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Chapter 3. Controlling Urban Runoff 1 

1 Chapter 3. Technical Guidance on Controlling Urban Runoff 

2 in the Chesapeake Bay 

3 Contents 

4 1 Introduction................................................................................................................................6 

5 1.1 Need for Urban Runoff Guidance Update ........................................................................6 

6 1.1.1 Purpose ...................................................................................................................6 

7 1.1.2 Intended Audience ................................................................................................10 

8 1.1.3 Water Quality Significance of Urban Runoff in the Chesapeake Bay 

9 Watershed ..............................................................................................................11 

10 1.1.4 Managing Urban Runoff to Reduce Nutrients and Sediment Loss........................15 

11 1.2 Overview of the Urban Runoff Chapter..........................................................................23 

12 1.2.1 Management Practices and Management Practices Scales...................................24 

13 1.2.2 Implementation Measures for Urban Runoff in the Chesapeake Bay 

14 Watershed to Control Nonpoint Source Nutrient and Sediment Pollution............26 

15 1.3 References.......................................................................................................................30 

16 2 Implementation Measures for Reducing Urban Runoff Volume.............................................33 

17 2.1 Maximize Infiltration, Evapotranspiration, and Harvest and Use .................................2.1 Maintai

18 2.2 Implement Policies to Preserve and Restore Redevelopment Hydrology ..................2.1.1 Establis

19 2.3 Use Planning and Development Techniques .................................................................2.2 Select A

20 2.32.1 The Impacts of Land Use on Hydrology and Geomorphology..............................43 

21 2.3.2 Use Appropriate Designs as Part of a Comprehensive Watershed Plan................45 

22 2.3.31 New Development and Redevelopment Strategies: Smart Growth, 

23 Conservation Design, and LID ..............................................................................48 

24 2.4 Use Conservation Design and LID Techniques..........................................................2.3.2 For Exi

25 2.5 Evaluate Codes and Ordinances.....................................................................................2.4 Costs of 

26 2.6 Evaluate Transportation-related Standards.................................................................2.4.1 Potentia

27 2.7 Minimize directly connected impervious areas ..........................................................2.4.2 Potentia

28 2.8 Implement Restoration................................................................................................2.4.3 Costs of 

29 2.8.1 Urban Tree Canopy............................................................................................2.4.4 Costs of 

30 2.8.2 Streams, Floodways, and Riparian Areas .............................................................2.5 Referen

31 2.9 Reduce Impacts of Existing Urban Areas.......................................................................65

32 2.9.1 Retrofits..................................................................................................................65

33 2.10.2 Redevelopment ......................................................................................................67
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Chapter 3. Controlling Urban Runoff 2 

1 2.10 Costs of Green Infrastructure/LID Practices...................................................................68

2 2.10.1 Potential Ancillary Benefits of LID/Green Infrastructure .....................................69

3 2.10.2 Potential Cost Savings of LID/Green Infrastructure..............................................70

4 2.10.3 Costs of Water Quality and Coastal Impairments..................................................72

5 2.10.4 Costs of Individual Practices .................................................................................72

6 2.11 References.......................................................................................................................82

7 3 Implementation Measures for Reducing Pollutant Concentrations with Source Controls 

8 and Treatment ...................................................................................................................... 3-82

9 233

10 3.1 Source Control/Pollution Prevention .......................................................................... 3-83

11 3.1.1 Identify Pollutants of Concern........................................................................... 3-83

12 234

13 3.1.2 Implement Pollution-Prevention and Source-Reduction Practices and Policies...3-88

14 239

15 3.1.3 Source Controls.................................................................................................. 3-89

16 3.1.4 Public Outreach.................................................................................................. 3-91

17 3.1.4 Downspout Disconnection................................................................................. 3-93

18 3.1.5 Inspections of Commercial/Industrial Facilities ................................................ 3-93

19 3.2 Runoff Treatment........................................................................................................ 3-95

20 3.2.1 Identify Pollutants of Concern........................................................................... 3-95

21 3.2.2 Select3.3........................... Implement Treatment Practices Appropriate to the POC 3-95

22 244

23 3.3 References................................................................................................................. 3-102

24 4 3.3.1....... Use New Approaches in Assessing Treatment Technology Effectiveness 247

25 3.3.2 Estimating Effectiveness of Stormwater Treatment Practices.............................248

26 3.4 Consider Long-term Maintenance ................................................................................250

27 3.5 Address Physical Site Limitations................................................................................251

28 3.6 Address Aesthetics and Safety......................................................................................251

29 4. Urban Runoff Management for the Redevelopment Sector ................................................ 3-110

30 252

31 4.1 Establish Stormwater Performance Standards for the Redevelopment Sector 

32 Consistent with the Goal of Restoring Predevelopment Hydrology ........................ 3-113

33 Introduction............................................................................................................................252

34 4.2 Challenges and Opportunities in the Redevelopment Sector........................................252

35 4.3 Stormwater Performance Goals for the Redevelopment Sector ...................................255
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Chapter 3. Controlling Urban Runoff 3 

1 4.4 Stormwater Management Practices for Redevelopment........................................... 3-114

2 255

3 4.2.1 5............................................................. Practice Integration and Assessment Tools 3-118

4 259

5 4.3 Site Evaluations ........................................................................................................ 3-119

6 4.4 Codes and Ordinance Review................................................................................... 3-120

7 4.5 Demonstration Projects............................................................................................. 3-120

8 4.6 IncentivesProgrammatic Practices for Early Adopters............................................. 3-120

9 the Redevelopment Sector .....................................................................................................260

10 4.7 Maximize Urban Forest Canopy............................................................................... 3-121

11 4.8 Amend Compacted Urban Soils................................................................................ 3-121

12 4.9 References........................................................................................................... 3-121262

13 5 Turf Management............................................................................................................... 3-125

14 265

15 5.1 Turf Management Implementation Measures...............................................................265

16 5.2 Background............................................................................................................... 3-126

17 : Turf Impacts.........................................................................................................................267

18 5.2 3........................................................................................................ Turf-Related Impacts 3-128

19 268

20 5.23.1 Soil Compaction............................................................................................... 3-128

21 268

22 5.3.2.2 Irrigation ..............................................................................................................269

23 5.3.3 Fertilizer Applications ..................................................................................... 3-128

24 269

25 5.2.3.4 Pesticide Applications...................................................................................... 3-129

26 270

27 5.2.4 Irrigation .......................................................................................................... 3-130

28 5.2.7 Energy and Air Quality.................................................................................... 3-130

29 5.34 Turf Management Strategies, Practices, Resources and Examples .......................... 3-131

30 271

31 5.34.1 Fertilizer Management..................................................................................... 3-131

32 5.3.2 Pesticide Management ..................................................................................... 3-135

33 5.3.3 Mowing............................................................................................................ 3-135

34 5.3.4 Soil Amendments............................................................................................. 3-135
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Chapter 3. Controlling Urban Runoff 4 

1 5.3.5 Water Management.......................................................................................... 3-136

2 5.3.6 Grass Species Selection ................................................................................... 3-138

3 5.3.7 Turf Assessments............................................................................................. 3-140

4 271

5 5.4.2 Low Input Turf and Lawns..................................................................................272

6 5.4.3.8 Turf Restrictions .............................................................................................. 3-143

7 274

8 5.3.9 4.4...................................................................Incentives for Landscape Conversion 3-144

9 274

10 5.3.10 4.5............................................Environmentally Friendly Landscape Requirements 3-145

11 275

12 5.3.11 4.6....................................................................................Xeriscaping Requirements 3-146

13 276

14 5.4.7 Fertilizer Prohibitions..........................................................................................277

15 5.4.8 Local Efforts to Regulate Home-based Fertilizer Application ............................278

16 5.4.9 Effectiveness of Fertilizer Bans...........................................................................279

17 5.4.10 Soil amendments, composting and microbial and fungal innoculation ...............280

18 5.5 References........................................................................................................... 3-147281

19 6. BMP Fact Sheets................................................................................................................ 3-153

20 283

21 6.1 Introduction............................................................................................................... 3-153

22 283

23 6.1.1 Additional BMP fact sheets ............................................................................. 3-153

24 283

25 6.1.2 Performance estimate summaries for Infiltration Practices ............................. 3-153

26 284

27 6.2 Rainwater Harvesting................................................................................................ 3-156

28 286

29 6.3 Green roofs................................................................................................................ 3-162

30 293

31 6.4 Blue Roofs ................................................................................................................ 3-168

32 299

33 6.5 Bioretention/Biofiltration.......................................................................................... 3-174

34 05
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Chapter 3. Controlling Urban Runoff 5 

1 6.6 Soil Restoration......................................................................................................... 3-188

2 19

3 6.7 Reforestation, Urban Forestry................................................................................... 3-194

4 25

5 6.8 Street Sweeping ........................................................................................................ 3-203

6 34

7 6.9 Constructed Wetlands ............................................................................................... 3-208

8 39

9 Appendix 1A: Methods and Tools for Controlling Stormwater Runoff

10 (Quantity and Quality) .................................................................................................. 3-21748

11 1A.1 Methods and Manuals........................................................................................... 3-21748

12 1A.2 Complex, LID-capable Models............................................................................. 3-21950

13 1A.3 Simpler Models......................................................................................................... 3-223

14 54

15 Appendix 2B: Procedures and Case Studies from the Section 438 Guidance..................... 3-22657
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Chapter 3. Controlling Urban Runoff 6 

1 1 Introduction 

2 1.1 Need for Urban Runoff Guidance Update 

3 1.1.1 Purpose

4 Technical Guidance on Controlling Urban Runoff in the Chesapeake Bay was developed to 

5 provide guidance on the most up-to-date, proven, and cost-effective practices for controlling 

6 urban runoff for federal land management in the Chesapeake Bay region, as required by 

7 Executive Order 13508. Federal agencies in the Chesapeake Bay watershed will find this 

8 guidance useful in managing urban runoff from the development and redevelopment of federal 

9 facilities and other land areas owned or managed by the federal government. 

10 At the same time, EPA recognizes that the great majority of land in the Chesapeake Bay 

11 watershed is nonfederal land and is managed by private landowners, states, and local 

12 governments. Indeed, the vast majority of actions to restore the Chesapeake Bay will need to 

13 take place on nonfederal lands and will need to be implemented by nonfederal actors. From the 

14 perspective of land management and water quality restoration/protection, federal and nonfederal 

15 land managers will need to employ the same set of “proven cost-effective tools and practices that 

16 reduce water pollution” are appropriate for both federal and nonfederal land managers to restore 

17 and protect the Chesapeake Bay. 

18 Therefore, EPA has written this document to be equally applicable to federal and nonfederal land 

19 management. It is EPA’s hope that all states, local governments, conservation districts, 

20 watershed groups, and citizens in the Chesapeake Bay watershed will find this document to be a 

21 useful guide to implementing the most effective and cost-effective practices available to restore 

22 and protect the Chesapeake Bay. 

23 Finally, many of the nutrient and sediment sources in the Chesapeake Bay watershed are similar 

24 to sources in other watersheds around the country, and many of the practices needed to protect 

25 and restore the Chesapeake Bay are the same as or very similar to those used in those other 

26 watersheds. Indeed, while EPA has made great efforts to assure that all relevant data for the 

27 Chesapeake Bay watershed has been considered and used as appropriate in preparing and 

28 publishing this guidance, EPA has also employed data from outside the Chesapeake Bay 

29 watershed when it was deemed to be relevant and applicable to the Chesapeake Bay. By the 

30 same token, for that reason, much of the information provided in this document is relevant to 

31 other areas of the United States, and EPA strongly recommends that practitioners outside the 

32 Chesapeake Bay watershed consider this document (including especially next generation tools 

33 and actions) in developing and implementing their own watershed plans and strategies to address 

34 nutrient and sediment pollution from nonpoint sources. 

35 The primary approaches approach recommended in this guidance to protect the Chesapeake Bay 

36 and its tributaries—as well as waters in much of the rest of the United States—from the effects 

37 of development areis to use green infrastructure/low impact development (LID) approaches and 

38 planning and development techniques, such as smart growth, that minimize the detrimental 

39 effects of development on the environment. Section 2 of this chapter focuses on such approaches.
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Chapter 3. Controlling Urban Runoff 7 

1 The objective of green infrastructure/LID is to maintain or restore the predevelopment site 

2 hydrology in regard to the temperature, rate, volume, and duration of flow. This can be 

3 accomplished during development, redevelopment, or retrofit. In some cases, achieving more 

4 runoff retention might be necessary for water quality protection, and this document does not 

5 preclude setting that performance objective. More specifically, this approach it is intended and 

6 designed to maintain or restore stream flows such that receiving waters, and stream channels, are 

7 not negatively affected by changes in runoff. This temperature, volumes, durations, and rates. 

8 That approach protects predevelopment hydrology and provides significant reductions in 

9 pollutant runoff. However, in some circumstances, specific pollutant control practices, (e.g., 

10 source controls) will need to be implemented to address pollutant runoff, and Section 3 of this 

11 chapter addresses those practices. 

12 Planning can help guide development to areas that minimize effects on sensitive resources and 

13 natural areas. Planning can help ensure that new and redevelopment sites are designed to reduce 

14 runoff volume through on-site stormwater retention.

15 This document 

16 • Emphasizes replicating predevelopment hydrology as a more reliable and effective 

17 stormwater management practice than traditional approaches that focus on pollutants 

18 without addressing hydrology. That emphasis is already expressed in a number of recent 

19 EPA documents and numerous states, cities, and expert groups, including the National 

20 Academy of Sciences (http://epa.gov/greeninfrastructure)

•

21 .

22 • Incorporates by reference the Technical Guidance on Implementing the Stormwater 

23 Runoff Requirements for Federal Projects under Section 438 of the Energy Independence 

24 and Security Act, EPA 841-B-09-001, December 2009, which provides the hydrologic 

25 analysis for this approach. Elements of that document are referenced here, but it is not 

26 repeated in its entirety; it is provided at http://www.epa.gov/owow/nps/lid/section438/. 

27 • Builds on that technical guidance by providing users with sources to the newest research 

28 on key management practices and approaches and refers the reader to other resources 

29 where appropriate

30 • Emphasizes those practices that can be most cost-effective—some, in fact, less costly 

31 than the conventional stormwater management alternative.

32 This document addresses technical management practices for restoring and maintaining surface 

33 water quality. Green infrastructure/LID is generally used for managing smaller storm events that 

34 compose the bulk of annual rainfall and therefore contributes the most to both pollutant loading 

35 and stream degradation. This document does not address other stormwater issues, primarily 

36 flood-control or stormwater program management. However, those issues are addressed at length 

37 in documents referenced here.

38 Such an approach of maintaining predevelopment hydrology is already required for federal 

39 facilities by the Energy Independence and Security Act (EISA) of 2007 (P.L. 110-140, H.R. 6) 

40 section 438. Subsequent, subsequent EPA guidance (EPA 841-B-09-001) provides advice on 

41 how to implement this at federal facilities. 
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Chapter 3. Controlling Urban Runoff 8 

1 EISAthat mandates certain federal facilities to comply with the following:

2 Stormwater runoff requirements for federal development projects. The 

3 sponsor of any development or redevelopment project involving a Federal facility 

4 with a footprint that exceeds 5,000 square feet shall use site planning, design, 

5 construction, and maintenance strategies for the property to maintain or restore, to 

6 the maximum extent technically feasible, the predevelopment hydrology of the 

7 property with regard to the temperature, rate, volume, and duration of flow. 

8 State and local stormwater programs established under the Clean Water Act Amendments of 

9 1987 were traditionally established to control pollutants that are associated with municipal and 

10 industrial discharges, e.g., nutrients, sediment, and metals. Increases in runoff volume and peak 

11 discharge rates have been regulated through state and local flood control programs but in many 

12 states have not been significantly addressed with regard to their role in water quality and habitat 

13 protection. Knowledge accumulated during the past 20 years has led to the conclusion that 

14 conventional approaches to control runoff have not resulted in adequate protection of the nations 

15 water resources, and, in fact, have had detrimental effects associated with increased volumes 

16 runoff (National Research Council 2008). An example of that detrimental effect is referenced in 

17 Figure 3-1. 

A Maryland Department of Natural Resources (DNR) study 

highlights the detrimental impact that development, loss of 

forest and temperature changes has had on brook trout, 

Maryland’s only native trout species, based on three decades 

of study. For every one percent increase in impervious land 

cover in a stream’s watershed, the odds of brook trout 

survival decreased by nearly 60 percent (Stranko, et.al. 

2008). 

18 Figure 3-1. Maryland Department of Natural Resources study 

19 This document emphasizes site-specific management practices from green infrastructure/LID 

20 that are driven by locally applicable performance objectives. Each site or watershed has its own 

21 unique circumstances—a combination of land uses, water resource needs, environmental 

22 conditions, regulatory drivers, and community attributes—that will affect which approaches are 

23 most successful in terms of effectiveness and community acceptance. The means selected will 

24 vary depending on the development setting and site-specific opportunities and constraints; 

25 however, designing to replicate predevelopment hydrology is the overall goal that best ensures 

26 achieving full designated uses of the waters. In cases where green infrastructure/LID is not 

27 feasible on-site or is otherwise inadequate to meet water quality objectives, additional measures 

28 shouldwould be consideredrequired, as discussed in Section 3 of this chapter. 

29 The past decade has brought significant growth in the use of approaches that seek to control 

30 runoff volume at the site scale using a variety of decentralized stormwater controls and runoff 

31 retention methods that have the objective of replicating the predevelopment hydrology as much 

32 as technically feasible. That type of holistic, hydrology-based approach to urban runoff 

33 management is termed low impact development or LID (also referred to variously as better site 

34 design, environmentally sensitive design, sustainable stormwater management, and green 
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Chapter 3. Controlling Urban Runoff 9 

1 infrastructure, among others). The approach has been proven to be technically achievable and 

2 cost-effective; examples demonstrating this are provided in Figures 3-2 and 3-3 that describe 

3 projects in Portland, Oregon, and in coastal North Carolina. 

4 The purpose of this document is to present an overview of the practices and resources available 

5 for federal facilities and others to achieve water quality goals in the most cost-effective and 

6 potentially successful manner, with the overall objective of improving water quality, habitat, and 

7 the environmental and economic resources of the Chesapeake Bay and its tributaries. 

Portland Bureau of Environmental Services (BES) completed the first design in what was to become 

the Tabor to the River program in 2007, solving drainage and watershed problems with LID, along 

with new combined sewer pipes. These facilities not only provide sewer capacity, but also watershed 

health benefits such as groundwater recharge and added vegetation that improves urban habitat 

conditions. 

The 1,472-acre basin is high-density residential development, with commercial land use, and 

approximately 37% impervious. 

Sewer capacity solutionsCapacity Solutions, in addition to new piping and rehabilitation, include 

LID Facilities: 

• 500 LID facilities in the public right-of-way (curb extensions, vegetated planters, and flow 

restrictors) 

• Runoff from 8 acres of parking and rooftops on private property controlled by LID facilities (e.g., 

vegetated planters, rain gardens, eco-roofs) 

Watershed Management Solutions: 

• Two revegetation projects to remove invasive species 

• 3,500 trees planted in the city’s right-of-way 

• Neighborhood education and project outreach 

• Improved access to the Willamette River from an adjacent neighborhood 

The success of that first project encouraged BES to expand to a larger, basin-wide program named 

Tabor to the River. Beginning its third year of implementation, the program strives to create a healthy 

urban watershed by integrating sewer rehabilitation, green stormwater management, tree planting 

and other watershed projects to improve sewer system reliability, stop sewer backups in basements 

and street flooding, control combined sewer overflows (CSOs), and restore watershed health. 

Sources: Portland BES Web site for Tabor to the River:

www.portlandonline.com/bes/index.cfm?c=47591;

Tsurumi, Naomi and Bill Owen Painting it Green—Replacing an All-Pipe Solution with an Integrated 

Solution Emphasizing Low Impact Development; American Society of Civil Engineers (ASCE), Low 

Impact Development Conference Proceedings, 2008 

8 Figure 3-2. LID Green Streets save Portland, Oregon, nearly $60 million while restoring water 

9 quality. 
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Chapter 3. Controlling Urban Runoff 10 

1 

Using LID on a development project in Middlesound North Carolina, where LID is encouraged to 

protect shellfish beds and coastal recreational waters, the developer saved money and realized 

marketing advantages compared to tradition stormwater design: 

• Gained 3 to 4 additional lots (from 56 to 59) 

• Reduced stormwater pipe by 89% 

• Decreased road widths 9% 

• Eliminated 9,000-ft curb and gutter 

• Eliminated 5 infiltration basins $ in construction and maintenance

• Eliminated 5 monitoring wells $ in construction and monitoring fees

• Eliminated 10,000 linear feet of stormwater force main 

• Saved $1.5 million in fill 

• Increased localized stormwater infiltration 

• Eliminated 3 Tsurumi stormwater pumps 

• Increased functional and recreation open space 

• Minimized wetlands intrusion and wildlife impacts 

• Buyers prefer green real estate 

• Promotes good neighbor 

• Decreased construction traffic 

“Your ideas and preliminary plans for incorporating LID for RidgefieldRidge Field are proving 

invaluable. After having it approved for a conventional stormwater system, we were concerned 

with the extreme costs of the system and development’s financial feasibility. However, with the 

utilization of an LID stormwater system we can dramatically reduce the costs and make the 

project viable again. In our estimates we are projecting a savings up to $1.5 million and adding 4 

lots. In addition, we will be saving many of the natural features and topography resulting in a 

‘greener,’ more conservation oriented neighborhood.”

