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Chapter 3. Controlling Urban Runoff 153 

1 6. BMP Fact Sheets 

1 

2 6.1 Introduction 

3 The following BMP fact sheets are included in this section. Each fact sheet includes a description 

4 of the practice, targeted pollutants, photos/diagrams, constraints/limitations, effectiveness, 

5 design, maintenance, and costs.

6 6.1 Rainwater harvesting 

7 6.2 Green roofs 

8 6.3 Blue roofs 

9 6.4 Bioretention 

10 6.5 Soil restoration 

11 6.6 Reforestation/urban forestry 

12 6.7 Street sweeping 

13 6.8 Constructed wetlands 

14 6.1.1 Additional BMP fact sheets 

15 In addition to the fact sheets included in this section, EPA has published information on fact 

16 sheets on other BMPs at the Green Infrastructure technology website: 

17 http://cfpub.epa.gov/npdes/greeninfrastructure/technology.cfm

18 Fact sheets on these technologies are also available at EPA’s Menu of BMPs website: 

19 http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=min_measure&min_meas

20 ure_id=5

21 These BMPs include:

• Downspout disconnection • Brownfield redevelopment

• Planter boxes • Infill and redevelopment

• Rain gardens • Green parking

• Permeable pavements • Pocket wetlands

• Vegetated swales • Compost Blanket

22 Downspout disconnection

23 Planter boxes

24 Rain gardens

25 Permeable pavements

26 Vegetated swales
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Chapter 3. Controlling Urban Runoff 154 

1 Brownfield redevelopment

2 Infill and redevelopment

3 Green parking

4 Green streets and highways

5 Pocket wetlands

6 6.1.2 Performance estimate summaries for Infiltration Practices 

7 The performance of low-impact development practices varies significantly based on the design 

8 and the regional climate. The performance of these practices was recently reviewed for the 

9 Chesapeake Bay region to estimate the capability for volume control and pollutant reduction. 

10 The Mid-Atlantic Water Program (MAWP) housed at the University of Maryland (UMD) led a 

11 project during 2006-2009 to review and refine definition and effectiveness estimates for BMPs 

12 implemented and reported by the Chesapeake Bay watershed jurisdictions prior to 2003 

13 (Developing Best Management Practice Definitions and Effectiveness Estimates for Nitrogen, 

14 Phosphorus, and Sediment in the Chesapeake Bay, December 2009 (“BMP Effectiveness 

15 Report”) www.chesapeakebay.net/websitesearchresults.aspx?menuitem=19557). The urban 

16 stormwater BMPs reviewed by the MAWP are posted at 

17 http://archive.chesapeakebay.net/pubs/BMP_ASSESSMENT_REPORT.pdf. The low impact 

18 development BMPs reviewed and their definition as reported in BMP assessment are as follows:

19 Bioretention: An excavated pit backfilled with engineered media, topsoil, mulch, and vegetation. 

20 These are planting areas installed in shallow basins in which the storm water is temporarily 

21 ponded and then treated by filtering through the bed components, and through biological and 

22 biochemical reactions within the soil matrix and around the root zones of the plants.

23 Permeable Pavement and Pavers: Pavement or pavers that reduce runoff volume and treat water 

24 quality through both infiltration and filtration mechanisms. Water filters through open voids in 

25 the pavement surface to a washed gravel subsurface storage reservoir, where it is then slowly 

26 infiltrated into the underlying soils or exists via an underdrain. 

27 Infiltration Trenches and Basins: A depression to form an infiltration basin where sediment is 

28 trapped and water infiltrates the soil. No underdrains are associated with infiltration basins and 

29 trenches, because by definition these systems provide complete infiltration. 

30 Filters: Filters capture and treat runoff by filtering through a sand or organic media.

31 Vegetated Open Channels: Open channels are practices that convey stormwater runoff and 

32 provide treatment as the water is conveyed, includes bioswales. Runoff passes through either 

33 vegetation in the channel, subsoil matrix, and/or is infiltrated into the underlying soils.

34 The effectiveness summary from the BMP Assessment Report in is provided in Table 3-44. The 

35 BMP Assessment Report provides a summary of assumptions, data sources, maintenance 

36 consideration, and other factors related to these LID practices in the Chesapeake Bay area. 

37 Among the assumptions used in preparation of the effectiveness estimates was that the BMPs 

38 were designed for an approximate 1 inch to 1.5 inch storm event across the impervious drainage 

area. This 1 inch to 1.5 inch rainfall is approximately the 95th 39 percentile rain event in the 
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Chapter 3. Controlling Urban Runoff 155 

1 Chesapeake Bay area. In reviewing the effectiveness values in this table, it is important to note 

2 the variability in the estimates, and that the majority of the pollutant removal is associated with 

3 the volume reduction that occur from either infiltration or evapotranspiration.

4 Table 3-44. Effectiveness summary from the BMP Assessment Report 

EMC Based 

Removal (PR) 

Runoff Reduction 

(RR) 

Mass Based Removal 

(TR) expressed as 

removal from 

collection areas 

(acres) 

TP TN* TSS TP TN TSS 

Bioretention 

C/D soils, underdrain 37 10 50 15 45 25 55 

A/B soils, underdrain 37 10 50 65 75 70 80 

A/B soils, no underdrain 37 10 50 80 85 80 90 

 ± 15 ± 20 ± 15 

Filter 

All (sand, organic, peat) 60 40 80 0 60 40 80 

 ± 15 ± 10 ± 10 

Vegetated Open Channels 

C/D soils, no underdrain 10 10 50 0 10 10 50 

A/B soil, no underdrain 10 10 50 40 45 45 70 

 ± 20 ± 20 ± 30 

Bioswale 37 10 50 65 75 70 80 

 ± 15 ± 20 ± 15 

Permeable Pavement (no sand/veg) 

 

C/D soils, underdrain 10 0 50 10 20 10 55 

A/B soils, underdrain 10 0 50 45 50 45 70 

A/B soils, no underdrain 10 0 50 75 80 75 85 

 ± 15 ± 20 ± 15 

Permeable Pavement (with sand, veg) 

C/D soils, underdrain 10 10 50 10 20 20 55 

A/B soils, underdrain 10 10 50 45 50 50 70 

A/B soils, no underdrain 10 10 50 75 80 80 85 

 ± 15 ± 15 ± 10 

Infiltration Practices (no sand/veg) 

A/B soils, no underdrain 25 0 95 80 85 80 95 

 ± 15 ± 15 ± 10 
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Chapter 3. Controlling Urban Runoff 156 

EMC Based 

Removal (PR) 

Runoff Reduction 

(RR) 

Mass Based Removal 

(TR) expressed as 

removal from 

collection areas 

(acres) 

TP TN* TSS TP TN TSS 

Infiltration Practices (with sand/veg) 

A/B soils, no underdrain 25 15 95 80 85 85 95 

 ± 15 ± 10 ± 10 

Source: Simpson, Thomas, and Sarah Weammert, Developing Best Management Practice Definitions and

Effectiveness Estimates for Nitrogen, Phosphorus, and Sediment in the Chesapeake Bay, Final Report, December 

2009.

1 6.2 Rainwater Harvesting 

2 Description of Practice 

3 Rainwater harvesting can play an important role in managing stormwater runoff and can reduce 

4 both the costs and energy needed to convey and treat runoff offsite. Rain barrels and cisterns can 

5 be used to reduce runoff volume and mitigate peak runoff flow rates for small and medium storm 

6 events. At the present, rainwater collected in harvesting systems is typically only used for non7 potable applications, such as irrigation, toilet flushing, and vehicle washing but uses may expand 

8 as demand for water increases. In addition to reducing stormwater runoff, rainwater harvesting 

9 has the secondary benefit of reducing potable water demand because non-potable uses represent 

10 up to 40 percent of overall household water demand. Rooftop runoff, because it typically 

11 contains low pollutant loads and is easily collected, is the source of most water collected in 

12 rainwater harvesting systems. 

13 Harvested rainwater can be routed and stored in two main types of vessels called cisterns or 

14 rainbarrels. Cisterns generally have a much larger capacity than rainbarrels. Cisterns can be 

15 designed to hold hundreds or thousands of gallons. Rainbarrels most often hold between 55–250 

16 gallons with 55–75 gallon barrels being the most commonly used sizes. To capture the rainwater, 

17 roof downspouts are piped to the rainbarrel or cistern. Most residential rainbarrels are installed 

18 outside as are many cisterns. However, cisterns can be installed inside residential and non19 residential buildings, outside and above or below grade. Bypass drains or systems are used to 

20 divert excess volume when the rainbarrel or cistern is full. 

21 Some systems require the use of filtration or disinfection systems depending on the intended use 

22 and the size of the system. Rainbarrels typically do not require such systems. Filtration and 

23 disinfection systems are used to reduce fouling, clogging, bacterial growth, slime formation and 

24 to treat the rainwater for its intended uses. 

25 In most areas of the country, the use of rainbarrels and cisterns is encouraged mainly to reduce 

26 the volume of runoff discharged from impervious surfaces. In arid or semi-arid areas or areas of 

27 period drought rainwater harvesting systems can play an important role in the provision of 

28 supplemental irrigation or wash waters. Around the globe, rainwater collection systems are often 

29 used to provide potable water. In the United States the use of harvested rainwater for potable 

30 uses is restricted due to public health concerns. 
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Chapter 3. Controlling Urban Runoff 157 

1 Rainwater harvesting systems are most effectively used to reduce runoff volume when they are 

2 integrated into a treatment train or system of practices that may include green roofs, permeable 

3 pavements or raingardens/bioretention cells. 

4 To optimize system performance, the system should be managed either manually or 

5 automatically to discharge the captured volume before the next significant storm event occurs. 

6 Such management strategies help to ensure that the maximum cistern/rain barrel capacity is 

7 available when a rain event occurs. For example, soaker hoses can be used with rainbarrels to 

8 slowly drain the rainbarrel in periods of non-irrigation use and automatic real-time control 

9 systems can be used for large non-residential systems to control the timing of and the release rate 

10 of water from the cistern to ensure capacity is available to capture the next storm. 

11 Hydrologic Performance and Targeted Pollutants 

12 Hydrologic Performance 

Volume Reduction Peak Flow Reduction Groundwater Recharge 

   

Key:  High effectiveness  Medium effectiveness Low effectiveness 

13 

14 Targeted Pollutants 

Sediment Nitrogen Phosphorus Metals Oil & Grease Bacteria Temperature 

       

Key:  High effectiveness  Medium effectiveness Low effectiveness

15 
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Chapter 3. Controlling Urban Runoff 158 

1 Photos and Diagrams 

2 

3 Figure 3-22. Typical Rainwater Harvesting System 

Source: NC Division of Water Quality. Technical Guidance: Stormwater Treatment Credit for Rainwater Harvesting 

Systems

4 Common Feasibility Constraints and Limitations 

5 • Requires a dedicated plumbing system for indoor use

6 • Optimal performance requires active management to ensure that storage containers are 

7 emptied between storms. 

8 • Local ordinances may restrict downspout disconnection or indoor use of harvested water.

9 Runoff Volume and Pollutant Load Removal Estimates 

10 The volume retained in a storm event is determined by the size of the storage container and its 

11 available volume at the time of the storm. Careful operation of the system to ensure that cisterns 

12 and rain barrels drain completely prior to a rain event can help to maximize the available 

13 volume. The use of real-time control systems can increase performance significantly. 

14 Pollutant removal by rainwater harvesting is minimal, and is generally limited to settling of 

15 suspended solids. Water quality may degrade in a cistern if bacteria are allowed to grow. 
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Chapter 3. Controlling Urban Runoff 159 

1 Practice Design 

2 Sizing is based on rainfall patterns, drainage area, water demand, and space and/or budgetary 

3 constraints. Cisterns should be sized to store water from multiple events, or to empty between 

4 events, if capacity for back-to-back storms is needed. 

5 Proper cistern capacity is calculated by balancing the expected rainfall volume with the 

6 anticipated water demand. Additional capacity may be incorporated to allow extended storage of 

7 rainwater for use during dry periods. 

8 Design considerations include:

9 • Piping for harvested rainwater should be labeled to prevent accidental use for potable 

10 applications. 

11 • Rain barrels and cisterns should be fitted with emergency overflows. 

12 • Cisterns constructed belowground must be fitted with pumps to deliver collected water. 

13 • Systems for indoor uses such as toilet flushing should be dual piped with potable water 

14 for back-up. A backflow prevention assembly should be used to prevent cross15 contamination of the potable supply line. Local building codes should be consulted. 

16 • Pretreatment may be desired prior to storage to prevent fouling of the storage tank. 

17 Screening, settling of suspended solids, and oil and grease separation (for parking lot 

18 runoff) may be beneficial. The first flush of runoff may be diverted from the storage tank 

19 to remove debris. 

20 • Treatment requirements for stored rainwater vary by municipality and intended end use. 

21 Typically, no treatment is required for outdoor irrigation, while filtration and/or UV 

22 disinfection may be required for indoor nonpotable uses. 

23 • Outdoor cisterns should be screened at each opening to prevent insects from entering. 

24 American Rainwater Catchment Systems Association/American Society of Plumbing Engineers 

25 issued Rainwater Catchment Design and Installation Standards (August 2009) to assist in 

26 properly and safely implementing systems. Several localities have implemented or adopted 

27 standards as part of their building codes. 

28 Maintenance Considerations and Resources 

29 A typical maintenance schedule is provided here. Maintenance needs will vary based on the type 

30 of system and location. 
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Chapter 3. Controlling Urban Runoff 160 

1 

2 Figure 3-23. Typical maintenance schedule for a rainwater harvesting system. 

Source: Federico, et. al., Geosyntec Consultants, Technical Memorandum: Large-Scale Cistern Standards, Report to 

Los Angeles County Department of Public Works, December 2009. 

3 Costs and factors affecting cost 

4 55-gallon rain barrels typically cost $50–100 for prefabricated units, or $30 for do-it-yourself 

5 kits. 

6 For cistern tanks, costs depend on the material used for construction, and costs are similar to 

7 other water storage tank systems. A tool for estimating tank and pump costs is available from the 

8 Water Environment Federation (WERF), the User’s Guide to the BMP and LID Whole Life Cost 

9 Model, Version 2.0, and associated spreadsheet tool. 

10 Table 3-45. Cistern tank costs. 

Cistern Tank Cost by Type ($/gallon, installation not included), 2009 

Fiberglass Steel Plastic Concrete 

10,000 gal and up 500-15,000 gal 50-1,500 gal 2,000 gal and up 

$ 1.33 $ 2.51 $ 1.43 $ 1.66 

Source: WERF BMP and LID Whole Life Cost Model, Version 2.0

11 Costs for large cistern systems are dependent on many site-specific factors, such as whether 

12 excavation is required for underground units. Cost items applicable to systems used for irrigation 

13 can include:

14 • Piping and pretreatment (screening) 

15 • Tank, pumps, valves 
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Chapter 3. Controlling Urban Runoff 161 

1 • Site preparation 

2 • Concrete pad for above-ground; excavation for buried 

3 Example system costs are provided in Table 3-46. 

4 Table 3-46. Summary of Cistern System Costs with Project Characteristics 

Site 

Capacity 

(gallons) 

Construction 

Material 

New/Retrofit 

Yr Installed Location Estimated Cost 

Landscape Architecture1

Library, Tucson, AZ 

11,600 Steel and Fiberglass New 2007 Aboveground $17,000 

(total cost) 

Fairmount Square1 

Grand Rapids, MI 

30,000 Concrete New Buried $40,000 

(total cost) 

Redbud Center1 

Austin, TX 

31,000 Steel New 2008 Aboveground $250,000 

(total cost) 

Santa Monica Main1

Library, CA 

200,000 Concrete New 2006 Buried $700,000 

 (total cost) 

Mark Miller Toyota2

Salt Lake City, UT 

1 @ 8000 

1 @ 2000 

Concrete New 2008 Buried $22,000 

(total cost) 

Hypothetical 

Office2Building, Arlington, 

VA 

10,000 Fiberglass New 2008 Buried $179,000 

(estimated total) 

Open Charter Elementary, 

Westchester CA2 

110,000 Modified RainStore3 

Infiltration System 

New 2004 Buried $500,000 

(not incl. design) 

Hall House, Los Angeles, 

CA1 

3,600 Polypropylene Retrofit 1998 Partially 

Buried 

$25,000 

(installed) 

Center for Community 

Forestry, Los Angeles, 

CA1 

216,000 Concrete New 2008 Buried $400,000 

(excludes soft costs, 

distribution system) 

1

Federico, et. al., Geosyntec Consultants, Technical Memorandum: Large-Scale Cistern Standards, Report to Los 

Angeles County Department of Public Works, December 2009.fairmoun 

2

 Water Environment Research Federation, User’s Guide to the BMP and LID Whole Life Cost Model, Version 2.0, 

2009. 

