . . . . . . . . . . . . . . . . . . . . .10Rain barrels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12Cisterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Ecoroofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Roof gardens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

When it gets to the ground . . . . . . . . . . . . . . .21Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Contained planters . . . . . . . . . . . . . . . . . . . . . . . . . . .24Vegetated swales . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26Vegetated infiltration basins . . . . . . . . . . . . . . . . . . . .28Flow-through planters . . . . . . . . . . . . . . . . . . . . . . . . .30Infiltration planters . . . . . . . . . . . . . . . . . . . . . . . . . . .32Pervious pavers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Pervious pavement . . . . . . . . . . . . . . . . . . . . . . . . . . .36Turf blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Taking it underground . . . . . . . . . . . . . . . . . . .41Drywells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Soakage Trenches . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

Planting Choices . . . . . . . . . . . . . . . . . . . . . . . .47Landscaping Examples . . . . . . . . . . . . . . . . . . . . . . . . .48

For more information . . . . . . . . . . . . . . . . . . .51

5

IntroductionWhy Sustainable Stormwater Management Matters

Before Portland was developed, forests and open spaces absorbed rainwater. Today, rainfalls on buildings, streets, sidewalks, and other hard surfaces and runs off into riversand streams. Stormwater runoff causes erosion, carries pollution and sediment to the

river, decreases groundwater recharge, and increases river temperatures. Sustainablestormwater management is a strategy that helps the City of Portland comply with pollutionprevention and resource protection regulations by managing water at its source.

Sustainable stormwater management is rapidlygaining acceptance in the United States, partic-ularly here in Portland. The increased interest isa response to mounting infrastructure costs ofnew development and redevelopment projects,more rigorous environmental regulations, andconcerns about the impact of growth on natural resources.

The strategy recognizes the relationshipbetween the natural environment and the builtenvironment, and manages them as integratedcomponents of a watershed. Sustainablestormwater management is an alternative tothe traditional piped approach. It promotesonsite collection and conveyance of stormwaterfrom roofs, parking lots, streets, and other sur-faces to infiltrate into the ground or collect forreuse, often reducing the need for costlyunderground structures.

The approach relies on vegetated natural sys-tems to slow and filter the water. Vegetationenhances both interception and evaporation ofrainfall through its leaves. Vegetation reducesstormwater runoff volume as well as pollutantsin urban runoff.

Studies show that natural landscaping at a resi-dential development can reduce annualstormwater runoff volume by as much as 65%.Natural drainage and native landscaping areas

in residential developments can remove up to80% of the suspended solids and heavy met-als, and up to 70% of nutrients like phospho-rous and nitrogen from stormwater runoff.

Sustainable stormwater management uses bothstructural devices such as rain barrels, cisterns,and planters, and non-structural devices likelandscaped swales and infiltration basins. Thesustainable approach is cost effective andattractive. It also addresses erosion, water pol-lution, combined sewer overflows and otherstormwater runoff problems all at once.

The information presented shows how to useone or a combination of technologies to effec-tively manage stormwater onsite and reducethe impacts of development on water quality.

This information is not intended as a substitutefor professional advice applicable to specificproject circumstances. Design approaches areoffered to facilitate understanding of the con-cepts and must be considered in terms of theproject, site conditions, local building codes,water availability, and regional climate. Readersare urged to seek professional assistancebefore applying any of these techniques. Thetechniques and other information presentedmay not represent the latest, approvedapproaches of the City of Portland.

residential and neighborhood facilities

Disconnected downspout rainbarrels garden swaleecoroof on garage

naturescapinglarge treesflagstone drivewaydriveway of pervious pavers

Commercial and industrial facilities

Disconnected downspoutDisconnected downspout ecoroof roof garden

pervious paver parking lot sidewalk planter with trees naturescapingparking lot swales

General factors that influence the selection of stormwater management facilities

This chart is a guide to typical site conditions, the benefits of specific approaches and how they

may influence your selection of stormwater management facilities. It is a general guide, not a

definitive analysis.

Site conditions will

vary, and exceptions

may apply. See

individual facility

descriptions for

specific details

such as siting,

permitting, and

design standards.

Dow

nspo

ut D

isco

nnec

tion

to

Land

scap

e

Rain

Bar

rels

Cist

erns

Ecor

oofs

Roof

Gar

dens

Tree

s

Vege

tate

d Sw

ales

Vege

tate

d In

filt

rati

on B

asin

Cont

aine

d Pl

ante

rs

Flow

-thr

ough

Pla

nter

Infi

ltra

tion

Pla

nter

Perv

ious

Pav

ers

Perv

ious

Pav

emen

t

Turf

Blo

ck

Soak

age

Tren

ches

Dry

wel

ls

Constraints When selecting an appropriate facility, it is important to assess your site for soil type,slope, amount of space, and proximity to your foundation and your neighbor’s property. For example,infiltration facilities do not perform well in soils that do not drain well (such as clay) or on sites thathave steep slopes due to erosion concerns.

Space limitations

Poorly-draining soils

Steep slopes

Benefits Some facilities are best for flow control (reducing total volume and/or velocity), other facilities are better for cleansing and filtering pollutants, some facilities do both, and some facilitiesachieve cooler air and water temperatures.

Air and water temperature reduction

Water quality

Flow control

l Most appropriate Moderately appropriate m Least appropriate

l l w l l l l m l l w l l l l l

m l l l l l w m l l m m m m m m

m l m l l l m m m l m m m m m m

l m m l l l l l l l l m m m l l

w m m l l m l l m l l w w w m m

l l l l l m l l m l l m w w l l

w

9

when itfalls onthe roof

Rooftops account for about 20% of thesurface area in the City of Portland. Rainon the roof drains through a pipe or

downspout. Downspouts connected directlyto the City’s combined sewer system con-tribute to combined sewer overflows (CSOs).CSOs occur when stormwater runoff fillscombined sewers to capacity and they over-flow to the Willamette River. Stormwater that doesn’t overflow goes to the City’ssewage treatment plant. Sending relativelyclean roof runoff into the sewer system also adds unnecessary treatment expense.

Solutions can be as simple as:

• Disconnecting the roof downspout fromthe sewer pipe and letting runoff flow toa lawn or garden.

• Directing runoff to a rain barrel or cisternto save for reuse.

• Adding an ecoroof or roof garden toabsorb rain.

Stormwater treatments described in this section include:

Downspout Disconnection

Rain Barrels

Cisterns

Ecoroofs

Roof Gardens


• For systems that free-fall to the air awayfrom the building, the collection areabelow the concentrated discharge musthave a minimum of 2 inches of gravel perstory of free-fall or other protective materi-al rated to withstand flows and be spacedaway from the building foundation accord-ing to the standards above.

• Refer to Portland’s StormwaterManagement Manual for detailed informa-tion on sizing, placement, and design.

You can also replace downspouts with otherstructures that convey roof runoff to the dis-charge point, such as: • Drip chains, usually made of steel, with a

minimum three-inch diameter;

• Scuppers, which collect and concentratethe runoff and allow it to free-fall; and

• Decorative gargoyles that concentrate therunoff and allow it to free-fall.

Permits• The City requires a permit to disconnect a

residential downspout, unless workingwith the Environmental ServicesDownspout Disconnection Program. The City requires a plumbing permit if the downspout is directed to an onsitestormwater management facility such as a cistern.

ExamplesBureau of Environmental Services WaterPollution Control Laboratory, 6543 N Burlington Avenue, under the St. Johns Bridge.

Oregon Convention Center, NE 1st Avenue and Lloyd Blvd.

Friends of Trees, 3117 NE ML King Jr. Blvd.