—Ridgefield Property Developer, February 2009 

Source: Todd Miller North Carolina Coastal Federation; Heather Burkert, and H.K Burkert & Co. 

2 Figure 3-3. Developer realizes savings and marketing value with LID while better protecting 

3 coastal waters. 

4 1.1.2 Intended Audience 

5 The primary audience for this document is stormwater managers in federal agencies and at the 

6 local, state, and federal levels who are responsible for meeting water quality goals and 

7 implementing water quality programs in developing and developed areas. Another key audience 

8 is the development community and their multidiscipline designers, because new and 

9 redevelopment projects offer the best opportunity to implement stormwater controls to mitigate 

10 development’s affects on water resources. Others who might benefit from this information are 

11 local public officials responsible for land use and water quality decision making, academia and 

12 research groups, environmental and community organizations, and the business community. 
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Chapter 3. Controlling Urban Runoff 11 

1 1.1.3 Water Quality Significance of Urban Runoff in the Chesapeake Bay 

2 Watershed 

3 This section discusses the water quality significance of urban runoff. Urban stormwater runoff is 

4 responsible for a significant portion of the nitrogen (N), phosphorus (P), and sediment loading to 

5 the Chesapeake Bay and the loading has been continuing to increase over time because of 

6 development. Understanding the core cause of this problem is essential to reducing this source.

7 This section contains background on the causes and consequences of stormwater discharges, i.e. 

8 the alterations to natural hydrology and the resulting impacts, and solutions that can be used to 

9 address the causes and consequences of stormwater discharges, and how to implement those 

10 solutions such that they will be applicable to all areas of the country and comply with section 

11 438 of EISA. 

12 In the natural, undisturbed environment, rainfall is quickly absorbed by trees, and other 

13 vegetation. Rainfall that is not intercepted by leaves infiltrates into the ground or is returned to 

14 the atmosphere by the process of evapotranspiration. Very little rainfall becomes stormwater 

15 runoff, and runoff generally occurs only with larger precipitation events. Traditional 

16 development practices cover large areas of the ground with impervious surfaces such as roads, 

17 driveways, sidewalks, and buildings. Once such development occurs, rainwater cannot infiltrate 

18 into the ground and as a result, runs off the site at rates and volumes that are much higher than 

19 would naturally occur. Under developed conditions, runoff occurs even during small 

20 precipitation events that would normally be absorbed by the soil and vegetation. The collective 

21 force of the increased runoff scours streambeds, erodes stream banks, and causes large quantities 

22 of sediment and other entrained pollutants to enter the waterbody each time it rains (Shaver et al. 

23 2007; Booth testimony 2008). 

24 As watersheds are developed and impervious surfaces increase in area, the hydrology of the 

25 watersheds fundamentally changes over time, which results in degraded aquatic ecosystems. In 

26 recognition of those problems, stormwater managers employed extended detention approaches to 

27 mitigate the effects of increased runoff peak runoff rates. However, wet ponds and similar 

28 practices inadequately protect downstream hydrology because of the following inherent 

29 limitations of the conventional practices (National Research Council 2008; Shaver et al. 2007): 

30 • Poor peak control for small, frequently occurring storms 

31 • Negligible volume reduction 

32 • Increased duration of peak flow 

33 Detention storage targets relatively large, infrequent storms, such as the 2- and 10-year/24-hour 

34 storms for peak flow rate control. As a result of that design limitation, flow rates from smaller, 

35 frequently occurring storms typically exceed those that existed on-site before land development 

36 occurred and these increases in runoff volumes and velocities typically result in flows erosive to 

37 stream channel stability (Shaver et al. 2007). Section 438 of EISA is intended to address the 

38 inadequacies of the historical detention approach to managing stormwater and promote more 

39 sustainable practices that have been selected to maintain or restore predevelopment site 

40 hydrology. 
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Chapter 3. Controlling Urban Runoff 12 

1 A 2008 National Research Council report on urban stormwater confirmed the shortcomings 

2 of current stormwater control efforts. Three of the report’s findings on stormwater 

3 management approaches are particularly relevant (National Research Council 2008).

4 1. Individual controls on stormwater discharges are inadequate as the sole solution to 

5 stormwater in urban watersheds. 

6 2. Stormwater control measures such as product substitution, better site design, downspout 

7 disconnection, conservation of natural areas, and watershed and land-use planning can 

8 dramatically reduce the volume of runoff and pollutant load from new development. 

9 3. Stormwater control measures that harvest, infiltrate, and evapotranspire stormwater are 

10 critical to reducing the volume and pollutant loading of small storms. 

11 

Courtesy of C. May, University of Washington. 

Predevelopment hydrology.

Courtesy of C. May, University of Washington. 

Post-development hydrology. 

Figure 3-4. Predevelopment and post-development hydrology (USDA).

12 Land cover changes that result from site development include increased imperviousness, soil 

13 compaction, loss of vegetation, and loss of natural drainage patterns result in increased runoff 

14 volumes and peak runoff rates. The cumulative effects of the land cover changes result in 
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Chapter 3. Controlling Urban Runoff 13 

1 alterations of the natural hydrology of a site, which disrupts the natural water balance and 

2 changes water flow paths. The consequences of these impacts include the following: 

3 1. Increased volume of runoff. With decreased area for infiltration and evapotranspiration 

4 due to development, a greater amount of rainfall is converted to overland runoff which 

5 results in larger stormwater discharges. 

6 2. Increased peak flow of runoff. Increased impervious surface area and higher connectivity 

7 of impervious surfaces and stormwater conveyance systems increase the flow rate of 

8 stormwater discharges and increase the energy and velocity of discharges into the stream 

9 channel. 

10 3. Increased duration of discharge. Detention systems generate greater flow volumes for 

11 extended periods. Those prolonged, higher discharge rates can undermine the stability of 

12 the stream channel and induce erosion, channel incision and bank cutting. 

13 4. Baseflow and sediment loading changes. Changes to baseflow are caused by alternations 

14 to the hydrologic cycle created by land cover changes and increased imperviousness, 

15 which prevents rain from recharging groundwater, where it serves as baseflow for 

16 streams. Such changes increase the flashiness of streams, resulting in elevated flows 

17 during or after storm events, and greatly diminished baseflows in between storms. Higher 

18 peak flows erode streambeds and stream banks.

19 5. Increased pollutant loadings. Impervious areas are a collection site for pollutants. When 

20 rainfall occurs, the pollutants are mobilized and transported directly to stormwater 

21 conveyances and receiving streams via the impervious surfaces. 

22 6. Increased temperature of runoff. Impervious surfaces absorb and store heat and transfer it 

23 to stormwater runoff. Higher runoff temperatures can have deleterious effects on 

24 receiving streams. Detention basins magnify this problem by trapping and discharging 

25 runoff that is heated by solar radiation (Galli 1991; Schueler and Helfrich 1988). 

26 7. Habitat modifications and stream morphology changes. Increased runoff rate and volume 

27 alter stream morphology. Highly erosive stormwater can wash out in-stream structures 

28 that serve as habitat. Large storms deepen, widen, and straighten channels, disconnecting 

29 streams from their floodplains and destroying meanders that serve to dissipate hydraulic 

30 energy.

31 The resulting increases in volume, peak flow, and duration are illustrated in the hydrograph in 

32 Figure 3-5, which is a representation of a site’s stormwater discharge with respect to time. The 

33 hydrograph illustrates the effects of development on runoff volume and timing of the runoff. 

34 Individual points on the curve represent the rate of stormwater discharge at a given time. The 

35 graph illustrates that development and corresponding changes in land cover result in greater 

36 discharge rates, greater volumes, and shorter discharge periods. In a natural condition, runoff 

37 rates are slower than those on developed sites, and the discharges occur over a longer period. The 

38 predevelopment peak discharge rate is also much lower than the post-development peak 

39 discharge rate because of attenuation and absorption by soils and vegetation. In the post40 development condition, there is generally a much shorter time before runoff begins because of 

41 increased impervious surface area, a higher degree of connectivity of those areas, and the loss of 

42 soils and vegetative cover that slow or reduce runoff. 
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Chapter 3. Controlling Urban Runoff 14 

1 

t

Q

Post-Development Condition

Pre-Development Condition

2 

3 Note: Q = volumetric flow rate; t = time 

4 Figure 3-5. Post-development hydrograph. 

5 

6 

7 Figure 3-6. Stream displaying the effects of stormwater runoff and channel downcutting. 
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Chapter 3. Controlling Urban Runoff 15 

1 1.1.4 Managing Urban Runoff to Reduce Nutrients and Sediment Loss

2 1.1.4.1 Preserving and Restoring Hydrology 

3 A new approach has evolved in recent years to 

4 eliminate or reduce the amount of water and 

5 pollutants that run off a site and ultimately are 

6 discharged into adjacent waterbodies. 

7 The fundamental principle is to employ systems and 

8 practices that use or mimic natural processes to do

9 any of the following: (1) infiltrate and recharge, 

10 (2) ) evapotranspire, or (3) harvest and use 

11 precipitation near where it falls. 

12 Green infrastructure practices include a wide variety 

13 of practices that use such mechanisms. They can be 

14 used at the site, neighborhood, and 

15 watershed/regional scales. In this document, the 

16 focus is on site-level practices, such as bioretention 

17 and water harvesting, but it also addresses the land 

18 management scales of planning (i.e., planning 

19 techniques such as smart growth), and site design 

20 (i.e., site design techniques such as conservation 

21 development). 

22 Although the performance objective of “restoring or 

23 maintaining predevelopment hydrology” applies at 

24 the site-level, flexibility exists to use nearby areas or 

25 areas directly adjacent to the facility to manage the runoff, i.e., evapotranspirate, infiltrate, or 

26 harvest and use. Where justifiable, it also might be appropriate to evapotranspirate, infiltrate or 

27 harvest and use an equivalent or greater amount of runoff offsite as long as the runoff is 

28 discharged or used in the same receiving subwatershed or watershed.

29 The objective of stormwater management should be to replicate predevelopment hydrology to 

30 protect and preserve both the water resources on-site and those downstream. For example, if 

31 before development, 25 percent of the annual rainfall runs directly into the stream and the 

32 remainder infiltrates into the ground or is evapotranspired into the air, the post-development goal 

33 should be to limit runoff to 25 percent of the annual precipitation while maintaining the correct 

34 aquifer recharge rate. That has the benefit, in most cases, of delivering water to the stream at 

35 approximately the same rate, volume, duration and temperature as the stream had naturally 

36 evolved before development. The result will be to eliminate or minimize the erosion of 

37 streambeds and streambanks, significantly reduce the delivery of many pollutants to waterbodies, 

38 and retain historical in-stream temperatures.

39 Restoring or maintaining predevelopment hydrology has emerged as a control approach for 

40 several reasons. Most importantly, the approach is intended to directly address the root cause of 

41 impairment. Current control approaches have been selected in an attempt to control the 

Figure 3-7. Parking lot bioswale and 

permeable pavers in Chicago.
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Chapter 3. Controlling Urban Runoff 16 

1 symptoms (peak flow, and excess pollutants), but the strategy is largely ineffectual because of 

2 the scale of the problem, the cumulative effects of multiple developments and the need to 

3 manage both site and watershed level effects. With current approaches, it is also difficult to 

4 adequately protect and improve water quality because the measures employed are not addressing 

5 the main problem, which is a hydrologic imbalance. 

6 Designing facilities on the basis of the goal of maintaining or restoring predevelopment 

7 hydrology provides a site-specific basis and an objective methodology with which to determine 

8 appropriate practices to protect the receiving environment. 

9 Using predevelopment hydrology as the guiding control principal also allows the designer to 

10 consider climatic and geologic variability and tailor the solutions to the project location. Thus, 

11 the need for a one–size-fits-all approach is rendered unnecessary because the design objective is 

12 dictated by the predevelopment site conditions and other technicalities of the project site and 

13 facility use. Site and, thus, is not merely a solution based

14 on the ease of administration. Instead of prescribed 

15 approaches dictating discharge volumes or flow rates, 

16 site assessments of historical infiltration and runoff rates 

17 will inform the designer and provide the basis for a 

18 suitable design. The use of this approach will minimize 

19 compliance complications that can arise from 

20 prescriptive design approaches that do not account for 

21 the variability of precipitation frequencies, rainfall 

22 intensities, and land cover and soil conditions that 

23 influence infiltration and runoff. 

24 More information on addressing hydromodification and 

25 riparian buffers are provided in separate volumes of this 

26 document. 

27 1.1.4.2 Defining Green Infrastructure/LID 

LIDi28 is a stormwater management strategy that many 

29 localities across the country have adopted. It is a

30 stormwater management approach and set of practices

31 that can be used to reduce runoff and pollutant loadings 

32 by managing the runoff as close to its source(s) as

33 possible. A set or system of small-scale practices, linked 

34 together on the site, is often used. LID approaches can be 

 

iThe term LID is one of many used to describe the practices and techniques employed to provide advanced 

stormwater management; green infrastructure, conservation design, and sustainable stormwater management are 

other common terms. However labeled, each of the identified practices seeks to maintain and use vegetation and 

open space, optimize natural hydrologic processes to reduce stormwater volumes and discharge rates, and use 

multiple treatment mechanisms to remove a large range of pollutants. In the context of this report, case studies 

ascribing to one of the above, or similar, labels were evaluated, and those terms are used interchangeably throughout 

the document. 

Figure 3-7. Parking lot bioswale and 

permeable pavers in Chicago.
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Chapter 3. Controlling Urban Runoff 17 

1 used to reduce the effects of development and redevelopment activities on water resources. In the 

2 case of new development, LID is typically used to achieve or pursue the goal of maintaining or 

3 closely replicating the predevelopment hydrology of the site. In areas where development has 

4 already occurred, LID can be used as a retrofit practice to reduce runoff volumes, pollutant 

5 loadings, and the overall effects of existing development on the affected receiving waters. 

6 In general, implementing integrated LID practices can result in enhanced environmental 

7 performance while at the same time reduce development costs when compared to traditional 

8 stormwater management approaches. LID techniques promote the use of natural systems, which 

9 can effectively reduceremove nutrients, pathogens, and 

10 metals from stormwater through runoff volume reduction, 

11 filtration, and other processes. These same systems can be 

12 designed to accommodate or bypass larger flows when

13 large rain events occur, when the LID practice is sized for 

14 small rain events. 

15 Cost savings can be achieved in reduced infrastructure, 

16 particularly in new development where land is available for 

17 surface practices, because the total volume of runoff to be 

18 managed is minimized through infiltration and 

19 evapotranspiration. By working to mimic the natural water 

20 cycle, LID practices protect downstream resources from 

21 pollutants and adverse hydrologic impacts that can degrade 

22 stream channels and harm aquatic life. 

23 It is important to note that typical, real-world LID designs usually incorporate more than one 

24 type of practice or technique to provide integrated treatment of runoff from a site. For example, 

25 in lieu of a treatment pond serving a new subdivision, planners might incorporate a bioretention 

26 area in each yard, disconnect downspouts from driveway surfaces, remove curbs or cut out 

27 drainage slots into curbs, and install grassed swales in common areas. Integrating small practices 

28 throughout a site instead of using extended detention wet ponds for treatment purposesto control 

29 runoff from a subdivision is the basis of the LID approach. 

30 Planning techniques such as Smart Growth minimize 

31 runoff by approachestechniques such as enhancing density 

32 along existing transportation and other infrastructure 

33 corridors, to reduce Greenfield development. 

34 Conservation designs minimize runoff by conserving 

35 undeveloped land and reducing the amount of impervious 

36 surface, which can cause increased runoff volumes. Open 

37 space can be used to treat the increased runoff from the 

38 built environment through infiltration or 

39 evapotranspiration. For example, developers can use

40 conservation designs to preserve important features on the 

41 site such as wetland and riparian areas, forested tracts, and 

42 areas of pervious soils. Development plans that outline 

43 the smallest site disturbance minimize stripping topsoil 

Runoff Storage Practices

• Parking lot, street, and 

sidewalk storage in 

underground infiltrating vaults

• Rain barrels and cisterns

• Depressional storage in 

landscape islands and in tree, 

shrub, or turf depressions

Green roofsExamples of 

Conservation Design

•Cluster development

•Undeveloped land conservation

Examples of Conservation 

Design 

• Cluster development 

• Undeveloped land 

conservation 

• Reduced pavement widths 

(streets, sidewalks) 

• Shared driveways 

• Reduced setbacks (shorter 

driveways) 

• Site fingerprinting during 

construction 

Examples of LID Practices 

• Infiltration basins and trenches 

• Permeable pavement 

• Disconnected downspouts 

• Rain gardens and other 

vegetated treatment systems 
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Chapter 3. Controlling Urban Runoff 18 

1 and compacting subsoil. Such simplistic, nonstructural 

2 methods reduce the need to build large runoff controls 

3 like retention ponds for treatment and larger stormwater 

4 conveyance systems, thereby decreasing the overall 

5 project cost. Reducing the total area of impervious

6 surface by limiting road widths and parking areas also 

7 reduces the volume of runoff that must be treated. 

8 Conservation designs benefit residents and their quality 

9 of life because of increased access and proximity to 

10 communal open space, a greater sense of community, and 

11 expanded recreational opportunities. 

12 LID practices are engineered structures or landscape 

13 features designed to capture and infiltrate, store, convey, or 

14 filter runoff in a manner that attempts to replicate 

15 predevelopment hydrology. 

16 Infiltration practices can also be used to achieve a goal of recharging groundwater while at the 

17 same time reducing runoff. Recharging groundwater is especially important in areas where 

18 maintaining drinking water supplies and stream baseflow is of special concern because of limited 

19 precipitation or a high withdrawal demands. Infiltration of runoff can also help to maintain 

20 stream temperatures because the infiltrated water that moves laterally to replenish stream 

21 baseflow typically has a lower temperature than overland 

22 flows, which might be subject to solar radiation. Another 

23 advantage of infiltration practices is that they can be 

24 integrated into landscape features in a site-dispersed 

25 manner. This feature can result in aesthetic benefits and, 

26 in some cases, recreational opportunities; for example, 

27 some infiltration areas can be used as playing fields 

28 during dry periods. 

29 Runoff storage practices reduce the volume and peak rate 

30 of runoff to protect streams from the erosive forces of 

31 high flows, and irrigate landscaping to providing 

32 aesthetic benefits such as more sustainable (i.e., more 

33 self-watering) landscape islands, tree boxes, and rain gardens. Designers can take advantage of 

34 the space beneath paved areas like parking lots and sidewalks to provide additional storage. For 

35 example, underground vaults can be used to store runoff in both urban and rural areas, and street 

36 tree designs have been developed to better enable use of that space for root growth to enable 

37 establishment of healthy urban tree canopy. 

38 Runoff conveyance practices can be used to slow flow 

39 velocities, lengthen the runoff time of concentration, and 

40 delay peak flows that are discharged off-site. LID 

41 conveyance practices can be used as an alternative to 

42 curb-and-gutter systems. LID conveyance practices often 

43 have rough vegetative surfaces that reduce runoff 

44 velocities and allow settling of solids. They promote 

Filtration Practices 

• Infiltration basins and 

trenches 

• Porous pavement 

• Disconnected downspouts 

• Rain gardens and other 

vegetated treatment systems 

Runoff Storage Practices 

• Parking lot, street, and sidewalk 

storage in underground 

infiltrating vaults 

• Rain barrels and cisterns 

• Depressional storage in 

landscape islands and in tree, 

shrub, or turf depressions 

• Green roofs 

Runoff Conveyance Practices 

• Eliminating curbs and gutters 

• Creating grassed swales and 

grass-lined channels 

• Roughening surfaces 

• Creating long flow paths over 

landscaped areas 

• Installing smaller culverts, pipes, 

and inlets 

• Creating terraces and check 

dams 

Filtration Practices 

• Bioretention/rain gardens 

• Vegetated swales 

• Vegetated filter strips/buffers 

Runoff Conveyance Practices 

• Eliminating curbs and gutters 

• Creating grassed swales and 

grass-lined channels 

• Roughening surfaces 

• Creating long flow paths over 

landscaped areas 

• Installing smaller culverts, pipes, 

and inlets 

• Creating terraces and check 

dams 

Filtration Practices 

• Bioretention/rain gardens 

• Vegetated swales 

• Vegetated filter strips/buffers 
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Chapter 3. Controlling Urban Runoff 19 

1 infiltration, filtration, and some biological uptake of 

2 pollutants. LID conveyance practices also can perform 

3 functions similar to those of conventional curbs, 

4 channels, and gutters. For example, they can be used to 

5 reduce flooding around structures by routing runoff to 

6 landscaped areas for treatment, infiltration, and 

7 evapotranspiration. 