5 References 

6 American Rainwater Catchment Systems Association, www.arcsa.org

7 Cabell Brand Center. 2009. Virginia Rainwater Harvesting Manual, Version 2.0. Salem, VA. 

8 (Draft Form) www.cabellbrandcenter.org ; 

9 http://cabellbrandcenter.org/RWH_Manual2009.pdf

10 Credit Valley Conservation. 2008. Credit River Stormwater Management Manual. Mississauga, 

11 Ontario; www.creditvalleyca.ca/sustainability/lid/stormwaterguidance/index.html

12 Federico, et. al.,Geosyntec Consultants. 2009., Technical Memorandum: Large-Scale Cistern 

13 Standards, Report to Los Angeles County Department of Public Works.

14 , December 2009
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Chapter 3. Controlling Urban Runoff 162 

1 Georgia Department of Community Affairs. 2009. Georgia Rainwater Harvesting Guidelines, 

2 Draft, April 2009. 

3 Gowland, D. and T. Younos. 2008. Feasibility of Rainwater Harvesting BMP for Stormwater 

4 Management. Virginia Water Resources Research Center. Special Report SR38-2008. 

5 Blacksburg, VA 

6 North Carolina Division of Water Quality. 2008. Technical Guidance: Stormwater Treatment 

7 Credit for Rainwater Harvesting Systems. Revised September 22, 2008. Raleigh, NC. 

8 http://h2o.enr.state.nc.us/su/documents/RainwaterHarvesting_Approved.pdf

9 North Carolina State University, Biological and Agricultural Engineering. Urban Waterways: 

10 Permeable Pavements, Green Roofs, and Cisterns. 

11 www.bae.ncsu.edu/stormwater/PublicationFiles/BMPs4LID.pdf

12 Seattle, WashingtonOregon, Department of Planning and Development. 2009., Rainwater 

13 Harvesting for Beneficial Use, Client Assistance Memo 520. April 2009.

14 Texas A&M University, AgriLife Extention Service, 

15 http://rainwaterharvesting.tamu.edu/index.html

16 Texas Water Development Board. 2005., The Texas Manual on Rainwater Harvesting – Third 

17 Edition, 2005. 

18 US Environmental Protection Agency, Office of Water. 2008. Municipal Handbook: Rainwater 

19 Harvesting Policies, December 2008. 

20 www.epa.gov/npdes/pubs/gi_munichandbook_harvesting.pdf

21 Virginia Department of Conservation and Recreation, Design Specification No.6 and Design 

22 Spreadsheet www.chesapeakestormwater.net/storage/first-draft-baywide-design23 specificationsi/BAYWIDE%20No%206%20RAIN%20TANKS%20AND%20CISTERNS.

24 pdf

25 Water Environment Research Federation. 2009., User’s Guide to the BMP and LID Whole Life 

26 Cost Model, Version 2.0, 2009. 
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Chapter 3. Controlling Urban Runoff 163 

1 6.3 Green roofs 

2 Description of Practice 

3 Green roofs attenuate flow and provide storage and evapotranspiration of stormwater. They are 

4 typically designed with an impermeable membrane that is root resistant, an engineered soil 

5 medium, plants, and in many cases an underdrain system. Some green roofs also have leak 

6 detection systems. The design of green roof systems significantly impacts performance. The two 

7 main categories of green roof designs are:

8 • Extensive, which have a shallow planting media layer (typically 2–6 inches”) and low9 growing, drought tolerant plants. 

10 • Intensive, which have a deeper media layer, and can be planted with a wider variety of 

11 plants, including trees and shrubs. Intensive green roofs can be fitted with walkways and 

12 used as recreational areas. 

13 Rain falling onto green roofs is both detained and retained in the soil medium. When the soil 

14 medium becomes saturated, the excess water percolates through to the drainage layer and is 

15 discharged through the roof downspouts. In between storm events, water absorbed by the soil 

16 media is returned to the atmosphere by evapotranspiration. Depending on the design and climate 

17 pattern of the region, green roofs can provide significant stormwater volume reduction on an 

18 annual basis, decrease peak flow rates and help to restore hydrologic function of the watershed 

19 by absorbing and attenuating runoff. 

20 In addition to providing stormwater retention, green roofs can be designed to provide ancillary 

21 benefits, such as enhancing site aesthetics, urban habitat for birds and insects, insulation value 

22 for energy conservation and increasing the longevity of roofing materials. 

23 Green roofs are common in Europe, but have only recently gained popularity in US as a practice 

24 for mitigating stormwater runoff. The International Green Roofs Projects Database

25 (www.greenroofs.com) lists over 1,000 green roof projects, mainly in the United States.

26 Hydrologic Performance and Targeted Pollutants 

27 Hydrologic Performance 

Volume Reduction Peak Flow Reduction Groundwater Recharge 

   

Key:  High effectiveness  Medium effectiveness Low 

effectiveness 

28 

29 Targeted Pollutants 

Sediment Nitrogen Phosphorus Metals Oil & Grease Bacteria Temperature 

      
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Chapter 3. Controlling Urban Runoff 164 

Key:  High effectiveness  Medium effectiveness Low effectiveness

1 Photos and Diagrams 

2 

3 

4 Figure 3-24. ASLA Headquarters Green roof 

5 Source: The Low Impact Development Center 

6 

7 Figure 3-25. Green Roof Section 

8 Source: MDE Stormwater Design Manual 
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Chapter 3. Controlling Urban Runoff 165 

1 Common Feasibility Constraints and Limitations 

2 • Slopes should be less than 30 percent%. Installations on pitched roofs require 

3 stabilization structures to prevent migration of the soil medium. Specialized drains are 

4 typically required for slopes above 5 percent%. 

5 • Roofs must be able to bear the load of a fully saturated medium. Extensive green roof wet 

6 weight is approximately 6 to 7 pounds per square foot per inch of depth. 

7 • Construction costs include transporting materials to a roof, which may require a crane. 

8 • Costs of green roof construction typically make it a cost-effective option only in dense 

9 urban areas. 

10 Runoff Volume and Pollutant Load Removal Estimates 

11 Runoff volume removal is a function of the green roof area, the specifics of the green roof 

12 design, and the local climate and rainfall pattern. Green roofs can retain the full volume of small 

13 storms, and they are commonly designed to detain brief periods of high intensity rainfall. 

14 Reported results for extensive roofs are summarized here. 

15 Table 3-47. Performance Estimates for Annual Flow Retained, Summer Flow Retained, and Peak 

16 Flow Shaving for Green Roofs 

Performance 

Measure 

Performance 

Estimate Location 

Depth of Media 

(not including submedia 

layers) Source 

50% Philadelphia 3.5 to 4 inches EPA, 2009 

75% Washington, D.C. 3 - 18 inches Glass, 2007 

65-70% East Lansing, MI 1 -2.4 inches VanWoert, 2005 

56% Portland, OR 5 inch Portland BES, 

2008 

Annual Flow 

Retained 

26% - 86% National Range Various Portland BES, 

2008 

Summer Runoff 95% Philadelphia 3.5 to 4 inches EPA, 2009 

30% to 96% National Range Portland BES, 

2008

Peak Flow 

Shaving 

60% Portland, OR 5 inch Portland BES, 

2008 

17 Pollutant removal in green roofs is strongly dependent on the specifics of the design, and on rates 

18 of atmospheric deposition. Studies have shown that green roofs do not often provide pollutant 

19 reductions, however, it is noted that the concentration of pollutants in direct rainfall is very low 

20 (therefore, there is relatively little pollutant to remove). Temporary export of nutrient may occur 

21 during initial establishment of the media and plants. Poorly designed green roof soil media can 

22 lead to export of low concentrations of nutrients and solids from the media, fertilizer and plants. 

23 For this reason, it is preferable to discharge the runoff from green roofs into bioretention or other 

24 unit if pollutant reduction is needed in addition to the volume reduction (EPA 2009). Green 

25 roofs, however, have been shown to export lower levels of pollutants than conventional roofs. 
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Chapter 3. Controlling Urban Runoff 166 

1 Material selection is an important consideration. Many roofing materials can export toxic 

2 chemicals that may be used in their construction (Clark et al, 2008). 

3 Practice Design 

4 Green roofs are most often constructed on flat or shallowly sloped roofs, but roofs with slopes up 

5 to 30 percent% accommodate green roofs with the use of mesh, stabilization panels, or battens. 

6 The area covered by green roofs is typically limited to 50 – 80 percent of the total roof area due 

7 to the need to accommodate HVAC (heating, ventilation and air conditioning) or other 

8 equipment (e.g. cell towers or solar panels) and roof access or other penetrations. Green roofs 

9 have also been designed to accommodate solar panels. 

10 A typical green roof profile would include the following layers: 

11 • Vegetation layer 

12 • Engineered growth media 

13 • Separation geotextile 

14 • Semi-rigid plastic geocomposite drain or mat 

15 • Root barrier 

16 • Waterproofing membrane 

17 Plant Selection - Plant selection varies depending on the type of green roof installed. Extensive 

18 green roofs should be planted with low-growing, drought tolerant plants, such as succulents. 

19 Sedums are frequently used. Intensive green roofs, which have deeper soil media, can 

20 accommodate a much wider variety of plants, including trees and shrubs. Intensive green roofs 

21 often require irrigation to support the larger plants. 

22 Soil medium - To minimize the potential for nutrient export, the soil medium should have a high 

23 mineral content. Use of compost has been found to produce elevated levels of nitrogen and 

24 phosphorus in effluent, at least in the short term (Moran et al, 2004). 

25 Maintenance Considerations and Resources 

26 Maintenance requirements vary depending on design specifics, with extensive green roofs 

27 typically requiring less maintenance than intensive green roofs. Maintenance typically includes:

28 • Periodic irrigation during plant establishment and dry periods. 

29 • Periodic weeding, fertilization (if needed), and infill planting 

30 • Periodic inspection of drainage outlets and waterproof membrane. 

31 Costs and factors affecting cost 

32 Costs depend on the media depth, the number and type of additional structural components in the 

33 design, the vegetation selected, and the need for structural roof modifications. Costs for 

34 extensive green roofs typically range from $8–$14 per square foot (PADEP, 2006). The 
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Chapter 3. Controlling Urban Runoff 167 

1 installation cost of the green roof is partially offset by increasing the life of the underlying roof,

2 and reducing heating and cooling demand within the building. 

3 Costs were reported to vary primarily by the installation type (WERF, 2009, and Portland BES,

4 2008): 

5 • Modular, tray-type installations: $19.50 per square foot 

6 • Custom applications with media spread across the surface: $8.75 per square foot.

7 Green roofs reduce energy costs and extend roof life. Green Roofs for Healthy Cities 

8 (www.greenroofs.org) provides a calculator to estimate the long term savings. 

9 A cost-benefit analysis of a hypothetical green roof concluded that green roofs had a higher net 

10 present value for the owner and the public, despite higher initial capital and O&M costs 

11 (Portland BES, 2008). Not all benefits were examined, but areas where economic benefits 

12 accrued included:

13 • For the public: (1) Reduced Stormwater Quantity; (2) Avoided Stormwater Infrastructure; 

14 (3) Improved Air Quality; (4) Enhanced Habitat 

15 • For the owner or developer: (1) Reduced Stormwater Fees; (2) Extended Roof Life; 

16 (3) Increased FAR allowance; (4) Reduced energy costs. 

17 Example Green Roof Design Guides in the Chesapeake Bay Watershed 

18 Area 

19 US General Services Administration (GSA). 2009. Guideline Scope of Work, Design Build 

20 Guidance Criteria Retrofitting Low-slope Roofs with a Vegetative Roof System. 

21 Pennsylvania Department of Environmental Protection (PADEP). 2006. Pennsylvania 

22 Stormwater Best Management Practices Manual, Document Number: 363-0300-002, BMP 6.5.1: 

23 Vegetative Roof. www.elibrary.dep.state.pa.us/dsweb/View/Collection-8305

24 New York State Department of Environmental Conservation. New York State Stormwater 

25 Management Design Manual, Draft Chapter 4.3.8 Green Roofs. December 2009. 

26 Whole Building Design Guide. Extensive Green Roof Resources Page. 

27 www.wbdg.org/resources/greenroofs.php?r=site_potential#rcas

28 References 

29 ASTM International. 2006. Standard Guide for Selection, Installation and Maintenance of Plants 

30 for Green Roof Systems. Standard E2400-06. ASTM International. West Conshohocken, 

31 PA. <http://, available Online: www.astm.org/Standards/ E2400.htm>. 

32 Berhage, R., A. Jarrett, D. Beattie and others. 2007. Quantifying evaporation and transpiration 

33 water losses from green roofs and green roof media capacity for neutralizing acid rain. 

34 Final Report. National Decentralized Water Resource Capacity Development Project 

35 Research Project. Pennsylvania State University. 
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Chapter 3. Controlling Urban Runoff 168 

1 Clark, S., B. Long, C. Siu, J. Spicher and K. Steele. 2008. Early-life runoff quality: green versus 

2 traditional roofs. Low Impact Development 2008. Seattle, WA. American Society of Civil 

3 Engineers. 

4 Dietz, M.E. 2007., Low-Impact Development Practices: A Review of Current Research and 

5 Recommendations for Future Directions, Water, Air, Soil Pollution, 186; 351-363, 2007. 

6 Dunnett, N. and N. Kingsbury. 2004. Planting Green Roofs and Living Walls. Timber Press. 

7 Portland, Oregon. 

8 Glass, Charles C. ., et al. 2007. Green Roof Water Quality and Quantity Monitoring, Howard 

9 University Department of Civil Engineering, University Park, MD. 

10 Green Roofs for Healthy Cities (www.greenroofs.org) 

11 International Green Roofs Projects Database (www.greenroofs.com) 

12 MDE (Maryland Department of Environment. (MDE). 2008. Chapter 5. Environmental Site 

13 Design. Green Roofs. 

14 Moran, A., W. Hunt and G. Jennings. 2004. Greenroof research of stormwater runoff quantity 

15 and quality in North Carolina. NWQEP Notes. No. 114. North Carolina State University. 

16 Raleigh, NC. 

17 North Carolina State University (NCSU). 2008. Green Roof Research Web Page. Department of 

18 Biological and Agricultural Engineering. www.bae.ncsu.edu/greenroofs. 

19 Portland BES (Bureau of Environmental Services). 2008 (BES). Cost Benefit Evaluation of 

20 Ecoroofs, City of Portland, Oregon.

21 , April 2008

22 Snodgrass, E., and L. Snodgrass. 2006. Green Roof Plants: a resource and planting guide. 

23 Timber Press. Portland, OR. 

24 USEPA (U.S. Environmental Protection Agency), 2009., Green Roofs for Stormwater Control, 

25 EPA/600/R-09/026. www.epa.gov/nrmrl/pubs/600r09026/600r09026.pdf. 

26 Van Woert, N., D. Rowe, A. Andersen, C. Rugh, T. Fernandez and L. Xiao. 2005. Green roof 

27 stormwater retention: effects of roof surface, slope, and media depth. Journal of 

28 Environmental Quality. 34: 1036–-1044. 

29 Weiler, S. and K. Scholz-Barth 2009. Green Roof Systems: A Guide to the Planning, Design, and 

30 Construction of Landscapes over Structure. Wiley Press,. New York, NY. 

31 Water Environment Research Federation. 2009., User’s Guide to the BMP and LID Whole Life 

32 Cost Model, Version 2.0, 2009. 
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Chapter 3. Controlling Urban Runoff 169 

1 6.4 Blue Roofs 

2 Description of Practice 

3 A blue roof is a roof design that is explicitly intended to provide temporary storage and slow 

4 release of stormwater runoff. In many locations, these approaches are also referred to as “rooftop 

5 detention”. They are most commonly used in dense urban areas where other methods of 

6 stormwater detention are impractical. Blue roofs are used to detain rooftop runoff onsite and 

7 reduce the rate of runoff from rooftops during rainfall events. A blue roof may be used as a 

8 standalone detention method, or because they do little to improve the water quality of runoff, as 

9 part of a treatment train that includes other low impact development and conventional best 

10 management practices (BMPs) such as bioretention, infiltration, wetland systems, or green roofs 

11 to enhance the function, improve the performance, and reduce the cost of those approaches. Blue 

12 roofs are one of the least expensive means for temporarily detaining stormwater on site and can 

13 be used where green roofs are not feasible, cost effective or otherwise desired due to competing 

14 needs. 

