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Photo by Lovena, Harrisburg, PA

Sustainable Site Development and Conservation Design Considerations for Stormwater Control

Robert Pitt, P.E., Ph.D., BCEE, D.WREDepartment of Civil, Construction, and Environmental EngineeringThe University of Alabama

Conservation Design Approach for New Development

• Better site planning to maximize soil and water resources and topography of site

• Emphasize water conservation and beneficial uses of stormwater on site

• Encourage infiltration of runoff at site• Treat water at critical source areas• Treat runoff that cannot be infiltrated at

site

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Roof Runoff Control Options

• Downspout disconnections

• Rain gardens

• Green roofs

• Beneficial use of roof runoff

Directly connected roof drainDisconnected roof drain

One of the simplest and most effective approaches for the control of stormwater is to reduce the amount of impervious areas that are directly connected to the drainage system. This can be accomplished by using less paved and roof areas (hard to do and meet design objectives), disconnect the impervious areas, or reduce the runoff from the impervious areas by infiltration, or other, methods. Reducing the runoff volume also reduces the pollutant discharges, reduces peak flows, and reduces combined sewer overflows.

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Roof drain disconnections

Burnsville, Minnesota, Rainwater Gardens

97% Runoff Volume Reduction

An example of the dramatic runoff volume reductions possible through the use of conservation design principles (17 rain gardens, at about $3,000 each, at 14 homes in one neighborhood)

Land and Water, Sept/Oct. 2004

.

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Rain Garden Designed for Complete Infiltration of Roof Runoff

Green roof, Portland, OR

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Green RoofingExtensive Green Roof

• Lighter

• <6” media depth

• Planted with sedums or native plant species

• Saturated weights from 12-50lbs/sq.ft.

Intensive Green Roof• Heavier• >12” media depth• Wider variety of

plants which need more care and irrigation

• Saturated weights from 80-100lbs/sq.ft.

Urban Heat Island Effect – Atlanta, GA

Urban Temp. - Day Suburban Temp. - Day

Images Courtesy of NASA

Urban Temp. - NightSuburban Temp. - Night

Can a green roof make an urban area look like a suburban area?

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Central Alabama

Average daily EToreference conditions (inches/day) (irrigated alfalfa)

January 0.035

February 0.048

March 0.072

April 0.102

May 0.156

June 0.192

July 0.186

August 0.164

September 0.141

October 0.096

November 0.055

December 0.036

Evapotranspiration (ET) is the major rain abstraction mechanism available for green roofs, besides some detention storage and evaporation.

Plant Crop Coefficient Factor (Kc)

Root Depth

(ft)

Cool Season Grass (turfgrass)

0.80 1

Common Trees 0.70 3

Annuals 0.65 1

Common Shrubs

0.50 2

Warm Season Grass

0.55 1

Prairie Plants (deep rooted)

0.50 6

Recent results showing green roof runoff benefits compared to conventional roofing (data from Shirley Clark, Penn State –Harrisburg)

Greater than 65% volume reductions due to ET

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Prince George’s County phot

Beneficial use of stormwater as a local resource needs to be seriously considered

Calculated Benefits of Various Roof Runoff Controls (compared to typical directly connected residential pitched roofs)

Annual roof runoff volume reductions

Birmingham, Alabama

(55.5 in. annual rain)

Seattle, Wash. (33.4 in.)

Phoenix, Arizona (9.6 in.)

Flat roofs instead of pitched roofs 13% 21% 25%

Cistern for reuse of runoff for toilet flushing and irrigation

(10 ft. diameter x 5 ft. high)

66 67 88

Planted green roof (but will need to irrigate during dry periods)

75 77 84

Disconnect roof drains to loam soils 84 87 91

Rain garden with amended soils

(10 ft. x 6.5 ft.)

87 100 96

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Pavement Runoff Control Options

• Bioretention

• Biofiltration (with underdrains)

• Porous Pavement

Infiltration/Biofiltration

• Infiltration trenches

• Infiltrating swales

• Infiltration ponds

• Porous pavement

• Percolation ponds

• Biofiltration areas (rain gardens, etc.)