8 Filtration practices capture pollutants by physical 

9 filtration of solids or cation exchange of dissolved 

10 pollutants. They also reduce runoff volume, recharge 

11 groundwater, increase stream baseflow, and reduce 

12 thermal impacts. Pollutant buildup can be of concern, 

13 pollutants are typically captured in the upper soil horizon 

14 and can be removed by replacing the topsoil, and life can 

15 be extended by selecting plants that also provide phytoremediation. 

16 Conservation landscaping reduces labor, watering, and chemical use. Properly preparing soils 

17 and selecting species adapted to the site increases the success of plant growth, stabilizing soils 

18 and allowing for biological uptake of pollutants. Pest resistance (reducing the need for 

19 pesticides) and improved soil infiltration from root growth are among the goals. Conservation 

20 landscaping is promoted by many entities in the 

21 Chesapeake Bay area and elsewhere. 

22 1.1.4.3 Ancillary Benefits of Designing to Restore 

23 and Preserve Predevelopment Hydrology 

24 Unlike traditional stormwater management, an approach 

25 to maintain or restore predevelopment hydrology meets 

26 multiple performance objectives and can offer ancillary 

27 benefits, including the following: 

28 Pollution abatement. LID practices more reliably reduce 

29 pollutant loadings by reducing the runoff volume. LID 

30 practices, to a lesser degree, can reduce pollutants by 

31 settling, filtering, adsorption, and biological uptake. That

32 improves habitat and enhances recreational uses.

33 Protection of downstream water resources. LID practices help to prevent or reduce hydrologic

34 effects on receiving waters, reduce stream channel degradation from erosion and sedimentation, 

35 improve water quality, increase water supply, and enhance the recreational and aesthetic value of 

36 our natural resources. LID practices can be used to protect water resources that are downstream 

37 in the watershed. Other potential benefits include reduced incidence of illness from swimming 

38 and wading, more robust and safer seafood supplies.

Conservation Landscaping 

• Planting native, drought-tolerant 

plants 

• Converting turf areas to shrubs 

and trees 

• Reforestation 

• Encouraging longer grass length 

• Planting wildflower meadows 

rather than turf along medians 

and in open space 

• Amending soil to improve 

infiltration 

• Integrated pest management 

Conservation Landscaping 

• Planting native, drought-tolerant 

plants 

• Converting turf areas to shrubs 

and trees 

• Reforestation 

• Encouraging longer grass length 

• Planting wildflower meadows 

rather than turf along medians 

and in open space 

• Amending soil to improve 

infiltration 

• Integrated pest management 
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Chapter 3. Controlling Urban Runoff 20 

1 Protect integrity of streams and floodplains to preserve ecological functions. Costs of 

2 streambank restoration can be reduced or avoided altogether. Using LID techniques also can help 

protect or restore floodplains, which can be used as park space or wildlife habitat.ii 3 

4 Groundwater recharge and stream baseflow. Growing water shortages nationwide increasingly 

5 indicate the need for holistic water resource management strategies to integrate stormwater, 

6 drinking water, and wastewater programs. Development increases impervious surfaces and 

7 runoff. Infiltration practices replenish groundwater and increase stream baseflow. Adequate 

8 groundwater rechargebaseflow to streams during dry weather is important because low 

9 groundwater levels can lead to low baseflows in dry weather. Greatergreater fluctuations in 

10 stream flows and temperatures occur when rainfall does not infiltrate, to the detriment of aquatic 

11 life. 

12 Water quality improvements/reduced treatment costs. KeepingIt is almost always less expensive 

13 to keep water clean can prevent the costs for cleaningthan it is to clean it up. The Trust for Public 

Landiii 14 notes that Atlanta’s tree cover has saved more than $883 million by preventing the need 

15 for stormwater facilities. A study by the Trust for Public Land and the American Water Works 

Associationiv 16 of 27 water suppliers found higher forest cover in a watershed reduced water 

17 treatment costs. According to the study, approximately 50 percent of the variation in treatment 

18 costs can be tied to the percentage of forest cover. It also found that for every 10 percent increase 

19 in forest cover, treatment and chemical costs decreased approximately 20 percent, up to about 60 

20 percent forest cover. 

21 Reduced incidence of combined sewer overflow (CSOs). Many municipalities with older sewer 

22 systems have CSOs, i.e. sewers that discharge sanitary wastewater during storms. LID 

23 techniques, by retaining and infiltrating runoff, reduce the frequency and amount of CSOs. Past 

24 efforts typically have solely concentrated on approaches focused on treating the sanitary waste 

25 together with the runoff. For the past several years, communities such as Portland (Oregon), 

26 Chicago, and the District of Columbia have been piloting and implementing LID approaches 

27 aimed at reducing runoff generated to the combined system. 

28 Habitat improvements. Innovative stormwater management techniques like LID or conservation 

29 design can be used to improve natural resources and wildlife habitat, maintain or increase land 

30 value, or avoid expensive mitigation costs. 

31 Reduced downstream flooding and property damage. LID practices, when applied throughout a 

32 watershed, can reduce flash flooding, and reduce property damage or risk during small storm 

33 events. 

 

iiTrust for Public Land. 1999. The Economic Benefits of Open Space.title?. Trust for Public Land, San Francisco, 

CA. 

iiiTrust for Public Land. 1999. The Economic Benefits of Open Space. 

<http://www.tpl.org/tier3_cd.cfm?content_item_id=1195&folder_id=727>. Accessed March 29, 2006. 

ivTrust for Public Land and American Water Works Association. 2004. Protecting the Source. Trust for Public Land, 

San Francisco, CA. 
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Chapter 3. Controlling Urban Runoff 21 

1 Reduce erosion and sediment loss. Designs that manage runoff on-site or as close as possible to 

2 its point of generation reduce erosion and sediment transport, as well as stream erosion. 

3 Real estate value/property tax revenue. Property owners will pay a premium to be near 

4 amenities like water features, open space, trails, and clustered subdivisions. EPA’s early 

Economic Benefits of Runoff Controlsv5 described many examples, and the trend will likely

6 increase as urbanization makes natural areas more scarce and precious. 

7 Lot yield. In cases where LID practices are incorporated on individual house lots and along 

8 roadsides as part of the landscaping, land that would normally be dedicated for a stormwater 

9 pond or other large structural control can be developed with additional housing lots. 

10 Aesthetic value. LID designs can enhance a property’s aesthetics using trees, shrubs, and 

11 flowering plants that complement other landscaping features, resulting in a perceived value of 

12 extra landscaping. 

13 Public spaces/quality of life/public participation. Placing water quality practices on individual 

14 lots provides opportunities to enhance public awareness of their natural environment. 

15 Homeowners often considerAn American Lives, Inc., real estate study found that 77.7 percent of 

16 potential homeowners rated natural open space as to be essential or very important in planned 

17 communities. 

18 Reduce air pollution through uptake by trees. Trees remove gaseous air pollution primarily by 

19 uptake via leaf stomata, though some gases are removed by the plant surface. Once inside the 

20 leaf, gases diffuse into intercellular spaces and can be absorbed by water films to form acids or 

21 react with inner-leaf surfaces (Smith 1990). In 1994 the U.S. Forest Service estimated that trees 

22 in Baltimore removed an estimated 499 metric tons of air pollution at an estimated value to 

23 society of $2.7 million (Nowak and Crane 2000) 

24 Reducing urban heat island effect through evapotranspiration. For trees over grass, mid-day 

temperatures have been reported to be are 0.7 degree Celsius (oC) to 1.3 o25 C cooler than in an 

26 open area. Reduced air temperature can improve air quality because the emission of many 

27 pollutants or ozone-forming chemicals are temperature dependent. Lower air temperature can 

28 reduce ozone formation (Souch and Souch 1993; Nowak at www.ufore.org) 

29 Reduced energy costs. Improve insulation against summer heat is provided with green roofs. 

30 Mature, shady, deciduous trees can reduce air conditioning costs up to 30 percent, while a wind 

31 break of evergreens can save 10–50 percent off heating costs in the winter 

32 (www.dnr.state.md.us/forests/publications/urban5.html). 

33 Saving money on drainage infrastructure. Curb, gutter, storm drain pipes, and runoff detention 

34 practices can be reduced by reducing the volume of runoff to be conveyed (WERF 2008; USEPA 

35 2007). 

 

vUSEPA (U.S. Environmental Protection Agency). 1995. Economic Benefits of Runoff Controls. (U.S. 

Environmental Protection Agency, Office of Water, Washington, DC. 
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Chapter 3. Controlling Urban Runoff 22 

1 Example Green Infrastructure Benefits Analysis by Philadelphia. An example of the wide 

2 array of benefits achievable is presented in Philadelphia’s Green City, Clean Water report 

3 summarizing the vision of using LID to mitigate stormwater overflows. Philadelphia has, like 

4 many older cities, a legacy of combined sanitary and storm sewers, and recently compared the 

5 costs and benefits of using green infrastructure to help mitigate the CSOs. Figure 3-8 presents an 

6 overview of the benefits the city envisions from a plan to implement green stormwater 

7 management. 

Economic 

Benefits 

About 250 people would be employed in green jobs per year 

Increase of more than 1 million recreational user-days per year would be enjoyed 

Reduction of approximately 140 fatalities cause by excessive heat over the next 40 

years 

Social Benefits 

Increase in property values of 2%–5% in greened neighborhoods 

1.5 billion pounds of carbon dioxide emissions avoided [partially through reduced 

heavy equipment requirements for alternative stormwater management] or absorbed 

Air quality benefits on average leading annually to: 1-2 avoided premature deaths, 20 

avoided asthma attacks, and 250 missed days of work or school 

Water quality and habitat improvements including: 5-8 billion gallons of CSO avoided 

per year; 190 acres of wetlands restored or created, 11 miles of stream restored. 

Environmental 

Benefits 

Reduction in electricity and fuel use [partially through reduced construction of 

alternative stormwater management infrastructure]. 

8 Source: Green City, Clean Waters: Philadelphia’s Program for Combined Sewer Overflow Control, A Long-Term 

9 Control Plan Update, Summary Report, 2009. http://planphilly.com/node/9842

10 Figure 3-8. Projected ancillary benefits of using LID and green infrastructure stormwater practices 

11 in Philadelphia to help achieve CSO mitigation. 

12 Figure 3-9 shows the benefits (and external costs) estimated for a 40 year period of two of the 

13 options Philadelphia compared for CSO solutions. The 50 percent LID, or green infrastructure 

14 option, is a scenario in which 50 percent of the impervious surface in the CSO area is managed 

15 through green infrastructure, and the remainder through conventional storage tunnels. The 30’ 

16 Tunnel option represents a scenario where large tunnels would be used to manage the CSO. 

17 Philadelphia selected these options for analysis purposes, and they do not represent 

18 implementation decisions by the City. This table demonstrates only the value of the ancillary 

19 benefits of using green infrastructure for CSO mitigation compared to the lack of ancillary 

20 benefits of traditional CSO management. The cost estimates for construction and maintenance 

21 can be found in the Long-Term Control Plan at http://www.phillywatersheds.org/ltcpu/. 

22 Estimated capital and O&M costs of individual green infrastructure elements considered by 

23 Philadelphia are provided in Section 23 of this chapter. 

24 
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Chapter 3. Controlling Urban Runoff 23 

1 

2 Source: Summary of Triple Bottom Line Analysis, City of Philadelphia Long-Term Control Plan, 

3 http://www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf

4 http://www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf

5 Figure 3-9. Summary of Philadelphia’s analysis of green infrastructure to help mitigate CSOs: 

6 Presentpresent value benefits of two options studied (Cumulative estimated through 2049 in 2009 

7 million USDISD) 

8 A broad overview of the ancillary benefits that can be realized from LID is provided by the 

9 Center for Neighborhood Technology in its Green Values Calculator (www.cnt.org/natural10 resources/green-values). 

11 1.2 Overview of the Urban Runoff Chapter 

12 This chapter provides recommendations for the approaches recommended for restoring or 

13 maintaining predevelopment hydrology for urban runoff to maintain or restore, to the maximum 

14 extent technically feasible, the predevelopment hydrology of the property with regard to the 

15 temperature, rate, volume, and duration of flow. 

16 Maintaining or restoring predevelopment hydrology is the stormwater management goal 

17 recommended in this document, as required by Congress in section 438 of EISA. A number of 

18 technical resources, guidance, and design manuals are available that review in detail the key 

19 techniques and topics pertinent to urban runoff control. Several of these documents are listed as 

20 the subject areas are addressed. The technical material that is available in these existing sources 

21 will not be repeated here. 
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Chapter 3. Controlling Urban Runoff 24 

1 1.2.1 Management Practices and Management Practices Scales 

2 The following presents an overview of the approach presented in this chapter to achieve this goal 

3 by implementing strategies at the regional and watershed scale down to the site scale, as follows: 

4 • At the regional or watershed scale, planning techniques such as smart growth and policies 

5 to allow conservation development, as part of watershed planning, can be used to lay the 

6 groundwork for ensuring that development has minimum impacts on water resources, 

7 including no net increase in stormwater runoff. This is important for both developed areas 

8 and for yet undeveloped areas. 

9 • At the site scale, using green infrastructure/LID practices, along with source control and 

10 pollution prevention, are necessary to achieve the goals of protecting and restoring the 

11 Chesapeake Bay. 

12 Applying LID practices at the site scale is recommended for new development, redevelopment, 

13 and retrofit. LID practices are flexible in design, so are widely applicable. LID practices such as 

14 functional conservation landscaping, bioretention, and swales require only a minimum 

15 modification from traditional landscaping design, often at no additional cost and potentially 

16 provide long-term reductions in cost. Many jurisdictions across the United States have adopted 

17 policies and design guides for such practices, including many in the Chesapeake Bay area. 

18 LID practices such as minimizing impervious surfaces, porous pavement, green alleys, green 

19 streets, cisterns and rain barrels, and green roofs have become widely accepted in cities that have 

20 needed to manage excess pollutant runoff, water shortages, or flash flooding. The technology is 

21 now well-proven and shown to be adaptable for implementation at new development, 

22 redevelopment, and retrofit sites. Relatively small-scale LID practices can be dispersed 

23 throughout a site, capturing runoff from small drainage areas for infiltration, evapotranspiration, 

24 or capture and use. A site can be designed based on a rooftop-to-stream treatment train approach 

25 that includes both source-control practices and runoff treatment practices. The treatment train 

26 approach allows site designers and stormwater managers to take advantage of every opportunity 

27 to prevent runoff pollution and reduce runoff volume close to its source, thereby protecting 

28 headwater streams, municipal drainage systems, and downstream receiving waters, as follows: 

29 • Minimize runoff generation by limiting the amount of directly connected impervious 

30 surface 

31 • Capture runoff for evaporation or reuse 

32 • Naturally infiltrate and filter runoff through landscaped areas 

33 • Direct surplus runoff to engineered practices such as bioretention and other infiltration 

34 devices 

35 • Prevent contamination of runoff using pollution prevention techniques 

36 • Manage off-site runoff using regional stormwater practices, if necessary 

37 This guidance provides an overview of the implementation measures recommended for 

38 managing urban stormwater to protect and restore the Chesapeake Bay or other waters affected 

39 by development. The implementation measures are action-oriented and, when considered 
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Chapter 3. Controlling Urban Runoff 25 

1 together, from watershed -scale to site scale, form a step-wise approach to addressing runoff 

2 volume and pollutant concentrations and for selecting management practices. 

3 Sections 1.2.2 Implementation Measures for Urban Runoff in the 

4 Chesapeake Bay Watershed to Control Nonpoint Source Nutrient and 

5 3 Sediment Pollution

6 Maintain or restore, to the maximum extent technically feasible, the 

7 predevelopment hydrology of this chapter summarize key elements of this approach:the 

8 property with regard to the temperature, rate, volume reduction, and duration of flow.

9 The implementation measure is:

•

10 Reduce urban runoff volume by understanding local land use-hydrology relationships and 

11 applying performance standards that protect or restore hydrology to predevelopment 

12 levels. Section 2 presents an approach of land use and growth management measures that 

13 guide development to areas that minimize effects on sensitive resources and open space 

14 and ensure that new and redevelopment sites are designed to reduce runoff volume 

15 through on-site stormwater retention. 

•

16 

•

17 Reduce Pollutant Concentrations with Source Controls and Treatment

•

18 The implementation measure is:

•

19 Reduce pollutant reduction through concentrations by implementing source 

20 controlcontrols and by treatment. practices as necessary to meet water quality goals. 

21 Section 3 addresses pollutant source controls that prevent pollutants from coming into 

22 contact with rainwater and runoff, as well as treatment controls that help to ensure that 

23 polluted runoff does not enter waterways.

•

24 

•

25 Sectors of urban development with particular importance for in the Chesapeake Bay 

26 watershed are redevelopment and turf management. Sections 4 and 5 summarize 

27 considerations associated with these two important sources of pollutants contributed by 

28 urban areas to the Chesapeake Bay. The subset of specific implementation measures for 

29 turf management are presented. 

30 

31 Section 6 consists of a series of fact sheets that briefly describe some of the key practices for 

32 which new research and guidance is available and include applicability, unit processes, 

33 feasibility constraints and limitations, runoff volume and pollutant load removal estimates as 

34 applicable, design and maintenance considerations, costs and factors that affect cost, and key 

35 references and resources. Photos and diagrams of typical applications are provided, as well. The 

36 fact sheets are intended to highlight new research and as well as seminal resources with the most 

37 up-to-date approach on thinking about each management practice. Those practices that which are 

38 adequately covered by other publicly available resources have links to existing sources. 
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Chapter 3. Controlling Urban Runoff 26 

1 1.2.2 Implementation Measures for Urban Runoff in the Chesapeake Bay 

2 Watershed to Control Nonpoint Source Nutrient and Sediment 

3 Pollution

4 Development or redevelopment projects with a footprint that exceeds 5,000 square feet 

5 should use site planning, design, construction, and maintenance strategies for the property 

6 to maintain or restore, to the maximum extent technically feasible, the predevelopment 

7 hydrology of the watershed and site with regard to the temperature, rate, volume, and 

8 duration of flow. (Note: That is based on the approach adopted by Congress for federal facilities 

9 in section 438 of the Energy Independence and Security Act, 2007)

Implementation Measures:

• Maximize infiltration, evapotranspiration, and harvest and use practices on-site, to the 

extent feasible. Examples of these practices include:

− Bioretention cells or raingardens

− Green streets, right-of-way and parking lot designs and retrofits

− Cisterns and interior and exterior use of runoff

− Green roofs

− Tree planting and urban forestry

− Soil amendments and turf management

• Design and implement policies to preserve or restore predevelopment hydrology with 

regard to the temperature, rate, volume and duration of flow, or more restrictive if needed 

for site-specific water quality protection. Implement at the regional, watershed and site 

scales, as appropriate. Consider the following factors: land use, hydrology, 

geomorphology, and climate. Use Options 1 or 2 or similar performance based 

approaches to achieve the desired hydrological goals:

− Option 1: Retain the 95th Percentile Rainfall Event (simplified method)

− Option 2: Conduct site-specific hydrologic analysis

• Use development and planning techniques to direct development to areas where 

development will:

− Have fewer impacts on water quality

− Preserve the integrity of healthy watersheds

− Achieve local objectives for infrastructure management and sustainability

• Use conservation design and LID techniques to

− Minimize the hydrologic impacts of the development and preserve natural 

drainage ways to the extent feasible

− Integrate green infrastructure/low impact development (LID) practices into the 

design and construction of the development, to the extent feasible and preferably 

at the neighborhood scale

• Evaluate and revise local codes and ordinances, as necessary, to promote implementation 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 27 

of green infrastructure/LID designs and practices and examine the following policies and 

mechanisms to identify opportunities, incentives and barriers to promote GI/LID:

− Zoning ordinances

− Subdivision codes

− Street standards and road design guidelines

− Parking requirements

− Setbacks (requirements for long driveways, etc.)

− Height limitations (encourage density where appropriate)

− Open space or natural resource plans

− Comprehensive plans

− Funding mechanisms and other fiscal policies to encourage the use of green 

infrastructure/LID practices

• Examine and revise transportation, public right of way and parking lot policies, guidance 

and standards to reduce impervious areas and water resource impacts

• Minimize directly connected impervious areas by:

− Disconnection of downspouts

− Infiltration of runoff onsite (preferably through bioretention practices

− Product substitution, e.g., use of permeable paving materials

− Harvest and use of runoff onsite

− Construction of green roofs

• Restore streams, floodways, and riparian areas to mitigate channel erosion and 

sedimentation and enhance the pollutant removal capacity of these areas

• Reduce the impacts of existing impervious areas through redevelopment and infill 

policies and strategies and identify and implement incentives for redevelopment that 

encourage the use of green infrastructure/LID designs and practices.