15 The four primary blue roof types are described below: 

16 • Roof-integrated Designs— - Roof-integrated designs are built during new construction or 

17 as modifications of existing roofs to intentionally store standing water over extended 

18 periods. 

19 

20 These designs utilize a roofing membrane or waterproofing system as the primary water 

21 detention structure. Therefore water is temporarily ponded directly on the roof surface. 

22 Roof integrated designs can be designed to store water as an open water surface or 

23 partially or completely within a porous media. 

24 

25 In addition, structures such as walkways, decks, or plazas can be constructed on top of 

26 roof integrated designs to minimize the impact of ponded water on roof access. 

27 Alternatively, porous media such as flexible paving tiles or granular media can be used as 

28 a permeable walking surface on all or part of the roof to allow for access, while reducing 

29 the amount of standing open water. 

30 

31 Roof-integrated designs can be constructed as a secondary roofing layer on top of an 

32 existing surface in the same manner as a physical root barrier in green roof designs. 

33 

34 • Modular Tray Designs— - Modular tray systems utilize plastic trays to temporarily 

35 detain water during rainfall events and release this water over some period of time 

36 following a rainfall event. This approach provides flexibility in both the size and 

37 configuration of the detention system and is, therefore, well-suited for retrofit designs. 

38 Equipment and other roof penetrations can be avoided through selective placement of the 

39 trays. Loading issues can be addressed though optimal density and placement 

40 configurations. The trays can be physically attached to the roof or underlying supporting 

41 grid and/or held in place with ballast composedcomprised of coarse stone or other 
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Chapter 3. Controlling Urban Runoff 170 

1 weighed materials. The depth of the ballast or media contained in the trays can be varied 

2 depending on the desire to reduce the presence of open water surfaces. 

3 

4 Modular trays can have any number of different outlet designs according to the goals of 

5 the installation (e.g., reduce peak flows, achieve specific lag time for target events, etc.). 

6 When the water is released, the drainage system for the existing roof continues to 

7 function as it did prior to the retrofit (i.e., hydraulic head and flow depths on the roofing 

8 surface during rainfall are not increased). 

9 

10 Modular tray blue roof designs can be selectively mixed with green roof components to 

11 improve aesthetics and provide some of the additional benefits of green roofs. 

12 The most challenging component of blue roof tray designs is the robustness of the 

13 hydraulic outlet design. Consistent and reliable drainage of the trays with little 

14 maintenance is a key consideration. Some designs allow for trays to be interconnected to 

15 effectively act as a larger “tank”. 

16 

17 • Roof-Dams/Roof-Checks— - Roof-dams or roof-checks effectively are impermeable or 

18 semi-permeable interim breaks in the surface flow paths installed on existing or new 

19 roofs that allow water to pond behind them as temporary detention. The dams can 

20 incorporate specific overflow or outlet designs to slowly release the stored water. In the 

21 same manner as a roof-integrated design, the roof is utilized as the primary water 

22 detention structure with the flows being restricted by the roof-dams. If retrofit onto 

23 existing roofs, the ability of the roof to accept additional ponding should be assessed and 

24 addressed. In older roof installations new roofing and additional water proofing may need 

25 to be installed in conjunction with the installation of the dams. 

26 

27 • Actively Controlled Systems— – Blue roofs that are used for temporary rooftop storage 

28 can be classified as "active" or "passive" depending on the types of control devices used 

29 to regulate drainage of water from the roof. Passive designs use hydraulic structures such 

30 as weirs, orifice plates or hydraulic regulators to control release rates from the roof. 

31 Active approaches allow for the use of a valve configuration and controller to regulate 

32 discharge of flows from rooftops. 

33 

34 The simplest design for an actively controlled blue roof is the retrofit or installation of a 

35 pneumatically or hydraulically actuated pinch valve on the roof leader drain pipe. This 

36 valve can be connected to a low cost micro-controller, which monitors hydraulic head on 

37 the valve and timing of storage on the roof surface. The controller can be programmed to 

38 release the ponded water according to some predetermined optimal approach based on 

39 analysis of the receiving storm sewer, downstream BMP, or receiving water. More 

40 complex designs can integrate communications with server-side and/or internet based 

41 data feeds, or telemetry to optimize release timing and quantities. 

42 

43 Blue roofs can be implemented effectively on shallowly sloped roofs in residential, 

44 manufacturing, commercial or industrial settings. Rooftop detention is a particularly good 
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Chapter 3. Controlling Urban Runoff 171 

1 storage option in densely developed areas where roofs make up a significant portion of the total 

2 site area. 

3 Blue roofs are well-suited to applications on commercial and residential buildings, which 

4 typically have large, flat roofs and little or no area available for storage on site surrounding the 

5 building. Such large roofs generate significant runoff quantities. Rooftop detention using blue 

6 roofs represents a cost effective and convenient storage option that can be applied to new 

7 construction in the urban environment to provide adequate storage volume and runoff reduction 

8 to comply with stormwater regulations. 

9 In addition to applications in densely developed areas, blue roof storage techniques also lend 

10 themselves well to implementation on sites with moderate to large flat roofs where flow from 

11 impervious non-roof area (e.g. parking lots, walkways, etc.) also contributes to the total runoff. 

12 In these situations, blue roofs are used to control rooftop runoff, while subsurface BMPs are used 

13 to control runoff from non-roof areas. The use of rooftop storage on such sites reduces the 

14 required volume for subsurface systems and allows these systems to be constructed over a 

15 smaller area. 

16 Key advantages include:

17 • Often the least expensive means for temporarily storing storm water at a site particularly 

18 when compared to subsurface storage or green roof systems. 

19 • Can reduce the size and/or improve the performance of downstream BMPs, such as 

20 bioretention cells of infiltration systems. 

21 • Easy to install – no additional excavation/construction required. 

22 • Existing commercially available products for flow control. 

23 • Readily coupled with other storage techniques, such as subsurface or surface storage. 

24 Hydrologic Performance and Targeted Pollutants 

25 Hydrologic Performance 

Volume Reduction Peak Flow Reduction Groundwater Recharge 

   

Key:  High effectiveness  Medium effectiveness Low 

effectiveness 

26 

27 Targeted Pollutants 

Sediment Nitrogen Phosphorus Metals Oil & Grease Bacteria Temperature 

       

Key:  High effectiveness  Medium effectiveness Low effectiveness
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Chapter 3. Controlling Urban Runoff 172 

1 Common Feasibility Constraints and Limitations 

2 • Storage using outlet controls limited to flat roofs or roofs with shallow slopes (e.g., < 1 

3 percent) due to increased ratio of ponding depth to available volume for steeper slopes. 

4 This problem can be addressed through the use of modular tray designs or roof-dams. 

5 • Limited benefit on sites where roof area makes up only a small portion of total 

6 impervious area. 

7 • Regular maintenance varies by design, but is an important consideration. Verification of 

8 system performance may be necessary. 

9 • Potential tampering must be considered in design. 

10 • Pest problems must be avoided through through proper design and maintenance, e.g., 

11 mosquitoes. 

12 • Local building codes should be checked to ensure designs are compliant. 

13 Photos and Diagrams 

14 

15 Figure 3-26. Rooftop detention being used to control runoff at a commercial property 

16 Source: with permission from the New York City Department of Environmental Protection 

17 Common Feasibility Constraints and Limitations 

18 Because blue roof designs generally hold less than four inches of ponded water on the roof for 

19 times ranging from a few minutes to many hours, blue roofs typically do not impact the 

20 availability of roof space for other uses. 

21 If such water ponding is incompatible with anticipated future uses of the roof, the blue roof may 

22 be designed to occupy a portion of the roof area, leaving additional roof space available for other 

23 purposes. If structures and equipment are mounted to the roof within the area intended for 

24 ponding water, it may be necessary to provide additional waterproofing around the structure or 

25 equipment or to elevate the equipment above the anticipated maximum water depth to prevent 
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Chapter 3. Controlling Urban Runoff 173 

1 damage and provide access for maintenance. Where roofs are intended to be used as means of 

2 egress or points of rescue for fire safety, walkway pavers should be provided to allow for safe 

3 passage to fire escapes from the roof surface. These pavers provide a dry walking surface to 

4 allow for safe movement through ponded water. In addition, decks, walkways or pavers may be 

5 incorporated into the design of a rooftop detention system to provide space on the rooftop for 

6 passive recreational use. 

7 The application of blue roof systems is most effective on roofs with a maximum slope of about 

8 1/8 inch per foot (or 1 percent% slope) or those with drainage configurations that can safely 

9 allow for the necessary volume detention. 

10 To prevent clogging, the owner should inspect drains and clear snow and ice as necessary after 

11 winter precipitation events in accordance with established maintenance procedures. As with 

12 conventional flat roofs, maintenance procedures for blue roof systems include the removal of 

13 accumulated snow prior to an anticipated rain event to prevent possible overloading. 

14 Homeowners or building maintenance staff may remove snow from the blue roof using the same 

15 removal methods used for conventional flat roofs. 

16 Runoff Volume and Pollutant Load Removal Estimates 

17 Blue roofs primarily provide a means for temporarily detaining water. Little direct impact on 

18 water quality can be achieved through the use of blue roofs alone. Some evaporation will occur 

19 in systems that detain water for extended periods. Evaporation rates on blue roofs approach pan 

20 evaporation rates. Pan evaporation rates can be significant under certain climatic conditions (e.g., 

21 hot, windy, low humidity days). 

22 Practice Design 

23 Blue roofs are most often constructed on flat or shallowly sloped roofs, but tray and roof dam 

24 designs can be used on slopes in excess of 5 percent%. On roof integrated designs where the roof 

25 is sloped, even very shallow slopes dramatically reduce detention capacity. Typically in retrofit 

26 situations the roof is reconstructed as a part of blue roof installation. With tray designs this may 

27 not be necessary. The designer must pay close attention to roof system manufacturer’s 

28 requirements to ensure that the roofing system and design are compatible with manufacturer’s 

29 warrantees and with the blue roof design. 

30 Maintenance Considerations and Resources 

31 Maintenance for most blue roof systems are similar to those required for typical flat roofing 

32 drainage systems and involve occasional snow and ice removal, regular inspection for debris 

33 clogging inlets, and inspection and repair of the roof. 

34 Costs and factors affecting cost 

35 Blue roofs are one of the least expensive means for temporarily detaining stormwater on site. 

36 The marginal cost of adding a blue roof to new construction is typically less than $2 per gallon of 

37 temporary storage where structural modifications to building design are not required (e.g., 
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Chapter 3. Controlling Urban Runoff 174 

1 designs take into account snow loads). As new approaches (e.g., tray designs) gain wider 

2 acceptance in the marketplace it is expected that blue roof detention may drop below $1 per 

3 gallon of temporary storage. 

4 References 

5 City of Valparaiso, Indiana. 2004. , Stimson Drain Stormwater Management Study Phase II 

6 Report, Appendix B, Rooftop Storage, 2004. 

7 www.valparaisoutilities.org/stormwater/ssph2/StimsonDrain/Appendices/AppendixB/25%

8 20-%20rooftop%20storage%20040915.pdf

9 Georgia Stormwater Management Manual; Volume Two: Technical Handbook, 2001. 

10 www.georgiastormwater.com

11 Guidebook Of Best Management Practices For Michigan Watersheds, Reprinted October, 1998, 

12 Roof Top Storage Pages RTS-1 And RTS-2 in Best Management Practices For 

13 Construction Sites, Urban Areas and Golf Courses. 

14 www.michigan.gov/documents/deq/deq-wb-nps-Intro_250601_7.pdf

15 Iowa Statewide Urban Design Standards Manual. 2009. www.iowasudas.org/design.cfm

16 Ontario Stormwater Management Planning & Design Manual, 2003. 

17 www.ene.gov.on.ca/envision/gp/4329eindex.htm

18 Pennsylvania Stormwater Best Management Practices Manual, BMP 6.8.2: Special Detention 

19 Areas – Parking Lot, Rooftop. 

20 www.stormwaterpa.org/assets/media/BMP_manual/chapter_6/Chapter_6-8-2.pdf
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Chapter 3. Controlling Urban Runoff 175 

1 6.5 Bioretention/Biofiltration 

2 Description of Practice 

3 Bioretention cells are small-scale, vegetated, shallow depressions that are used to reduce runoff 

4 volumes and pollutants through the process of soil filtration, interception, vegetative uptake, 

5 biological processes, infiltration, retention and evapotranspiration. Bioretention cells can be used 

6 as stand alone systems or as part of a treatment train. Bioretention cells are typically designed 

7 with native soils and or/an engineered soil mix, and plants that are selected to be tolerant of a 

8 range of wet and dry conditions. In some cases site conditions or design goals may require the 

9 use of gravel for additional volume retention or the use of overflow devices. Where groundwater 

10 recharge is required, bioretention can help protect the quality of infiltrated stormwater. 

11 The use of soil based vegetated systems have distinct advantages over the use of nonbiological 

12 infiltration trenches or similar designs for the following reasons (Davis, et al.., 2009): 

13 • Roots promote media permeability. 

14 • Surface vegetation can be used to slow stormwater flows and filter sediments. 

15 • Roots support microbial populations needed for pollutant biodegradation. 

16 • Phytoremediation uptakes and breaks down pollutants. 

17 It is recommended that, where feasible, designs use a variety of hardy native plants that are 

18 adapted for both wet and dry soil conditions to ensure long-term plant survival and vigor. If 

19 native plants are not available, the use of nonnative, noninvasive species that typically do not 

20 require fertilizer, irrigation or pest control except at establishment is appropriate. 

21 Bioretention cells can be used in a wide set of applications in the built environment to manage 

22 runoff from roofs, lawns, and streets and other impervious areas such as parking lots and 

23 sidewalks. Bioretention practice typically fall in to the following categories: 

24 • Residential rain gardens 

25 • Tree boxes (common and expanded) and shrub bioretention cells 

26 • Sidewalk or right of way planter boxes 

27 • Parking lot islands 

28 • Street curbs extensions and bump-outs. 

29 • Wooded bioretention areas 

30 • Bioretention swales 
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Chapter 3. Controlling Urban Runoff 176 

1 Hydrologic Performance and Targeted Pollutants 

2 Hydrologic Performance For Design Storm Events 

Volume Reduction Peak Flow Reduction Groundwater Recharge 

   

Key:  High effectiveness  Medium effectiveness Low effectiveness 

3 

4 Targeted Pollutants 

Sediment Nitrogen Phosphorus Metals Oil & Grease Bacteria Temperature 

       

Key:  High  Medium  Low 

5 

6 Photos and Diagrams 

7 

8 Figure 3-27. Bioretention Cell for Street and Yard Drainage. 

9 Source: Larry Coffman, Prince George’s County, Somerset Subdivision 
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Chapter 3. Controlling Urban Runoff 177 

1 

2 Figure 3-28. An Urban Bioretention System Treats Sidewalk and Road Runoff. 

3 Source: Abby Hall, US EPA 

4 

5 

6 Figure 3-29. Typical Bioretention Cell Cross-Section. Not to Scale. 

7 Source: LID Center 

8 
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Chapter 3. Controlling Urban Runoff 178 

1 

2 Figure 3-30. Wooded Bioretention Can Increase Pollutant Uptake And Requires Specific Design 

3 Modifications for Tree Growth and Avoiding Engineering Conflicts 

4 Source: Urban Watershed Forestry Manual, Part 2, CWP and USDA, 2006 

5 

6 

7 
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Chapter 3. Controlling Urban Runoff 179 

1 

2 Figure 3-31. Bioretention Swales With and Without Underdrain. 

3 Source: Seattle Public Utilities 

4 

Figure 3-32. Infiltration Planter Box. 

Source: Portland Bureau of Environmental Services 

5 

6 Common Feasibility Constraints and Limitations 

7 Bioretention practices should not be used in some applications, including:

8 • slopes are greater than 20 percent 
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Chapter 3. Controlling Urban Runoff 180 

1 • “hot spots” that have a high potential for groundwater contamination, e.g., gas station 

2 runoff or areas where chemicals are stored or managed 

3 • large drainage areas from impervious areas greater than 15,000 square feet (unless a 

4 system of separate cells is used to manage the runoff) 

5 • areas of shallow bedrock or high water tables where infiltration is not feasible (note: 

6 design modification may be used to compensate for these conditions where surface 

7 retention is desired) 

8 • applications that have high sediment loadings unless use pretreatment systems and/or 

9 increase maintenance 

10 Stormwater infiltration can affect groundwater quality; however, the incidence of groundwater 

11 contaminated to an unhealthy level from stormwater is low. Many factors contribute to the risk 

12 (Clark, et al., 2009) 

13 Estimated Effectiveness for Runoff Volume and Pollutant Load Reduction 

14 Volume Reduction. Guidance manuals are referenced in this fact sheet, and by state and local 

15 jurisdictions, that provide instruction on methods for calculating volume reduction based on 

16 infiltration rates and storage volumes. Evapotranspiration also provides some volume reduction. 