Liberty Centre Parking Garage, NE Oregon between 6th and 7th

George Middle School, 10000 N Burr

STORMWATER SOLUTIONS HANDBOOK - Environmental Services - City of Portland Oregon10

BenefitsDownspout disconnection reducesstormwater in the sewer system. Storingroof runoff for irrigation or gray water sys-tems conserves potable water and canreduce water bills. Disconnection is simple,inexpensive, effective, and easily integratedinto the landscape design. In Portland, over47,000 residential properties have discon-nected downspouts, removing more thanone billion gallons of roof water every yearfrom the combined sewer system.

MaintenanceMaintenance is minimal. Check periodicallyto ensure the discharge location has propererosion control and drainage. Check mate-rials for leaks or defects, and remove accu-mulated leaves or debris, especially fromgutters. Most materials can last for aboutten years, and can easily be replaced.

CostDownspout disconnection is inexpensive. Intargeted neighborhoods, the City payshomeowners $53 for each downspout they

disconnect themselves, or will do the workfor free. Materials such as elbows and exten-sions are readily available at hardware, build-ing supply, and home improvement stores.

Safety and Siting Requirements• A common method of residential discon-

nection is to cut the downspout above thesewer standpipe, plug the standpipe andattach an elbow and extension piece thatdirects runoff to the discharge point. Inmany cases, a splash block at the end ofthe extension conveys water away fromfoundations and prevents erosion.

• Roof runoff must be discharged at leastfive feet away from any property lines.

• Make sure the discharge from the pipedoes not flow toward the building orneighboring property.

• In east Portland, the discharge pointshould be at least six feet away from base-ments and two feet away from crawlspaces and porches.

DOWNSPOUTDISCONNECTION(splashblock disconnection)

In conventional construction, roof runoff flows through gutters and down-spouts to a drywell, storm sewer or combined sewer. Disconnecting down-spouts helps keep clean roof runoff from overloading the sewer system

when it rains. Roof runoff can be redirected to a yard, garden, swale, orstormwater planter, or to a rain barrel or cistern for storage.

Downspouts can be disconnected on residential, commercial and industrialproperties. The system you choose can be as simple or complex as your goalsand site requirements allow.

The

system

you

choose

can

be

simple

or

complex


RAIN BARRELSRain barrels placed at the end of roof downspouts capture and store roof

runoff for non-potable water use, like irrigation. Rain barrels come in awide variety of materials, designs, and colors. Common sizes for residential

use are 55 gallons and 90 gallons. They are usually installed on the ground nextto buildings.

Commercial or industrial properties are more likely to use cisterns because oftheir larger capacity and durability.

BenefitsUsing rain barrels to temporarily store andreuse rainwater slows and reducesstormwater runoff from the site. Theyconserve non-potable water and mayreduce water use charges. Rain barrels areinexpensive, easy to install and maintain,and readily available.

MaintenanceInspect periodically for leaks, especiallyspigots and other connection points.Make sure debris does not clog the sys-tem. Screen all vents to prevent mosquitobreeding. For maximum stormwater bene-fits, empty the barrel between rain eventsin the wet season. Clean the rain barrelinterior annually by brushing or disinfect-ing with vinegar or other non-toxic clean-ers. The washout can be disposed ofonsite to vegetated areas if disinfectingagents are adequately diluted so they donot harm plants. A rain barrel and its sys-tem components have a lifespan of about20 years.

CostDo-it-yourself rain barrels can be constructedfor under $30. Ready-made 55 gallon to 90gallon rain barrels generally cost from $50 to$300 uninstalled. All rain barrels must bemosquito proof, have approved overflowpoints and meet city standards.

rain

barrels

are

containers

that

capture

the roof

runoff

flowing

out

of a

downspout


Safety and Siting Requirements

• A typical residential rain barrel designincludes an opening in the sealed lid toaccept downspout flow, an overflow pipefor when the barrel is full, and a spigotat or near the bottom to attach a hose orfaucet. A screen at the opening controlsmosquitoes and other insects. Severalrain barrels can be connected to storemore rainwater.

• Locate rain barrels on a flat surface nextto or near roof downspouts.

• In areas with soils that drain well, youcan direct overflow from the rain barrelsonto the yard or landscape areas. Thearea must meet the safety requirementslisted under downspout disconnect.

• Only collect roof water for reuse. Do notreuse water from parking or pedestrianareas, surface water runoff, or bodies ofstanding water.

• Refer to Portland’s StormwaterManagement Manual for detailed sizing,placement, and design information.

Permits• Rain barrels attached to a downspout that

do not connect back into the building’swater system do not require permits.

ExamplesFriends of Trees, 3117 NE ML King Jr. Blvd.


CISTERNSAcistern is a structure that captures and stores roof runoff. The collected

water can be used for landscape irrigation and some interior uses, suchas toilets and washing machines. It is possible to use a cistern system for

household drinking water if it has proper filtration, inspection and permitting.Cisterns are constructed of durable material, such as concrete, plastic, polyethyl-ene, or metal. They are larger and usually more permanent than rain barrels,ranging in size from 100 gallons to 10,000 gallons. They can be placed above-ground, underground or on a rooftop.

A roof washer or filter removes contaminants and debris before the runoffenters the cistern. A pipe from the cistern conveys the stored water, either bygravity or pump, to the designated interior or exterior use. In some instances, anoverflow system conveys excess runoff to a destination location. At sites withsoils that drain well, the overflow can be conveyed to onsite landscaped areas orinto perforated underground pipes if permitting requirements are met.

BenefitsUsing a cistern to store and reuse rainwaterreduces or eliminates stormwater runoff fromthe site. It conserves potable water andreduces water charges with an installedmeter. Cisterns are available from manysources, and are relatively easy and inexpen-sive to install and maintain, especially if theyare above ground. Rainwater can be used forpotable applications if the water is treatedand meets state and federal safe drinkingwater standards, and the system meets per-mitting requirements.

MaintenanceInspect the cistern periodically to ensuredebris does not clog the system. Check forleaks at connection points. Clean the cisterninterior annually with a brush and vinegar orother non-toxic cleaner that will not degradewater quality or harm the cistern. The

washout from cleaning can be disposed ofonsite to vegetated areas if disinfectingagents are adequately diluted so they do notharm plants. Schedule cleaning during dryweather. A cistern and its components have alifespan of 20 to 50 years, depending onlocation and material.

CostCosts for a cistern, not including installation,range from about $250 for a 200-gallon cis-tern to $5,000 for a 10,000-gallon cistern.

Safety and Siting Requirements• Only collect roof water for reuse. Do not

reuse water from parking or pedestrianareas, surface water runoff, or bodies ofstanding water.

• With the proper permitting, undergroundcisterns in areas with soils that drain wellmay be approved to overflow into under-ground perforated pipes.

Water

collected

in a

cistern

can be

reused

in the

landscape


• In areas where soils do not drain well,overflow to a city system is required.


Permits• Installing a cistern requires a plumbing

permit from the City’s Bureau ofDevelopment Services (BDS) because instal-lation usually involves altering or addingplumbing components.

• Any pumps or other electrical controlsrequire an electrical permit from BDS.

• Any cistern footings, foundations, enclo-sures, and roof structures require a build-ing permit from BDS.

• Rooftop cisterns require a building permitfor structural review and approval by BDS.

• Underground tanks require a grading anderosion control permit.

ExamplesDaVinci Middle School (aboveground)2508 NE Everett Street

Portland State University-Stephen Epler Hall(underground)SW 12th and Montgomery

Oregon Natural Resources Council (ONRC)(underground)5825 N Greeley Avenue

aboveground underground


ECOROOFS (extensive roof or green roof)

An ecoroof is a lightweight vegetated roof system used in place of a con-ventional roof. Ecoroofs are typically made of a waterproof membrane,drainage material, a lightweight layer of soil, and a cover of plants.

Choose species appropriate for a rooftop environment - dry and hot in summer,wet in winter. Ecoroofs are not intended to be accessed except for maintenance, unless walkways or plazas are incorporated into the design.