− Retrofit existing urban areas to achieve the desired performance goals

− Assess candidate sites, prioritize, and implement practices based on expected 

cumulative benefit to the subwatershed or watershed

− Assess retrofit potential of significant runoff sources such as streets, highways, 

parking lots and rooftops.

− Develop and implement redevelopment programs that identify opportunities for a 

range of types and sizes of redevelopment projects to mitigate water resource 

impacts that:

o establish appropriate redevelopment stormwater performance standards 

consistent with the goal of restoring predevelopment hydrology with regard to 

the temperature, rate, volume and duration of flow, or more restrictive if 

needed for site-specific water quality protection

o include development of an inventory of appropriate mitigation practices (e.g. 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 28 

permeable pavement, infiltration practices, green roofs) that will be 

encouraged or required for implementation at redevelopment sites that are 

smaller than the applicability threshold

o include site assessment to determine appropriate GI/LID practices

o review codes and ordinances and modify as appropriate to allow and 

encourage GI/LID practices

o implement GI/LID demonstration projects

o incentivize early adopters of GI/LID practices

o maximize urban forest canopy to reduce runoff

o conduct soil analyses and amend compacted urban soils to promote infiltration

1 

2 Reduce Pollutant Concentrations by implementing source control measures and by 

3 treatment practices as necessary to meet water quality goals

4 Source Control/Pollution Prevention

Implementation Measures:

• Identify the pollutants of concern (POCs) to help target the selection of pollution 

prevention/source control that are most appropriate, for example, nutrients and sediment

• Implement pollution prevention/source control practices, i.e. nonstructural, programmatic 

efforts as basic, routine land management practices to target specific pollutants

• Require source controls on

− New and redevelopment site plans for commercial/industrial facilities

− Commercial industrial facilities through development of a Stormwater Pollution 

Prevention Plan (SWPPP)

− Municipal facilities through development of SWPPPs

• Develop and implement ongoing outreach programs aimed at behavior change to prevent 

pollution and control it at its source. Methods for impact and effectiveness evaluation 

should be incorporated into these outreach and education programs.

• Implement residential downspout disconnection program

• Conduct inspections of commercial/industrial facilities to provide compliance assistance 

or to ensure implementation of controls
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 29 

1 Runoff Treatment

Implementation Measures:

• Identify the pollutants of concern (POCs) to help target the section of treatment 

approaches that are most appropriate

• Select treatment practices based on applicability to the POCs

− Use practices to reduce of runoff volume as the preferred and most reliable 

approach to reducing pollutant loading to receiving waters

− Use treatment practices as needed if reduction of runoff is not feasible

− Base the selection of treatment practice on

o treatment effectiveness for the POC to ensure discharge quality

o long-term maintenance considerations to ensure continued adequate 

maintenance and recognition of life-cycle costs

o site limitations to ensure appropriateness of practice to the site

o aesthetics and safety to ensure public acceptance

2 Turf Management Implementation Measures

Implementation Measures:

• Reduce turf management inputs (nutrients, pesticides, irrigation water)

• Reduce total turf area cultivated through initial design or redesign of existing landscapes

• Reduce total area maintained under high input prescription management programs

• Convert nonessential turf to low or lower maintenance vegetated areas such as 

naturalized forest, meadow, native plantings, xeriscapes or turf cultivars that require little 

or no inputs

• Increase infiltrative and retention capacity of maintained turf

• Reduce sediment loadings from turf areas

• Examine municipal codes and ordinances and/or other facility, corporate or agency policy 

directives and guidance for opportunities to

− Adopt or revise policy or guidance to reduce total turf area, nonessential turf area 

and high input turf areas through requirements and/or incentive programs

− Employ management practices that have a decreased potential impact on water 

resources

• Conduct a municipal or facility wide assessment of turf area within the jurisdiction or 

facility property. This assessment should include

− a map of the jurisdiction or facility and include the identification of all turf areas

− an inventory or calculation of the total turf area in acres or hectares using GIS 

techniques or other methods
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 30 

− an evaluation to determine essential and nonessential turf areas

− identification and delineation of all high and low input turf areas

− an evaluation of all turf management activities and inputs preferably by turf 

category or significant turf area within the jurisdiction or facility

− assessments of turf health and infiltrative capacity and opportunities to increase 

soil health to promote the infiltrative capacity of turf areas

• Develop a management plan that contains

− an analysis of options to reduce or eliminate nonessential turf or convert essential

turf to low input turf

− stated goals and objectives regarding the reduction of turf related inputs (water, 

fertilizers, pesticides, fossil fuels) on a municipal or facility wide basis

− an analysis of options to reduce potable water use through the use of hardy 

cultivars or the use of recycled water or harvested runoff

− an identification of areas where soil amendments be used to enhance soil health 

and the infiltration capacity of the soils

− areas of turf that could be used to manage runoff

− areas of turf that could be replaced by lower maintenance cultivars or other 

grasses such as switch grass

− a training program for landscaping personnel

− an implementation schedule

• Develop and implement ongoing public education and outreach programs on turf 

reduction and Bay-friendly lawn and turf management. Programs should target behavior 

change and promote the adoption of water resource friendly practices by increasing 

awareness, promoting appropriate behaviors and actions, providing training and 

incentives. Impact and effectiveness evaluation should be incorporated into these 

outreach and education programs.

• Conduct a life-cycle cost benefit analysis to reduce inputs and maintenance burden of 

managed turf areas.

1 

2 1.3 References 

3 Allmendinger, Nicholas E., James E. Pizzuto, Glenn E. Moglen, and Mikolaj Lewicki. 2007. A 

4 sediment budget for a sediment budget for an urbanizing watershed, 1951-1996, 

5 Montgomery County, Maryland, U.S.A. Paper No. J05051 of the Journal of the American 

6 Water Resources Association. Received April 25, 2005; accepted March 29, 2007.

7 CNT (Center for Neighborhood Technology). No date. Green Values Stormwater Toolbox. 

8 Center for Neighborhood Technology, Chicago, IL. <www.cnt.org/natural-resources/green9 values>. Accessed February 23, 2010.
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 31 

1 Maryland Department of Natural Resources. No date. Trees Save Energy. DNR, Annapolis, MD. 

2 <http://www.dnr.state.md.us/forests/publications/urban5.html>. Accessed February 23, 

3 2010.

4 National Research Council. 2008. Urban Stormwater Management in the United States. The 

5 National Academies Press and the Committee on Reducing Stormwater Discharge

6 Contributions to Water Pollution, Washington, DC. 

7 Nowak, D.J., and Crane, D.E. 20001998. The Urban Forest Effects (UFORE) Model: quantifying 

8 urban forest structure and functions. In Hansen, M. and T. Burk (eds.) Resources 

9 Inventories in the 21st Century. U.S. Department of Agriculture Forest Service General 

10 Technical Report NC-212: 714–72). St. Paul, MN.

11 <http://www.ufore.org/about/files/NowakCrane_UFORE.pdf>.Integrated Tools 

12 Proceedings. < http://www.ufore.org/about/files/NowakCrane_UFORE.pdf> Accessed 

13 February 22, 2010. 

14 Philadelphia Water Department. No date. Green City, Clean Water. Office of Watersheds. 

15 Philadelphia, PA. <http://www.phillywatersheds.org/ltcpu/>. Accessed February 23, 2010.

16 Philadelphia Water Department. 2009. Summary of Triple Bottom Line Analysis, City of 

17 Philadelphia Long-Term Control Plan. Office of Watersheds, Philadelphia PA. 

18 <http://www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf> Accessed February 23, 2010.

19 Plan Philly. 2009. Green City, Clean Waters: Philadelphia’s Program for Combined Sewer 

20 Overflow Control, A Long-Term Control Plan Update, Summary Report, 2009. University 

21 of Pennsylvania School of Design, Philadelphia, PA. <http://planphilly.com/node/9842>. 

22 Accessed February 23, 2010.

23 Reese, A. 2009. Volume-based hydrology: Examining the shift in focus from peak flows and 

24 pollution treatment to mimicking predevelopment volumes. Stormwater 10(6). 

25 <http://www.stormh2o.com/september-2009/volume-based26 hydrology.aspxhttp://www.stormh2o.com/september-2009/volume-based-hydrology.aspx>. 

27 Accessed January 15, 2010. 

28 Smith, W.H. 1990. Air Pollution and Forests. Springer-Verlag, New York, NY. 

29 Souch, C.A., and C. Souch. 1993. The effect of trees on summertime below canopy urban 

30 climates: a case study, Bloomington, Indiana. J. Arboric. 19(5):303–312.

31 Stranko, S.A., R.H. Hilderbrand, R.P. Morgan II, M.W. Staley, A.J. Becker, A. Roseberry32 Lincoln, E.S. Perry, and P.T. Jacobson. 2008. Brook Trout Declines with Land Cover and 

33 Temperature Changes in Maryland. North American Journal of Fisheries Management 

34 28:1223–1232 doi: 10.1577/M07-032.1 <http://afsjournals.org/doi/abs/10.1577/M07-

35 032.1http://afsjournals.org/doi/abs/10.1577/M07-032.1> and 

36 <http://www.dnr.state.md.us/dnrnews/pressrelease2008/100308.html

37 <http://www.dnr.state.md.us/dnrnews/pressrelease2008/100308.html>. Accessed February 

38 22, 2010. 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 32 

1 Trust for Public Land. 1999. The Economic Benefits of Open Space. San Francisco, CA. 

2 <http://www.tpl.org/tier3_cd.cfm?content_item_id=1195&folder_id=727>. Accessed 

3 March 29, 2006.

4 Trust for Public Land and American Water Works Association. 2004. Protecting the Source.

5 Trust for Public Land, San Francisco, CA and American Water Works Association, 

6 Denver, CO.

U.S. Department of Agriculture. 2000. Resources Inventories in the 21st 7 Century. U.S. 

8 Department of Agriculture Forest Service General Technical Report NC-212 (pp. 714–

9 720). U.S. Department of Agriculture, St. Paul, MN.

10 <http://www.nrs.fs.fed.us/pubs/276>.< http://www.nrs.fs.fed.us/pubs/276> Accessed 

11 February 22, 2010.

12 USEPA (U.S. Environmental Protection Agency). 1995. Economic Benefits of Runoff Controls

13 (U.S. Environmental Protection Agency, Office of Water, Washington, DC.

14 USEPA (U.S. Environmental Protection Agency). 2009. Technical Guidance on Implementing 

15 the Stormwater Runoff Requirements for Federal Projects under Section 438 of the Energy 

16 Independence and Security Act. 

17 <http://www.epa.gov/owow/NPS/lid/section438/pdf/final_sec438_eisa.pdfhttp://www.epa.

18 gov/owow/NPS/lid/section438/pdf/final_sec438_eisa.pdf>. Accessed January 15, 2010. 

19 Weinstein, N. C. Glass, J.P. Heaney, J. Lee, W. Huber, P. Jones, C, Kloss, M. Quigley, E. 

20 Strecker, and K. Stephens. 2005. Decentralized Stormwater Controls for Urban Retrofit 

21 and Combined Sewer Overflow Reduction. Water Environment Research Foundation, 

22 Alexandria, VA. 

23 WERF (Water Environment Research Foundation). 2008. Using Rainwater to Grow Livable 

24 Communities: Benefits of Green Development. 

25 <http://www.werf.org/livablecommunities/pdf/benefits.pdfhttp://www.werf.org/livablecom

26 munities/pdf/benefits.pdf>. Accessed January 15, 2010. 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 33 

1 2 Implementation Measures for Reducing Urban Runoff

2 Volume 

3 The shortcomings of traditional, detention-based stormwater control efforts, and the need to use 

4 approaches to reduce runoff volume to protect water quality, have been well-documented (NRC 

5 2008; USEPA 2009).

6 This section presents an approach of land use and growth management measures that guide 

7 development to areas that minimize effects on sensitive resources and open space and ensure that 

8 new and redevelopment sites are designed to reduce runoff volume through on-site stormwater 

9 retention.

10 Development or redevelopment projects with a footprint that exceeds 5,000 square feet 

11 should use site planning, design, construction, and maintenance strategies for the property 

12 to maintain or restore, to the maximum extent technically feasible, the predevelopment 

13 hydrology of the watershed and site with regard to the temperature, rate, volume, and 

14 duration of flow. (Note: Based on the approach adopted by Congress for Federal facilities in 

15 Section 438 of the Energy Independence and Security Act, 2007)

Implementation Measures:

• Maximize infiltration, evapotranspiration, and harvest and use practices on-site, to the 

extent feasible. Examples of these practices include

− Bioretention cells or raingardens

− Green streets, row of way and parking lot designs and retrofits

− Cisterns and interior and exterior use of runoff

− Green roofs

− Tree planting and urban forestry

− Soil amendments and turf management

• Design and implement policies to preserve or restore predevelopment hydrology with 

regard to the temperature, rate, volume and duration of flow, or more restrictive if needed 

for site-specific water quality protection. Implement at the regional, watershed and site 

scales, as appropriate. Consider the following factors: land use, hydrology, 

geomorphology, and climate. Use Options 1 or 2 or similar performance based 

approaches to achieve the desired hydrological goals

− Option 1: Retain the 95th Percentile Rainfall Event (simplified method)

− Option 2: Conduct site-specific hydrologic analysis

• Use development and planning techniques to direct development to areas where 

development will

− Have fewer impacts on water quality

− Preserve the integrity of healthy watersheds

− Achieve local objectives for infrastructure management and sustainability
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 34 

• Use conservation design and LID techniques to

− Minimize the hydrologic impacts of the development and preserve natural 

drainageways to the extent feasible

− Integrate green infrastructure/low impact development (LID) practices into the 

design and construction of the development, to the extent feasible and preferably 

at the neighborhood scale

• Evaluate and revise local codes and ordinances, as necessary, to promote implementation 

of green infrastructure/LID designs and practices and examine the following policies and 

mechanisms to identify opportunities, incentives and barriers to promote GI/LID

− Zoning ordinances

− Subdivision codes

− Street standards and road design guidelines

− Parking requirements

− Setbacks (requirements for long driveways, etc.)

− Height limitations (encourage density where appropriate)

− Open space or natural resource plans

− Comprehensive plans

− Funding mechanisms and other fiscal policies to encourage the use of green 

infrastructure/LID practices

• Examine and revise transportation, public right of way and parking lot policies, guidance 

and standards to reduce impervious areas and water resource impacts

• Minimize directly connected impervious areas by

− Disconnection of downspouts

− Infiltration of runoff onsite (preferably through bioretention practices

− Product substitution ,e.g., use of permeable paving materials

− Harvest and use of runoff onsite

− Construction of green roofs

• Restore streams, floodways, and riparian areas to mitigate channel erosion and 

sedimentation and enhance the pollutant removal capacity of these areas

• Reduce the impacts of existing impervious areas through redevelopment and infill 

policies and strategies and identify and implement incentives for redevelopment that 

encourage the use of green infrastructure/LID designs and practices.

− Retrofit existing urban areas to achieve the desired performance goals

− Assess candidate sites, prioritize, and implement practices based on expected 

cumulative benefit to the subwatershed or watershed

− Assess retrofit potential of significant runoff sources such as streets, highways, 

parking lots and rooftops.

− Develop and implement redevelopment programs that identify opportunities for a 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 35 

range of types and sizes of redevelopment projects to mitigate water resource 

impacts that

o establish appropriate redevelopment stormwater performance standards 

consistent with the goal of restoring predevelopment hydrology

o include development of an inventory of appropriate mitigation practices (e.g. 

permeable pavement, infiltration practices, green roofs) that will be 

encouraged or required for implementation at redevelopment sites that are 

smaller than the applicability threshold

o include site assessment to determine appropriate GI/LID practices

o review codes and ordinances and modify as appropriate to allow and 

encourage GI/LID practices

o implement GI/LID demonstration projects

o incentivize early adopters of GI/LID practices

o maximize urban forest canopy to reduce runoff

o conduct soil analyses and amend compacted urban soils to promote infiltration

1 

2 2.1 Maximize Infiltration, Evapotranspiration, and Harvest and Use

3 The shortcomings of traditional, detention-based stormwater control efforts, and the need to use 

4 approaches to reduce runoff volume to protect water quality, have been well-documented (NRC 

5 2008, EPA 2009). 

6 The implementation measure is:

7 Reduce urban runoff volume by understanding local land use-hydrology relationships and 

8 applying performance standards that protect or restore hydrology to predevelopment 

9 levels.

10 This section presents an approach of land use and growth management measures that guide 

11 development to areas that minimize effects on sensitive resources and open space and ensure that 

12 new and redevelopment sites are designed to reduce runoff volume through on-site stormwater 

13 retention

14 The recommended approaches for reducing runoff volume are the following:

•

15 Maintain or restore predevelopment hydrology, at least with regard to the temperature, 

16 rate, volume, and duration of flow. 

17 − Maximize infiltration, evapotranspiration, and harvest and use practices on-site

•

18 Select the approach for achieving this performance goal on the basis of the scale being 

19 addressed (i.e., regional, watershed, site) and on an understanding of the land use, 

20 hydrology, geomorphology, and climate type for the site or watershed

•

21 Use appropriate designs as part of a comprehensive watershed plan

22 − For new development and redevelopment
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 36 

1  Use development planning techniques such as smart growth to determine 

2 where to develop to

3 o Have minimum impact on water quality

4 o Protect existing healthy watersheds

5 o Achieve local objectives for infrastructure management

6  Use conservation design techniques to

7 o Minimize the hydrologic modifications of the developments

8 o Enable the effective integration and placement of Green 

9 Infrastructure/LID practices

10  Use Green Infrastructure/LID practices to manage stormwater on-site for 

11 smaller storm events for protection of water quality (in addition to meeting 

12 local regulations for flood control)

13  Minimize impervious areas by using techniques such as reducing street widths 

14 or parking lot sizes

15  Minimize directly connected impervious areas, such as downspout 

16 disconnection

17  Use LID Practices: Maximize infiltration, evapotranspiration , and harvest and 

18 use practices

19  Restore streams, floodways, and riparian areas to mitigate channel erosion that 

20 contributes to sediment pollution, and restore the natural pollutant removal 

21 capability of these ecosystems

22 − For existing urban areas (i.e., retrofits):

23  Use designs appropriate to new development and redevelopment (above)

24  Redevelop existing impervious areas through infill strategies, including

25 incentives for redevelopment

26 2.1 Maintain or Restore Predevelopment Hydrology

27 Restoring or maintaining predevelopment hydrology has emerged as the generally preferred 

28 approach for controlling urban runoff and protecting water quality for several reasons. Most 

29 importantly, this approach addresses the root cause of impairment. Traditional control 

30 approaches attempt to control the symptoms (e.g., peak flow, excess pollutants), but that is 

31 largely ineffectual in protecting streams and water quality because of the scale of the problem, 

32 the cumulative effects of multiple developments, and the need to manage both site- and 

33 watershed-level effects. The problems associated with traditional control approaches in 

34 protecting water quality are presented in the Introduction to this chapter. This section presents 

35 the approaches for obtaining the goal of restoring or maintaining predevelopment hydrology. 

36 To maintain or restore site or watershed hydrology, the watershed shouldmust function 

37 hydrologically after development as it did before human induced land alterations. In the 

38 Chesapeake Bay, most areas before development were forested with mature trees, and the bulk of 

39 the rainfall was intercepted, infiltrated, or evapotranspired. 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 37 

1 To mimic the natural behavior of the landscape the stormwater management system should be 

2 designed to manage runoff through the following: 

3 • Infiltration and groundwater recharge 

4 • Evapotranspiration 

5 • Harvest or rainfall and use of captured rainfall on-site 

6 On sites where inadequate area or the intended use of the development precludes managing the 

7 desired volume on-site, off-site mitigation should be considered within the same subwatershed. 

8 The intent of maintaining or restoring site and watershed hydrology is to preserve or restore 

9 stream and groundwater hydrology so that the system is stable and resilient enough to support 

10 aquatic biota, stream channel stability, and historical aquifer recharge rates. That will help ensure 

11 that receiving waters are not negatively affected by changes in runoff temperature, volumes, 

12 durations, and rates. 

13 2.2 Implement Policies1.1 Establishing Performance Design 

14 Objectives

15 The performance-based approached described in the following 

16 paragraphs is intended to Preserve and Restore Redevelopment 

17 Hydrology

18 provide designers the option of selecting either a simplified method or a more site-specific 

19 methodology that allows the designer to factor in site conditions. Both options give the designer 

20 flexibility in selecting appropriate, technically feasible practices to reduce the volume of 

21 stormwater discharged to the maximum extent technically feasible (METF). In the simplified 

22 option, the performance standard has already been determined. In the second option, the 

23 performance standard will be determined by site evaluation and subsequent continuous 

24 simulation modeling methods.