17 The following factors influence the annual stormwater volume reduction achievable on a broader 

18 level: 

19 • Local climate and rainfall patterns. 

20 • Local soil characteristics, including the soils underlying the constructed bioretention cell. 

21 • Local evapotranspiration rates driven by climate conditions, vegetation type, and length 

22 of growing season. 

23 • Site conditions such as location in a sunny area or in deep shade 

24 • Ratio of cell media volume to drainage area. Increasing the volume of media relative to 

25 the drainage area has been demonstrated to reduce outflow. 

26 • Use of underdrain versus infiltration to underlying soil 

27 • Care during construction to ensure construction site erosion does not clog the system 

28 Pollutant Reduction. Pollutant concentration reductions can be obtained in the bioretention 

29 system to further reduce overall loading. Many factors associated with the pollutants, water, soil, 

30 plants, microbes, and system design affect pollutant removal performance. 

31 For example, nutrient removal can be influenced by the following factors: 

32 • the amount of organic material and the potential for the media to decay and leach 

33 nutrients. 

34 • the form of phosphorus or nitrogen as it enters the cell, and transforms in the cell. 

35 • biological transformation of nutrients in the cell in microbial and plant processes 

36 • cation exchange capacity and ability to sorb nutrients 
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Chapter 3. Controlling Urban Runoff 181 

1 • the presence of an anaerobic/saturated zone which influences denitrification potential 

2 • soil media composition and volume 

3 • Plant species, community composition, size, coverage and health 

4 Phosphorus removal requires the use of a low phosphorus index soil mix with a high cation 

5 exchange capacity (Li, et al., 2009). Layering of media targeted at specific pollutants may 

6 enhance water quality benefits (Li, et al., 2009). 

7 A summary of some pollutant specific removal information is provided below (Davis, et al., 

8 2009). 

9 • Suspended Solids – Reductions can be as high as 99 percent. New facilities may export 

10 TSS from the washout of fines in the media. 

11 • Phosphorus – Reduction is highly variable, typically from 50 – 80 percent. Effluent 

12 phosphorus at some locations has been higher than influent concentrations, largely due to 

13 high initial levels of soil phosphorus. 

14 • Nitrogen – Because of the complex interactions of nitrogen species, total nitrogen 

15 removal is difficult to achieve. Nitrogen removal may be increased with the use of a 

16 higher percentage of organic matter in the soil mix (Hinman, et al., 2005), provided the 

17 organic matter does not contain high nitrogen concentrations. Bioretention effectively 

18 removes organic nitrogen in the media’s organic material. Nitrate, however, is very 

19 mobile, and only when the media remains saturated for an extended period denitrification 

20 is possible. 

21 • Heavy Metals – Dissolved and particulate-bound metals are removed by filtration of 

22 particulate metals and adsorption of dissolved species in the mulch and bioretention 

23 media. Metals have been shown to be primarily removed in the first 1 to 2 inches of the 

24 surface mulch layer (Hinman, et al., 2005). 

25 • Oil & Grease – Sorption of low concentrations of motor oil to organic material in the soil 

26 mix have resulted in removal efficiencies of 96–99 percent. Native bacteria in the mulch 

27 then biodegrade the hydrocarbons in a few days 

28 • Chlorides – Bioretention does not treat chlorides and, where exposed to salting practices, 

29 has been found to leach chlorides year round. 

30 • Bacteria – Removals of bacteria have been monitored to be between 70 percent 

31 (Hathaway and Hunt, 2008) and 91 percent, through process that include filtration, 

32 drying, and exposure to sunlight. 

33 The reductions in mass loading of N and P achievable with bioretention have been shown to be 

34 due to the decrease in runoff volume, not necessarily decreases in concentration. Field tests have 

35 shown considerable mass reductions to be achieved even when increases in concentrations occur 

36 across the bioretention cell from nutrients contained in the media (Hunt, Jarrett, Smith, and 

37 Sharkey, 2006). For this reason, a volume reduction performance goal is recommended. 

38 Understanding the ranges of effluent concentrations observed, though, is valuable to evaluate 

39 performance. 
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Chapter 3. Controlling Urban Runoff 182 

1 Typical influent and effluent concentration ranges. The range of observed concentrations of 

2 nutrients in stormwater runoff in the National Stormwater Quality Database is provided in the 

3 Table 3-48, to give an indication of influent concentration ranges. 

4 For effluent quality, the following are noted: 

5 • Effluent concentration goals of the New York State Design Manual, Chapter 10 

6 Enhanced Phosphorus Removal (Quigley, Strecker, Pitt, Karimipou, 2008) 

7 – less than or equal to 0.1 mg/l TP 

8 – less than equal to 0.06 mg/L dissolved phosphorus 

9 • Reported effluent concentration results from field studies in the Mid-Atlantic (Davis, et. 

10 al 2009) 

11 – from 0.06 to 0.56 mg/l TP 

12 – from 0.08 to 2.8 mg/l TN 

13 Table 3-48. Selected Median Concentration of Nitrogen and Phosphorus Pollutants from Urban 

14 Land Uses 

NH3 

(mg/L) 

N02+NO3 

(mg/L) 

Nitrogen, Total 

Kjeldahl (mg/L) 

Phosphorus, total 

(mg/L) 

Residential 0.32 0.6 1.4 0.3 

Commercial 0.5 0.6 1.6 0.22 

Industrial 0.5 0.73 1.4 0.26 

Freeways 1.07 0.28 2 0.25 

Open Space 0.18 0.59 0.74 0.31 

Source: Pitt, R., A. Maestre, and R. Morquecho. 2004. The National Stormwater Quality Database (NSQD, version 

1.1). University of Alabama, Department of Civil and Environmental Engineering, Tuscaloosa, AL. 

http://rpitt.eng.ua.edu/Research/ms4/Paper/Mainms4paper.html. Updated February 16, 2004. Accessed February 3, 2010. 

15 Cold weather performance. Bioretention can provide effective infiltration in cold weather. Dietz 

16 and Clausen (2007) report that, despite measureable frost, 99 percent of runoff was either 

17 evapotranspirated or infiltrated for bioretention in Connecticut. The University of New 

18 Hampshire reports similar favorable performance in winter conditions (Roseen, et al 2009), and 

19 rapid thawing of bioretention media is reported when runoff enters. 

20 Summaries of Volume and Pollutant Loading Reductions Achievable 

21 A wide range of performance results have been observed in field tests, and authors cite the 

22 difficulty of using such data to prepare general performance estimates (Dietz, 2007; Li and 

23 Davis, 2009, Allen, et al, 2009). Volume reductions of from 75 percent to greater than 90 percent 

24 on an annual average basis have been reported with bioretention (Geosyntec Consultants, Urban 

25 Stormwater BMP Performance Monitoring, International Stormwater BMP Database, 

26 WERF/ASCE/EPA, 2009); these values typically reflect precipitation patterns of the study area 

27 where most of the annual rainfall occurs in small events of approximately an inch depth or less. 
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Chapter 3. Controlling Urban Runoff 183 

1 For understanding and comparing performance results, estimates should be for an annual basis 

2 using long-term, region-specific weather data for a specific design scenario. 

3 A review of recent performance estimates provided in Table 3-49 leads to the following 

4 observations (Simpson, et al. 2009): 

5 • The majority of the load reduction is from runoff reduction, therefore reporting the runoff 

6 reduction component is essential for understanding system performance (Center for 

7 Watershed Protection and Chesapeake Stormwater Network, 2008). 

8 • Volume reduction can be a surrogate for, or approximate indicator of, the pollutant 

9 removal achieved. 

10 Table 3-49: Generalized Bioretention Performance Estimates for the Chesapeake Bay Area 

11 Demonstrate that the Majority of the Load Reduction is from Runoff Reduction 

12 

Source: Chesapeake Bay Program, Tom Simpson, Sarah Weamert, et al., 2009 

Notes: 

13 • Soil classification (A, B, C, D) per USDA National Resource Conservation Service (NRCS) 

14 • Event Mean Concentration-based Removal expressed as Percent Reduction (PR) 

15 • Mass Based Removal expressed as percent removal of total load by mass (TR) 

16 • Nitrogen concentration reduction is low potentially because the(estimated at 10%). The solubility of nitrate, the 

17 potential for organic nitrogen and ammonia to mineralize in the bioretention media to the nitrate form, and the 

18 lack of anaerobic conditions, organic matter carbon source, and time needed for denitrification contribute to 

19 nitrogen export. 

20 • Assumptions included: 1) highly impervious urbanized land use; 2) generalized for design criteria typical of Bay 

21 area jurisdictions; 3) low phosphorus soil media; 4 ) forannual loading reduced from rain events up to 1” to 1.5” 

22 depth. 

23 • Total removal estimated by the calculation TR = RR + {(100-RR) * PR)}, rounded to a factor of 5. 

24 • Authors caution that the estimates, based on limited data and generalized for simplicity, may not represent true 

25 long-term performance throughout the watershed. Performance is highly variable even under controlled 

26 conditions. 

27 Practice Design 

28 Several design considerations influence the overall performance of bioretention, including:

29 • The potential for clogging should be assessed and pretreatment, such as such as mulch, 

30 should be provided if necessary. If grass swales are used, care should be taken to ensure 
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Chapter 3. Controlling Urban Runoff 184 

1 that sediment will not accumulate to point where it overtakes the vegetation and becomes 

2 costly to remove. 

3 • Well draining soils allow for rapid infiltration, but if the infiltration rate is too rapid, 

4 nitrate may pass though without treatment. 

5 • Soils with slow infiltration rates may decrease the overall stormwater volume retention. 

6 Infiltration tests at the site should be performed to better estimate expected performance. 

7 In these conditions, if a specified volume is to be retain the designer should consider 

8 designing the subbase with gravel or other materials to retain the requisite volume. 

9 • When conditions necessitate the use of underdrains the discharge rate should be as slow 

10 as feasible to maximize infiltration. Overflows are preferred to maintain maximum 

11 infiltration. Other options include positioning the discharge orifice on the sidewall above 

12 the bottom of the invert. 

13 • An impermeable liner, with an underdrain, may be used to prevent migration of 

14 stormwater from the bioretention cell, if needed. These systems provide water quality 

15 improvements because of the pollutant reductions available from the vegetated system 

16 and moderate volume reductions from evapotranspiration. 

17 Hydrology and Volume Reduction 

18 Considerations in the hydrologic performance of bioretention design include (Li, et al.., 2009; 

19 Davis, et al.., 2009): 

20 • Underdrained systems display the poorest hydrologic performance. 

21 • Adding an internal storage zone below the underdrain improves performance, allowing 

22 more time for infiltration, and potentially denitrification. 

23 • Reduced rates have been reported in colder months. 

24 • Infiltration and evapotranspiration reduce discharge volume by 50-90 percent%

25 depending upon system variables.

26 Maintenance Considerations and Resources 

27 Typical maintenance activities are as follows: 

28 • Supplemental irrigation may be needed during the first 2 to 3 years after planting. 

29 Drought-tolerant species may need little additional water after this period, except during 

30 prolonged drought, when supplemental irrigation may become necessary for plant 

31 survival. 

32 • Weeds should be removed by hand until vegetation is established. Although plants may 

33 need pruning to maintain healthy growth, routine mowing should not be required. Dead 

34 or diseased plants should be removed and replaced. Mulch should be re-applied when 

35 erosion is evident to maintain a 2-3 inch depth. 

36 • Inspect at least two times per year for sediment buildup, trash removal, erosion, and to 

37 evaluate the vegetation. Sediment should be removed in a manner that minimizes soil 
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Chapter 3. Controlling Urban Runoff 185 

1 disturbance if buildup reaches 25 percent of the ponding depth. Ensure pretreatment 

2 devices, if used, are maintained. 

3 • Some manuals recommend replacing the top few inches of bioretention media every few 

4 years and/or when infiltration rates slow down too much. 

5 Costs and factors affecting cost 

6 Costs vary according to many factors including soil depth, plant selections, slope conditions and 

7 the contractor’s familiarity with the practice. Typically costs are (WERF, User’s Guide to the 

8 BMP and LID Whole Life Cost Model, Version 2.0, and associated spreadsheets, 2009):

9 • For residential raingardens: Between $6 per square foot (installed by the owner) to $16 

10 per square foot of raingarden surface area (professional installed). 

11 • For urban curb-contained bioretention, $16–29 per square foot, driven by the cost of 

12 curbing and other urban-related infrastructure that may be used for conventional 

13 landscaping. 

14 • Bioretention cells often replace areas that would have been landscaped, so the life-cycle 

15 cost can be less than the landscaped alternative. 

16 Some factors influencing costs are:

17 • Material availability and transport 

18 • Site conditions (e.g. traffic, utilities) 

19 • Native soils, subgrade soils such as clay that result in the need for underdrain or overflow 

20 device 

21 • Specific stormwater management requirements, such as enhanced nutrient removal. 

22 • The need for, and the type of, pretreatment 

23 • Vegetation type and scale 

24 • Soil medium specifications and availability 

25 • Size of installation 

26 The Prince George’s County Bioretention Manual (2007) and WERF’s BMP and LID Whole Life 

27 Cost Model (2009) provide reported costs and templates to facilitate project cost estimation. 

28 Example Bioretention Design Manuals in the Chesapeake Bay Watershed 

29 Area 

30 Delaware Department of Environmental Resources and Environmental Control, Green 

31 Technology: Standards, Specifications, and Details for BMPs, Sections 2.4 and 2.5, 2005. 

32 Pennsylvania Stormwater Best Management Practices Manual, BMP 6.4.5 Rain 

33 Garden/Bioretention, 2006. 
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Chapter 3. Controlling Urban Runoff 186 

1 Prince George’s County, Maryland, Bioretention Manual, Revised December 2007; and Low2 Impact Development Design Strategies: An Integrated Design Approach, EPA 841-B-00-003, 

3 2000. 

4 Prince George’s County, Maryland, Low-Impact Development Hydrologic Analysis, EPA 841-B5 00-002, 2000. 

6 U.S Fish and Wildlife Service, Bayscapes, www.fws.gov/ChesapeakeBay/Bayscapes.htm

7 Virginia Department of Conservation and Recreation, Stormwater Design Specification No. 9: 

8 Bioretention, 2009. 

9 References 

10 Caltrans. 2002., Draft Biofilter Pilot Phosphorus Investigation, 2002. 

11 Center for Watershed Protection and Chesapeake Stormwater Network. 2008., Technical 

12 Memorandum: The Runoff Reduction Method, 2008. 

13 Clark, Shirley; R. Pitt, R. 2009. Field Groundwater Contamination Potential from Infiltration of 

14 Urban Stormwater Runoff. 

15 Colwell, Shanti R., R.R. Horner, D. B. Booth. 2000.et al., Characterization of Performance 

16 Predictors and Evaluation of Mowing Practices in Biofiltration Swales, Center for Urban 

17 Water Resources Management, Seattle, WA, 2000. 

18 Davis, Allen P., W.F. Hunt, R.G. Traver, and M. Clar. 2009., Bioretention Technology: 

19 Overview of Current Practice and Future Needs, Journal of Environmental Engineering, 

20 vol. 135, no. 3, pp. 109-117, March 2009. 