BenefitsAn ecoroof can capture and retain 60% ofthe annual precipitation that falls on it.Nearly all of the rainfall is absorbed duringwarm weather storm events and stormwaterdetention and peak attenuation is alsonotable during saturated winter months. Thisreduces the runoff flow rate, volume andtemperature of roof runoff. Ecoroofs can out-last conventional roofs by twenty years ormore. An ecoroof also filters air pollutants;reduces outdoor air temperatures and theresulting urban heat island effect; increaseswildlife habitat and urban green space; insu-lates the building and lowers heating andcooling costs; and is visually attractive.Buildings in the Central City that have City-certified ecoroofs can receive from one tothree square feet of additional floor area ratio(FAR) for each square foot of ecoroof.

VegetationThere are many options for ecoroof plantings.Choose drought tolerant species such assedums, succulents, or hardy perennials.Plants should be low maintenance, able totolerate shallow soil, and be self-sustainingwithout fertilizers or pesticides and minimumsummer irrigation.

MaintenanceLike a conventional roof, an ecoroof requiressome care to maintain optimum function.This may include occasional summer watering, weeding, and mulching, particularlyduring the plant establishment period. If theroof includes grasses or other annual plants,occasionally cut and remove dry vegetation to ensure that combustible material does notaccumulate. Inspect the roof regularly tocheck drainage and vegetation. Some addi-tional plantings may be needed to fill in bare soil areas.

CostAn ecoroof initially costs more than a conven-tional roof, but typically lasts twice as long(about 40 years). Costs range from $10 to$15 per square foot for new construction and$15 to $25 per square foot for re-roofing.Long-term savings from deferred repair andreplacement, lower heating and cooling costs,and reduced maintenance help offset theshort-term capital costs. As the ecoroofindustry develops, costs may decrease.

Ecoroofs

can

out last

conventional

roofs

by twenty

years or

more


Safety and Siting Requirements• Consult a design professional

• Locate ecoroofs on flat or pitched structuresup to a slope of 25%.

• Roof strength must be adequate to hold10-25 pounds per square foot above therequirements for a basic roof.

• Choose the area and depth of the ecoroofbased on your water-retention goals, structure, and planting requirements.Thicker ecoroofs provide more flow controland allow for more vegetation options, but require additional structural support.

• Include overflow structures such as drains or downspouts.


Permits

• Ecoroofs usually require certification from a structural engineer to receive City approval.

• Ecoroofs may require alteration of downspouts or other piping, requiring aplumbing permit from the Bureau ofDevelopment Services.

• If applying for the Floor Area Ratio (FAR)bonus program, an ecoroof design is subject to Environmental Services reviewand the City Design Review.

ExamplesJean Vollum Natural Capital Center, 721 NW 9th Avenue

Hawthorne Hostel, 3031 SE Hawthorne Blvd.

Multnomah County building, 501 SE Hawthorne Blvd.

Metro Regional Headquarters600 NE Grand Avenue

FILTER FABRIC

GROWING MEDIUM

DRAINAGE LAYER(as needed)

WATERPROOFMEMBRANE

ROOT BARRIER (as needed)

ROOF STRUCTURE

Ecoroof2006


ROOF GARDENS(intensive roof)

Aroof garden is a heavyweight vegetated roof system used in place of aconventional roof. Roof gardens typically consist of a waterproof mem-brane, drainage layer, and a thick layer of soil (typically 12 inches or

more), vegetation, and hardscaping to allow access to the garden (e.g., planters,stepping stones, benches).

Because a roof garden can support pedestrian traffic, it can be designed as abuilding amenity, with walkways, terraces, plazas or seating areas. It differs froman ecoroof by its greater soil depth and weight, accessibility, and the greaterrange of plants it can accommodate.

BenefitsA roof garden reduces runoff flow rate, volume, and temperature. Roof gardens canoutlast conventional roofs by twenty years.They also filter air pollutants, reduce outdoorair temperatures and the resulting urban heatisland effect, increase wildlife habitat; insulatethe building and lower energy costs. Long-termsavings from deferred repair and replacement,lower heating and cooling costs, and reducedstructural maintenance help offset the short-term capital costs. In addition, turning previ-ously wasted rooftop space into an accessibleand appealing area adds value to the building.

VegetationRoof gardens can be planted with a wide vari-ety of vegetation including trees, shrubs, herbs,succulents, and grasses. Plants should bedrought tolerant and self-sustaining, withoutthe need for fertilizers or pesticides. Theyshould be appropriate for the limited soildepths, moisture, and nutrient level.

MaintenanceLike a conventional roof, a roof gardenrequires care to maintain optimum function.This includes irrigation, and manual weedingand mulching, especially during the plantestablishment period. Maintenance and irriga-tionneeds will depend on design and vegeta-tion used. If the roof includes grasses or otherannual plants, cut and remove dry vegetationto prevent combustible material from accumu-lating. Check drainage and vegetation regular-ly. Some plant replacement may be necessary.

CostThe initial cost of a roof garden is more than aconventional roof, but will last longer. Costsalso depend on the type and amount ofwaterproofing and drainage material, depth ofsoil, amount of hardscaping and size and typeof plant material.

roof gardens

can

support

pedestrian

traffic


Safety and Siting Requirements• Consult a design professional

• Locate roof gardens on flat or shallow-pitched roof structures.

• Building structures must be adequate tohold the additional weight on the roof.

• Roof gardens can contain picnic, park orother multiple use areas. They can includewalkways for recreation or maintenance.

• Include overflow structures such as drainsor downspouts.


Permits• Roof gardens require substantially upgrad-

ed structural support. Bureau ofDevelopment Services (BDS) approvalrequires a signed document from a struc-tural engineer.

• Roof garden retrofits usually need alter-ation of downspouts or other piping,requiring a plumbing permit from BDS.

• The stormwater management portion ofthe facility must be reviewed byEnvironmental Services.

ExamplesMarket Building, 200 SW Market Street

The PacWest Building, 1211 SW 5th Avenue

Terry Shrunk Plaza, SW 3rd and 4th Avenuesand Madison and Jefferson Streets, is astreet-level roof garden over an undergroundparking garage.

Portland State University-Native AmericanStudent Center, 710 SW Jackson Street

FILTER FABRIC

GROWING MEDIUM

DRAINAGE LAYER(as needed)

WATERPROOF MEMBRANE

ROOT BARRIER (as needed)

ROOF STRUCTURE

DEPTHSCANVARY

Roof Garden2006

21

whenit getsto theground

Landscape Solutions

Plants and trees add visual appeal and canincrease property values. Careful land-scaping can also help manage stormwa-

ter, save energy, reduce pollution and improveair quality. Even sites with space constraintsor poor drainage can benefit from landscap-ing for stormwater management. It doesn’thave to be complex or expensive, and it canoften reduce the development costs by elimi-nating the need for inlets, drains, andstormwater piping.

Stormwater treatments include:

Trees

Contained Planters

Vegetated Swales

Vegetated Infiltration Basins

Flow-Through Planters

Infiltration Planters

Paving SolutionsEven when an area requires paving, there arestill options to infiltrate stormwater into theground.

Stormwater treatments include:

Pervious Pavers

Pervious Pavement

Turf Block


TREESAdding trees to landscaping is easy, attractive, and has many stormwater bene-fits. A single mature tree with a 30 foot crown can intercept over 700 gallons ofrainfall annually. Evergreen trees will capture more rainwater in winter monthsthan deciduous trees.

BenefitsTrees capture and hold rainfall in leaves andbranches. They slow runoff flow and candecrease stormwater volume by 35% ormore for small storms. Trees improve waterquality by filtering rainwater and holding soilsin place, which is especially important alongstream banks. Their shade reduces pavementheat, which in turn lowers runoff tempera-ture. Tree wells can provide additional bene-fits by accepting runoff from sidewalks orother paved areas.