25 This guidance provides two options that site designers can use to establish appropriate 

26 performance goals toward achieving the goal of maintaining or restoring predevelopment 

27 hydrology; however, it is noted that in many situations it might be feasible and beneficial to 

28 design to have no runoff from a site. The discussion of the two options does not preclude the use 

of more protective performance goals. Option 1, the methodology based on retention of the 95th 29 

30 percentile rainfall event, is a simple way to establish the performance goal and does not require 

31 detailed analysis of the site conditions or a continuous simulation modeling approach. It is 

32 assumed that using that performance standard will generally result in designs that protect or 

restore site hydrology. However, there could be situations where Option 1 (retaining the 95th 33 

34 percentile rainfall event) is not protective enough to maintain or restore the predevelopment 

35 hydrology of the project (for example, in some headwater streams) or is overprotective (in the 

36 case of naturally impermeable surfaces). In such cases, Option 2 (site-specific hydrologic 

37 analysis) could be used to determine the performance design objective necessary to preserve 

38 predevelopment runoff conditions. The expectation is that Option 2 can be used in situations 

39 where the designer has the requisite data and resources to analyze site infiltration, 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 38 

1 evapotranspiration, interception, and potential harvest and use scenarios to establish these design 

2 objectives and to design the runoff management system to meet the goals of maintaining and 

3 restoring site hydrology. More detailed descriptions of the two options follow. 

Option 1: Retain the 95th 4 Percentile Rainfall Event 

5 Under Option 1, managers design, construct, and maintain stormwater management practices that 

6 manage rainfall on-site, and prevent the off-site discharge of the precipitation from all rainfall 

events less than or equal to the 95th percentile rainfall event to the METF. The 95th 7 percentile 

8 rainfall event is the event whose precipitation total is greater than or equal to 95 percent of all 

storm events over a given period of record. For example, to determine what the 95th 9 percentile 

10 storm event is in a specific location, all 24-hour storms that have recorded values over a 30-year 

period would be tabulated, and a 95th 11 percentile storm would be determined from that record, i.e., 

5 percent of the storms would be greater than the number determined to be the 95th 12 percentile 

storm. Thus the 95th 13 percentile storm would be represented by a number such as 1.5 inches, and 

14 that would be the design storm. The designer selects a system of practices, to the METF, that 

15 infiltrate, evapotranspire, or harvest and reuse that volume multiplied by the total area of the 

facility/project footprint. Methods and data used to estimate the 95th 16 percentile event are 

17 discussed in the appendix 2 of this document. 

For the purposes of this document, retaining all storms up to and including the 95th 18 percentile 

19 storm event is analogous to maintaining or restoring the predevelopment hydrology with respect 

20 to the volume, flow rate, duration, and temperature of the runoff for most sites. 

21 Where technically feasible, the goal of Option 1 is that 100 percent of the volume of water from 

storms less than or equal to the 95th 22 percentile event over the footprint of the project should must 

23 not be discharged to surface waters. In some cases, runoff can be harvested and reused and 

24 ultimately can be discharged to surface waters or a sanitary treatment system; such direct or 

25 indirect discharges must be authorized. For example if runoff is captured for nonpotable uses 

26 such as toilet flushing or other uses that are not irrigation related, the waters could be discharged 

27 into the sanitary sewer system or other appropriate system depending on local requirements. 

Runoff volumes that exceed the 95th 28 percentile event can be managed by using overflow or 

29 diversion strategies and practices as well as the detention practices used for flood control. 

30 Designers should also account for potential thermal effects of structures such as roofs and paved 

31 surfaces that can increase the temperature of stormwater runoff. Designers should select 

32 materials that minimize temperature increases (consider material such as concrete versus asphalt; 

33 vegetated roofs. and the like and use them as appropriate). 

34 Rationale for Selecting Option 1. Option 1 was selected because retention of 100 percent of all 

rainfall events equal to or less than the 95th 35 percentile rainfall event was estimated to be a 

36 conservative and protective representation of the natural hydrology on most sites. On most sites, 

37 little or no runoff occurs from small, frequently occurring storms, and such storms account for a 

38 large proportion of the annual precipitation volume. When development occurs, the hydrologic 

39 balance of the site is disturbed and as a result runoff occurs from both small and large storms. 

40 There is an increase in the number of runoff events, and an increase in the runoff volume, 
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Chapter 3. Controlling Urban Runoff 39 

1 duration, rate, and temperature. Receiving water degradation and habitat loss occur from this 

2 changed hydrologic regime. 

Table 3-1 contains representative 95th 3 percentile storm event volumes in inches from selected 

4 U.S. cities. Figure 3-10 contains a plot representing storm event frequency for Washington, DC. 

In Figure 3-10, the 95th 5 percentile storm event has been identified and is approximately 1.5 

6 inches. 

Calculating the 95th 7 Percentile Rainfall Event 

This document’s appendix 2 contains information on how to calculate the 95th 8 percentile rainfall 

9 event for a specific area. A long-term record of daily rainfall amounts (ideally, at least 30 years) 

is needed to calculate the 95th 10 percentile rainfall. 

11 Designers opting to use Option 1 would need to do the following: 

1. Calculate or verify the precipitation amount from the 95th 12 percentile storm event (that 

13 number would be typically expressed in inches, e.g., 1.5 inches) 

14 2. Employ on-site stormwater management controls to the METF that infiltrate, 

15 evapotranspire, or harvest and use the appropriate design volume 
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Chapter 3. Controlling Urban Runoff 40 

Table 3-1. Example 95th 1 percentile storm events for select U.S. cities 

City 

95th percentile event 

rainfall total 

(in) City 

95th percentile event 

rainfall total 

(in) 

Atlanta, GA 1.8 Kansas City, MO 1.7 

Baltimore, MD 1.6 Knoxville, TN 1.5 

Boston, MA 1.5 Louisville, KY 1.5 

Buffalo, NY 1.1 Minneapolis, MN 1.4 

Burlington, VT 1.1 New York, NY 1.7 

Charleston, WV 1.2 Salt Lake City, UT 0.8 

Coeur D’Alene, ID 0.7 Phoenix, AZ 1.0 

Cincinnati, OH 1.5 Portland, OR 1.0 

Columbus, OH 1.3 Seattle, WA 1.6 

Concord, NH 1.3 Washington, DC 1.5 

Denver, CO 1.1 

2 Adaptedadapted from Hirschman and Kosco 2008 

3 

Figure 3-10. Rainfall frequency spectrum showing the 95th 4 percentile rainfall event for Washington, 

5 DC (Reagan National Airport ~1.5 inches) 
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Chapter 3. Controlling Urban Runoff 41 

• The 95th 1 percentile event can be calculated by using the following procedures below 

2 (summarized from Hirschman and Kosco. 2008. Managing Stormwater in Your 

3 Community: A Guide for Building an Effective Post-Construction Program, Center for 

4 Watershed Protection):Obtain a long-term rainfall record from a nearby weather station 

5 (daily precipitation is fine, but try to obtain at least 30 years of daily record). Long-term 

6 rainfall records can be obtained from many sources, including NOAA at 

7 www.nesdis.noaa.gov

8 • Remove from the data set all data for small rainfall events that are 0.1 inch or less and 

9 snowfall events that do not immediately melt. Such events should be deleted because they 

do not typically cause runoff and could cause the analyses of the 95th 10 percentile storm 

11 runoff volume to be inaccurate. 

12 • Use a spreadsheet or simple statistical package to sort the rainfall events from highest to 

13 lowest. In the next column, calculate the percentage of rainfall events that are less than 

14 each ranked event (event number / total number of events). For example, if there were 

15 1,000 rainfall events and the highest rainfall event was a 4-inch event, 999 events are less 

16 than the 4-inch rainfall event (or a percentile of 999 / 1,000, or 99.9 percent). 

• Use the rainfall event at 95 percent as the 95th 17 percentile storm event. 

18 Option 2: Site-Specific Hydrologic Analysis 

19 Under Option 2, the predevelopment hydrology would be determined on the basis of site-specific 

20 conditions and local meteorology by using continuous simulation modeling techniques, 

21 published data, studies, or other established tools. The designer would then identify the 

22 predevelopment condition of the site and quantify that the post-development runoff volume and 

23 peak flow discharges are equivalent to predevelopment conditions. The post-construction rate, 

24 volume, duration and temperature of runoff shouldmust not exceed the predevelopment 

25 conditionsrates, and the predevelopment hydrology should be replicated through site design and 

26 other appropriate practices to the METF. Additional discussions of appropriate methodologies to 

27 use in assessing site hydrology have been included in this document’s appendix 2. 

28 The predevelopment hydrologic condition of the site is the combination of runoff, infiltration, 

29 and evapotranspiration rates and volumes that typically existed on the facility site before 

30 development on a greenfields site (meaning any construction of infrastructure on undeveloped 

31 land such as meadows or forests). In practice, determining the predevelopment hydrology of a 

32 site can be difficult if no suitable reference site is available. As a result, reference conditions for 

33 typical land cover types in the locality often are used to approximate what fraction of the 

34 precipitation ran off, soaked into the ground, or was evaporated from the landscape. Using 

35 reference conditions can be problematic if suitable data are not available or unique site 

36 conditions exist that do not fit within a typical land use cover type for the area, e.g., meadow or 

37 forest. The intent is not to restore the site to pre-Columbian conditions but to develop or 

38 redevelop the site to ensure that a stable hydrologic regime is in place to protect groundwater, 

39 surface water, and receiving stream channel stability. 

40 For redevelopment sites, existing site conditions and uses of the site can influence the amount of 

41 runoff that can be managed on-site through infiltration, evapotranspiration, and harvest and use 

42 and, thus, affect the achievement of the performance design objective. In the context of some 
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Chapter 3. Controlling Urban Runoff 42 

1 redevelopment projects, fully restoring predevelopment hydrology can be difficult to achieve. In 

2 such cases, EPA recommends using a systematic analysis to determine what practices can be 

3 implemented. The Technical Guidance on Implementing the Stormwater Runoff Requirements 

4 for Federal Projects under Section 438 of the Energy Independence and Security Act, EPA 841-

5 B-09-001, December 2009, (http://www.epa.gov/owow/nps/lid/section438) provides 

6 methodology for federal facilities in determining METF. Examples of conditions that could 

7 prevent a fully restored predevelopment hydrology are a combination of the following:

8 • The 1) the presence of shallow bedrock; 2) contaminated soils, near-surface groundwater; 

9 or 3) other factors such as underground facilities or utilities. 

10 • The design of the site precludes the use of soil amendments, plantings of vegetation or 

11 other designs that can be used to infiltrate and evapotranspirate runoff. 

12 • Water harvesting and reuse are not practical or possible because the volume of water used 

13 for irrigation, toilet flushing, industrial make-up water, wash-waters, and the like, is not 

14 significant enough to warrant designing and using water harvesting and reuse systems 

15 • Modifications to an existing building to manage stormwater are not feasible because of 

16 structural or plumbing constraints or other factors as identified by the facility 

17 owner/operator. 

18 • Small project sites where the lot is too small to accommodate infiltration practices 

19 adequately sized to infiltrate the volume of runoff from impervious surfaces. 

20 • Soils that cannot be sufficiently amended to provide for the requisite infiltration rates. 

21 • Situations where site use is inconsistent with the capture and reuse of stormwater or other 

22 physical conditions on-site that preclude the use of plants for evapotranspiration or 

23 bioinfiltration. 

24 • Retention or use of stormwater on-site or discharge of stormwater on-site via infiltration 

25 has a significant adverse effect on the site or the downgradient water balance of surface 

26 waters, groundwaters or receiving watershed ecological processes. 

27 • State and local requirements or permit requirements that prohibit water collection or 

28 make it technically infeasible to use certain green infrastructure/LID techniques. 

29 • Retention or use of stormwater on the site would cause an adverse water balance to either 

30 or both the receiving surface waterbody or groundwater. 

31 

32 In cases where a technical infeasibility exists that precludes full implementation of the 

33 performance design goal, stormwater practices to infiltrate, evapotranspire, or harvest and use 

34 on-site the maximum amount of stormwater technically feasible should be implemented.
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Chapter 3. Controlling Urban Runoff 43 

1 2.3 Use Planning2 Select Approaches to Achieve Performance 

2 Goals Based on Scale of Implementation and Development 

3 Techniques

4 Site-Specific Conditions

5 2.32.1 The Impacts of Land Use on Hydrology and Geomorphology 

6 An evaluation of the land use and hydrology/geomorphology of a watershed or site is an 

7 important first step in designing to maintain or restore predevelopment hydrology and mitigate 

8 pollutant loading. 

9 One of the key strategies to reduce runoff is to change the pattern of land development to one 

10 that is less destructive to water quality. Land use is the largest driver of changes in stormwater 

11 runoff, and developed and urbanized lands contribute the largest volumes of increased runoff. 

12 The progression of development has led to the increased urbanization of the population. The 

13 urbanization of land, however, has outpaced the urbanization of the population, indicative of 

14 sprawl-type development. Between 1975 and 1995 the amount of urbanized land more than 

15 doubled in the Baltimore-Washington Metropolitan area. That trend has been witnessed 

16 nationally. Table 3-2 shows how land development in the United States outpaced population 

17 growth from 1970 to 1990. 

18 Table 3-2. A comparison of population growth rates of U.S. cities versus 

19 corresponding

20 urbanized land growth rates shows the pattern of growth 

21 Sprawl, 1970—1990 (NRC 2008) 

% Increase city population Average % increase in city urbanized land 

< 10% 38% 

11%–30% 54% 

31%–50% 72% 

> 50% 112% 

22 

23 These urbanization patterns have significant effects on land use as the predeveloped conditions 

24 of forests, meadows, and agricultural lands are replaced by hardened landscapes. Impervious 

25 surfaces, such as roads and roofs are the predominate land cover in urban areas. For example 

26 • Roads and parking lots are as much as 70 percent of total impervious cover in ultra-urban 

27 areas (National Research Council 2008) 

28 • Roads tend to capture and export more stormwater pollutants than other land covers in 

29 highly impervious areas, especially for small rainfall events (National Research Council 

30 2008) 

31 Even urban land cover that is not hardscape does not infiltrate rainfall as it would before 

32 development. Urban soils have much higher bulk density (the mass of dry soil divided by its 

33 volume, which serves as a predictor of porosity) than undisturbed soils because of soil 
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Chapter 3. Controlling Urban Runoff 44 

1 compaction typical of construction practices and urban uses. As shown in Table 3-3 the bulk 

2 density of urban soils is closer to concrete than to undisturbed soils. The ability of soils with such

3 levels of compaction to infiltrate and retain stormwater is greatly diminished and results in 

4 greater quantities of runoff. The lack of an absorptive humus layer, and active soil biota, can also 

5 play a role in reducing infiltration rates. 

6 As a result of such compaction, the runoff from urban soils often resembles that of impervious 

7 surfaces, especially for larger storm events. 

8 Table 3-3. Bulk Density of Urban Soils is Closer to Concrete than to 

9 Undisturbed Soils (Schueler and Holland 2000)

Material 

Bulk density 

(grams per cubic centimeter) 

Undisturbed Soil 1.1 to 1.4 

Urban Lawn 1.5 to 1.9 

Fill Soil 1.8 to 2.0 

Soil Adjacent to Buildings and Roadways 1.5 to 2.1 

Concrete 2.2 

10 Source: Schueler and Holland 2000

11 An understanding of such effects is essential to effectively mitigate them. Watershed and site 

12 assessments enable a better understanding of the factors contributing to hydromodification, so 

13 that appropriate mitigation techniques can be selected. The site assessment process should 

14 evaluate the hydrology, topography, soils, vegetation, and water features (i.e., wetlands, riparian 

15 areas, and floodplains) to identify how stormwater moves through the site before development. 

16 Additional information on the site assessment process is provided in Section 3 of this document. 

17 In addition, to protect stream channels from increased erosion, it is necessary to control the total 

18 time—the duration—stream channels are subject to geomorphically significant flows. The flows 

19 can result in channel erosion caused by the additional energy imparted to the stream channel by 

20 the increases in runoff velocities and volumes. The extended high flows typically lead to stream 

21 channel destabilization because the stream did not evolve under those conditions and lacks the 

22 capacity to dissipate this increased energy without scouring the stream bed. In response, both the 

23 channel and banks are incised, creating increased sediment transport. Those problems are 

24 aggravated as the flow travels downstream, with other altered watersheds contributing their 

25 increased volumes. 

26 The traditional stormwater management approach was based on primarily on flood protection, 

27 and often focused on not exceeding a predevelopment flow rate, but it did not take into account 

28 additional volume. When there is greater volume to be discharged, the duration of the peak flow 

29 rate is longer than under predevelopment condition. When multiple discharges of this type enter 

30 a receiving stream, the flow peaks that once were sequential become additive, creating much 

31 higher peak flows in the stream than existed in predevelopment conditions. The relationships 

32 between hydrologic and geomorphic changes and biological parameters can be analyzed using 

33 protocols such as that laid out in WERF’s Protocols for Studying Wet Weather Impacts and 

34 Urbanization Patterns (WERF 2008). 
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Chapter 3. Controlling Urban Runoff 45 

1 To achieve the goal of overall waterbody health, other jurisdictions have established various 

2 performance objectives. The following are examples of state and local performance criteria 

3 developed to address the goal of restoring or maintaining predevelopment hydrology: 

4 • Santa Clara Valley, California. The hydromodification control limits post-construction 

5 runoff to pre-construction rates or durations. Performance criteria to demonstrate 

6 compliance include (1) the project must use stormwater controls to maintain pre7 construction stream erosion potential and (2) post-construction stormwater discharge 

8 rates and flow durations must be equivalent to pre-construction values for flows from 

9 10 10 percent of the 2-year peak flow up to the full, 10-year peak flow (Santa Clara 

10 Valley 2005). 

11 • Western Washington. Stormwater discharges must match developed discharge durations 

12 to predeveloped durations for the range of predeveloped discharge rates from 50 percent 

13 of the 2-year peak flow up to the full, 50-year peak flow (Western Washington 

14 Stormwater Management Manual 2005). 

•

15 Coastal areas of North Carolina. Any development over 12 percent imperious must 

16 control approximately 3.6 inches of rainfall, or the one-year, 24-hour storm, if the project 

17 is within a half mile of shellfishing waters. For areas outside the boundary, the trigger for 

18 stormwater controls is 25 percent impervious with a requirement to control 1.5 inches of 

19 rainfall.

20 2.3.2 Use Appropriate Designs as Part of a Comprehensive Watershed 

21 Plan 

22 This section contains an overview of example strategies, policies, and practices that land 

23 managers on different scales (federal, state, local) have used to reduce the effects of development 

24 and redevelopment on receiving water hydrology. Section 3 contains a description of strategies 

25 and practices that can be used to protect water quality and reduce pollutant loading from 

26 developed areas. 

27 The strategies and approaches used to achieve a community’s hydrologic stormwater goals will 

28 depend on the scale at which the approach is be applied—regional, local jurisdiction, watershed, 

29 subdivision/facility campus, building lot. Issues and potential tools for different scales of 

30 implementation are provided in Table 3-4.

31 Such strategies should be included as part of a comprehensive watershed plan to protect the 

32 resources in the watershed and downstream. Development approaches should be viewed across a 

33 watershed or region, down to the local scale, to help achieve communities’ desired goals for 

34 water resources while avoiding unintended consequences, such as flooding or inadequate base 

35 stream flow. Comprehensive planning is an effective nonstructural tool to reduce the amount of 

36 impervious surface in a watershed and to guide future development in a manner that best protects 

37 water quality. Resources for preparing watershed plans are provided in Table 3-5. 

38 Table 3-4: Strategies and tools for implementing stormwater protection goals at different scales 

Scale 

Example strategies at 

different scales Example programs and initiatives 
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Chapter 3. Controlling Urban Runoff 46 

Scale 

Example strategies at 

different scales Example programs and initiatives 

National Association of 

Regional Councils 

Promotes information exchange to help regional organizations 

achieve goals. 

National 

EPA’s Green Infrastructure

and LID websites, U.S. 

Department of Defense LID 

Policy 

Provide national-level guidance 

Regional Commissions 

facilitate cooperation (such 

as similar ordinances for 

development equity) and 

leverage funds for outreach, 

etc. 

Northern Virginia Regional Commission: Example program 

www.onlyrain.org.