21 Davis, Allen P., M. Shokouhian, H. Sharma, C. Minami, D. Winogradoff. 2003.et al., Water 

22 Quality Improvement Through Bioretention: Lead, Copper, and Zinc Removal, Water 

23 Environment Research, 75, 73-82, January/February 2003. 

24 Davis, Allen P., M. Shokouhian, H. Sharma, C. Minami.. 2006.et al., Water Quality 

25 Improvement through Bioretention Media: Nitrogen and Phosphorus Removal, Water 

26 Environment Research, vol. 78, no. 3, pp. 284-293, March 2006. 

27 DiBliasi, C., Houng Li, Allen P. Davis, Upal Ghosh. 2009., Removal and Fate of Polycyclic 

28 Aromatic Hydrocarbon Pollutants in an Urban Stormwater Bioretention Facility, 

29 Environmental Science and Technology, 2009, 43, 494–502.

30 Dietz, M.E., and J. C. Clausen. 2005., A Field Evaluation of Rain Garden Flow and Pollutant 

31 Treatment, Water, Air, and Soil Pollution, vol. 167, pp.123-138, 2005. 

32 Dietz, M.E. 2007., Low-Impact Development Practices: A Review of Current Research and 

33 Recommendations for Future Directions, Water, Air, Soil Pollution, 186; 351-363, 2007. 

34 Hathaway, Jon M, and William Hunt., Urban Waterways: Removal of Pathogens in Stormwater, 

35 North Carolina Cooperative Extension Urban Waterways Series, AGW-588-16W. 
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Chapter 3. Controlling Urban Runoff 187 

1 Hinman, Curtis, et al. 2005.., Low Impact Development Technical Guidance Manual for Puget 

2 Sound, Puget Sound Action Team, Washington State University Pierce County Extension, 

3 May 2005. 

4 Hinman, Curtis. 2007., Maintenance of Low Impact Development Facilities, Puget Sound Action 

5 Team, 2007. 

6 Hon, G.E. et al. 2002.., Sustainable Oil and Grease Removal from Stormwater Runoff Hotspots 

using Bioretention, Paper for the 74th 7 Annual Conference and Exhibition of the 

8 Pennsylvania Water Environment Association, State College, PA, June 2002. 

9 Hsieh, Chi-hsu, A.P. Davis, and B.A. Needleman. 2007., Nitrogen Removal from Urban 

10 Stormwater Runoff Through Layered Bioretention Columns. Water Environment Research, 

11 79(12), p.2404-2411, 2007. 

12 Hsieh, Chi-hsu, and Allen P. Davis. 2005., Evaluation and Optimization of Bioretention Media 

13 for Treatment of Urban Storm Water Runoff , Journal of Environmental Engineering, vol. 

14 131, no. 11, pp 1521-1531, November 2005. 

15 Hunt, William F., and Nancy White. 2001., Designing Rain Gardens (Bioretention Areas), North 

16 Carolina Cooperative Extension Service, 2001, available at: 

17 www.engr.uga.edu/service/outreach/Stormwater%20BMP/BioretentionOverview.pdf, 

18 (accessed August 2007). 

19 Hunt, William F., A. R. Jarrett, J. T. Smith, and L. J. Sharkey. 2006.et al., Evaluating 

20 Bioretention Hydrology and Nutrient Removal at Three Field Sites in North Carolina, 

21 Journal of Irrigation and Drainage Engineering, pp. 600-608, November/December 2006. 

22 Geosyntec Consultants (Quigley, Strecker), Robert Pitt, Shohreh Karimipour. 2009. , New York 

23 State Stormwater Design Management Design Manual, Chapter 10 Enhanced Phosphorus 

24 Removal Standards, December 2009 Draft. 

25 Geosyntec Consultants (Quigley, M, and Clary J., et. al). 2009. Urban Stormwater BMP 

26 Performance Monitoring, International Stormwater BMP Database, WERF/ASCE/EPA 

27 and Partners, 2009. www.bmpdatabase.org

28 Li, Houng and A.P. Davis. 2009., Water Quality Improvement through Reductions of Pollutant 

29 Loads Using Bioretention, Journal of Environmental Engineering, vol. 135, no. 8, pp. 567-

30 576, August 2009. 

31 Li, Houng, L.J. Sharkey, W.F. Hunt, and A.P. Davis. 2009., Mitigation of Impervious Surface 

32 Hydrology Using Bioretention in North Carolina and Maryland, Journal of Hydrologic 

33 Engineering, vol. 14, no. 4, pp. 407-415, April 2009. 

34 Roseen, R.M., T.P Ballestero, J.J. Houle, P. Avellaneda, J. Briggs, G. Fowler, and R. Wildey. 

35 2009. Seasonal Performance Variations for Storm-Water Management Systems in Cold 

36 Climate Conditions ASCE Journal of Environmental Engineering, 135(3): 128-137. 2009.
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Chapter 3. Controlling Urban Runoff 188 

1 Simpson, Tom W., and S.E. Weammert. 2008. , Infiltration and Filtration Practices: Definition 

2 and Nutrient and Sediment Reduction Effectiveness Estimates, The Mid-Atlantic Water 

3 Program at the University of Maryland, 2008. 

4 http://archive.chesapeakebay.net/pubs/bmp/Infiltration_and_Filtration_Practices.pdf

5 Sun, X., and A. P. Davis. 2007., Heavy Metal Fates in Laboratory Bioretention Systems, 

6 Chemosphere, vol. 66, pp. 1601-1609, 2007. 

7 Tackett, Tracey, Bioretention Soil Specifications, available at: 

8 http://depts.washington.edu/urbhort/html/education/BioretentionSoilSpecs.pdf, (accessed 

9 January 2010). 

10 University of New Hampshire. 2006., Low Impact Stormwater Management Project at the 

11 University of New Hampshire: A Final Report to the New Hampshire Estuaries Project, 

12 2006. 

13 U.S. Department of Agriculture and Center for Watershed Protection. 2006., Urban Watershed 

14 Forestry Manual, Part 2, Conserving and Planting Trees at Development Sites, 2006. 

15 U.S. Environmental Protection Agency - Region 1. 2008., Stormwater Best Management 

16 Practices (BMP) Performance Analysis, 2008.

17 U.S. Environmental Protection Agency. 1999., Stormwater Technology Fact Sheet: Bioretention, 

18 EPA 832-F-99-012, Office of Water, Washington, D.C., September 1999.

19 Washington State Department of Ecology, Evaluation of Emerging Stormwater Treatment 

20 Technologies. 

21 Water Environment Research Federation. 2007., Critical Assessment of Stormwater Treatment 

22 and Control Selection Issues, 2007.

23 Water Environment Research Federation. 2009., Flow Control and Water Quality Treatment 

24 Performance of a Residential Low Impact Development Pilot Project in Western 

25 Washington, 2009.

26 Water Environment Research Federation. 2006., Infiltration vs. Surface Water Discharge: 

27 Guidance for Stormwater Managers, 2006. 

28 Water Environment Research Federation. 2009., User’s Guide to the BMP and LID Whole Life 

29 Cost Model, Version 2.0, 2009. 
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Chapter 3. Controlling Urban Runoff 189 

1 6.6 Soil Restoration 

2 Description of practice 

3 Soil restoration techniques can be, applied after construction, is used to improvedeeply till

4 compacted soils. The addition of compost can increase soil organic content, provide beneficial 

5 bacteria and fungi, and improve or restore soil water retention capacity and overall soiltheir 

6 porosity by amending them with compost. Compost is aerobically decomposed organic waste 

7 and amending a soil with compost increases the soil’s permeability. The addition of soil 

8 amendments can delay and water holding capacity. This delays and often reducereduces the peak 

9 stormwater run-off flow rate, and volume, and decreasedecreases irrigation water requirements. 

10 Amending soils will also reduce fertilizer and pesticide requirements. Soil restoration techniques 

11 may also be used as part of a system to provide additional retention or infiltration capacity to 

12 manage runoff from disconnected guttersto enhance the runoff reduction performance of 

13 downspout disconnections, grass channels, filterstrips, and impervious areas. and filter strips

14 Volume/specific pollutants addressed

15 The primary water quality improvements which result from restoring soil through tillage and 

16 compost amendments are increased infiltration and the resulting runoff reduction.

17 Development sector(s) in which it is applied

18 Compost amended soils are suitable for any pervious area where soils have been or will be 

19 compacted by the grading and construction process. Compost amendments can be applied to the 

20 entire pervious area of a development or be targeted in select areas of the site to enhance the 

21 performance of runoff reduction practices. Some common design applications include:

22 Reduce runoff from compacted lawns and bare

23 • Enhance rooftop disconnections on poor soils 

24 • Increase volume of runoff infiltrated from rooftops or other areas

25 Increase volume of runoff infiltratedreduction within a grass channel or 

26 • Increase runoff reduction within a filter strip 

27 • Increase volume of runoff reduced by a the function of a tree cluster or reforested area of 

28 the site (VADCR, 2009). 

29 Hydrologic Performance and Targeted Pollutants

30 The primary water quality improvements which result from restoring soil through tillage and 

31 compost amendments are increased infiltration and the resulting reduction in runoff volumes. 

32 Reducing runoff volume with compost generally reduces pollutant transport and loading off site 

33 (Faucette, et al, 2005; Faucette et al, 2007).

34 
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Chapter 3. Controlling Urban Runoff 190 

1 Photo/diagram 

2 

3 Figure 3-33. Soil Amendments (Source: VADCR Specification No. 4) 

4 Common feasibility constraints and limitations 

5 Compost amendments are not recommended where:

6 • Existing soils have high infiltration rates (e.g., HSG “A and B” soils), although compost 

7 amendments may be needed at mass-graded B soils to maintain runoff reduction rates. 

8 • The water table or bedrock is located within 1.5 feet of the soil surface. 

9 • Slopes exceed 10 percent, unless surface applied as a compost blanket%.

10 • Existing soils are saturated or seasonally wet 

11 • The use of tillage with soil amendmentsThey would harm roots of existing trees (stay 

12 outside the tree drip line) 

13 • The downhill slope runs toward an existing or proposed building foundation 

14 • The contributing impervious surface area exceeds the surface area of the amended soils 

15 (VADCR, 2009). 

16 SelectionIn addition, in many situations, different types of the compost amendments should 

17 occur based on thecan adversely impact water quality objectives of the jurisdiction or the project. 

18 Compost amendments should, therefore precautions must be formulated to not adversely affect 

19 water qualitytaken. Properties such as nutrient content, soil moisture holding capacity, metals 

20 uptake capacity, shrink/swell, product maturity, pathogen, residual chemical content and weed 

21 seed content require a high level of scrutiny to insure the appropriate amendments are being used 

22 (Lenhart, 2007). 
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Chapter 3. Controlling Urban Runoff 191 

1 Runoff volume and pollutant load removal estimates 

2 Balousek conducted research that demonstrated that One study concluded that compost3 amended, chisel-plowed, and deep-tilled plot treatments showed runoff reductions from 74 to 91 

4 percent, compared to the control. Chisel-plowed and deep-tilled treatment showed cumulative 

5 runoff reductions of 40 to 53 percent, compared to the control (Balousek, 2003). The runoff 

6 reduction volume achieved by soil restoration depends on the site application and the pre7 construction hydrologic soil group (VADCR, 2009). 

8 The use of compost amendments can reduce or eliminateHowever, while the need for 

9 supplementalcontinuous fertilization from inorganic fertilizer sources. Someto establish and 

10 maintain the turf is reduced, if not eliminated, at compost-amended sites, studies, however, 

11 show that the concentrations of many pollutants can increase in the surface runoff after soils are 

12 amended amending with compost, hence the need for specification standards where nutrient 

13 runoff is to be limited. A study conducted by the USEPA ORD (Pitt et al, 1999) found that 

14 surface runoff from the compost-amended soils had greater concentrations of almost all 

15 constituents, compared to the surface runoff from the control sites. The concentration increases 

16 in the surface runoff and subsurface flows from the compost-amended soil test site were quite 

17 large, typically in the range of 5 to 10 times greater. Subsurface flow concentration increases for 

18 the compost-amended soil test sites were also common and about as large. When the decreased 

19 surface flow quantities were considered in conjunction with the increased surface runoff 

20 concentrations, it was found that all of the surface runoff mass discharges were reduced by large 

21 amounts (to 2 to 50 percent of the unamended discharges). However, many of the subsurface 

22 flow mass discharges are expected to increase, especially for ammonia, phosphate, total 

23 phosphorus, nitrates, and total nitrogen. The large phosphorus and nitrogen compound 

24 concentrations found in surface runoff and subsurface flows at the compost-amended soil sites 

25 decreased significantly during the time of the tests (about 6 months). The older test sites also had 

26 lower nutrient concentrations than the new sites, but still had elevated concentrations when 

27 compared to the soil-only test plots. 

28 Use of compost and soil amendments with quality control specifications will help avoid potential 

29 issues such as excess nutrient runoff. 

30 The qualitytype of compost is being used (i.e. feed stock, maturity, presence of pesticides and 

31 herbicides) must be considered to minimize the adverse effects of water quality. One recent 

32 study concluded that due to its high nutrient content, but low leaching properties, mature 

33 compost made from deciduous leaves makes suitable compost for soil amendment in applications 

34 for water quality (Lenhart, 2007). Two studies conducted at the University of Georgia found that 

35 when quality compost was used and compared to conventional seeding and mulching 

36 applications, runoff nitrogen loading was reduced by 58-92% and runoff phosphorus loading was 

37 reduced by 83%-97% (Faucette, et al, 2005: Faucette, et al, 2007).

38 Practice design 

39 • The depth of compost amendment is based on the relationship between the surface area of 

40 the soil amendment to the contributing area of impervious cover that it receives. VADCR 

41 Stormwater Design Specification No. 4 (www.chesapeakestormwater.net/storage/

42 first-draft-baywide-design-specificationsi/BAYWIDE%20No%204%20SOIL
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Chapter 3. Controlling Urban Runoff 192 

1 %20AMENDMENT%20SPECIFICATION.pdf) includes a table (Table 3) which 

2 provides guidance as to the depth of compost, incorporation depth, and incorporation type 

3 based on the area to be amended and the contributing impervious area. 

4 • USEPA’s Compost Blanket Factsheet includesTo maximize the benefits of compost 

5 addition, these guidelines set an amended soil organic content goal of between eight and 

6 specifications for compost blankets for constructionthirteen percent, by weight. As a 

7 general rule of thumb this goal can be achieved by incorporating two units of loose soil 

8 with one unit of loose compost (a 2:1 ratio). Final depth of amended soil will be between 

9 eight and post-construction use. 

10 (http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=factsheet_results

11 &view=specific&bmp=118.

12 ten inches, dependent upon the equipment used. (Chollak and Rosenfeld, 1998)

13 • The compost material should be well composted, free of viable weed seeds, and stable 

14 with regard to oxygen consumption and carbon dioxide generation. The compost 

15 shouldshall have a moisture content that has no visible free water or dust produced when 

16 handling the material. VADCR Stormwater Design Specification No. 4 

17 (www.chesapeakestormwater.net/storage/first-draft-baywide-design18 specificationsi/BAYWIDE%20No%204%20SOIL%20AMENDMENT%20SPECIFICAT

19 ION.pdf) and the Low Impact Development Center 

20 (www.lowimpactdevelopment.org/epa03/saspec_print.htm) provide technical 

21 specifications for the compost material. 

22 • Soil tests should be conductedare required during two stages of the compost amendment 

23 process. The first testing is done to ascertain pre-construction soil properties at proposed 

24 amendment areas. The second soil analysis is taken to determine whether any further 

25 nutritional requirements, pH, and organic matter adjustments are necessary for plant 

26 growth. 

27 VADCR Stormwater Design Specification No. 4 

28 (www.chesapeakestormwater.net/storage/first-draft-baywide-design29 specificationsi/BAYWIDE%20No%204%20SOIL%20AMENDMENT%20SPECIFICATION.p

30 df) includes design criteria for soil amendments used to enhance downspout disconnections, 

31 grass channels, vegetated filter strips, in addition to several Bay-specific regional design 

32 variations. 

33 The City of Redmond, Washington Guidelines for Landscaping with Compost-Amended Soils 

34 (www.redmond.gov/insidecityhall/publicworks/environment/pdfs/compostamendedsoils.pdf) 

35 (Chollak and Rosenfeld, 1998) provides detailed justification, design specifications and cost36 benefit analysis of using compost-amended soils. 

37 The Composting Council and the Clean Washington Council developed guidance (Development 

38 of a Landscape Architect Specification for Compost Utilization, 

39 www.cwc.org/organics/org972rpt.pdf) which contains a series of short and long compost use 

40 specifications for various landscape applications. Both product specifications and end use 

41 instructions are provided. 
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Chapter 3. Controlling Urban Runoff 193 

1 Maintenance considerations and resources 

2 VADCR recommends specific practices be used during the first year after amendment to help 

3 ensure success where turf is the appropriate groundcover. The establishment of other landscape 

4 cover types, such as forest cover or native plantings, may require fewer or no follow-up chemical 

5 inputs after the site has been stabilized. VADCR recommendations for turf are: 

6 Successful soil compost amendments require certain tasks be undertaken in the first year.

7 • Initial inspections: For the first six months following amendments, the site should be 

8 inspected at least once after each storm event that exceeds a half- inch. 