MaintenanceSelecting appropriate trees reduces mainte-nance needs. Trees usually require watering inthe summer and wind protection in the firstone to three years. Stake loosely for the firstyear. Routine maintenance includes rakingand disposing of leaves and debris, removingweeds, pruning dead branches, and control-ling pests.

CostCosts vary with the type and size of the tree,but the general range is $20 to $100 each,not including planting. Local non-profitgroups often supply free or low-cost treesthat are appropriate for our climate.

Safety and Siting Requirements

• Trees provide the greatest stormwater andenvironmental benefit when their canopycovers impervious areas and intercepts waterbefore it falls to the ground.

• Choose trees suitable for the soil type,amount and intensity of sunlight and spacerequirements.

• Street trees are regulated by Portland Parks& Recreation. Call 503-823-PLAY for moreinformation.

• Locate utilities before digging. Call 503-246-6699. (Portland)

• Refer to Portland’s Stormwater ManagementManual for information on sizing, place-ment, and design.

Permits• No permits are required for planting trees on

private property.

• Planting or removing trees from the publicright-of-way requires a tree permit from theCity Forester.

• Natural area trees are regulated by E-Zonerequirements.

adding

trees

is easy,

and has

many

benefits


• To receive stormwater management creditper the Stormwater Management Manual,new deciduous trees must be at least 2”caliper and new conifers must be at least6 feet tall. In the right-of-way, new treesmust be at least 2” caliper for residentialareas and 3.5” caliper in commercial andindustrial zones.

• For Clean River Rewards credit treesmust be at least 15 feet tall and on private property. This does not includetrees in the public right-of-way such asstreet trees.

ExamplesSW Park Blocks

Friends of Trees, 3117 ML King Jr. Blvd.

NE Ainsworth Linear Arboretum, NE Ainsworth from ML King Jr. Blvd. to NE 42nd

SE Ladd’s Addition

Hoyt Arboretum


CONTAINED PLANTERS(contained planter boxes)

Acontained planter is filled with soil and plants that accept precipita-tion only, not stormwater runoff from another source. It is placedabove ground on an impervious surface. Rainwater is temporarily

stored above the soil, and then filters down through the planter. In somecases, weep holes provide drainage through the bottom of the planter ontothe impervious surface. Contained planter boxes can be prefabricated pots orconstructed in place. They come in all shapes and sizes, are made of stone,concrete, brick, plastic lumber or wood, and can hold a variety of plants.

BenefitsA contained planter reduces impervious areaand stormwater runoff. Contained planters aresimple, cost-effective, and visually appealing.They can be placed on many types of flatimpervious surfaces, such as sidewalks, plazas,and rooftops.

VegetationPlanters can contain small trees, shrubs, flow-ers, bulbs, and groundcovers. Trees are espe-cially recommended because they providecanopy cover for impervious surfaces not cov-ered by the planter. Self-sustaining plants thatdo not require additional fertilizers or pesti-cides are recommended.

Maintenance Contained planters require minimal mainte-nance. Check them periodically to maintainadequate drainage. They are likely to needsummer watering and weeding. Potted plantsrequire more water than the same plantsgrowing in the ground.

CostThe cost of contained planter boxes varies,depending on the size and materials.

Safety and Siting Requirements• Locate planters on virtually any impervious

surface. They can be any shape or size, assite requirements, budget and maintenancedictates.


Permits• Planters located on ground level within the

public right-of-way may require approvalfrom the City Forester and PortlandDepartment of Transportation.

contained

planters

can be

placed

on many

types

of flat

impervious

surfaces


Examples1100 block of the downtown Portland transit mall

Federal Building, 1200 SW 3rd Ave.

GROWINGMEDIUM FILTER FABRIC

WEEP HOLES FOR DRAINAGE

IMPERVIOUS SURFACE

Contained Planterrevised 2006


VEGETATED SWALES(bioswales, grassy swales)

Swales are gently sloping depressions planted with dense vegetation orgrass that treat stormwater runoff from rooftops, streets, and parking lots.As the runoff flows along the length of the swale, the vegetation slows

and filters it and allows it to infiltrate into the ground. Where soils do not drainwell, swales are typically lined and convey runoff to a drywell or soakage trench.Swales can include check dams to help slow and detain the flow. A swale canlook like a typical landscaped area.

BenefitsThe plants in a swale filter and slowstormwater runoff while sediments and other pollutants settle out. Swales are cost-effective, attractive and can provide wildlifehabitat and visual enhancements. Single ormultiple swale systems can treat and disposeof stormwater runoff from an entire site.Swales can reduce the number and cost ofstorm drains and piping required whendeveloping a site.

VegetationSwales can be planted with a variety of trees,shrubs, grasses, and ground covers. Plantsthat can tolerate both wet and dry soil condi-tions are best. Plant grassy swales with nativebroadleaf, dense-rooted grass varieties. Avoidtrees in areas that require enhanced structur-al stability, such as bermed side slopes.Summer irrigation and weed pulling may berequired in the first one to three years.

MaintenanceInspect swales periodically, especially aftermajor storm events. Remove sediment andtrash, clean and repair inlets, curb cuts,check dams, and outlets as needed. Maintainside slopes to prevent erosion and ensure

proper drainage. With proper constructionand maintenance, swales can last indefinitely.

CostCosts vary but swales typically cost less than astandard piped, drainage system.

Safety and Siting Requirements• Swales located closer than 10 feet from

building foundations need a variance fromBureau of Development Services (BDS)

• Locate swales at least 5 feet from anyproperty line

• Grade the site so that water drains to the swale, or provide some form of conveyance such as a trench or berm todirect the runoff into the swale if sitegrading is impractical.

• Many parking lot planting islands can beexcavated and retrofitted into swale systems with curb cuts.


swales

have

many

options

in design

and

planting


Permits• Swales that accept roof runoff may require

altering downspouts or other piping and aplumbing permit from the Bureau ofDevelopment Services (BDS).

• Depending on the area of ground distur-bance, a clearing and grading permit maybe required from BDS.

• The stormwater management portion ofthe facility may need review from theBureau of Environmental Services (BES).

• Stormwater systems on non-residentialsites need a commercial building permit.

ExamplesOMSI and PCC annex parking lots, 1945 S.E. Water Ave.

Water Pollution Control Lab, 6543 North Burlington Ave.

Parkrose Middle School, 11800 NE Shaver

Glencoe Elementary School, 825 SE 51st Ave.

Siskiyou Green Street, NE Siskiyou between35th Place and 36th Ave.

GROWINGMEDIUM

EXISTING SOIL

CURB CUT

LOW PLANTINGSUNDER CAROVERHANG

Vegetated Swale2006

CHECK DAMS

IMPERVIOUSSURFACE

OVERFLOW TOAPPROVED DESTINATION

(As needed)

WHEELSTOP

(for parkingapplication)


VEGETATEDINFILTRATION BASINS(rain gardens)

Vegetated infiltration basins are landscaped depressions that are either exca-vated or created with bermed side slopes. An inlet pipe from or sheet flowover impervious surfaces conveys stormwater runoff into the basin, where

it is temporarily stored until it infiltrates into the ground. Basins often providecomplete onsite infiltration for small storm events. Check dams or weirs can beused to detain the flow. They can be sized to infiltrate large storms in areas wheresoils drain well, or they may require a safety overflow or disposal method.

BenefitsBasins or rain gardens eliminate or dramati-cally reduce stormwater flow rates and vol-umes. They improve water quality by settlingand filtering out pollutants, they rechargegroundwater, and they can provide stormwa-ter storage capacity in a large drainage area.Trees planted in infiltration basins can shadebuildings and parking lots or other pavedareas, reducing runoff temperatures. The vegetation also helps prevent soil erosion,provides wildlife habitat, and is visually attractive. Vegetated infiltration basins canhave an informal or formal design and areeasily integrated into the overall landscape or site design.