Washington Metropolitan Council of Governments: Example 

Symposium—Innovative Stormwater Controls on Roads &

Highways, November 2009 

Interstate, multijurisdictional 

partnerships 

Chesapeake Bay Program: state, federal, academic and 

nonprofit partnership. 

www.chesapeakebay.net/partnerorganizations.aspx

Public-Private Partnerships 

(any scale)

The Healthy Lawn and Clean Water Initiative, Chesapeake 

Bay Executive Council and the fertilizer industry agree on 

voluntary Pphosphorus reductions in fertilizer

http://archive.chesapeakebay.net/pubs/Lawn_Care_MOU.pdf

The Growing Home Campaign. Provides incentives for 

homeowners to increase urban canopy with cost shared by 

landscape industry. 

www.baltimorecountymd.gov/Agencies/environment/growinghome 

Regional 

University-Public-Private 

Partnerships 

Designing and monitoring pilot or demonstration facilities. 

Outreach with university and extension programs. 

Stormwater programs at Villanova, University of Maryland, and 

North Carolina State University working together in partnership

Ordinances that allow LID, 

fees to enable programs, 

fines, technical assistance 

D.C.’s Impervious Area Fee 

Spotsylvania, Virginia, Ordinance 

Lycoming County, Pennsylvania (Draft), prepared under PA 

Act 167 

Smart Growth policies Baltimore County, Maryland, designates land management 

areas; www.baltimorecountymd.gov/Agencies/planning/

masterplanning/smartgrowth.html%20

The Philadelphia Green program revitalizes and maintain 

abandoned land and public spaces by partnering with

government, businesses, and the community 

Local 

Jurisdiction 

Green Street policies The Port Towns’ (Maryland) 2010 Legislative Priorities include 

Fund at least one Green Street in each of the Port Towns. 

http://porttowns.org

Watershed Urban Pollutant tradinga: 

Support development of 

programa,b 

Region states are evaluating programsc. EPA Region 3 is 

evaluating the use of urban stormwater trading for the 

Chesapeake Bay.

Virginia Soil and Water Conservation Board Guidance

Document on Stormwater Nonpoint Nutrient Offsets, Approved 

July 23, 2009. http://townhall.virginia.gov/L/GDocs.cfm
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Chapter 3. Controlling Urban Runoff 47 

Scale 

Example strategies at 

different scales Example programs and initiatives 

Use watershed-scale 

hydraulic and pollutant 

models to optimize control 

type and location 

Models such as BMP-DSS (BMP Decision Support System) 

have been used in Maryland as planning tools 

Inter-jurisdictional 

cooperation for purposes of 

load management and TMDL 

application 

Chesapeake Bay Program 

Local Watershed Groups 

where Volunteers lead 

projects; form or engage 

EPA’s Watershed Central provides blog and information: 

http://wiki.epa.gov/watershed/index.php

Anne Arundel County, Maryland Master Watershed Stewards 

Academy 

Fee-in-lieu or off-site 

mitigation when compliance 

on-site is not feasible 

Washington, DC, Proposed Off-Site Stormwater Mitigation Fee

Total Maximum Daily Load 

(TMDL) provides framework 

for prioritizing efforts 

Restoring the Legendary Lynnhaven Oysters: 

Coordinated Actions Lower Bacteria Levels and Reopen 

Shellfish Areas in the Lynnhaven River Watershed, 

www.epa.gov/owow/TMDL/tmdlsatwork/pdf/lynnhaven_river_s

ound_byte.pdf; and 

www.epa.gov/owow/nps/Success319/state/va_3bays.htm

Subdivision

or facility 

campus 

Smart Growth, Conservation 

Development

Arlington, Virginia’s MetroRail Corridor 

Lancaster County, Pennsylvania 

Downtown Silver Spring, Maryland 

Sussex County, Delaware 

Building Lot LID Practices Design guides for LID prepared by federal, state, and, local 

entities 

1 Notes 

2 a. Lal, Harbans, Nutrient Credit Trading: A Market-based Approach for Improving Water Quality 

3 NTSC/NRCS/USDA; www.wsi.nrcs.usda.gov/products/w2q/mkt_based/docs/nitrogen_credit_trading.pdf

4 b. EPA. 2003 Fact Sheet: Water Quality Trading Policy. www.epa.gov/owow/watershed/trading/2003factsheet.pdf;

5 and Water Quality Trading Policy, www.epa.gov/owow/watershed/trading/finalpolicy2003.pdf

6 c. Chesapeake Bay Foundation, Facts About Nutrient Trading from the Chesapeake Bay Foundation, 

7 www.cbf.org/Document.Doc?id=141

8 Table 3-5. Resources for preparing watershed plans 

Reference Information provided 

National Management Measures to Control 

Nonpoint Source Pollution from Urban Areas. 

EPA-841-B-05-004. USEPA 2005. 

Provides overview of elements in developing and 

implementing watershed protection plans 

Handbook for Developing Watershed Plans to 

Restore and Protect our Waters. EPA 841B-08-

002. USEPA 2008. 

Describes processes and tools used to quantify 

existing pollutant loads, develop estimates of load

reductions needed, identify appropriate 

management measures, and track progress 

9 
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Chapter 3. Controlling Urban Runoff 48 

1 The strategy selected for protecting and restoring watershed hydrology depends on the existing 

2 condition of the landscape: new development strategies have a different focus than retrofit 

3 activities in an existing urban landscape. Where redevelopment or infill development occurs, 

4 measures and practices to restore the predevelopment hydrology should be used, but because that 

5 will likely be constrained by existing development features, a different suite of approaches might 

6 be more suitable than those recommended for new development. 

7 2.3.31 New Development and Redevelopment Strategies: Smart Growth, 

8 Conservation Design, and LID

9 The objective in new development is preventing additional runoff, pollutant loading, and the 

10 corresponding degradation in the watershed. Control measures focus first on Smart Growth, 

11 Conservation Design, and the use of LID practices. 

12 Development Planning Techniques such as Smart Growth 

13 New development creates extensive areas of impervious cover, and increased runoff volumes. 

14 The developments are necessarily supported by additional roads and other associated 

15 infrastructure, compounding the effects. Communities should consider the cumulative impact of 

16 large scale development, including the loss of natural areas and degraded streams and rivers. 

17 Decisions about where and how to develop affect water quality perhaps more than any other 

18 factor. Preserving and restoring natural landscape features (such as forests, floodplains, and 

19 wetlands) is an integral part of green infrastructure. Efficient land use such as redevelopment of 

20 already degraded sites can also serve to protect ecologically sensitive areas from development. 

21 Underused shopping centers or excess parking lot area can be targeted for development cost 

22 effectively when considering that the supporting infrastructure is likely already in place.

23 Development planning techniques such as Smart Growth should be used to accomplish the 

24 multiple goals of sound community development with minimum detrimental effects on water 

25 quality. Sound principles of both smart growth and water quality protection can achieved by a 

26 using these approaches for new development, redevelopment, and retrofit. To achieve the 

27 common goals of smart growth and water quality protection, new development should be within 

28 or adjacent to existing development when possible. Examples of guidance to be used in planning 

29 development are provided in Table 3-6. Those documents also contain information on the water 

30 quality benefits that the pollution-avoidance strategies provide. 

31 Table 3-6. Existing guidance on smart growth approaches 

Document Highlights 

Using Smart Growth Techniques as Stormwater Best 

Management Practices,

www.epa.gov/dced/stormwater.htm 

Detail policies and techniques that are integral 

non-structural stormwater practices 

Smart Growth for Clean Water: Helping Communities 

Address the Water Quality Impacts of Sprawl, National 

Association of Local Governmental Environmental 

Professionals, Trust for Public Land, ERG 

www.nalgep.org/publications/PublicationsDetail.cfm?Li

Identifies approaches that can improve water 

quality, profiles successful local partnerships, 

and identifies barriers and solutions to 

implement smart growth for clean water 

programs. 
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Chapter 3. Controlling Urban Runoff 49 

nkAdvID=42157

Protecting Water Resources with Higher-Density 

Development, www.epa.gov/dced/water_density.htm

Provides research and example scenarios of 

how higher densities may better protect water 

quality—especially at the lot and watershed 

levels. 

Water Quality Scorecard: Incorporating Green 

Infrastructure Practices at the Municipal, 

Neighborhood, and Site Scales

www.epa.gov/dced/water_scorecard.htm

Provides policy guidance and case studies for 

protecting open space, promoting infill, 

designing better streets and parking lots, and 

adopting site-level green infrastructure 

practices. 

1 

2 The Smart Growth Network has established the 10 primary principles of Smart Growth, which 

3 are listed in Figure 3-11. Many of these principles indirectly mitigate the impacts of growth on 

4 water resources, but the three listed in bold font, in particular, can be used to reduce or avoid the 

5 stormwater related impacts of both new development and redevelopment. 

• Create Range of Housing Opportunities and Choices: Providing quality housing for people of all 

income levels is an integral component in any smart growth strategy. 

• Create Walkable Neighborhoods: Walkable communities are desirable places to live, work, learn, 

worship, and play and, therefore, are a key component of smart growth. 

• Encourage Community and Stakeholder Collaboration: Growth can create great places to live, work 

and play—if it responds to a community’s own sense of how and where it wants to grow. 

• Foster Distinctive, Attractive Communities with a Strong Sense of Place: Smart growth encourages 

communities to craft a vision and set standards for development and construction that respond to 

community values of architectural beauty and distinctiveness, as well as expanded choices in housing 

and transportation. 

• Make Development Decisions Predictable, Fair and Cost Effective: For a community to be successful 

in implementing smart growth, the private sector must embrace it. 

• Mix Land Uses: Smart growth supports the integration of mixed land uses into communities as a 

critical component of achieving better places to live. 

• Preserve Open Space, Farmland, Natural Beauty and Critical Environmental Areas: Open space 

preservation supports smart growth goals by bolstering local economies, preserving critical 

environmental areas, improving our communities quality of life, and guiding new growth into existing 

communities. 

• Provide a Variety of Transportation Choices: Providing people with more choices in housing, 

shopping, communities, and transportation is a key aim of smart growth. 

• Strengthen and Direct Development Toward Existing Communities: Smart growth directs 

development toward existing communities already served by infrastructure, seeking to use the 

resources that existing neighborhoods offer, and conserve open space and irreplaceable natural 

resources on the urban fringe. 

• Take Advantage of Compact Building Design: Smart growth provides a means for communities to 

incorporate more compact building design as an alternative to conventional, land-consumptive 

development. 

6 Source: The Smart Growth Network: www.smartgrowth.org/about/principles/default.asp?res=1024#top

7 Figure 3-11. The 10 primary principles of smart growth 
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Chapter 3. Controlling Urban Runoff 50 

1 The primary smart growth principles that can be used to reduce the hydrological impacts of 

2 development and redevelopment activities are as follows: 

3 • Conserve Undeveloped Land to preserving critical environmental areas. This maintains 

4 natural riparian buffers, floodplains, natural drainage ways, predevelopment hydrology, 

5 and watershed functions. Protecting natural areas such as forests, grasslands, and 

6 wetlands, and other open spaces that serve to filter, infiltrate, and evapotranspirate 

7 rainfall and snowmelt help maintain the stability of the watershed. 

8 • Use Compact Site Design to reduce the extent of land disturbance, minimize

9 infrastructure requirements to service the community, and reduce the overall impervious 

10 footprint (also see Conservation Design below). 

11 • Direct Development to Existing Communities and Infrastructure to reduce the 

12 development of greenfields. This makes use of existing transportation networks, and 

13 reduces sprawl and the addition of new impervious surfaces. Redevelopment of existing 

14 communities and Brownfields can result in positive water quality impacts and limits the 

15 changes in land cover in undeveloped areas that result in stormwater volume increases 

16 (Refer to Redevelopment Management Sector for additional detail). 

17 2.4 Use Conservation Design and LID Techniques 

18 While planning techniques such as smart growth focus on where to locate development and 

19 redevelopment, techniques such as conservation design promote the best practices to mitigate the 

20 impacts of properly sited development. The design goal is to mitigate the overall hydrologic 

21 modifications by protection of natural areas and ecosystem functions. Conservation design 

22 methods include (City of Portland 2004):

23 • Fitting development to the terrain to minimize land disturbance 

24 • Confining construction activities to the least area necessary and away from critical areas 

25 • Preserving areas with natural vegetation (especially forested areas) as much as possible 

26 • On sites with a mix of soil types, locating impervious areas over less permeable soil (e.g., 

27 till), and trying to restrict development over more porous soils (e.g., outwash) 

28 • Clustering buildings together 

29 • Minimizing impervious areas 

30 • Maintaining and using the natural drainage patterns

31 Existing guidance on Conservation Design is provided in Table 3-7 

32 Implementing these methods often requires an evaluation of institutional issues that influence 

33 growth and development. Using policies requiring compacting development, conserving 

34 open space, and protecting environmental assets is often impeded by zoning requirements 

35 (Arendt 1999). When considering using conservation design policies to protect water 

36 resources, the following zoning issues should examined both to determine if existing policies 

37 are promoting sprawl and to identify impediments that could preclude adoption or 

38 implementation of more environmentally sound designs. 
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Chapter 3. Controlling Urban Runoff 51 

1 Table 3-7. Existing guidance on conservation design approaches 

Document Highlights 

Conservation Design for Stormwater Management: A Design 

Approach To Reduce Stormwater Impacts from Land Development 

and Achieve Multiple Objectives, Delaware Department of Natural 

Resources and Environmental Control and The Environmental 

Management Center of the Brandywine Conservancy, 1997 

www.dnrec.state.de.us/DNREC2000/Divisions/Soil/Stormwater/New/D

elaware_CD_Manual.pdf

Approaches, design procedures, 

and case studies. 

Randall Arendt, Growing Greener: Putting Conservation into Local 

Plans and Ordinances, National Lands Trust-American Planning 

Association-American Society of Landscape Architects, 1999. 

Evaluates the regulatory and 

zoning issues for implementing 

conservation design strategies 

Site Planning for Urban Stream Protection, Tom Schueler/ 

Metropolitan Washington Council of Governments, 1995, 

www.mwcog.org/store/item.asp?PUBLICATION_ID=56

Reduce pollutants and protect 

aquatic resources through 

improved construction site 

planning. 

Center for Watershed Protection 

www.cwp.org/Resource_Library/Better_Site_Design/index.htm

Library of References 

2 

3 • Separate Lot Size from Density. Avoid specifying minimum lot sizes, where 

4 appropriate, because it can promote sprawl and dispersed development patterns, thereby 

5 leading to increased impervious surfaces. Instead, consider specifying the maximum 

6 number of dwellings permitted on the buildable acreage involved or the maximum 

7 buildable acres on a given size parcel to promote cluster development and common, 

8 undivided conservation land. 

9 • Account for Environmental Constraints in Density Calculations. Land that is 

10 unbuildable because of environmental constraints should be discounted from the total 

11 land area used in density calculations. Including only usable land as the basis for density 

12 calculations ensures that intended densities are met and not skewed when developments 

13 satisfy set-aside provisions with inherently unbuildable land.

14 • Establish Minimum Permitted Lot Sizes. The amount of land conserved through 

15 subdivisions is directly related to the permitted difference between maximum density and 

16 the minimum lot size. For example, in a one-acre district where the minimum permitted 

17 lot size is one-half acre of unconstrained land, the remaining unconstrained land plus the 

18 constrained land would compose the open space.

19 • Design Complete, Smart Streets that Minimize Imperviousness. Street design 

20 standards and engineering practices should encourage streets to be no wider than is 

21 necessary to move traffic (cars, pedestrians, bicycles, as is appropriate for the 

22 community) effectively. Shared driveways, reduced driveway widths, two-track 

23 driveways, and rear garages and alleys should be encouraged for all single-family 

24 developments to reduce total impervious area. Encourage designers to use alternative 

25 designs that reduce curb and gutter, or allow curb cuts to enable street drainage into 

26 swales or bioretention. 

27 • Encourage Efficient Provision of Parking. Alternative and flexible parking 

28 requirements (shared parking, off-site parking, etc) should be allowed to reduce parking 
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Chapter 3. Controlling Urban Runoff 52 

1 surface area and flexibility and incentives should be provided to developers to induce a 

2 reduction in parking area. 

3 • Minimize Frontages and Setbacks. Reducing frontages and setbacks conserves land, 

4 reduces impervious surfaces, and helps to promote the creation of more walkable 

5 neighborhoods by bringing buildings closer together to walkable distances.

6 • Establish Minimum Required Open Space. Minimum requirements for open space 

7 help to promote conservation designs, reduce impervious surface area, and can help 

8 enhance the quality and the total amount of land to be preserved.

9 Green Infrastructure/LID Practices 

10 LID is a term used to describe land planning and engineering strategies that are used to manage 

11 stormwater or runoff to preserve or restore the predevelopment hydrologic condition of the site 

12 or development. When LID practices are implemented on a site, significantly less runoff occurs; 

13 therefore, pollutant loading is reduced. 

14 A primary goal is the protection or restoration of water quality and aquatic habitat. EPA and 

15 others also refer to LID as green infrastructure for wet-weather control. Many design guides have 

16 been developed that provide detailed design information on LID practices. Several of those are 

17 listed in the appendix 1 as design tools. The recognized initial leading publication is Low-impact 

18 Development Strategies, An Integrated Design Approach, by Prince George’s County, Maryland, 

19 and EPA, Document Number EPA 841-B-00-003, June 1999. 

20 This approach uses engineered, small-scale hydrologic controls or practices distributed across, 

21 and integrated with, the site or development. A green infrastructure/LID design functions to 

22 replicate the natural hydrology through storage, detention, infiltration, evapotranspiration, or 

23 harvest and use. The objectives are to reduce runoff volume, attenuate peak runoff rates, or filter 

24 and remove pollutants from runoff. By incorporating controls specifically into upland areas, 

25 effects on wetlands and other sensitive areas can be reduced or eliminated. 

26 Many types of LID practices exist, with many variations of each practice. Projects are most 

27 successful when practitioners integrate them into a site design and use them in a treatment train 

28 approach. In such an approach, the overflow from one practice flows into a second or third 

29 practice, such as a green roof followed by a cistern, with the overflow to a planter box with its 

30 own overflow and underdrain. Site conditions, applicable performance requirements, and cost 

31 typically influence the selection of appropriate LID practices. Table 3-8 lists some of the major 

32 types of practices, and a fact sheet or link for each is provided in Section 65. 

33 Table 3-8. Typical LID practices (Fact sheets, or links to fact sheets, 

34 are provided in Section 5)

LID BMPs for site plans

Alternative 

TurnaroundsaBioretention/Bio

infiltration

Permeable Pavement and Pavers

Rainwater Harvesting Conservation EasementsaInfiltration Trenches and 

Basins

Development DistrictsaBlue Roofs with Water Eliminating Curbs and GuttersaGreen Roofs (Eco 
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Chapter 3. Controlling Urban Runoff 53 

Harvesting roofs)

Green Design StrategiesaInfrastructure Planninga

Narrower Residential Streetsa Open Space Designa

Protection of Natural Featuresa Riparian/Forested Buffera 

Street Design and Patternsa Urban Forestrya,b

Site Scale LID Practices

Bioretention (Rain Gardens)a,b Rainwater Harvestingb

Green Roofs (Eco roofs)a,b Blue Roofs with Water Harvestingb

Green Parkinga Grassed Swalesa

Infiltration Trench aInfiltration Basina 

Permeable Interlocking Concrete PavementaPervious Concrete Pavement a

Porous Asphalt Pavement aVegetated Filter Stripa

Soil restorationb Constructed wetlandsb

Compost Blanketsa

1 Notes

2 a. Fact sheet provided at 

3 http://cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=min_measure&min_measure_id=5 

4 b. Fact sheet provided in Section 6 of this chapter

5 The performance of LID practices in reducing the annual volume of runoff varies significantly 

6 according to the specific design of the practice and the regional climate. Depending on the site 

7 design and area rainfall patterns, runoff can be can be maintained at predevelopment conditions 

8 by careful site planning and design. Several design guides have been developed that detail the 

9 procedures for site analysis and LID practice sizing. Some of the best design guides for LID are 

10 provided in Table 3-9. Additional resources are listed in the appendix 1 and in the fact sheets in 

11 Section 6. 

12 Table 3-9. Example nationally applicable LID design methods and manuals 

Prince George’s County, Maryland, Low-Impact Development Design Strategies: An Integrated Design 

Approach, EPA 841-B-00-003, 2000. 

Prince George’s County, Maryland, Low-Impact Development Hydrologic Analysis, EPA 841-B-00-002, 

2000. www.epa.gov/nps/lid/ 

USEPA, Stormwater Best Management Practices Design Guide, Office of Research and Development, 

EPA/600/R-04/121, Volumes 1-3 (121, 121A, 121B), September 2004. 

http://www.epa.gov/nrmrl/pubs/600r04121/600r04121.htm 

Center for Watershed Protection Urban Subwatershed Restoration Manual Series

(http://www.cwp.org/Store/usrm.htm) 

Center for Watershed Protection Managing Stormwater in Your Community: A Guide for Building an 

Effective Post-Construction Program 

(http://www.cwp.org/Resource_Library/Center_Docs/SW/pcguidance/Manual/

PostConstructionManual.pdf)

U.S. Naval Facilities Engineering Command, Low Impact Development, Draft, Unified Design Criteria,

UFC 3-210-10, October 2004. http://www.wbdg.org/ccb/DOD/UFC/ufc_3_210_10.pdf

U.S. Army Corps of Engineers. Low Impact Development for Sustainable Installations: Stormwater 

Design and Planning Guidance for Development within Army Training Areas. Public Works Technical 

Bulletin 200-1-62. October 2008. 
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Chapter 3. Controlling Urban Runoff 54 

Geosyntec Consultants and Wright Water Engineers. Urban Stormwater BMP Performance Monitoring. 