9 • Spot Reseeding: Inspectors should look for bare or eroding areas in the contributing 

10 drainage area or around the soil restoration area, and make sure they are immediately 

11 stabilized with grass cover. 

12 • Fertilization: Depending on the amended soils test, a one-time, spot fertilization may be 

13 needed in the fall after the first growing season to increase plant vigor. 

14 • Watering: Water once every three days for first month, and then weekly during first year 

15 (Apr – Oct), depending on rainfall. (VADCR) 

Item Unit Estimated unit cost (2005 Dollars) 

Soil and site preparation S.Y. $5 - $8 

Mechanical grading and tilling S.Y. $18 - $27 

Soil amendments C.Y. $15 - $30 

Blower application S.Y. $0.45 - $1.00 

16 

17 Costs and factors affecting cost 

18 Costs include the amendment and the application into the existing soil. Typical costs are 

19 provided below (http://www.lowimpactdevelopment.org/ffxcty/5-1_soilamendments_draft.pdf):

Item Unit Estimated unit cost (2005 Dollars) 

Soil and site preparation S.Y. $5 - $8 

Mechanical grading and tilling S.Y. $18 - $27 

Soil amendments C.Y. $15 - $30 

Blower application S.Y. $0.45 - $1.00 

20 

21 Cost calculations based on amending soils on 1⁄4 acre area to manage runoff for a 1⁄2 acre area 

22 were prepared by the Low Impact Development Center for Fairfax County, Virginia, in 2005, as 

23 follows:

Item Required Cost per Year (2005 Dollars)

0 1 2 3 4 5 6 7 8 9 10 ... 25

Installation 25,000

Aerate 250 250 250 250 250
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Chapter 3. Controlling Urban Runoff 194 

Re-amend 25,000

Total cost 25,000 250 250 250 250 250 25,000

Annualized 

Cost

$1,125/year (includes re-amending in year 25)

1 

2 Enhancement of existing soil with well composted material derived from yard debris compost or 

3 biosolid amendment to form a Tilled Compost-Amended Turf (TCT) will have higher soil 

preparation costs than that of Topsoil Amended Turf (TAT)1 or Minimum Input Turf (MIT)24 

5 procedures (MIT is the most common procedure used in residential and commercial 

6 development). TCT practices will require a larger volume of material to be delivered to the site 

7 and more extensive site preparation procedures to ensure the amendment is well mixed with the 

8 existing soil. Additional soil analyses will be required to determine the optimum quantities of the 

9 various soil amendments.

10 However, turf grown on compost-amended soil can save homeowners, residences, and 

11 businesses money on water and fertilizer when compared to the other types of turf. A study 

12 conducted by the City of Redmond, Washington found that turf grown on tilled compost13 amended soil by hydroseed application pays for itself:

14 1) Between the fifth and sixth year when compared to topsoil-seed,

15 2) During the first year when compared to topsoil-sod,

16 3) Between the sixth and seventh year when compared to minimum-seed, and

17 4) Between the second and third year when compared to minimum-sod (Chollak and Rosenfeld, 

18 1998).

19 References 

20 Balousek. 2003. Quantifying decreases in stormwater runoff from deep-tilling, chisel-planting 

21 and compost amendments. Dane County Land Conservation Department. Madison, 

22 Wisconsin. 

23 Chollak, T. and P. Rosenfeld. 1998. Guidelines for Landscaping with Compost-Amended Soils. 

24 City of Redmond Public Works. 

25 www.ci.redmond.wa.us/insidecityhall/publicworks/environment/pdfs/compostamendedsoil

26 s.pdf

 

1

 The Topsoil Amended Turf method consists of the following: scarification of subsoil and rock removal,

importation and even distribution of additional topsoil, fertilizer and lime application, integration of soil layers by 

rototilling, grading and rolling of soil, seed, sod, or hydroseeding application.

2

 The Minimum Input Turf soil preparation consists of some rock removal and grading, even distribution of 

imported topsoil, fertilizer and lime application, grading and rolling of the soil, seed, sod or hydroseeding 

application.
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Chapter 3. Controlling Urban Runoff 195 

1 Clean Washington Council and Composting Council. , 1997. Development of a landscape 

2 architect specification for compost utilization. Seattle, WA and Bethesda, MD. Prepared 

3 by: E&A Environmental Consultants. www.cwc.org/organics/org972rpt.pdf

4 Faucette, L. B., J. Governo, C.F. Jordan, B. G Lockaby, H. F. Carino, and R. Governo. 2007. 

5 Erosion control and storm water quality from straw with pam, mulch, and compost 

6 blankets of varying particle sizes. Journal of Soil and Water Conservation. 62:6: 404-413.

7 Faucette B, C. Jordan, M. Risse, M. Cabrera, D. Coleman, and L. West. 2005. Evaluation of 

8 storm water from compost and conventional erosion control practices in construction 

9 activities. Journal of Soil and Water Conservation. 60:6: 288-297.

10 Pitt, R. J. Lantrip and R. Harrison. 1999. Infiltration through disturbed urban soils and compost11 amended soil effects on runoff quality and quantity. Research Report EPA/600/R-00/016. 

12 Office of Research and Development. U.S. EPA. Washington, D.C. 

13 Lenhart, J. 2007. Compost as a soil amendment for water quality treatment facilities. 

14 Proceedings 2007 LID Conference. Wilmington, NC 

15 Low Impact Development Center. Guideline for Soil Amendments. 

16 www.lowimpactdevelopment.org/epa03/soilamend.htm

17 VA Department of Conservation and Recreation (VADCR), 2009. Draft VA DCR Stormwater 

18 Design Specification No. 4 – Soil Compost Amendment Version 1.5. July 2, 2009. 

19 www.chesapeakestormwater.net/storage/first-draft-baywide-design20 specificationsi/BAYWIDE%20No%204%20SOIL%20AMENDMENT%20SPECIFICATI

21 ON.pdf
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Chapter 3. Controlling Urban Runoff 196 

1 6.7 Reforestation, Urban Forestry 

2 Description of Practice 

3 Forests are the most beneficial land use to protect the water quality of the Chesapeake Bay 

4 (USDA Forest Service, Urban Tree Canopy Goal Setting, 2006). Reforestation is the protection, 

5 enhancement and expansion of tree canopy in urban and suburban areas, in yards, parks, along 

6 streets, and public places. Urban forests provide significant environmental benefits though 

7 management of urban stormwater, but also provide multiple other benefits such as increasing 

8 property values, reduce energy costs for cooling in the summer, buffer wind and noise, improve 

9 air quality, provide habitat for wildlife, and beautify the landscape. In urban areas, trees provide 

10 an important stormwater management function by intercepting rainfall that would otherwise run 

11 off of paved surfaces and be transported into local waters though the storm drainage system, 

12 picking up various pollutants along the way (CWP and USFS, 2009). Trees also enhance 

13 stormwater management by evapotranspirating large quantities of stormwater, while the roots 

14 help to reduce soil compaction, enabling more infiltration of stormwater. In general, trees 

15 stabilize soils, reduce stormwater runoff, maintain the base flow of streams and filter nutrients 

16 and sediment (CWP, 2007). 

17 Reforestion can be achieved using many tools, such as developing an urban tree canopy (UTC) 

18 goal for a site or community, and achieving this goal through the use of regulations, policies 

19 and/or incentives to plant trees and help ensure continued growth. 

20 

21 Figure 3-34. Urban Watershed Forestry Objectives, By Goal 

22 Source: Cappiella, K.,et. al . 2005. Urban Watershed Forestry Manual. Part 1: Methods for Increasing Forest Cover in 

23 a Watershed, USDA Forest Service, Newtown Square, PA. 

24 
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Chapter 3. Controlling Urban Runoff 197 

1 Photo/diagram 

2 

3 Figure 3-35. Urban Tree Canopy (Source: CWP & USDA, 2009) 

4 Common Feasibility Constraints and Limitations 

5 • Developers have little incentive to leave or restore trees on development projects. 

6 • Unless regulations or incentives are in place, property owners may not protect existing or 

7 plant additional trees. 

8 • Utility corridor needs lead to tree losses and damage 

9 • Human safety (Fire response and transportation projects) often require tree removal 

10 Runoff Volume and Pollutant Load Removal Estimates 

11 On average, forests approximately 1/10 of the nitrogen to the Chesapeake Bay compared to 

12 developed lands (1.7 lbs acre compared to 14.8 lbs/acre). More specifically, riparian forests that 

13 buffer streams significantly reduce the amount of excess nutrients that enter the water, 

14 sometimes by as much as 30 to 90 percent (CBP, 2007). 

15 Forested areas have less runoff than developed areas, as indicated by the smaller runoff 

16 coefficient used when comparing to disturbed or impervious areas. 
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Chapter 3. Controlling Urban Runoff 198 

Table 3-50: Site Cover Runoff Coefficients (Source: Hirschman et al, 2008)11 

Soil Condition Runoff Coefficient 

Forest Cover 0.02 – 0.052, 3 

Disturbed Soils/Managed Turf 0.15 – 0.252,4 

Impervious Cover 0.95 

Derived from research by Pitt et al (2005), Lichter and Lindsey (1994), Schueler (2001a), Schueler, (2001b), Legg et 

al (1996), Pitt et al (1999), Schueler (1987) and Cappiella et al (2005) 

Range dependent on original Hydrologic Soil Group (HSG) 

Forest - A: 0.02 B: 0.03 C: 0.04 D: 0.05 

Disturbed Soils - A: 0.15 B: 0.20 C: 0.22 D: 0.25 

2 Research has shown that trees are the most effective at reducing the runoff from small, more 

3 frequent storms (CWP and USDA, 2009). 

4 Practice Design 

5 There are many local, regional and site-specific practices that can be implemented to conserve 

6 existing urban forest and increase forest restoration. Local and state governments can develop 

7 policies or plans which incorporate urban forestry, encourage/require practices such as stream 

8 buffers, and provide incentives for developers and property owners to conserve or restore urban 

9 forests. The following resources will provide more information about these options. 

10 • Guidelines for Developing and Evaluating Tree Ordinances (International Society of 

11 Arboriculture) - www.isa-arbor.com/publications/ordinance.aspx

12 • Protecting Water Resources with Higher Density Development (USEPA) - 

13 www.epa.gov/dced/pdf/protect_water_higher_density.pdf

14 • Forest Friendly Development (Alliance for the Chesapeake Bay) - 

15 www.alliancechesbay.org/pubs/projects/deliverables-145-8-2005.pdf

16 In addition, local governments can lead by example and invest in urban forestry themselves. For 

17 example, the Philadelphia (PA) Water Department Office of Watersheds (see 

18 www.phillyriverinfo.org/Programs/SubprogramMain.aspx?Id=TreeVitalize) contends that “trees 

19 are one of the most effective, least costly methods of storing and controlling stormwater runoff.” 

20 The Office of Watersheds has already contributed to the planting of over 500 trees within the 

21 City of Philadelphia and hopes to increase this number through its involvement with the regional 

22 TreeVitalize Program (see www.treevitalize.net). As part of this program, Office of Watersheds 

23 will partner with the Fairmount Park Commission to receive $300,000 over a three year period to 

24 plant up to 84 acres of forested riparian buffers throughout Philadelphia’s park system (PWD, 

25 2009). 

26 Federal Implementation of the Chesapeake Executive Council Directive on Forest Conservation 

27 provides specific actions to help achieve the goals of urban forest conservation and restorations. 

28 (www.chesapeakebay.net/press_ec2007forests.aspx?menuitem=20276) 

29 An example of local leadership in reforestation is Baltimore County’s Growing Home Campaign. 

30 Benefit information is provided, including links to American Forests “Personal Climate Change 
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Chapter 3. Controlling Urban Runoff 199 

1 Calculator”, and the National“national Tree BenefitsBenefits’ calculator from Casey Trees, a 

2 local non-profit. These tools help to educate the public on the multiple benefits of trees. The 

3 County provides financial incentives to plant trees through a public-private partnership with local 

4 nurseries and tree retailers, as follows: 

5 • The Growing Home Campaign includes an educational brochure that provides concise 

6 information for homeowners about planting urban trees and a cash incentive in the form 

7 of a $10 coupon. The brochure is distributed through public libraries, senior centers and 

8 parks facilities, the County web site (( www.growinghome.info), and citizen watershed 

9 organizations. 

10 • Citizens bring $10 tree coupons to any of 50 participating nursery retailers in Baltimore 

11 County and cooperating jurisdictions (Harford County and the City of Baltimore). The 

12 retailers return coupons used for tree purchases to Baltimore County, which captures data 

13 on tree planting locations and costs. The County then reimburses retailers for $5 of their 

14 $10 discount provided to citizens. 

15 • The Growing Home Campaign has resulted in the purchase and planting of some 5,600 

16 trees by homeowners since 2006, with a total economic impact of >$500,000. Every 

17 dollar of County coupon match, which comes from a capital improvement program 

18 project for stormwater retrofits, currently leverages about $18 of private investment in the 

19 urban tree canopy. 

20 The Center for Watershed Protection (www.cwp.org) and the USDA Forest Service has 

21 developed new designs for stormwater management practices for use in incorporating functional 

22 tree-based stormwater management systems into developments. These “stormwater forestry 

23 practices” address potential limitations through design modifications, species selection, and 

24 other methods. The designs listed below harness the benefits of trees to increase the effectiveness 

25 of stormwater practices, while providing other benefits to the community, such as cooling and 

26 shade, aesthetics, and wildlife habitat (CWP and USDA, 2009). The fact sheets listed below are 

27 available at www.forestsforwatersheds.org/reduce-stormwater. 

28 • Wooded wetland 

29 • Emergent pond/wetland system 

30 • Bioretention and bioinfiltration facilities 

31 • Alternating side slope plantings 

32 • Tree check dams 

33 • Forested filter strip 

34 • Multi-zone filter strip 

35 • Linear storm water tree pit 

36 • Stormwater treatment dry ponds 

37 Trees design in dense urban environments presents many challenges with the infrastructure of 

38 streets, sidewalks, and utilities. Resources for addressing these issues include Reducing 

39 Infrastructure Damage by Tree Roots: A Compendium of Strategies (Costello and Jones, 2003). 

40 Other planning considerations such as neighborhood character in tree selection and placement 
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Chapter 3. Controlling Urban Runoff 200 

1 are essential for a successful community street tree program (The Road to a Thoughtful Street 

2 Tree Master Plan: A Practical Guide to Systematic Planning and Design, Simons and Johnson, 

3 2008). 

4 Practices to prevent root compaction and provide additional space under pavements for tree root 

5 growth are gaining acceptance. One example is Minnesota’s MARQ2 project that used an 

6 elevated-pavement type structural support system for the planting of 179 trees along a 

7 redeveloped streetscape in the downtown area. The system was designed to manage stormwater 

8 as one of its functions, to help prevent combined sewer overflows 

9 (http://www.stormh2o.com/march-april-2010/reshaping-minneapolis10 project.aspxwww.ci.minneapolis.mn.us/public-works/Marq2/about.asp). 

11 More information on using trees to manage stormwater arecan be found at:

12 • Urban Watershed Forestry Manual Part 2: Conserving and Planting Trees at 

13 Development Sites - www.forestsforwatersheds.org/storage/part2forestrymanual.pdf

14 • Stormwater Management: Using Trees and Structural Soils to Improve Water Quality - 

15 www.cnr.vt.edu/urbanforestry/stormwater

16 • Watershed Forestry Resource Guide – Reducing Stormwater Runoff - 

17 www.forestsforwatersheds.org/reduce-stormwater

18 Maintenance Considerations and Resources 

19 The benefits of urban trees can be extended with appropriate selection, planting design, and 

20 maintenance. American Forests estimates that the average life expectancy of a downtown urban 

21 street tree is just 13 years, while their rural counterparts can live up to 100 years or more. 

22 Symptoms of tree decline from urban stressors can take years to appear. Common causes of 

23 urban tree mortality include:

24 • Damage to roots or soils from nearby construction activities 

25 • Air pollution 

26 • Physical damage from lawnmowers, vehicles or vandals 

27 • Damage from disease and insects 

28 • Trees planted in too small a space 

29 • Improper planting and pruning techniques 

30 • Tree stakes or grates left on too long 

31 • Poor, compacted soils 

32 • Lack of watering 

33 • Removal or damage during maintenance of nearby utilities or sidewalks 

34 • Competition from invasive plant species (CWP and USDA, 2009). 