VegetationVegetated infiltration basins can be plantedwith a variety of trees, shrubs, grasses, andground covers. Trees are highly recommendedfor their shading and temperature reductionbenefits. Avoid permanent irrigation wherepossible. Basins are likely to need wateringand weed pulling during the first one to three years.

MaintenanceInspect the vegetation and structure periodicallyand after major storm events. Vegetation main-tenance is similar to that used for other typesof managed landscapes. Maintenance needsinclude removing sediment and debris; cleaningand repairing inlets, embankments, berms,dams, and outlets as needed; controlling ero-sion; and ensuring proper drainage. Some plantreplacement may be necessary. With properconstruction and maintenance, a vegetatedinfiltration basin can last indefinitely.

CostThe cost of vegetated infiltration basins variesdepending on size, site conditions, and the typeand size of the vegetation used. Costs comparefavorably with conventional stormwater man-agement facilities.

Safety and Siting Requirements• Vegetated infiltration basins work best in

areas that drain relatively shallow slopes ofusually less than 5%. Runoff from steeperslopes can be piped into the basin withproper erosion control measures in place.

rain gardens

can be

sized to

handle

small

or large

storm

events


• Infiltration basins located closer than tenfeet from building foundations need avariance from Bureau of DevelopmentServices (BDS).

• Locate basins at least five feet away fromproperty lines.

• Underlying soils should have a minimuminfiltration rate of two inches per hour andshould not be compacted.

• Where needed include an emergency over-flow disposal system to a drywell or to theCity’s storm system.

• Infiltration basins may not be appropriatein areas with high water tables. Theyshould not be designed as a pond, andshould drain a storm event within 30hours.

• Refer to Portland’s StormwaterManagement Manual for details on sizing,placement, and design.

Permits• Depending on the size of ground distur-

bance, a clearing and grading permit maybe required from the Bureau ofDevelopment Services.

• The stormwater management portion ofthe facility will need review from theBureau of Environmental Services (BES).

• Stormwater systems on non-residentialsites need a commercial building permits.

ExamplesBuckman Heights Apartments, 430 NE 16th Ave.

Glencoe Elementary School, 825 SE 51st Ave.

Oregon Convention Center, NE 1st Ave. and Lloyd Blvd.

Wattles Boys and Girls Club9330 SE Harold Street

GROWINGMEDIUM

Vegetated Infiltration Basin2006

IMPERVIOUSSURFACE

OVERFLOW TOAPPROVED DESTINATION

(As needed)EXISTING

SOIL GRAVEL TRENCH(optional)

Photo © Wisconsin Department of Natural Resources


FLOW-THROUGHPLANTERSFlow-through planters are structures or containers with impervious bottoms

or placed on impervious surfaces. They do not infiltrate into the ground.They can be placed in or above the ground level. Flow-through planters

are filled with gravel, soil, and vegetation and are typically waterproofed. Theytemporarily store stormwater runoff on top of the soil and filter sediment andpollutants as water slowly infiltrates down through the planter. Excess watercollects in a perforated pipe at the bottom of the planter and drains to a desti-nation point or conveyance system. Flow-through planters come in many sizesand shapes, and are made of stone, concrete, brick, plastic lumber or wood.

BenefitsBecause flow-through planters can be builtimmediately next to buildings, they are idealfor constrained sites with setback limitations,poorly draining soils, steep slopes, or contam-inated areas. Flow-through planters reducestormwater flow rates, volume, and tempera-ture, and improve water quality. They can alsoprovide shading and energy benefits whensited against building walls. They can be anattractive landscape feature and providewildlife habitat.

VegetationFlow-through planters can contain a varietyof shrubs, small trees, and other plantsappropriate for seasonally moist and dry soilconditions. Summer irrigation and weedpulling may be required. Minimize the needfor permanent irrigation as much as possibleby using native and well-adapted plants.

MaintenanceInspect plants and structural componentsperiodically. Maintenance is similar for all con-tainer plantings. Other maintenance needsmay include removing sediment, cleaning andrepairing pipes, and maintaining properdrainage. Downspouts, curb cuts, and otherfeatures where debris may obstruct flow mustbe inspected and cleaned periodically.

flow-through

planters

temporarily

store

runoff-

cleaning it

before it

drains

to a

conveyance

system


CostThe cost of flow-through planter boxes variesdepending on size and materials. For newdevelopment and redevelopment, they areoften less expensive than conventionalstormwater management facilities.

Safety and Siting Requirements• Flow-through planters are recommended for

compact sites because their size can vary.

• An approved overflow to a proper destination disposal point is required.

• Flow-through planters can be located nextto building foundations or in other situationswhere infiltration is a concern.

• They are ideal for sites with soil that does not drain well, and are suitable to allsoil types.

• Refer to Portland’s Stormwater ManagementManual for details on sizing, placement, and design.

Permits• Flow-through planters that alter existing

plumbing such as downspouts, or add newpipes for disposal require a plumbing permitfrom the Bureau of Development Services(BDS).

• Depending on the area of ground distur-bance, in-ground systems may need a clear-ing and grading permit from BDS.

• The stormwater management portion of thefacility will need review from the Bureau ofEnvironmental Services (BES).

• Stormwater systems on non-residential sitesneed a commercial building permit.

ExamplesPearl Court Apartments, 920 NW Kearney St.

Rebuilding Center of Our United Villages,3625 N. Mississippi Ave.

George Middle School, 10000 N. Burr

Portland State University-Helen Gordon ChildDevelopment Center, SW 12th and Mill andSW 13th and Market

PSU Stephen Epler Hall

OVERFLOW

GRAVEL

GROWINGMEDIUM

PIPE TO APPROVED

DESTINATION

PERFORATED PIPEto run length of planter

BUILDING

DOWNSPOUTOR OTHER CONVEYANCESYSTEM

SPLASH ROCKS / BLOCK

FILTER FABRIC

WATERPROOF BUILDING(AS NEEDED)

2006

Flow-Through Planter


INFILTRATION PLANTERSInfiltration planters are structures or containers with open bottoms to allow

stormwater to slowly infiltrate into the ground. They contain a layer of gravel,soil, and vegetation. Stormwater runoff temporarily pools on top of the soil, and

then slowly infiltrates through the planter into the ground. Infiltration planterscome in many sizes and shapes, and are made of stone, concrete, brick, plasticlumber, or wood. Infiltration planters are not recommended for soils that don’tdrain well. Use flow-through planters instead.

BenefitsInfiltration planters are ideal for space-limitedsites with good drainage. They reducestormwater runoff flow rate, volume, tempera-ture and pollutants, and recharge groundwater.Infiltration planters can be attractive, and areeasily integrated into the overall landscapedesign. They can also provide energy benefitswhen sited near building walls.

VegetationInfiltration planters can contain a variety ofshrubs, small trees, and other plants appropri-ate for seasonally moist and dry soil conditions.Avoid permanent irrigation if possible. Plantersare likely to need watering and weeding in thefirst one to three years.

MaintenanceInspect plants and structural components peri-odically. Remove sediment and clear debrisfrom inlet pipes and curb cuts to maintainproper drainage.

CostCosts vary depending on size and materials. Fornew development and redevelopment, infiltra-tion planters are often less expensive than moreconventional stormwater management facilities.

Safety and Siting Requirements• Infiltration planters located closer than ten

feet from foundations need a variance fromBureau of Development Services (BDS).

• Locate planters at least five feet from anyproperty line.

• Infiltration planters are only suitable for soiltypes that drain well.

• Place them flush to the ground or above it.

• An approved overflow to a proper destination point is required.