2009. http://www.bmpdatabase.org/MonitoringEval.htm 

The Low-Impact Development Center, http://www.lowimpactdevelopment.org/; several LID manuals 

1 

2 Specific to the Chesapeake Bay area, a literature review and assessment of the reported 

3 performance of many LID practices was recently conducted for the region to estimate the 

4 capability of the practices for volume control and pollutant reduction. The Mid-Atlantic Water 

5 Program housed at the University of Maryland reviewed and compiled effectiveness estimates 

6 for BMPs implemented and reported by the Chesapeake Bay watershed jurisdictions (Developing 

7 Best Management Practice Definitions and Effectiveness Estimates for Nitrogen, Phosphorus, 

8 and Sediment in the Chesapeake Bay, December 2009 

9 (www.chesapeakebay.net/websitesearchresults.aspx?menuitem=19557). The report estimates 

10 that the performance of the infiltration practices such as bioretention, as designed and with safety 

11 factor considerations, could reduce runoff from the first 1 - inch to 1.5 inch of runoff up to 80 

12 percent, for the purposes of conservatively estimating wide-scale effectiveness in the region. 

That equates to about the 85th to 95th 13 percentile storm event in the region. Additional information 

14 on these findings are provided in Section 6.1.2 Performance estimate summaries for Infiltration 

15 Practices, and in the Bioretention fact sheet in Section 6.

16 By using design procedures outlined in the LID manuals such as those in Table 3-9 and in 

17 appendix 1 of this document, practices can achieve runoff reduction to restore or maintain 

18 predevelopment hydrology. 

19 The effectiveness of conservation design with LID in reducing runoff is demonstrated in 

20 subdivision-wide results recently reported. Sources for information on existing LID subdivisions 

21 are provided in Table 3-10. 

22 Table 3-10. Sources of information on existing LID subdivisions 

Name, location, and reference Performance summary 

Meadow on the Hybelos, 8.27-acres Puget Sound 

area in Pierce County, Washington. 

www.sldtonline.com/content/view/344/75

2007 to 2008: LID subdivision designs performed 

better than design objectives, and exceeded the 

local requirement that post-development discharge 

volume not exceed predevelopment discharge 

volume. The researchers also reported that that 

underdrains significantly impair hydrologic 

performance (WERF 2009). 

Cross Plains, WI; Burnsville, MN; Somerset, MD: 

Jordon Cove, CT (ASCE/WERF/EPA International 

Stormwater BMP Database, Urban Stormwater 

BMP Performance Monitoring—Geosyntec 

Consultants and Wright Water Engineers 2009).

www.bmpdatabase.org

Annual runoff reductions from 40% to 90% over the 

monitoring period were observed, with significantly

reduced performance when rain events occurred 

under already saturated conditions. 

23 
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Chapter 3. Controlling Urban Runoff 55 

1 2.5 Evaluate Codes and Ordinances

2 LID approaches and practices, smart growth and conservation development strategies can all be 

3 hindered by existing codes and ordinances often because of the lack of understanding of the 

4 practices that in some cases differ from the traditional stormwater management approaches used 

5 in land management. Resources that planners, municipal officials, and designers can use to 

6 evaluate codes and ordinances for revision to accommodate these approaches are provided in 

7 Table 3-11. 

8 Table 3-11. Resources for evaluating codes and ordinances 

Water Quality Scorecard: Incorporating Green 

Infrastructure Practices at the Municipal, Neighborhood, 

and Site Scales, 

www.epa.gov/dced/water_scorecard.htm%20%20

Provides policy guidance and case studies for 

protecting open space, promoting infill, 

designing better streets and parking lots, and 

adopting site-level green infrastructure 

practices. 

Out of the Gutter, National Resources Defense Council, 

July 2002 

http://www.nrdc.org/water/pollution/gutter/gutter.pdf

NRDC recommends LID, for Washington, DC, 

including specific observation and 

recommendations for revisions to existing codes 

and ordinances. 

A Catalyst for Community Land Use Change , National 

NEMO Network 2008 Progress Report: 

http://nemonet.uconn.edu/about_network/publications/2

008_report.htm

Examples of local regulations for water quality 

protection 

Puget Sound Partnership Low Impact Development 

Local Regulation Assistance 

www.psp.wa.gov/Project

Assistance to help local governments integrate 

LID into their development standards and 

regulations. 

Better Site Design: A Handbook for Changing 

Development Rules in Your Community, Center for 

Watershed Protection, 1998 

www.cwp.org/Store/bsd.htm

Examples and case studies for changing 

development regulations to promote better site 

design, also referred to as environmentally 

sensitive design or LID 

Plan Review checklist and flow chart, Office of 

Watersheds, Philadelphia Water Department: 

www.phillyriverinfo.org/WICLibrary/%20DevelopmentPr

ocess_Final.pdf

Example of how to prioritize stormwater 

planning early in the overall plan review process 

for development projects. 

Audit of Pavement Standards for the Saluda-Reedy 

Watershed, Mitigating the Impacts of Impervious 

Surfaces in Greenville and Pickens Counties, South 

Carolina, Saluda-Reedy Watershed Consortium c/o 

Upstate Forever, 2006. www.upstateforever.org

Identifies opportunities for flexibility in street 

width, parking ratios, sidewalk and driveway, 

and other aspects of paving. 

9 

10 The following list contains the most common elements of local codes and ordinances that can 

11 cause unnecessary construction of impervious surface areas (CWP 1998 Water Quality 

12 Scorecard; USEPA 2009). Communities should carefully review existing policy mechanisms to 

13 determine opportunities to revise codes and ordinances to reduce water resource effects that can 

14 result from creating impervious surfaces: 
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Chapter 3. Controlling Urban Runoff 56 

1 • Zoning ordinances can be used to specify the type and intensity of land uses allowed on a 

2 parcel. Some zoning ordinances are used to dictate single-use, low-density uses such as 

3 residential. Dispersing low-density development across the watershed can negatively 

4 affect receiving waters by constructing significantly more impervious surfaces. 

5 • Subdivision codes or ordinances can be used to specify development requirements for a 

6 parcel. Housing footprint minimums, setback distances from the street, road width, street 

7 configuration, open space requirements, and lot size are all often specified in subdivision 

8 codes and often inadvertently require constructing unnecessary impervious cover. 

9 • Street standards or road design guidelines are used to dictate the width of the road, 

10 turning radius, street connectivity, and intersection design requirements. Communities 

11 should review street and road standards to determine if road designs can be changed to 

12 reduce impervious surface cover and still meet transportation and safety requirements. 

13 • Parking requirements are generally set to the minimum, not the maximum, number of 

14 parking spaces required for retail and office parking. Setting minimums often leads to 

15 designing parking lots with enough peak demand periods, such as the day after 

16 Thanksgiving, which can create acres of unused pavement during the rest of the year. 

17 • Setbacks are used to define the required distance between a building and the right-of-way 

18 or lot line. Many setback requirements specify the use of long driveways especially when 

19 large lots are a requirement for development. Establishing maximum setback lines for 

20 residential and retail developments can reduce the creation of unnecessary impervious 

21 surface areas by bringing buildings closer to the street. 

22 • Height limitations are used to limit the number of floors in a building. Limiting height 

23 can spread development out if square footage is unmet by vertical density. 

24 • Open space or natural resource plans are used to identify land parcels that are or will be 

25 set aside for recreation, habitat corridors, or preservation. Such plans help communities 

26 prioritize their conservation, parks, and recreation goals and protect important areas from 

27 development. 

28 • Comprehensive plans might be required by state law, and many cities, towns, and 

29 counties prepare comprehensive plans to support zoning codes. Most comprehensive 

30 plans include elements that are intended to address land use, open space protection or 

31 creation, natural resource protection, transportation, economic development, and housing. 

32 These elements are important facets of a comprehensive watershed protection approach. 

33 Increasingly, local governments are identifying areas of existing green infrastructure and 

34 outlining opportunities to add new green infrastructure throughout the community to 

35 protect water resources. 

36 2.6 Evaluate Transportation-related Standards

37 Minimize/reduce impervious areas by using techniques such as reduced street widths 

38 and parking areas

39 One direct method of addressing impervious area is to physically limit the size of the impervious 

40 area. These strategies are most often applied when designing road widths and parking areas. 

41 Many urban and suburban streets are sized to meet code requirements for emergency service 
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Chapter 3. Controlling Urban Runoff 57 

1 vehicles, on-street parking, and free flow of traffic. Such code requirements often result in streets 

2 being oversized for their typical everyday functions. The Uniform Fire Code requires that streets 

3 have a minimum 20 feet of unobstructed width; a street with parking on both sides would require 

4 a width of at least 34 feet. In practice, many suburban and urban streets can be much wider than 

5 that as local design practices have increased street widths to 40 and 50 feet. Those designs result 

6 in increased runoff and associated pollutant loadings. 

7 Many communities have adopted narrower street width standards while also accommodating 

8 emergency vehicles by developing alternative street-parking configurations, designing adequate 

9 turnarounds, prohibiting parking near intersections, providing vehicle pullout space, and using 

10 smaller block lengths. Examples are provided in Table 3-12. A key to identifying and 

11 successfully codifying narrow street widths is coordination among departments, including fire, 

12 transportation, and public works. 

13 Table 3-12. Examples of adopted narrow street widths 

Jurisdiction 

Street width 

(feet) Parking condition 

Phoenix, AZ 28 parking both sides 

Santa Rosa, CA 30

26–28

20

20

parking both sides, < 1,000ADT

parking one side

no parking

neck downs @ intersection

Orlando, FL 28 

22 

parking both sides, res. Lots < 55 feet wide 

parking both sides, res. Lots > 55 feet wide 

Birmingham, MI 26 

20 

parking both sides 

parking one side 

Howard County, MD 24 parking unregulated 

Kirkland, WA 12 

20 

24 

28 

alley 

parking one side 

parking both sides—low-density only 

parking both sides 

Madison, WI 27 

28 

parking both sides, <3DU/AC 

parking both sides, 3-10 DU/AC 

ADT: Average Daily Traffic; DU/AC: dwelling units per acre

Source: Adapted from Cohen 2000, and CWP 1998. 

http://www.stormwatercenter.net/Assorted%20Fact%20Sheets/Tool4_Site_Design/narrow_streets.htm

14 The same principles apply to parking areas. Zoning requirements often require that parking be 

15 provided for the maximum business day, resulting in unused parking and impervious area for the 

16 majority of the year. Reassessing the actual needed parking area can minimize impervious area. 

17 Green street and highway design is necessary to help mitigate the effects of stormwater runoff 

18 from those surfaces. A proven example of a green street is Seattle’s pilot Street Edge 

19 Alternatives Project (SEA Streets), completed in 2001. It is an LID design that provides drainage 

20 that more closely mimics the natural landscape before development .Seattle Public Utilities 

21 accomplished this by reducing impervious surfaces to 11 percent less than a traditional street, by 
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Chapter 3. Controlling Urban Runoff 58 

1 providing surface detention in swales, and adding more than 100 evergreen trees and 1,100 

2 shrubs. Monitoring shows that the design has successfully reduced the volume of stormwater 

3 runoff by 99 percent. http://www.seattle.gov/util/About_SPU/Drainage_&_Sewer_System/

4 GreenStormwaterInfrastructure/NaturalDrainageProjects/StreetEdgeAlternatives/index.htm. 

5 Resources for additional information on street and highway design for LID is provided in 

6 Table Table 3-13. 

7 Table 3-13. Resources for information on street and highway design for LID 

Document Highlights 

Green Highway Partnership (GHP), with weekly 

electronic newsletter, www.greenhighways.org

Tracks practices for green highways and green 

infrastructure, including innovative storm water 

management, LID and transportation 

legislation. 

Project 25-20(01): Evaluation of Best Management 

Practices for Highway Runoff Control, Low Impact 

Development Highway Manual, National Cooperative 

Highway Research Program, 

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_56

5.pdf 

Provides scientific and economic information 

for selection and design of best management 

practices (BMPs) to control highway runoff, 

including BMPs to treat: nutrients, TPH, PAH, 

metals, pathogens, pesticides, temperature, 

TSS, trash 

Anacostia Waterfront Transportation Architecture 

Design Standards 

http://ddot.dc.gov/ddot/cwp/view,a,1249,q,627063,ddotN

av_GID,1744,ddotNav,|33960|.asp

Guidelines for transportation design to support 

the economic and environmental health of the 

region, incorporating LID design practices. 

Portland Green Street Program, Portland, Oregon, 

Bureau of Environmental Services (BES) 

www.portlandonline.com/BES/index.cfm?c=44407

Design information, project reports, technical 

guides, newsletter 

Tabor to the River, Portland BES 

www.portlandonline.com/bes/index.cfm?c=47591

Comprehensive, 500-street, watershed retrofit 

program detailed. 

Natural Drainage Projects, Seattle, Washington, Seattle 

Public Utilities (SPU), 

www.seattle.gov/util/naturalsystems

Design information and details on LID street 

design and elements, porous pavement 

specification, project reports 

8 2.7 

9 Minimize directly connected impervious areas 

10 Not all impervious areas are created equal. Impervious areas that are directly connected to the 

11 storm sewer system convey excess stormwater volumes more rapidly and with greater impact 

12 than impervious areas that do not have a direct connection (i.e., disconnected). The term effective 

13 impervious area (EIA) is used to describe this concept. EIA is the measure of how much 

14 impervious surface is directly connected to the conveyance system. One of the first steps to 

15 mitigating the effects of imperviousness is evaluating the opportunities to disconnect it so the 

16 rain can be infiltrated, evapotranspired, or harvested and used. 

17 • Downspout Disconnection. Downspout disconnection is the process of separating roof 

18 downspouts from the sewer system and redirecting roof runoff onto pervious surfaces, 

19 most commonly a lawn, or to a stormwater management practices such as a bioretention 

20 cell or cistern. 
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Chapter 3. Controlling Urban Runoff 59 

1 • Product Substitution. Using permeable pavements can reduce directly connected 

2 impervious area because pervious materials are substituted for impervious materials 

3 while maintaining the intended function. Permeable pavements can be used to infiltrate 

4 stormwater, making areas that were once a source of stormwater a means of reducing the 

5 volume of runoff. Similarly, green roof retrofits reduce the imperviousness of rooftops by 

6 using engineered soil media and vegetation to lower the runoff potential. 

7 • Maximizing Opportunities to Infiltrate, Evapotranspirate, and Harvest and Use.

8 Infiltration and evapotranspiration is often accomplished by incorporating bioretention 

9 into street designs. Bioretention offers an effective multipurpose stormwater management 

10 strategy. Bioretention features can be tree boxes that collect stormwater runoff from the 

11 street (similar to conventional tree boxes), planter boxes, curb extensions, or bioswales. 

12 To adapt to street configurations, grades, soil conditions, and space availability, a range 

13 of shapes, sizes, and layouts can be used. Using existing rights-of-way and using 

14 techniques such as curb cuts to facilitate stormwater movement are common practices. 

15 Rainwater harvesting has recently become recognized as a stormwater management tool because 

16 of its ability to reduce stormwater runoff volumes from impervious surfaces. It also serves as a 

17 source substitute for potable water and can enhance water supplies and decrease the cost and 

18 impacts of supplying water to urban areas. Collected rainwater is ideal for nonpotable 

19 applications, such as landscape irrigation, toilet and urinal flushing, cooling system make-up, and 

20 vehicle washing. Such collection and use is a key component of an integrated water resources 

21 management approach. Performance of rainwater harvesting systems depends on the volume of 

22 water stored and the demand for the stored water.

23 Rainwater harvesting has been practiced by civilizations for centuries, and is now actively used 

24 in many countries that experience chronic or seasonal water shortages. In this country, though, 

25 rainwater harvesting has been primarily used for flash flooding control, or otherwise managing 

26 drainage problems. Now, in states such as Georgia, Virginia, and Texas, government-supported 

27 organizations have prepared manuals and guidelines for residential and commercial water 

28 harvesting for drought preparedness. In the Northwest, residential and commercial rainwater 

29 harvesting is used for stormwater management. In western cities, rainwater harvesting is 

30 becoming more common—Los Angeles County and Tucson, Arizona, for example—but water 

31 rights issues could restrict its use in some states.

32 Design and installation manuals relevant to the Chesapeake Bay area, references to example city 

33 ordinances, and other information on rainwater harvesting is provided in the fact sheet in 

34 Section 6.

35 2.8 Implement Restoration

36 2.8.1 Urban Tree Canopy

37 Use LID Practices: Infiltration/evapotranspiration with increased urban tree canopy

38 Significant potential exists to reduce runoff volumes on an annual basis using increased urban 

39 tree canopy (UTC). Interception in the tree canopy provides some capture in small events, but 
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Chapter 3. Controlling Urban Runoff 60 

1 trees can evapotranspirate significant amounts—up to 200 to 800 gallons per day for some 

2 mature tree species (ITRC 2009). Each deciduous tree in the Baltimore area in the 2009 weather 

3 pattern evapotranspired (in leaf-on period) approximately (personal communication, David 

4 Nowak, U.S. Forest Service):

5 • 2.6 gallons/day for a small tree (1 m radius crown)

6 • 260 gallons/day for a large tree (10 m radius crown) 

7 For dense urban environments—and where utility conflicts can be managed—new technologies 

8 include 

9 • Structures or structural soils that allow root growth under sidewalks and vehicle areas. 

10 • Permeable pavements that enable stormwater to flow to roots while supporting loads; 

11 • Flexible sidewalk material (example: Belleview, Washington, 

12 http://www.ci.bellevue.wa.us/rubber_sidewalk.htm,

13 • Large-diameter soaking hoses or vaults built into tree pits that collect and infiltrate a first 

14 portion of runoff for evapotranspiration. 

15 Using those technologies, little or no additional land is consumed in managing stormwater.

16 Converting paved areas or compacted turf to functional conservation landscaping can also 

17 improve infiltration and some street tree maintenance issues can be better managedreduce runoff. 

18 Native grasses and shrubs with deep roots and more leaf area evapotranspirate more than turf and 

19 help keep the soil from compacting, allowing more infiltration. 

20 To estimate the effectiveness of adding urban tree canopy and green roofs at reducing the 

21 stormwater runoff volumes in a dense urban environment, Casey Trees and LimnoTech 

22 developed the Green Build-out Model to quantify the stormwater benefits of trees and green 

23 roofs for different coverage scenarios in Washington, DC. The model was applied to an intensive 

24 greening scenario and a moderate greening scenario. Nearly all the waters in Washington, DC,

25 are seriously polluted by urban stormwater runoff and the sewage overflows it causes. The Green 

26 Build-out Model demonstrates that trees and green roofs—just a portion of the types of 

27 infrastructure practices available—can be used to achieve substantial reductions in stormwater 

28 runoff and sewage discharges to the rivers. Key findings show for an average year 

29 • The intensive greening scenario eliminates more than 1.2 billion gallons of stormwater 

30 • Reductions in stormwater runoff volume of up to 10 percent across the city, with up to 27 

31 percent reductions in individual sewersheds under the most intensive greening scenario 

32 • The DC Water and Sewer Authority could realize between $1.4 and $5.1 million per year 

33 in annual operational savings in the area because of reduced pumping and treatment 

34 costs. 

35 • General hydrological relationships, including unit area planning factors, and modeling 

36 methodologies that are transferable to other municipalities. 
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Chapter 3. Controlling Urban Runoff 61 

1 Using trees to help managing stormwater and protect water quality is becoming accepted by 

2 some engineers and land managers as sustainability becomes more important in land design. A 

3 statement by the Chesapeake Bay Executive Council in 2006 emphasizes the point. 

4 Forests are the most beneficial land use for protecting water quality, due to their 

5 ability to capture, filter, and retain water, as well as air pollution from the air. 

6 Forests are also essential to the provision of clean drinking water to over 10 

7 million residents of the watershed and provide valuable ecological services and 

8 economic benefits including carbon sequestration, flood control, wildlife habitat, 

9 and forest products. 

10 A summary of resources for estimating stormwater management benefits of tree canopy are 

11 provided in Table 3-14. Additional information is provided in the Reforestation/Urban Forestry 

12 and Bioretention Fact Sheets in Section 6. 