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Small depressions graded near parking lots or buildings for infiltration (older method, using regular turf grass) (MD and WI).

Portland, Oregon, bioretention areas to capture and treat parking lot runoff.

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Parking lot medians easily modified for bioretention (OR and MD).

Larry Coffman

Larry Coffman

Recent Bioretention Retrofit Projects in Commercial and Residential Areas in Madison, Wisconsin

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Neenah Foundry Employee Parking Lot Grass Filter/Biofilter, Neenah, Wisconsin

Bioretention and biofiltration areas having moderate capacity

Surface overflow

Portland, Oregon

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Stormwater filters and bioretention areas in ultra urban setting (Melbourne, Australia)

Street-side tree biofilters in downtown area (Melbourne, Australia)

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Porous paver blocks have been used in many locations to reduce runoff to combined sewer systems, thereby reducing overflow frequency and volumes (Sweden, Germany, and WI).

Not recommended in areas of heavy automobile use due to groundwater contamination (provide little capture of critical pollutants, plus most manufactures recommend use of heavy salt applications instead of sand for ice control).

Essen, Germany

Singapore

Singapore

Austin, TX

Davos, SwitzerlandZurich

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Temporary parking or access roads supported by turf meshes, or paver blocks, and advanced porous paver systems designed for large capacity.

Soil modifications for rain gardens and other biofiltration areas can significantly increase treatment and infiltration capacity compared to native soils.

(King County, Washington, test plots)

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Grass Filtering of Stormwater Sediment

Runoff from Pervious/

impervious area

Trapping of sedimentsand associated pollutantsReducing velocity of

runoff

Infiltration

Reduced volume and treated runoff

Sedimentparticles

Particulate Removal in Shallow Flowing Grass Swales and in Grass Filters

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Head (0ft)

Date: 10/11/2004

2 ft

25 ft

6 ft

3 ft

116 ft

75 ft

TSS: 10 mg/L

TSS: 20 mg/L

TSS: 30 mg/L

TSS: 35 mg/L

TSS: 63 mg/L

TSS: 84 mg/L

TSS: 102 mg/L

Large capacity grass swales and channels designed for both conveyance and water quality objectives.

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Grass Swales Designed to Infiltrate Large Fractions of Runoff (Alabama).

Also incorporate grass filtering before infiltration

Swales can be both interesting and fit site development objectives.

Street Edge Alternative (SEA St) Seattle, WA

Tuscaloosa, AL

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WI DNR photo

Conventional curbs with inlets directed to site swales

WI

MS

Treatment of Flows in Excess of Infiltration Capacity

• Wet detention ponds, stormwater filters, or correctly-sized critical source area controls needed to treat runoff that cannot be infiltrated.

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Wet Detention Ponds

Suspended Solids Control at Monroe St. Detention Pond, Madison, WI (USGS and WI DNR data)

Consistently high TSS removals for all influent concentrations (but better at higher concentrations, as expected)

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Wet detention pondsThe regional swales will direct excess water into the ponds.

Typical pond section:

The pond surface areas vary from 0.5 to 1% of the drainage areas, depending on the amount of upland infiltration. The ponds have 3 ft. of standing water above 2 ft. of sacrificial storage. The live storage volume provides necessary peak flow control.

Treatment of Runoff from Critical Source Areas

• Flow diversion

• Treatment trains having combinations of effective unit processes targeted to pollutants of interest

• Pollution prevention through the use of non-contaminating exposed materials

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Critical Source Area ControlCovering fueling area

Berm around storage tanks

correctly-sized critical source area controls needed to treat runoff originating from heavily contaminated areas

Austin sand filter

MCTT

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Multi-Chambered Treatment Train (MCTT) for stormwater control at large critical source areas

Milwaukee, WI, Ruby Garage

Maintenance Yard MCTT Installation

Pilot-Scale MCTT Test

Results

Ruby Garage MCTT samplesinfluent effluent

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Upflow filter insert for catchbasins

Able to remove particulates and targeted pollutants at small critical source areas. Also traps coarse material and floatables in sump and away from flow path.