• Refer to Portland’s Stormwater ManagementManual for details on sizing, placement, and design.

infiltration

planters

allow

runoff

to

slowly

soak

into

the

ground


Permits

• Infiltration planters that require alterationof downspouts or other piping require aplumbing permit from BDS.

• Depending on the size of ground distur-bance, in-ground systems may need aclearing and grading permit from BDS.

• The stormwater management portion ofthe facility must be reviewed by theBureau of Environmental Services (BES).

• Stormwater systems on non-residentialsites need commercial building permits.

ExamplesLiberty Centre Parking Garage, 600 NE Holladay

Buckman Terrace Apartments, 303 NE 16th Ave.

The ReBuilding Center of Our United Villages,3625 N. Mississippi Ave. (on Missouri Street)

PSU Green Street, SW 12th between Montgomery and Mill

Mississippi Commons3701 N Mississippi Avenue

GROWINGMEDIUM

FILTER FABRIC

WALLOPENING

IMPERVIOUSSURFACE

STRUCTURALWALL

2006

Infiltration Planter

GRAVEL

EXISTINGSOIL


PERVIOUS PAVERS(unit pavers)

Pervious pavers are typically made of pre-cast concrete, brick, stone, or cob-bles. Pavers usually form interlocking patterns, and are placed within a rigidframe on top of a sand bed or an under drain system. Sand or gravel fills

the gaps between pavers, allowing water to pass to the underlying subgradethen infiltrate into the ground. Some pavers also have small voids in the pave-ment surface to increase permeability. Pervious pavers are available in many col-ors, shapes, sizes, and textures, and can support heavy traffic loads and weights.They can replace conventional asphalt or concrete paving in parking lots, roads,and sidewalks.

BenefitsBy infiltrating precipitation, pervious paversreduce stormwater runoff flow rate, volume,and temperature, and filter pollutants. Theyhelp recharge groundwater and maintainstream base flows. Pervious pavers mayreduce or eliminate the need for an under-ground storm drain system or a curb and gut-ter system. They are durable and attractive,and allow great flexibility of design. Perviouspaver areas can serve as an overflow forother stormwater management techniques.

MaintenanceIt is important to control site erosion and sed-imentation to prevent clogging. Annual vacu-um sweeping helps maintain permeability.The gaps between pavers may require occa-sional weeding or scorching and sand orgravel replenishment. Because perviouspavers are easily lifted and reset, they areeasy to repair or replace.

CostPervious paver systems range in cost depend-ing on the size of the installation and theinstallation technique. Data gathered fromBureau of Environmental ServicesWestmoreland Pilot Project (2004) indicate anestimated cost of $5 per square foot installed,including base rock.

Safety and Siting Requirements• Follow the manufacturer’s installation

specifications.

• Use over soils that drain well such as gravelly or loamy sand.

• Do not use pervious pavers in areas withhigh sediment loads that can clog pores in the pavement.

• Pervious pavers are not allowed in areaswhere hazardous material is stored ortransported.


pervious

pavers

can

support

heavy

weights

while

allowing

water

to soak

into the

ground


Permits• Pavers used in public areas and City rights-

of-way require City review for drainageand Americans with Disabilities Act (ADA)compliance. Contact the Portland Office ofTransportation (PDOT) or the City’s Bureauof Development Services (BDS) with ques-tions about use in these areas.


ExamplesOregon Natural Resources Council buildingparking lot, 5825 N. Greeley Ave.

Multnomah Arts Center, SW 31st and Capital Hwy

SE Westmoreland, SE 21st and Rex and SE Knapp

East Holladay ParkNE 128th and Holladay


PERVIOUS PAVEMENT(porous pavement, porous concrete/asphalt)

Pervious pavement is made of either pervious asphalt or pervious concrete.Both materials resemble conventional asphalt and concrete, but have moreair spaces that allow water to pass through the pavement into a reservoir

base of crushed aggregate, then infiltrate into the ground. Pervious pavement isdesigned to accept precipitation only and is typically thicker than traditional con-crete to support the same loads.

Pervious asphalt consists of coarse stone aggregate and asphalt binder, withvery little fine aggregate. Water percolates through the small voids left in the fin-ished asphalt. A thick layer of gravel underneath allows water to drain throughquickly. Pervious asphalt looks similar to conventional asphalt, although with arougher surface, which accounts for its common name “popcorn mix.”

Pervious concrete consists of specially formulated mixtures of Portland cement,open-graded coarse aggregate, and water. It has enough void space to allowrapid percolation of water and resembles exposed aggregate concrete.

BenefitsPervious pavement reduces stormwaterrunoff flow rate and volume, rechargesgroundwater and maintains stream baseflows. The subgrade also filters pollutants.Pervious pavement is less prone to crackingor buckling from freezing and thawing.Studies indicate it requires less frequentrepair and patching than conventionalpaving. In some cases, pervious pavementmay reduce or eliminate the need for anunderground storm drain system or a curband gutter system. Pervious pavement is aneffective method of managing stormwaterrunoff without limiting use of the space.

MaintenanceIt is important to control site erosion andsedimentation of the pavement surface toprevent clogging and maintain permeability.

Cleaning or vacuuming the surface once ortwice a year maintains porosity. Properlyinstalled pervious paving systems last morethan 20 years.

CostPervious concrete pavements range in costdepending on the size of the installation. Inthe Bureau of Environmental Services NorthGay Avenue Project (Summer 2005), a pervi-ous concrete street cost about $100 persquare yard installed, including base rock.

Safety and Siting Requirements• Follow manufacturer’s installation

instructions.

• Weather conditions during installation canaffect the performance and longevity ofpervious pavement. Check with manufac-turers for guidelines.

Pervious

pavement

allows

precipitation

to

percolate

through

to the

ground


• Slope must be less than 10% over thepaved area.

• Use pervious pavement over soils thatdrain well, like gravelly or loamy sand.

• Do not use pervious pavements in areaswith high sediment loads.

• Pervious pavement is not allowed in areaswhere hazardous material is stored ortransported.

• Most systems include an under layer of atleast 12 inches of clean gravel over a layerof geotextile fabric. The under layer servesas an underground detention basin andshould include an overflow outlet to pre-vent water from rising through the pave-ment.


Permits• Pervious pavement systems used to

replace public parking or walkway areasrequire a building permit from the City’sBureau of Development Services.


ExamplesThe Rebuilding Center of our United Villages,parking lot, 3625 N. Mississippi Ave.

N. Gay Avenue between N. Wygant and N. Sumner(pervious concrete and asphalt)

Pervious Concrete at Broadway Pump Station,NE 91st and Broadway

Ecotrust Building Parking Lot (Drive aisles),721 NW 9th Ave.

Pervious concrete

base rock


TURF BLOCK(grass grid, open-cell unit paver, geoblock)

Turf block consists of interlocking concrete or plastic cells filled with soil andplanted with turf grass or a low-maintenance groundcover. Water passesthrough the turf block into a reservoir base of crushed aggregate, then

infiltrates into the subgrade. Turf block accepts precipitation only, not stormwa-ter runoff. It is available in a variety of colors, shapes, sizes, and textures. Turfblock is best suited for areas of low traffic and infrequent parking, such aspatios, walkways, and terraces, residential driveways, overflow parking areas,emergency access roads, and street shoulders.

BenefitsTurf block reduces stormwater runoff flowrate, volume, and temperature, filters pollu-tants, helps recharge groundwater and maintain stream base flows, and controls erosion. In some cases, turf block may reduceor eliminate the need for an undergroundstorm drain system or a curb and gutter system. It has a green appearance and structural strength.

VegetationTurf block systems can be planted with a vari-ety of grasses and low growing groundcoversthat can withstand foot and vehicular trafficand occasional heavy loads. Self-sustainingnative species are recommended.