35 The Urban Watershed Forestry Manual Part 3: Urban Tree Planting Guide (CWP, 2006) 

36 (available at www.forestsforwatersheds.org/storage/Part3ForestryManual.pdf)provides detailed 
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Chapter 3. Controlling Urban Runoff 201 

1 guidance on urban tree planting, including site assessment, planting design, site preparation, and 

2 planting and maintenance techniques. 

3 Costs and Factors Affecting Cost 

4 The costs of reforestation will vary greatly based upon how and where the trees are incorporated 

5 into the urban/suburban landscape. A recent source of information on program cost includes the 

6 American Public Works Association urban forestry handbook. This project was supported by the 

7 USDA Forest Service Urban and Community Forestry Program on the recommendation of the 

8 National Urban and Community Forestry Advisory Council. The handbook series is titled Urban 

9 Forestry Best Management Practices for Public Works Managers, and the individual handbooks 

10 are:

11 • Volume 1 Budgeting and Funding

12 • Volume 2 Staffing

13 • Volume 3 Ordinances, Regulations, & Public Policies

14 • Volume 4 Urban Forest Management Plan

15 This series is available free for download at APWA Press, 

16 www.apwa.net/About/CoopAgreements/urbanforestry. 

17 The cost-benefit of planting trees will also vary, however, and research is being done to attempt 

18 to quantify the value of urban tree canopy. American Forests (www.americanforests.org) has 

19 developed a tool to calculate the value of urban tree canopy in metropolitan areas. For example, 

20 American Forests determined that 34 percent% of Montgomery, Alabama was covered by tree 

21 canopy in 2002. The stormwater retention capacity of Montgomery’s urban forest is 227 million 

ft322 . The cost to manage this volume of runoff in traditional infrastructure is estimated at $454 

23 million. In addition, Montgomery’s urban forest is estimated to remove 3.2 million lbs of 

24 pollutants from the air annually and this benefit is valued at $7.9 million (American Forests, 

25 2004). Even in arid locations trees are important. In 2007, American Forests found that 

26 Albuquerque, New Mexico’s tree canopy provided 20 million cubic feet in stormwater detention 

27 services, valued at $123 million (American Forests, 2009). 

28 Further, forests filter pollutants from runoff therefore allowing fewer contaminants to reach 

29 potable water sources. This results in less treatment costs for local governments. 
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Chapter 3. Controlling Urban Runoff 202 

1 

2 Figure 3-36. Relationship between forest cover and water treatment costs. 

3 Practice/program evaluation 

4 The USDA Forest Service provides a Guide for Chesapeake Bay Communities (see 

5 www.jmorgangrove.net/Morgan/UTC-FOS_files/UTC_Guide_Final_DRAFT.pdf) to assist them 

6 with the setting and evaluation of urban tree canopy goals. Setting tree canopy goals is essential 

7 to achieving program success. Principles of an effective urban forest program and several case 

8 studies across the United States are provided in the US Forest Service-supported guide Planning 

9 the Urban Forest: Ecology, Economy, and Community Development (Schwab, American 

10 Planning Association, 2009). 

11 References 

12 American Forests., 2009. Urban Ecosystem Analysis Albuquerque, New Mexico: Calculating the 

13 Value of Nature. www.americanforests.org/downloads/rea/Alb_5%2022.pdf

14 American Forests., 2004. Urban Ecosystem Analysis Montgomery, AL : Calculating the Value 

15 of the Urban Forest. www.americanforests.org/downloads/rea/AF_Montgomery.pdf

16 Baltimore County, Maryland, Growing Home Campaign, 

17 www.baltimorecountymd.gov/Agencies/environment/growinghome/index.html
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Chapter 3. Controlling Urban Runoff 203 

1 Cappiella, K., T. Schueler, and T. Wright. 2005. Urban Watershed Forestry Manual. Part 1: 

2 Methods for Increasing Forest Cover in a Watershed. USDA Forest Service, Newtown 

3 Square, PA. 

4 Cappiella, K., T. Schueler, and T. Wright. 2005. Urban Watershed Forestry Manual. Part 2: 

5 Conserving and Planting Trees at Development Sites. USDA Forest Service, Newtown 

6 Square, PA. 

7 Center for Watershed Protection (CWP) and the USDA U.S. Forest Service (USDA), 2009. 

8 Webpage accessed on December 17, 2009. www.forestsforwatersheds.org

9 Chesapeake Bay Program, 2007. Chesapeake Bay Program Announces Forest Conservation 

10 Goals for Watershed. Press Release. December 5, 2007. 

11 www.chesapeakebay.net/press_ec2007forests.aspx

12 Costello, L.R., and K.S. Jones, Reducing Infrastructure Damage by Tree Roots: A Compendium 

13 of Strategies, University of California Cooperative Extension, Published by the Western 

14 Chapter of the International Society of Arborculture. 

15 Ernst, C., R. Gullick, and K. Nixon. 2004. Protecting the Source: Conserving Forests to Protect 

16 Water. OpFlow. American Waterworks Association. Vol. 30, No. 5. 

17 Forests for Watersheds, www.forestsforwatersheds.org

18 Hirschman, D., K. Collins, and T. Schueler, 2008. Technical Memorandum: 

19 The Runoff Reduction Method. Center for Watershed Protection. 

20 Legg, A. R. Bannerman and J. Panuska. 1996. Variation in the relation of runoff from residential 

21 lawns in Madison, Wisconsin. USGS Water Resources Investigations Report 96-4194. 

22 Lichter J. and P. Lindsey. 1994. Soil compaction and site construction: assessment and case 

23 studies. The Landscape Below Ground. International Society of Arborculture 

24 Pitt, R. S. Chen, S. Clark and J. Lantrip. 2005. Soil structure effects associated with urbanization 

25 and the benefits of soil amendments. World Water and Environmental Resources Congress. 

26 Conference Proceedings. American Society of Civil Engineers. Anchorage, AK. 

27 Pitt, R. J. Lantrip and R. Harrison. 1999. Infiltration through disturbed urban soils and compost28 amended soil effects on runoff quality and quantity. Research Report EPA/600/R-00/016. 

29 Office of Research and Development. U.S. EPA. Washington, D.C. 

30 Philadelphia Water Department, 2009. TreeVitalize - Comprehensive Tree Planting Program. 

31 www.phillyriverinfo.org/Programs/SubprogramMain.aspx?Id=TreeVitalize Website 

32 accessed: December 18, 2009. 

33 Schueler, T. 1987. Controlling urban runoff: a practical manual for planning and designing urban 

34 best management practices. Metropolitan Washington Council of Governments. 

35 Washington, DC. 
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Chapter 3. Controlling Urban Runoff 204 

1 Schueler, T. 2001a. The compaction of urban soils. Watershed Protection Techniques. 3(2): 661-

2 665. 

3 Schueler, T. 2001b. Can urban soil compaction be reversed? Watershed Protection Techniques. 

4 3(2): 666-669. 

5 Schwab, James C., Editor. 2009., Planning the Urban Forest: Ecology, Economy, and 

6 Community Development. American Planning Association, Planning Advisory Service, 

7 Report Number 555, January 2009. 

8 Simons, Ken, and Gary R. Johnson. 2008., The Road to a Thoughtful Street Tree Master Plan: A

9 Practical Guide to Systematic Planning and Design, University of Minnesota, 2008. 

10 Stormwater Magazine, Editorial Project Profile, Reshaping Downtown Minneapolis. Stormwater 

11 Magazine, March-April, 2010. http://www.stormh2o.com/march-april-2010/reshaping12 minneapolis-project.aspx

13 USDA. 2002. Fact Sheet #4: Control Stormwater Runoff with Trees. Center for Urban Forest 

14 Research, Pacific Southwest Research Station, Davis, California. July 2002.

15 USDA, Urban Tree Canopy Goal Setting – A Guide for the Chesapeake Bay, Forest Service, 

16 Northeastern Area, State and Private Forestry, Chesapeake Bay Program Office, Annapolis, 

17 MD. 
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Chapter 3. Controlling Urban Runoff 205 

1 6.8 Street Sweeping 

2 Description of Practice 

3 Street sweeping can provide significant pollutant removal, but many municipalities use sweepers 

4 that do not perform effectively, or that can actually cause more water quality issues (NURP, 

5 Sutherland, Bannerman, Pitt 2004). Aesthetics is main reason most municipalities use sweepers, 

6 not water quality, and for this use “mechanical” broom sweepers can perform well. However, 

7 they do not provide the level of water quality benefit that can be obtained using improved 

8 sweepers. 

9 Streets and roads composecomprise up to 20 percent% of total impervious cover in suburban 

10 subwatersheds and up to 40 percent% in highly urban subwatersheds. Contaminated particulates 

11 or “street dirt” accumulates along curbed roads between rainfall events. During intense rainfall 

12 events additional particulates can be washed on to these paved surfaces from adjoining land 

13 areas. This wet weather wash-on has been demonstrated to be quite important in understanding 

14 the pollutant removal benefits of street sweeping (Sutherland and Jelen 1996). Sources of 

15 pollutants include wash-on, atmospheric deposition, vehicle emissions, cargo spills, and wear 

16 and tear, breakup of street surface, road salts and deicers, litter, bird droppings, grass clippings, 

17 leaves and other organic material and sanding. This results in the accumulation of stormwater 

18 pollutants such as sediment, nutrients, metals, hydrocarbons, bacteria, pesticides, trash and other 

19 toxic chemicals (CWP 2008). 

20 These pollutants typically remain on streets until they are washed into the storm drain system 

21 during a rainfall event. However, some communities use street sweeping to remove some of 

22 these pollutants and prevent them from being conveyed into the storm drain system (CWP 2008). 

23 Street sweeping and vacuuming includes the use of self-propelled and walk-behind equipment to 

24 remove sediment from streets and roadways, and to clean paved surfaces in preparation for final 

25 paving. Sweeping and vacuuming prevents sediment from entering storm drains or receiving 

26 waters (CASQA 2003). 

27 Targeted Pollutants (Highly Dependent on Equipment Type) 

28 Targeted Pollutants 

Sediment Hydrocarbons Trash Nutrients 

    

Key:  High effectiveness  Medium effectiveness Low effectiveness 
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Chapter 3. Controlling Urban Runoff 206 

1 Photos 

2 

3 Figure 3-37. The majority of pollutants on streets are closest to the curb 

4 Source: www.quincyma.gov/Living

5 Common Feasibility Constraints and Limitations 

6 The following are common feasibility constraints and limitations of street sweeping: 

7 • Sweeping and vacuuming may not be effective when sediment is wet or when tracked 

8 soil is caked (caked soil may need to be scraped loose) (CASQA 2003). 

9 • Be careful not to sweep up any unknown substances or any object that may be potentially 

10 hazardous (CASQA 2003). 

11 • The use of kick brooms or some sweeper attachments tend to spread dirt rather than 

12 remove it (CASQA 2003). On the other hand, gutter brooms can be very effective at 

13 capturing street dirt. 

14 • Access to the curb is paramount to street sweeping efficiency, as the majority of 

15 pollutants on streets are closest to the curb. Parked cars can restrict access. Compliance 

16 with an appropriately enforced no-parking zone may provide access for street sweeping 

17 to the curb (CWP 2008). 

18 Pollutant Load Removal Estimates 

19 The ability of street sweepers to remove common stormwater pollutants varies depending on the 

20 sweeper technology being used, climate factors such as rainfall patterns, sweeper operation 

21 (including sweeper speed), sweeper maintenance (including broom wear), sweeping frequency, 

22 pavement conditions, the number of parked cars encountered, and the chemical and physical 

23 characteristics of the pollutants that have accumulated on the pavement. In addition, it can be 

24 difficult to estimate pollutant removal rates for street sweepers because of the difficulty in 

25 measuring particulate matter transported in runoff (APWA 2009),

26 Pros and cons of sweeper type on pollutant removal performance:

27 • Mechanical street sweepers are more effective at removing larger-sized particles than 

28 fine-grained particles and nutrients. Newer high efficiency sweepers pick up much 

29 smaller particles, as well (Sutherland and Jelen, 1997; Pitt, Bannerman, and Sutherland, 

30 2004). 
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Chapter 3. Controlling Urban Runoff 207 

1 • Mechanical sweepers are typically the least expensive and are better suited to pick up 

2 trash and coarse-grained sediment particles (CWP 2008). This provides less water quality 

3 benefits, but this practice could be used as the first pass of tandem sweeping operations 

4 when followed by a sweeper that can remove the pollutant-heavy fine-sized particles left 

5 behind by the mechanical sweeper. 

6 • Regenerative air and high efficiency sweepers are better at removing fine-grained 

7 sediment particles, but are less effective on wet surfaces (although may still out-perform 

8 mechanical sweepers) and are more expensive (CWP 2008). 

9 • Street sweeping is presumed to be more effective at reducing stormwater pollutants in 

10 arid and semi-arid climates where pollutants can accumulate over longer intervals on 

11 street and curb surfaces (CWP 2008). 

12 Practice Design 

13 • Because they operate as a mobile BMP on-the-go, street sweeping may be of particular 

14 value in reducing pollutants from ultra-urban areas where few BMPs are feasible (Law et 

15 al. 2008). 

16 • Street cleaning equipment can be most effective in areas where the surface to be cleaned 

17 is the major source of contaminants. These areas include freeways, large commercial 

18 parking lots, and paved storage areas (Pitt, Bannerman, and Sutherland 2004).

19 • Improving or initiating street sweeping activities can reduce the amount of stormwater 

20 pollution that is conveyed into local aquatic resources. It requires examination of existing 

21 street sweeping technology and operations (if any) and identification of where 

22 improvements can be made to reduce the amount of pollution that has accumulated on 

23 public streets and roadways. (CWP 2008). 

24 • Develop a list of areas where street sweeping activities could have the greatest influence 

25 on water quality. For example, an area with high accumulations of pollutants may suggest 

26 that more regularly scheduled street sweeping is needed. Also, street sweeping may be 

27 concentrated on the dirtiest streets in sensitive subwatersheds (CWP 2008). 

28 • At a minimum, sweeping should occur during periods of heavy accumulation, such as 

29 early spring removal of deicing chemicals and sand in temperate climates (CWP 2008). 

30 During the fall, leaf removal should be conducted with specialized equipment, such as 

31 vactor trucks, as seasonal leaves can contribute 25 percent% of nutrient loading in catch 

32 basins. 

33 • Include municipal parking lots in the sweeping schedule. 

34 Costs and factors affecting cost 

35 Several factors influence the overall cost of street sweeping: 

36 • Street sweeping is major investment and operators must be specially trained on how to 

37 properly drive and maintain them. Training should be held at least once a year for staff to 

38 provide them with a thorough understanding or the proper implementation of sweeping 
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Chapter 3. Controlling Urban Runoff 208 

1 and other pollution prevention/good housekeeping practices, and safety procedures (CWP 

2 2008). 

3 • Costs can vary significantly based on the type of sweeper, operation and maintenance 

4 expenses, and sweeping frequency. The capital cost for a conventional street sweeper is 

5 between $60,000 and $120,000 with newer technologies approaching $180,000 (CASQA 

6 2003).

7 • Rental rates for self-propelled sweepers vary depending on hopper size and duration of 

rental. Expect rental rates from $58/hour (3 yd3 hopper) to $88/hour (9 yd38 hopper), plus 

9 operator costs. Hourly production rates vary with the amount of area to be swept and 

10 amount of sediment. Match hopper size to the area and expected sediment load to 

11 minimize time spent dumping (CASQA 2003).

12 Practice/Program Evaluation 

13 It is important to evaluate the process and measurable performance goals and implementation 

14 milestones made for a street sweeping program. 

15 Table 3-51. Examples of measurable goalsMeasurable Goals and implementation 

16 milestonesImplementation Milestones for 

improving municipal street sweeping activitiesImproving Municipal Street Sweeping Activities 117 

18 (adapted from CWP 2008) 

Example measurable goalsExample Measurable 

Goals

Time frame Priority 

Goals related to program startup 

Identify and collect basic information about municipal 

street sweeping activities 

Essential 

Add the information about street sweeping activities 

to the simple database or binder that contains basic 

information about each municipal operation 

Essential 

Develop a digital GIS or hard copy map showing the 

location of all municipal street sweeping activities 

Complete shortly after program 

startup; updated regularly after 

that 

Optional but 

Recommended 

Prioritize local pollution prevention/good 

housekeeping efforts Year 1, repeat every 5 years Essential 

Goals related to preventing or reducing stormwater pollution 

Collect additional information about the way that 

street sweeping activities are conducted within your 

community. Include sweeper type; efficiency of fine

sediment fraction removed, sweeping frequency, 

miles swept/coverage, and parking policies and 

enforcement along sweeping routes. 