Upflow FilterTM

Pelletized Peat, Activated Carbon, and Fine Sand

y = 2.0238x0.8516

R2 = 0.9714

0

5

10

15

20

25

0 5 10 15 20

Headloss (inches)

Flo

w (

gp

m)

Performance Plot for Mixed Media on Suspended Soilds for Influent Concentrations of 500 mg/L, 250mg/L, 100 mg/L and 50 mg/L

0

100

200

300

400

500

600

Influent Conc. Effluent Conc.

Su

sp

en

de

d S

oil

ds

(m

g/L

)

High Flow 500

Mid Flow 500

Low Flow 500

High Flow 250

Mid Flow 250

Low Flow 250

High Flow 100

Mid Flow 100

Low Flow 100

High Flow 50

Mid Flow 50

Low Flow 50

High Zinc Concentrations have been Found in Roof Runoff for Many Years at

Many Locations• Typical Zn in stormwater is about 100 g/L, with industrial

area runoff usually several times this level.• Water quality criteria for Zn is as low as 100 g/L for

aquatic life protection in soft waters, up to about 5 mg/L for drinking waters.

• Zinc in runoff from galvanized roofs can be several mg/L• Other pollutants and other materials also of potential

concern.• A cost-effective stormwater control strategy should include

the use of materials that have reduced effects on runoff degradation.

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2005: Testing Frame Set-Ups at Penn State-Harrisburg and the University of Alabama at Birmingham

Six frames and 12 panels being tested at each site

Examples Utilizing these Concepts• Retrofitted bioretention and wet ponds at big box

commercial development in VT

• Beneficial use of stormwater at university in AL

• Multi-faceted conservation design at residential development in WI

• Multi-faceted conservation design at industrial site in AL

• Large rain garden at transportation corridor in WI

• Green infrastructure retrofitted in combined sewer area in MO

• Groundwater effects with dry wells in NJ

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Big box development stormwater management options.

Summary of Measured Areas• Totally connected impervious areas: 25.9 acres

– parking 15.3 acres

– roofs (flat) 8.2 acres

– streets (1.2 curb-miles and 33 ft wide) 2.4 acres

• Landscaped/open space 15.4 acres

• Total Area 41.3 acres

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Stormwater Controls• Biofiltration areas (parking lot islands)

– 52 units of 40 ft by 8 ft– Surface area: 320 ft2

– Bottom area: 300 ft2

– Depth: 1 ft – Vertical stand pipe: 0.5 ft. dia. 0.75 ft high– Broad-crested weir overflow: 8 ft long, 0.25 ft wide

and 0.9 ft high– Amended soil: sandy loam

• Also examined wet detention ponds

Runoff Volume Changes

Base conditions

With biofiltration

Runoff volume (106 ft3/yr)

2.85 1.67

Average Rv 0.59 0.35

% reduction in volume

n/a 41%

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Birmingham Southern College Campus (map by Jefferson County Stormwater Management Authority)

Birmingham Southern College Fraternity Row

Acres % of Total

Roadways 0.24 6.6%

Parking 0.89 24.5

Walks 0.25 6.9

Roofs 0.58 16.0

Landscaping 1.67 46.0

Total: 3.63 100.0

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Supplemental Irrigation Inches per month (example)

Average Use for 1/2 acre (gal/day)

Late Fall and Winter (Nov-March)

1 to 1-1/2 230 - 340

Spring (April-May) 2 to 3 460 - 680

Summer (June-August)

4 910

Fall (Sept-Oct) 2 to 3 460 - 680

Total: 28 (added to 54 inches of rain)

Capture and Reuse of Roof Runoff for Supplemental Irrigation

Tankage Volume (ft3) per 4,000 ft2 Building

Percentage of Annual Roof Runoff used for Irrigation

1,000 56%

2,000 56

4,000 74

8,000 90

16,000 98

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Combinations of Controls to Reduce Runoff Volume