MaintenanceMaintenance is similar to a regular lawn,requiring mowing, irrigation, raking, andoccasional reseeding. Native grass speciessuitable for the specific area can minimizemaintenance needs. It is important to controlsite erosion, sedimentation, and soil compaction to prevent clogging and maintain permeability.

CostInstallation costs $4 to $6 per square foot,higher than for conventional concrete orasphalt paving. This cost may be offset if it is not necessary to install an undergrounddrainage system or curb and gutter drainage system.

Safety and Siting Requirements• Follow manufacturer’s installation and sit-

ing instructions.

• Use only in gravelly sand, loamy sand orother pervious native soils.

• Like other pervious pavement, turf blocksare not allowed for areas where haz-ardous material is stored or transported.

• Use in low to moderate traffic areas with-out high weight-bearing loads.


turf block

accepts

precipitation

that falls

on it

and can

withstand

traffic


Permits• Using turf blocks in public parking areas,

walkways or rights-of-way requires abuilding permit from the City’s Bureau ofDevelopment Services, with review fromthe Portland Office of Transportation.


ExamplesDosha Building, 2281 NW Glisan

SE Water Avenue - across from OMSI

Washington School for the Blind2310 E 13th streetVancouver, Washington

41

Underground stormwater managementsystems are more complex than manyof the techniques in this guide. The

U.S. Environmental Protection Agency regu-lates drywells and soakage trenches to pre-vent surface contaminants from pollutingdrinking water in wells. Underground sys-tems, except for those taking only residentialroof runoff, must be registered with the stateDepartment of Environmental Quality. Thesesystems can be valuable stormwater manage-ment tools when properly sized, sited andmaintained. They keep stormwater out ofcombined sewers, eliminate the need for curbdrains and piping, and recharge groundwaterto provide year-round stream flow. They canbe cost-effective and do not require space onthe ground surface or roof.

Underground systems used in conjunctionwith above ground treatment systems areknown as a treatment train. For example,stormwater is directed first to a swale or infil-tration basin and any overflow goes to theunderground disposal facility. The techniqueprotects water quality while disposing ofstormwater runoff on site.

In areas of Portland with high water tables,this type of disposal is not permitted.Underground facilities must also be a suffi-cient distance from private drinking waterwells. Before installing an undergroundstormwater disposal system, check the zoningin your neighborhood.

Stormwater Treatments include:

Drywells

Soakage Trenches

taking itunder-ground


DRYWELLSAdrywell is an underground perforated pipe surrounded with gravel that

collects stormwater runoff and infiltrates it into the ground. Stormwaterfrom roofs, parking lots, and other impervious surfaces flows through an

inlet pipe that empties into the drywell. Drywells are made from concrete orplastic in a variety of widths and depths. A catch basin may be required fordrainage areas other than residential roofs.

Drywells can be installed under any surface with adequate drainage. They arenot allowed for wastewater drainage or in wellhead protection areas. Plants canbe established on top of the facility, however there is a need for occasionalaccess for maintenance and inspection.

BenefitsDrywells reduce runoff flow rate, volume,and temperature, and help recharge ground-water. They are disposal only systems and are usually paired with a water quality or pretreatment facility.

MaintenancePeriodically inspect drywell systems to ensureproper operation and structural stability.Maintenance needs include controlling erosion, removing excessive debris, andcleaning and repairing inlet and outlet pipes.Clogged drywells must be refurbished orreplaced. A drywell can last up to 30 yearswith proper construction and maintenance.

CostDrywells are commonly available from con-struction supply companies, and are relativelyinexpensive to install and maintain.Depending on their size, drywell systems costfrom $1,200 to $1,500 including installation.

Safety and Siting Requirements• Drywells are prohibited where there is per-

manent or seasonal groundwater within10 feet of the bottom of the drywell.

• Use drywells in soils that drain well and inareas with low water tables. Drywells areprohibited in some parts of northeastPortland near the Columbia River.

• Place drywells at least 10 feet from thebuilding foundation or basement, 20 feetfrom any cesspool, and five feet from anyproperty lines.

• Pits for drywells must be at least four feetin diameter and five feet deep. Minimumdrywell diameter is 28 inches.

• Drywells must be at least 500 feet fromprivate drinking water wells.


drywells

collect

runoff

and

allow

it to

percolate

into

the soil


Permits• All drywells, except those that drain only

residential rooftops, must be registeredwith the Oregon Department ofEnvironmental Quality before receivingCity permits.

• The City’s Bureau of DevelopmentServices (BDS) must approve drywell sit-ing and sizing.

• New or altered plumbing connectionsrequire a plumbing permit from BDS.

ExamplesDrywells are located on private propertythroughout Portland, and in many publicstreets on the east side of the WillametteRiver. Because they are subsurface facilities,there are no examples to view.

note: Silt basin/collection box or an equivalentwasher is optional but recommended forroof runoff.

Silt basins are highly recommended forall other surfaces.


SOAKAGE TRENCHES(infiltration trenches)

Soakage trenches are shallow lined trenches backfilled with sand andcoarse stone. The trench surface can be covered with grating, stone, sand,grass or similar vegetation. They accept stormwater runoff from roofs,

parking lots, and other impervious surfaces, and can be placed under anyground-level porous surface such as yards and landscaped areas. Stormwaterrunoff flows through an inlet pipe into an underground concrete collection boxthat removes sediment and debris (for roof runoff a washer or equivilant tech-nology - above or below ground - may be used). The runoff then enters thetrench through a perforated pipe that allows it to drain through the backfillmaterial and soak slowly into the underlying soil. It is usually not necessary tohave an overflow mechanism to a secondary disposal or conveyance system.

Soakage trenches can pollute groundwater if not properly sited, designed, andoperated. They are regulated under the federal Underground Injection Control(UIC) program. Contact the Oregon Department of Environmental Quality forrequirements.

BenefitsSoakage trenches reduce runoff flow rate,volume, and temperature and rechargegroundwater. With a sufficient amount ofsand or soil for filtration, they may be used tomeet pollution reduction requirements.

VegetationGrasses, small plants, or shrubs can be usedover the soakage trench. Trees or other deep-rooted plants may damage the piped con-veyance system.

MaintenanceInspect soakage trenches periodically andafter major storm events to ensure properoperation and structural stability.Maintenance needs include controlling ero-sion and debris accumulation; cleaning,repairing, or replacing the piping and fabric

filter as needed; removing sediment from thesilt basin or collection box, and replacingclogged aggregate. With proper constructionand maintenance, a soakage trench can lastup to 30 years.

CostSoakage trenches usually cost between $20 and $30 per cubic foot.

Safety and Siting Requirements• Soils must have a tested infiltration rate of

at least two inches per hour. The bottomof the trench must be at least four feetfrom the water table or any rock layer,hardpan, or other impervious under-ground layer.

• A soakage trench, sized to City of Portlandstandards, can serve a maximum of15,000 square feet of impervious area.

soakage

trenches

are

regulated

to

prevent

pollution


• Install soakage trenches on slopes of lessthan 20%.

• Place the soakage trench at least 10 feetfrom the building foundation or basementand five feet from any property lines.

• Install the trench in native soil level withand parallel to the site contour.

• Portland’s Stormwater ManagementManual provides details on sizing, place-ment and design of soakage trenches.

Permits• All soakage trenches, with the exception

of those that drain residential rooftopsonly, must be registered with the OregonDepartment of Environmental Qualitybefore receiving any City permits.

• The City’s Bureau of Development Services(BDS) must approve soakage trench sitingand sizing.

• New or altered plumbing connectionsrequire a plumbing permit from BDS.

• For soakage trenches sited on slopes ofgreater than 20%, City approval requires astamped and signed geotechnical reportaddressing slope stability.