Essential 

Prescribe pollution prevention/good housekeeping 

practices to improve the way that municipal street 

sweeping activities are conducted within your 

community 

Essential 

Develop implementation plan for prescribed street 

sweeping program 

Year 1 

Essential 

Secure funding and resources to implement Begin in Year 1 Essential 
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Chapter 3. Controlling Urban Runoff 209 

prescribed street sweeping program 

Implement prescribed street sweeping program Begin in Year 2 Essential 

Goals related to program evaluation 

Develop measurable performance goals and 

implementation milestones 

Essential 

Evaluate progress in meeting measurable goals and 

implementation milestones, including pollution 

prevent/good housekeeping practices 

Complete shortly after program 

startup; updated regularly after 

that 

Essential 

1) These goals assume that street sweeping is at the top of your prioritized municipal operations list. 

1 

2 The methods used to evaluate success in meeting measurable goals and implementation 

3 milestones can be as simple as a semi-annual or annual inspections used to identify the 

4 improvements that have been put in place and the improvements that still need to be made (CWP 

5 2008). 

6 References 

7 California Stormwater Quality Association (CASQA). 2003. California Stormwater BMP 

8 Handbook, Construction. January 2003. 

9 www.cabmphandbooks.com/Documents/Construction/SE-7.pdf

10 Center for Watershed Protection (CWP). 2008. Urban Subwatershed Restoration Manual 9: 

11 Municipal Pollution Prevention/Good Housekeeping Practices. Verison 1. Ellicott City, 

12 MD, September 2008. www.cwp.org/Store/usrm.htm#9

13 Center for Watershed Protection (CWP). 2006. Technical Memorandum 1. Literature Review. 

14 Research in Support of an Interim Pollutants Removal Rate for Street Sweeping and Storm 

15 Drain Cleanout Activities. Ellicott City, MD, 2006. 

16 Neely L. Law, et al. 2008.., Deriving Reliable Pollutant Removal Rates for Municipal Street 

17 Sweeping and Storm Drain Cleanout Programs in the Chesapeake Bay Basin. Center for 

18 Watershed Protection, Ellicott City, MD, September 2008. 

19 www.cwp.org/Resource_Library/Restoration_and_Watershed_Stewardship/municipal.htm

20 Sutherland, R.C. and Jelen, S.L. 1997. Contrary to Conventional Wisdom: Street Sweeping can 

21 be and Effective BMP. In James, W. Advances in Modeling the Management of 

22 Stormwater Impacts, vol. 5. Published by CHI, Guelph, Canada, pp 179-190, 1997. 

23 Sutherland, R.C. 2009. Recent street sweeping pilot studies are flawed. IN: APWA Reporter, 

24 September 2009.

25 Pitt, Robert;: Roger Bannerman, and Roger Sutherland. 2004.; The Role of Street Cleaning in 

26 Stormwater Management, Water World and Environmental Resources Conference 2004, 

27 Environmental and Water Resources Institute of the American Society of Civil Engineers, 

28 Salt Lake City, Utah. May 27 – June 1, 2004. 

29 http://rpitt.eng.ua.edu/Publications/StormwaterTreatability/Street%20Cleaning%20Pitt%20

30 et%20al%20SLC%202004.pdf
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Chapter 3. Controlling Urban Runoff 210 

1 6.9 Constructed Wetlands 

2 Description of Practice 

3 Wetland systems are designed for flood control and removal of pollutants from stormwater. Like 

4 natural wetlands, stormwater wetlands (a.k.a. constructed wetlands) temporarily store the water 

5 and have the capacity to improve water quality through microbial breakdown of pollutants, plant 

6 uptake, retention of stormwater, settling and adsorption (Barr 2001). Constructed wetlands, like 

7 wet ponds, incorporate wetland plants into the design and require relatively large contributing 

8 drainage areas. As stormwater runoff flows through the wetland, pollutant removal is achieved 

9 through settling and biological uptake. Constructed wetlands have zones and plants similar to 

10 wet ponds but often with less fluctuation and the ability to maintain a higher diversity (Shaw 

11 2003). 

12 Wetlands are among the most effective stormwater practices in terms of pollutant removal and 

13 also offer aesthetic and habitat value. Although natural wetlands can sometimes be used to treat 

14 stormwater runoff that has been properly pretreated, stormwater wetlands are fundamentally 

15 different from natural wetland systems. Constructed wetlands are designed specifically for the 

16 purpose of treating stormwater runoff, and typically have less biodiversity than natural wetlands 

17 in terms of both plant and animal life. Several design variations of the constructed wetland exist, 

18 each design differing in the relative amounts of shallow and deep water, and dry storage above 

19 the wetland. Sediment forebays and micropools are often designed as part of constructed 

20 wetlands to prevent sediment from filling the wetland. (Barr 2001) 

21 A distinction should be made between using a constructed wetland for stormwater management 

22 and diverting stormwater into a natural wetland. The latter practice is not recommended because 

23 altering the hydrology of the existing wetland with additional stormwater can degrade the 

24 resource and result in plant die-off and the destruction of wildlife habitat. In all circumstances, 

25 natural wetlands should be protected from the adverse effects of development, including impacts 

26 from increased stormwater runoff. This is especially important because natural wetlands provide 

27 stormwater and flood control benefits on a regional scale. (USEPA 2006) 

28 Photos and Diagrams 

29 

30 Figure 3-38. Stormwater Wetland 

31 Source: USEPA 2006 
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Chapter 3. Controlling Urban Runoff 211 

1 

2 Figure 3-39. Drawing of a wetland 

3 Source: Shaw 2003 

4 

5 Figure 3-40. Plan Diagram of a Shallow Marsh Constructed Wetland 

6 Source: Barr 2001/Schueller 1992 

7 

8 Figure 3-41. Stormwater wetland at the University of Maryland, College Park. 

9 Runoff from the parking lot enters the wetland from the left, flows in a roughly U-shaped 

10 counterclockwise pattern, and discharges via a riser a the top center of the wetland. 

11 Photo by A.H. Baldwin. (Source: Simpson 2009) 
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Chapter 3. Controlling Urban Runoff 212 

1 

2 Figure 3-42. Photo of Constructed Wetland Basin 

3 Source: VA DCR 2009

4 

5 Figure 3-43. Plan View Constructed Wetland Basin 

6 Source: VA DCR 2009
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Chapter 3. Controlling Urban Runoff 213 

1 

2 Figure 3-44. Pond/Wetland Combination 

3 Source: VA DCR 2009

4 

5 Figure 3-45. Plan and Cross Section of Shallow Wetland 

6 Source: VA DCR 2009
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Chapter 3. Controlling Urban Runoff 214 

1 Common Feasibility Constraints and Limitations 

2 Constructed wetlands are widely applicable and can be applied in most regions of the United 

3 States, however, there are limitations in specific climates and areas, including:

4 • Arid and semi-arid climates where evaporation makes it difficult to retain water in a 

5 shallow pool 

6 • ultra urban areas with little pervious surface available for the large land area required 

7 • “hot spots” that have a high potential for groundwater contamination, e.g., gas station 

8 runoff or areas where chemicals are stored or managed 

9 • retrofit or new construction in areas with minimal land 

10 • cold water trout streams because of thermal effects of heating a shallow pool which can 

11 discharge warmer water 

12 • breeding ground for mosquitoes in improperly designed systems 

13 • careful selection of plants that will sustain life over the lifetime of the project 

14 • nutrient release may occur during the non-growing season 

15 • consideration of impact on natural wetlands and forests 

16 (Adapted from USEPA 2006) 

17 Pollutant Reduction. Considerable variations exist in both methods of reporting treatment 

18 effectiveness, and a broad range of effectiveness is noted for individual sites. In a literature 

19 review conducted for estimating the effectiveness of these practices in the Chesapeake Bay 

20 region, effectiveness estimates for urban constructed wetlands were 60 percent% for total 

21 suspended solids, 20 percent% for total nitrogen and 45 percent% for total phosphorus, and 

22 volume reduction was not noted as significant source of pollutant removal. (Simpson 2009). One 

23 study found that an experimental system evaluated exhibited had little potential long-term, 

24 consistent for mass removal of total nitrogen and total phosphorus, depending on the 

25 concentrations in the incoming runoff (Nietch 2005). 

26 Results from the studies show that some bacteria removal and inactivation can occur in 

27 constructed wetlands. The factors of light, time, and temperature, as well as other factors (e.g., 

28 predation, sedimentation, sorption, filtration, pH, BOD, pH, and DO) can also contribute to the 

29 inactivation of indicator bacteria in constructed wetland BMPs (USEPA 2006). 

30 Cold weather performance. Cold winter temperatures may cause freezing of the permanent pool 

31 or freezing at inlets and outlets. Also in the winter, high salt concentrations in runoff from road 

32 salting, as well as high sediment loads from road sanding, can impact wetland vegetation. During 

33 the spring snowmelt, can carry a relatively high pollutant load with the high volume of runoff. 

34 One of the greatest challenges of stormwater wetlands, particularly shallow marshes, is that 

35 much of the practice is very shallow. Therefore, much of the volume in the wetland can be lost as 

36 the surface of the practice freezes. One study found that the performance of a wetland system 

37 was diminished during the spring snowmelt because the outlet and surface of the wetland had 

38 frozen. Sediment and pollutants in snowmelt and rainfall events "skated" over the surface of the 

39 wetland, depositing at the outlet of the wetland. When the ice melted, this sediment was washed 
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Chapter 3. Controlling Urban Runoff 215 

1 away by storm events (Oberts, 1994). Several design features can help minimize this problem, 

2 including:

3 • "On-line" designs allowing flow to move continuously can help prevent outlets from 

4 freezing 

5 • multiple cells, with a berm or weir separating each cell, can help retain storage for 

6 treatment above the ice layer during the winter season 

7 • freeze-resistant outlets (i.e., weirs or pipes with large diameters) 

8 • planting salt-tolerant vegetation, such as pickle weed or cord grass when wetlands drain 

9 highway runoff, or parking lots 

10 • using a large forebay can help to capture the sediment from road sanding. 

11 (Adapted from EPA 2006) 

12 Summaries of Volume and Pollutant Loading Reductions Achievable 

13 Practice Design 

14 Several design considerations influence the overall performance of stormwater wetlands, 

15 including:

16 • Sufficient drainage area to maintain water in the permanent pool, which is typically about 

17 25 acres in humid area and more in drier regions 

18 • upstream slopes of up to about 15 percent% with shallow local slopes large enough to 

19 ensure hydraulic conveyance (generally about three to five foot drop minimum from inlet 

20 to outlet) 

21 • minor design adjustments for regions of karst (i.e., limestone) topography to include an 

22 impermeable liner 

23 • wetlands can intersect the groundwater table, which might affect pollutant reduction 

24 capabilities 

25 • incorporation of a sediment forebay, a small pool (typically about 10 percent% of 

26 permanent pool volume), to trap coarse particles 

27 • surface area of the stormwater wetland should be at least 1 percent% of the drainage area 

28 • length-to-width ratio of at least 1.5:1 to prevent “short circuiting”

29 • inclusion of both very shallow (<6 inches) and moderately shallow (<18 inches) to 

30 provide a longer flow path through the wetland and encourage plant diversity 

31 (Adapted from USEPA 2006) 
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Chapter 3. Controlling Urban Runoff 216 

1 Design Variations 

2 There are three basic design variations of constructed wetland: 

3 • Shallow Marsh: Most of the wetland volume is in the relatively shallow high marsh or 

4 low marsh depths with the only deep portions in the forebay at the inlet and the 

5 micropool at the outlet. These systems are appropriate at the terminus of a storm pipe 

6 drain or open channel (usually after upland runoff reduction). 

7 • Pond/Wetland System: Combining the Wet Pond and shallow marsh designs requires less 

8 surface area than the shallow marsh alone because of the relatively deep volume of the 

9 Wet Pond. These systems are appropriate in moderately to highly urbanized areas. 

10 • Linear Wetland Cells: Systems installed within the conveyance system or zero-order 

11 stream channels.

12 (Adapted from VADCR 2009) 

13 Maintenance Considerations and Resources 

14 Typical maintenance activities are as follows (USEPA 2009): 

15 

16 Figure 3-46. Constructed wetland maintenance activities.

17 Costs and factors affecting cost 

18 The construction cost of urban constructed wetlands varies depending on the design, location, 

19 site-specific conditions, etc, being primarily driven by the most amount of earthwork and 

20 planting. (USEPA Wetlands Fact Sheet, 1999). Construction cost estimates and references are 

21 provided by EPA in the Menu of BMPs Stormwater Wetland Fact Sheet: 

22 (http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail

23 &bmp=74&minmeasure=5). 
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Chapter 3. Controlling Urban Runoff 217 

1 The following table provides an example of costs taken from North Carolina case studies 

2 provided in (Urban Waterways, North Carolina State University Cooperative Extension, 2000, 

3 www.neuse.ncsu.edu/SWwetlands.pdf). 

4 

5 Figure 3-47. Constructed wetland construction costs.

6 

7 Unit costs for typical wetlands maintenance items are located in Appendix A of EPA’s 2009 

8 Stormwater Wet Pond and Wetland Management Guidebook

9 (www.epa.gov/npdes/pubs/pondmgmtguide.pdf) 

10 Example Constructed Wetland Design Manuals in the Chesapeake Bay Watershed Area 

11 Virginia Department of Conservation and Recreation Stormwater Design Specification No. 13 

12 Constructed Wetlands, Version 1.6, September 30, 2009. 

13 www.vwrrc.vt.edu/swc/NonProprietaryBMPs.html

14 References 

15 Barr Engineering Company. 2001. Minnesota Urban Small Sites BMP Manual, Stormwater Best 

16 Management Practices for Cold Climates. Prepared for the Metropolitan Council. 

17 www.metrocouncil.org/environment/Water/BMP/CH3_STConstWLSwWetland.pdf

18 Hunt, William, B.A. Doll. 2000.et. al. Urban Waterways, Designing Stormwater Wetlands for 

19 Small Watersheds, North Carolina State University Cooperative Extension, 2000, 

20 www.neuse.ncsu.edu/SWwetlands.pdf
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Chapter 3. Controlling Urban Runoff 218 

1 Nietch, Chris, et.al. 2005. Nutrient-based ecological consideration for stormwater Management 

2 basins: Ponds and Wetlands, Paper in the Proceedings of the World Water and 

3 Environmental Congress, Anchorage, Alaska, May 15-19, 2005. 

4 Schueler, T. R., 1992. Metropolitan Washington Council of Governments. Design of Stormwater 

5 Wetland System: Guidelines for Creating Diverse and Effective Stormwater Wetlands in 

6 the Mid-Atlantic Region. Washington D.C., 1992.

7 Shaw, Daniel and Rusty Schmidt, 2003. Plants for Stormwater Design: Species Selection for the 

8 Upper Midwest. Minnesota Pollution Control Agency, Saint Paul, MN, July 2003. 

9 Simpson, Tom, Sarah Weammert and Andrew Baldwin., 2009. Urban Wet Ponds and Wetlands 

10 Best Management Practice. 

11 Struck, Scott, A. Selvakumar, M. Borst. 2006.et.al. Performance of Stormwater Retention Ponds

12 and Constructed Wetlands in Reducing 

13 Microbial Concentrations. USEPA Urban Watershed Management Branch, Water Supply and 

14 Water Resources Division, National Risk Management Research Laboratory, EPA/600/R15 06/102. www.epa.gov/nrmrl/pubs/600r06102/600r06102.pdf, September 2006.

16 U.S. Environmental Protection Agency (USEPA).), 2006. NPDES Stormwater Wetland Fact 

17 Sheet: Minimum Measure: Post-Construction Stormwater Management in New 

18 Development and Redevelopment, Office of Wastewater Management, Washington, D.C., 

19 May 2006. 

20 http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=d

21 etail&bmp=74&minmeasure=5

22 U.S. Environmental Protection Agency (USEPA).), 2009. Stormwater Wet Pond and Wetland 

23 Management Guidebook, EPA 833-B-09-001. Office of Wastewater Management, 

24 Washington, D.C., February 2009. http://www.epa.gov/npdes/pubs/pondmgmtguide.pdf

25 Virginia Department of Conservation and Recreation (VADCR).), 2009. Draft VA DCR 

26 Stormwater Design Specification No. 13: Constructed Wetlands Version 1.5, July 2, 2009