Total Annual Runoff (ft3/year)

Increase Compared to Undeveloped Conditions

Undeveloped 46,000 --

Conventional development 380,000 8.3X

Grass swales and walkway porous pavers

260,000 5.7

Grass swales and walkway porous pavers, plus roof runoff disconnections

170,000 3.7

Grass swales and walkway porous pavers, plus bioretention for roof and parking area runoff

66,000 1.4

Elements of Conservation Design for Cedar Hills Development

(near Madison, WI, project conducted by Roger Bannerman, WI DNR and USGS)

• Grass Swales

• Wet Detention Pond

• Infiltration Basin/Wetland

• Reduced Street Width

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Available at: http://pubs.usgs.gov/sir/2008/5008/pdf/sir_2008-5008.pdf

The most comprehensive full-scale study comparing advanced stormwater controls conducted.

90% of the site runoff is associated with rains between 0.2 and 3 inches in depth. These are the events that need attention when trying to reduce runoff at this site. 50% of the rains, by count, are less than 0.15 inches in depth.

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Parallel study areas, comparing test with control site

ExplanationWetpond Infiltrations BasinSwalesSidewalkDrivewayHousesLawnsRoadwayWoodlot

N

500 0 500 1000 Feet

Cedar Hill Site Design, Crossplains WI

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Roger Bannerman

Initially installed infiltration area had preferential flow paths and compacted soils

Deep Tilled to 18 inches and Planted Native Plants to Restore Infiltration

Infiltration Basin with Compacted Soils

Roger Bannerman

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WI DNR photos

Reductions in Runoff Volume for Cedar Hills (calculated using WinSLAMM

and verified by site monitoring)Type of Control Runoff

Volume, inches

Expected Change (being monitored)

Pre-development 1.3

No Controls 6.7 515% increase

Swales + Pond/wetland + Infiltration Basin

1.5 78% decrease, compared to no

controls

15% increase over pre-development

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Water Year

Construction

Phase

Rainfall

(inches)

Volume Leaving

Basin (inches)

Percent of Volume

Retained (%)

1999 Pre-construction 33.3 0.46 99%

2000 Active construction 33.9 4.27 87%

2001 Active construction 38.3 3.68 90%

2002

Active construction (site is

approximately 75% built-out)

29.4 0.96 97%

Monitored Performance of Controls at Cross Plains Conservation Design

Development

WI DNR and USGS data

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Aerial Photo of Site under Construction (Google Earth)

• On-site bioretention swales• Level spreaders• Large regional swales• Wet detention ponds• Critical source area controls• Pollution prevention (no Zn!)• Buffers around sinkholes•Extensive trail system linking water features and open space

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Conservation Design Elements for North Huntsville, AL, Industrial Park

• Grass filtering and swale drainages

• Modified soils to protect groundwater

• Wet detention ponds

• Bioretention and site infiltration devices

• Critical source area controls at loading docks, etc.

• Pollution prevention through material selection (no exposed galvanized metal, for example) and no exposure of materials and products.

• Trail system throughout area.

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A new industrial site in Huntsville, AL, has 52 approximately two acre individual building sites. Each of the sites will be served with a grass-lined bioretention channel that will carry site water to a larger swale system. The slopes of the channels vary from about 1 to 6.5%. The peak flow from each construction site was calculated to be about 16 ft3/sec (corresponding to the Huntsville, AL, 25 yr design storm of 6.3 inches for 24 hours). The on-site swales will also have modified soils to increase the CEC and organic matter content to protect groundwater resources.

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Slope Bare soil shear stress (lb/ft2)

Unvegetated mat shear stress, effect on soil (lb/ft2)

Safety factor (allowable shear stress of 0.05 lb/ft2)

Maximum velocity with mature vegetation (ft/sec)

1% 0.14 0.012 4.2 3.1

3% 0.28 0.023 2.2 4.8

5% 0.42 0.035 1.4 5.5

6.5% 0.46 0.039 1.3 6.4

The bare swale soil has an allowable shear stress of about 0.05 lb/ft2. The calculated values for unprotected conditions are all much larger. Therefore, a North American Green S75 mat was selected, having an allowable shear stress of 1.55 lb/ft2 and a life of 12 months. Check dams are needed when slopes are >5% due to high velocities.