ExamplesBecause they are subsurface facilities, thereare no installed examples to view.

note: Silt basin/collection box or an equivalentwasher is optional but recommended forroof runoff.

Silt basins are highly recommended forall other surfaces.

47

plantchoicesLandscapingExamplesMany types of plants are well suit-ed for onsite stormwater manage-ment. You can design your site tofit in with any number of aesthet-ics and still provide stormwatermanagement and other landscap-ing benefits.

Here are a few examples fromaround Portland, with photo-graphs of each facility followed by a list of the plants included ineach. Note the placement ofplants listed here such as in thebottom, on the slopes of, andupland of a facility. Differentplants will have a different toler-ance to wet and dry conditions.Consider the constraints of eachsite; all plants pictured here willnot be suitable for every situation.See the Portland StormwaterManagement Manual for a more comprehensive list of appropriate plants.

Stormwater Facility ScienceThe surface area of a typical stormwater facilityallows runoff to pond and evaporate while sedi-ments settle into a layer of mulch. The organicmulch layer prevents soil bed erosion and retainsmoisture for plant roots. It also provides a medi-um for biological growth and the decompositionor decay of organic matter.

The soil stores water and nutrients to supportplant life. Worms and other soil organisms arevery good at degrading organic pollutants, likepetroleum-based compounds. They also help mixorganic material, increase aeration, and improvewater infiltration and water holding capacity.Bacteria and other beneficial soil microbesprocess the majority of pollutants, includingmost of the nitrogen.

The stiff structure of plants such as rushes andsedges slows water passage and traps sedimentswithin the surface area of the facility.


Stormwater PlantersMississippi Commons q Grooved rush Juncus patensr Red twig dogwood Cornus sericea s American cranberry bush Viburnum trilobum var.t Camas lily Camassia leichtlinii u Yellow-eyed grass Sisyrinchium californicumv Sword fern Polystichum munitumw Hardstem bulrush Scirpus acutus

(Not pictured)Creeping Oregon grape Mahonia repensCurly sedge Carex rupestris

Stormwater PlantersThe ReBuilding Center q Red twig dogwood Cornus stoloniferar Baltic rush Juncus balticuss Highbush cranberry Viburnum edulet Pacific ninebark Physocarpus capitatusu Tufted hairgrass Deschampsia caespitosav Slender rush Juncus tenuisw Nootka rose Rosa nutkanax Pacific crabapple Malus fuscay Douglas spiraea Spiraea douglasii

or Hardhack

Not Pictured:Common camas Camassia quamashYellow monkey flower Mimulus guttatusDouglas iris Iris douglasianaSlough sedge Carex obnupta

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NOOTKA ROSE RUSH


Infiltration Basins / RaingardensBuckman Heights Apartmentsq Tall Oregon grape Mahonia aquifoliumr Douglas spiraea Spiraea douglasii

or Hardhacks Siberian iris var. Iris sibiricat David viburnum Viburnum davidiiu Daylily var. Hemerocallis sp. var.v Littleleaf boxwood Buxus microphylla var.

Parking lot SwalesGlencoe Elementary Schoolq Creeping Oregon grape Mahonia repensr Grooved rush Juncus patenss Slough sedge Carex obnuptat Salal Gaultheria shallonu Spanish lavender Lavandula stoechas var.v Blue arctic willow Salix purpurea nanaw Native wetland grass mixx Sugar Maple Acer Sacharrum y Vine Maple Acer Circinatum

Not pictured:Dense sedge Carex densaKinnikinnick Arctostaphylos uva-ursiTall blue oat grass Helictotrichon

sempervirens

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OREGON GRAPE HARDHACK

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EcoroofHamilton West ApartmentsPlants include the following mix:Cascade stonecrop Sedum divergensSpanish stonecrop Sedum hispanicum var.White stonecrop Sedum albumBiting stonecrop Sedum acreReflexed stonecrop Sedum reflexumTasteless stonecrop Sedum sexangularIceplant Delosperma var.Autumn joy sedum Sedum telephium var. Blue fescue Festuca glaucaTwo-row stonecrop Sedum spurium var.Pink Dianthus sp. var.

ICE PLANTSEDUM

EcoroofMultnomah County Building (deeper soil base) Plants include the following mix:Corn poppy Papaver rhoeasEnglish wallflower Cherianthus CheiriSweet William Dianthus barbatusMaiden pink Dianthus deltoidesSpurred snapdragon Linaria maroccanaPlains coreopsis Coreopsis tinctoriaMissouri evening primrose Oenothera missouriensisTelephium sedum Sedum telephium var.


For More InformationGeneral StormwaterCity of Portland Stormwater Management ManualOutlines regulations, specifications and requirements for stormwater facilitieswww.portlandonline.com/bes/index.cfm?c=35117

Center for Watershed Protectionwww.stormwatercenter.net

International Stormwater Best Management Practices (BMP) Databasewww.bmpdatabase.org

City of Portland Clean River Rewards Programwww.CleanRiverRewards.com503-823-1371

City AgenciesCity of Portland, Environmental Services503-823-7740www.portlandonline.com/bes/index.cfm?c=34598

City of Portland, Office of Sustainable Development503-823-7222www.portlandonline.com/osd

City of Portland, Bureau of Development Services503-823-7300www.portlandonline.com/bds

Portland Parks Urban Forestry503-823-4489www.portlandonline.com/parks/index.cfm?c=38294

Downspout DisconnectionCity of Portland, Environmental Services, Downspout Disconnection Program503-823-5858www.portlandonline.com/bes/index.cfm?c=31246


Utility Locate - Call before you dig503-246-6699

DrywellsOregon DEQ Underground Injection Control Program503-229-5886www.deq.state.or.us/wq/groundwa/uichome.htm

EcoroofsCity of Portland, Environmental Services, Ecoroof Program503-823-7740www.portlandonline.com/bes/index.cfm?c=34663

Ecoroofs EverywhereThis local non-profit provides free or low-cost information, technical design assistance andconstruction assistance.503-823-7616www.ecoroofseverywhere.org

Infiltration BasinsInfiltration Basin (Rain Garden) in Bellingham, WAwww.psat.wa.gov/Publications/Rain_Garden_book.pdf

A Rain Garden in Every Communityhttp://basineducation.uwex.edu/rockriver/rgcommunity.cfm

Landscape SolutionsAmerican Society of Landscape Architects Oregon Chapterwww.aslaoregon.org

Paving SolutionsU.S. Environmental Protection Agency (EPA)Fact sheet and list of vendorswww.epa.gov/owm/mtb/porouspa.pdf

Interlocking Concrete Pavement InstituteTrade organization has information on many styles and vendorswww.icpi.org

Asphalt Pavement Association of Oregon503-363-3858www.apao.org

PermitsOregon Department of Environmental Quality (DEQ)503-229-5189www.deq.state.or.us/wq/wqpermit/wqpermit.htm

Portland Bureau of Development Services: 503-823-7300503-823-7300www.portlandonline.com/bds

Portland Office of Transportation503-823-5185www.portlandonline.com/transportation

PlantsCity of Portland, Environmental Services, Plant ListLists beneficial, nuisance and prohibited plants, along with useful information,including sources of native plants.www.portlandonline.com/bes/index.cfm?&a=40732&c=32142

Stormwater Management Manual, plant listwww.portlandonline.com/shared/cfm/image.cfm?id=55831

Native Plant Society of Oregonwww.npsoregon.org

U. S. Natural Resource Conservation ServiceU. S. native plants guide: http://plant-materials.nrcs.usda.gov/technical/websites/nat.html

Rain barrels and cisternsKing County, WA guide to rain barrels and list of PNW vendors.http://dnr.metrokc.gov/wlr/PI/rainbarrels.htm

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1120 SW Fifth AvenuePortland Oregon

97204

503-823-7740

www.cleanriverspdx.org

portland stormwater solutions handbook

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