Annual Runoff Volume (ft3/year)

Drainage Area

Proposed Stormwater Components

Base Conditions

With Controls

A Pond, swale, and site bioretention

6.3 x 106 2.5 x 106 (61%)

B Small pond and swale 5.4 x 106 1.7 x 106 (69%)

C Pond and swale 2.5 x 106 0.83 x 106 (68%)

D (including off-site area)

Off-site pond, swale, and site bioretention

11 x 106 5.8 x 106 (50%)

Total site 25 x 106 11 x 106 (56%)

Different site subareas have different combinations of controls. Base conditions are for conventional development.

Calculated using WinSLAMM and 40 years of rain records

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Annual Particulate Solids Discharges

(lb/year)

Drainage Area

Proposed Stormwater Components

Base Conditions

With Controls

A Pond, swale, and site bioretention

98,000 4,400 (96%)

B Small pond and swale 54,000 3,800 (93%)

C Pond and swale 19,000 1,200 (94%)

D (including off site area)

Off-site pond, swale, and site bioretention

120,000 9,250 (92%)

Total site 290,000 19,000 (93%)

Conventional Development

Conservation Design

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Conventional Development

Conservation Design

Sediment Reductions

Volume Reductions

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City of Lodi, Columbia County WI

Paved Area = 20%

Drainage Basin Area = 16 acres

Lodi, Wisconsin, Transportation Area Rain Garden

John Voorhees

Overflow Weirs

Lodi Rain Garden Features

Cell A

Cell B

Cell C

Access Path

Sitting Area

Flow Diversion Structure

Inlet

John Voorhees

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To Rain Garden

Overflow to Creek

Flow Diversion Structure

J h V

Rain Garden Backfill Material

Growing Media

Aggregate for Water Storage

Underdrain Pipe Sends Excess Water to Creek

John Voorhees

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Soil/Peat/Sand Mixing

John Voorhees

Cell B

Cell A

John Voorhees

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Cell B Cell C

Cell A

John Voorhees

Prairie Plants

Planting Plan

Cell ACell B

Cell C

Scrubs

John Voorhees

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Lodi rain garden vegetation (Planted in Spring 2004);

excellent cover 6 to 15 months after planting

Fall 2004

Summer 2005

Spring 2005 John Voorhees

Lodi, WI, Rain Garden CostsPipe Underdrain and Endwalls $700

Flow Regulation Structure $3000

Plants $2200

Shrubs $450

Backfill $11600

Excavation $2200

Select Crushed Material/Riprap $3850

Storm Sewer and Manholes $3500

Total $4.70/sf $27500

John Voorhees

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Appropriate Combinations of Controls

• No single control is adequate for all problems

• Only infiltration reduces water flows, along with soluble and particulate pollutants. Only applicable in conditions having minimal groundwater contamination potential.

• Wet detention ponds reduce particulate pollutants and may help control dry weather flows. They do not consistently reduce concentrations of soluble pollutants, nor do they generally solve regional drainage and flooding problems.

• A combination of biofiltration and sedimentation practices is usually needed, at both critical source areas and at critical outfalls.

Combinations of Controls Needed to Meet Many Stormwater Management Objectives

• Smallest storms should be captured on-site for reuse, or infiltrated

• Design controls to treat runoff that cannot be infiltrated on site

• Provide controls to reduce energy of large events that would otherwise affect habitat

• Provide conventional flood and drainage controls

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Pitt, et al. (2000)

• Smallest storms should be captured on-site for reuse, or infiltrated

• Design controls to treat runoff that cannot be infiltrated on site

• Provide controls to reduce energy of large events that would otherwise affect habitat

• Provide conventional flood and drainage controls

Combinations of Controls Needed to Meet Many Stormwater Management Objectives