13 Table 3-14. Resources for estimating stormwater benefits of tree canopy and vegetation 

Citygreen software by American Forests 

www.americanforests.org/productsandpubs/citygreen

Trees Reduce Stormwater website by American Forests 

www.americanforests.org/graytogreen/stormwater

Analyzes the ecological and economic 

benefits of tree canopy and other green 

space 

i-Tree suite of software Tools from USDA Forest Service 

www.itreetools.org

Tools enable quantification on a per tree 

basis or on a watershed scale 

Phytotechnology Technical and Regulatory Guidance, 

The Interstate Technology & Regulatory Council, 2009 

Provides guidance on using vegetation for 

soil remediation, and estimates of 

transpiration rates. 

Casey Trees, Washington, D.C. Green Build-out Model

www.caseytrees.org/planning/greenerdevelopment/gbo/index.php

The Green Build-out Model demonstrated 

that trees and green roofs can be used to 

achieve substantial reductions in stormwater 

runoff and sewage discharges to the rivers. 

14 

15 2.8.2 Streams, Floodways, and Riparian Areas

16 Use LID Practices: Rainwater Harvesting

17 Rainwater harvesting has recently become recognized as a stormwater management tool because 

18 of its ability to reduce stormwater runoff volumes from impervious surfaces. It also serves as a 

19 source substitute for potable water and can enhance water supplies and decrease the cost and 

20 impacts of supplying water to urban areas. Collected rainwater is ideal for nonpotable 

21 applications, such as landscape irrigation, toilet and urinal flushing, cooling system make-up, and 

22 vehicle washing. Such collection and use is a key component of an integrated water resources 

23 management approach. Performance of rainwater harvesting systems depends on the volume of 

24 water stored and the demand for the stored water.

25 Rainwater harvesting has, of course (1) been practiced by civilizations for centuries, and (2) is 

26 now actively used in many countries that experience chronic or seasonal water shortages. In this 

27 country, though, rainwater harvesting has been primarily used for flash flooding control, or 
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1 otherwise managing drainage problems. Now, in states such as Georgia, Virginia, and Texas, 

2 government-supported organizations have prepared manuals and guidelines for residential and 

3 commercial water harvesting for drought preparedness. In the Northwest, residential and 

4 commercial rainwater harvesting is used for stormwater management. In western cities, 

5 rainwater harvesting is becoming more common—Los Angeles County and Tucson, Arizona, for 

6 example—but water rights issues could restrict its use in some states.

7 Design and installation manuals relevant to the Chesapeake Bay area, references to example city 

8 ordinances, and other information on rainwater harvesting is provided in the fact sheet in 

9 Section 6.

10 Restore streams, floodways, and riparian areas

11 Using stream and floodplain restoration, managers attempt to restore the ecological and 

12 hydrological functions and processes of a stream and its floodplain. The stream corridor is 

13 typically considered to consist of the stream channel, riparian zone, and flood plains (level areas 

14 near the channel, formed by the stream and flooded during moderate-to-high flow events). 

15 Stream corridors are influenced by the cumulative effects of upland and upstream activities and 

16 practices, including agricultural production, forestry, recreation, other land uses, or urban 

17 development. Specific restoration goals can include flood control, sediment control, improving 

18 drainage, stabilizing banks, and improving habitat. Figure 3-12 shows the effect of increasing 

19 urbanization on stream channel erosion and floodplain disconnection. Correcting stream damage 

20 using stream restoration techniques is a costly undertaking with uncertain rewards; preventing 

21 the damage by using the techniques described in this guidance is a more reliable approach.

22 
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Chapter 3. Controlling Urban Runoff 63 

1 

2 Figure 3-12. Impacts of urbanization on stream channel erosion and floodplain disconnection. 

3 Restoring impaired waterways is important to restoring predevelopment hydrology and reducing 

4 loading from larger and scouring flows. Degraded streams can themselves become a source of 

5 downstream pollution, such as when Pphosphorus-laden sediments are mobilized during high6 flow events. In such cases, stream restoration can be a useful strategy to improve downstream 

7 water quality. However, it is important to keep in mind that the elevated flows causing sediment 

8 mobilization must also be addressed. Stream stabilization requires restoration of the stream’s 

9 energy signature. The predevelopment hydrology of the watershed shouldmust be restored to 

10 regain the predevelopment character of the stream; however, in existing urban areas that might 

11 be a longer-term goal. 

12 A summary of existing information of the effects of stream hydromodification on the quality of 

13 the Chesapeake Bay is provided in Table 3-15. The studies demonstrate the importance of stream 
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Chapter 3. Controlling Urban Runoff 64 

1 restoration and protection in achieving pollutant reduction in the Chesapeake Bay, particularly 

2 for sediment and the Pphosphorus that accompanies sediment loading. 

3 Table 3-15. Studies quantifying the impact of sediment loading stream hydromodification on 

4 Chesapeake Bay water quality 

Study Findings 

A Summary Report of Sediment Processes in 

Chesapeake Bay and Watershed, U.S. Geological 

Survey, Water-Resources Investigations Report 03-4123, 

2003 

Summarizes the impacts and sources of 

sediment and notes that sediment yield from 

urbanized areas can remain high after active 

construction is complete because of increased 

stream corridor erosion from altered hydrology 

Schueler, Thomas, et.al, The Practice of Watershed 

Protection, Technical Note #119 from Watershed 

Protection Techniques 3(3):729–734, Center for 

Watershed Protection, 2000. 

Stream enlargement, and the resulting transport 

of excess sediment, is caused by urban 

development 

U.S. Environmental Protection Agency. 2001. Protecting 

and Restoring America’s Watershed’s: Status, Trends, 

and Initiatives in Watershed Management, EPA 840-R00-001. 

www.epa.gov/owow/nps/urbanm/pdf/urban_guidance.pdf.

Straightened and channelized streams carry 

more sediments and other pollutants to their 

receiving waters. Up to 75% of the transported 

sediment from the Pocomoke watershed on the 

Eastern Shore of Maryland was found to be 

erosion from within the stream corridor 

Gellis, Allen C., et. al. Synthesis of U.S. Geological 

Survey Science for the Chesapeake Bay Ecosystem and

Implications for Environmental Management, Chapter 6: 

Sources and Transport of Sediment in the Watershed. 

2007, U.S. Geological Survey Circular 1316. 

Sediment sources are throughout the 

Chesapeake Bay watershed, with more in 

developed and steep areas 

Gellis, A.C., et al, 2009, Sources, transport, and storage 

of sediment in the Chesapeake Bay Watershed. U.S. 

Geological Survey Scientific Investigations Report 2008–

5186 

In the Piedmont region, streambank erosion 

was a major source of sediment in developed 

Little Conestoga Creek; 30% of sediment from 

the Mattawoman Watershed on the Coastal 

Plain (flat land) is from streambanks 

Devereux, Olivia H., et al., Suspended-sediment sources 

in an urban watershed, Northeast Branch Anacostia 

River, Maryland. Hydrological Processes, Accepted 

2009. 

Streambank erosion was the primary source of 

sediment in the Northeast Branch Anacostia 

River

5 

6 Stream restoration can help to restore the natural ecosystem function of Nnitrogen removal that 

7 occurs in streams. Studies that evaluate the Nnitrogen removal ability of restored streams are 

8 summarized in Table 3-16. 

9 In addition to the water quality improvements that can be achieved through stream restoration, 

10 the flood management community has become increasingly aware of the benefits of restoration 

11 in preventing flood damages. The Association of State Floodplain Managers has prepared a 

12 white paper called Natural and Beneficial Floodplain Functions: Floodplain Management—

13 More than Flood Loss Reduction (www.floods.org), which emphasizes the multiple benefits of 

14 protecting and restoring streams and their associated floodplains. 

15 
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Chapter 3. Controlling Urban Runoff 65 

1 Table 3-16. Studies evaluating the Nnitrogen removal ability of restored streams in the 

2 Chesapeake Bay watershed 

Study Finding 

Kausal, Sujay S., et.al. Effects of Stream 

Restoration on Denitrification in an Urbanizing 

Watershed. Ecological Applications, 18(3), 2008, 

pp. 789-804. 

Streams with ecological functions intact remove 

Nnitrogen at a much higher rate than degraded 

urban streams, and stream restoration practices 

can restore this Nnitrogen removal function. 

Klocker, Carolyn A, et. al. Nitrogen uptake and 

denitrification in restored and unrestored streams in 

urban Maryland, USA. Aquatic Sciences, Accepted 

October 2009.

Degraded urban streams, deeply eroded and 

disconnected from their floodplain have 

substantially lower rates of Nnitrogen removal that 

than streams hydraulically connected to their 

riparian banks via low slopes, and reconnecting the

stream to the floodplain can increase. 

3 

4 Techniques for stream and floodplain restoration are described in the Hydromodification section 

5 of this document. Example references for stream restoration, and for information on the effects 

6 of urban runoff on stream ecosystems, are provided in Table 3-17. 

7 Table 3-17. References on urban stormwater effects on streams with emphasis on restoration and 

8 habitat 

USDA Natural Resources Conservation Service, Part 654 Stream Restoration Design 

National Engineering Handbook, 210–VI–NEH, August 2007 

Federal Interagency Stream Restoration Working Group (FISRWG) (1998). Stream Corridor Restoration: 

Principles, Processes, and Practices, ISBN-0-934213-60-7, Distributed by the National Technical 

Information Service at 1-800-533-6847. 

Infiltration vs. Surface Water Discharge: Guidance for Stormwater Managers, Final Report. 03-SW-4, 

Water Environment Research Federation (WERF 2006) Appendix B. Assessment of Existing Watershed 

Conditions: Effects on Habitat. 

9 

10 2.9 Reduce Impacts of3.2 For Existing Urban Areas

11 2.9.1 (i.e., Retrofits)

12 Many urban areas were developed without any or with few stormwater controls designed to 

13 protect water quality and prevent stream channel degradation. This section of the document 

14 contains recommendations for practices that can be used in such areas to try to reverse 

15 degradation that has already occurred in the past by reducing the volume, rates, and duration of 

16 runoff. Specifically, the recommended control measures on existing urban land focus on retrofits 

17 to roof downspouts, roads, parking lots, and areas of compacted soils. 

18 An effective retrofit strategy for urbanized areas combines planning techniques such as smart 

19 growth and green infrastructure/LID techniques. A comprehensive guide on retrofits for existing 

20 urban areas is the Center for Watershed Protection’s Urban Stormwater Retrofit Practices (CWP 

21 2007). 
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Chapter 3. Controlling Urban Runoff 66 

1 The CWP Urban Stormwater Retrofit Practices manual focuses on stormwater retrofit practices 

2 that can capture and treat stormwater runoff before it is delivered to the stream. The manual 

3 describes both off-site storage and on-site retrofit techniques that can be used to remove 

4 stormwater pollutants, minimize channel erosion, and help restore stream hydrology. Guidance 

5 on choosing the best locations in a subwatershed for retrofitting is provided in a series of 13 

6 profile sheets. The manual then presents a method to assess retrofit potential at the subwatershed 

7 level, including methods to conduct a retrofit inventory, assess candidate sites, screen for priority 

8 projects, and evaluate their expected cumulative benefit. The manual concludes by offering tips 

9 on retrofit design, permitting, construction, and maintenance considerations. 

10 Table 3-18 presents common locations where additional storage and infiltration for stormwater 

11 can be provided in a subwatershed, and also common locations for on-site retrofits. 

12 Table 3-18. Common locations for additional stormwater storage and infiltration and on-site 

13 retrofits 

Common on-site retrofit locations in a subwatershedCommon Storage Retrofit Locations

Common On-Site Retrofit Locations in a Subwatershed

Where How 

Road Right of 

Ways 

Direct runoff to a depression or excavated stormwater bioretention/infiltration treatment 

area within the right-of-way of a road, highway, transport or power line corridor. 

Prominent examples include highway cloverleaf, median and wide right-of-way areas. 

Near Large 

Parking Lots 

Provide stormwater infiltration treatment in open spaces near the downgradient outfall 

of large parking lots (5 acres plus). 

Conveyance 

Systems 

Investigate the upper portions of the existing stormwater conveyance systems (such as 

ditches) to look for opportunities to improve the performance. That can be done either 

by creating in-line storage cells (small dams with overflows) that allow infiltration or by 

splitting flows to off-line infiltration/treatment areas in the drainage corridor 

Hotspot 

Operations 

Install filtering or bioretention treatment to remove pollutants from confirmed or severe 

stormwater hotspots discovered during field investigation 

Small Parking 

Lots 

Insert stormwater treatment, preferably depressed bioretention or expanded tree boxes, 

in or on the margins of small parking lots (less than 5 acres). In many cases, the 

parking lot is delineated into a series of smaller, on-site treatment units. 

Individual Streets Look for opportunities with the street, its right-of-way, cul-de-sacs and traffic calming 

devices to infiltrate and treat stormwater runoff before it gets into the street storm drain 

network 

Individual 

Rooftops 

Disconnect downspouts from storm drains, store and use the rainwater, and infiltrate 

excess stormwater runoff close to the source 

Little Retrofits Convert or disconnect isolated areas of impervious cover to infiltration and bioretention, 

and treat excess runoff in an adjacent pervious area using low tech approaches such as 

a filter strip 

Hardscapes 

Landscapes 

Reconfigure the drainage of high-visibility urban landscapes, plazas, and public spaces 

to capture and use, infiltrate and evapotranspirate, and treat excess stormwater runoff 

with landscaping and other urban design features. 

Underground Provide stormwater infiltration or treatment in an underground location when no surface 

land is available for surface treatment. Use this as a last resort at dense, ultra-urban 

sites. 

14 
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Chapter 3. Controlling Urban Runoff 67 

1 Examples of LID road retrofits in the Chesapeake Bay watershed are included in Table 3-19.

2 Table 3-19. Examples of Maryland LID road retrofits

Site Reference 

Knollbrook Drive and Talbert 

Lane median and the Ray Road 

stormdrain outfall in the 

Takoma Branch subwatershed 

Final Technical Report, Pilot Projects for LID Urban Retrofit Program, In 

the Anacostia River Watershed, Phase IV, USEPA: Prince Georges 

County, Maryland, 2007 

U.S. Route 1 and Maryland 

Route 201 at I-95 (Bioretention) 

www.princegeorgescountymd.gov/Government/AgencyIndex/DER/ESG/

pdf/Final Technical Report Phase III.pd

Decatur Street Improvement, 

Edmonston, MD (holistic green 

street—multiple LID retrofits) 

www.lowimpactdevelopment.org/greenstreets/projects.htm; 

http://edmonston.us.com/GreenStreetGroundbreaking.html

Route 202 Median 

(Bioretention) 

www.co.pg.md.us/Government/AgencyIndex/GoingGreen/pdf/2009-

annual-green-report.pdf

Route 201 Median 

(Bioretention) 

www.co.pg.md.us/Government/AgencyIndex/GoingGreen/pdf/2009-

annual-green-report.pdf

Peace Cross Green Highway 

Project—NW Prince 

George’s County, adjacent to 

the Anacostia River. Network: 

• Baltimore Avenue 

• Bladensburg Road 

• Annapolis Road 

www.princegeorgescountymd.gov/Government/AgencyIndex/DER/ESG/

pdf/Final%20Technical%20Report_Phase%20III.pdf

www.springerlink.com/content/l682122767u41k7x/fulltext.pdf

Route 202/I-495 interchange 

(Bioretention) 

www.co.pg.md.us/Government/AgencyIndex/GoingGreen/pdf/2009-

annual-green-report.pdf

3 

4 2.10.2 Redevelopment

5 Implementation of an effective redevelopment program is essential to restoring water quality, as 

6 discussed previously in this document. Section 4 of this guidance provides information on 

7 important issues that should be addressed in redevelopment policies, and example practices that 

8 are appropriate for redevelopment. Figure 3-13 lists the stormwater retrofit and redevelopment 

9 programs that several cities have adopted or are piloting using green infrastructure/LID 

10 approaches. Implementation measures for redevelopment programs include establishing 

11 appropriate redevelopment performance standards, creating an inventory of appropriate 

12 mitigation practices for a range of project sizes, conducting site assessments as part of practice 

13 selection, review of codes and ordinances, implementing demonstration projects, providing It 

14 also lists information on incentives, maximizing forest canopy, and mitigating compacted soils. 
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Chapter 3. Controlling Urban Runoff 68 

1 

2 

3 Figure 3-13. Municipal stormwater retrofit/redevelopment programs. 

4 2.104 Costs of Green Infrastructure/LID Practices 

5 Cost is a primary factor in selecting stormwater management practices. The most important LID 

6 practices, i.e., good development planning practices that minimize effects, do not cost more and 

7 provide multiple other benefits in addition to water quality. When selecting stormwater 

8 management practices or implementing policy decisions, consider factors beyond capital, O&M, 

9 and life cycle cost such as the following: 

10 • Understanding the ancillary benefits that can be associated with LID/green infrastructure 

11 practices 

12 • Understanding the potential cost savings of using distributed LID practices compared to 

13 conventional stormwater controls; this has been demonstrated in cities evaluating 

14 combined sewer overflow solutions (PWD 2009), and in the construction of new 

15 residential subdivisions (USEPA 2007) 

16 • Flexibility inherent in these practices allows them to be integrated into the urban 

17 environment in many cases (NRDC 2006), such as water harvesting, or under-sidewalk 

18 supportedelevated pavement systems (such as infiltrating storage vaults or tree root 

19 vaults, as in the Minneapolis downtown MARQ2 street redesign that included load20 bearing structurally supported space for street tree roots under the sidewalk and adjacent 

21 areas, http://www.stormh20.com/march-april-2010/reshaping-minneapolis22 project.aspxhttp://www.ci.minneapolis.mn.us/public-works/Marq2/about.asp) 

Some Municipal Highlights for Retrofit and Redevelopment Approaches and Practices: 

Portland, Oregon, Bureau of Environmental Services: “A Sustainable Approach to Stormwater 

Management”, http://www.portlandonline.com/bes/index.cfm?c=34598

Seattle, Washington, Seattle Public Utilities “Natural Drainage Systems: Green Stormwater 

Infrastructure”, 

http://www.seattle.gov/util/About_SPU/Drainage_&_Sewer_System/GreenStormwaterInfrastructure/i

ndex.htm

Kansas City, Missouri, “10,000 Raingardens” Program, www.rainkc.gov

Philadelphia, Pennsylvania, “Greenworks Philadelphia”, www.phila.gov/green

EPA’s Green Infrastructure website: Case Studies of Green Municipalities, 

http://cfpub.epa.gov/npdes/greeninfrastructure/gicasestudies.cfm#Municipal

Some Municipal Highlights for Retrofit and Redevelopment Approaches and Practices: 

Portland, Oregon, Bureau of Environmental Services: A Sustainable Approach to Stormwater 

Management, http://www.portlandonline.com/bes/index.cfm?c=34598 

Seattle, Washington, SPU/Natural Drainage Systems: Green Stormwater Infrastructure,

http://www.seattle.gov/util/About_SPU/Drainage_&_Sewer_System/GreenStormwaterInfrastructure/i

ndex.htm

Kansas City, Missouri, www.rainkc.gov

Philadelphia, Pennsylvania, www.phila.gov/green

www.lowimpactdevelopment.org/recognition/categories.htm
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Chapter 3. Controlling Urban Runoff 69 

1 • Costs are expected to decrease as the practices become more standard, for example, the 

2 costs of permeable pavement and of green roofs have been reported to have decreased in 

3 regions where they have been used on a larger scale. That is quantified in estimates by 

4 PWD reported in this section. 

5 • Jurisdictions have found costs to be equivalent or less than conventional stormwater 

6 management practices. An example is Spotsylvania County, Virginia, described in Figure 

7 3-14. 

Spotsylvania County has allowed LID for several years. The development community has realized cost 

savings from LID, after initial skepticism. The county gives examples of just a few of the many 

successful LID projects: 

• Mt. Zion Baptist Church—Historical Church in developed area. Needed to add-on to the church but 

could not afford the land for a basin, instead used grass-paver type systemGrassTracTM for parking 

lot instead of pavement and stone in the travel way. An underground tank captures and infiltrates 

rainwater. Originally, a 42” diameter outlet was planned, now a 6” PVC pipe works, with minimal 

runoff. Used a landscaping rain garden before the drainage inlets. The net savings was 

approximately 45 percent from estimated costs in 2008. 

• Patriot Park—This development had no outlet as a result of 1930’s development design. 

Evapotranspiration rates were used to establish a potential water uptake per plant. By using the 

required buffer and landscaping features the traditional SWM basin was eliminated and there 

would be no downstream impact because rain is retained onsite for up to a 100 yr storm event. 

• Fence Company—The project was to have bioretention with an underground stormwater storage 

system. Once installed, the owner found that the bio-retention with underground storage cost 

approximately 30 percent less than a traditional basin with riser and land needed. Positives noted

o More land for storage of his material 

o Lower costs for installation, 

o Easier to access and maintain. 

Spotsylvania has standardized agreements for BMP installation, inspection, and maintenance. 

- When it comes to the economics of LID practices for the most part you will not get an accurate 

figure until you show your applicants how to do it right. I have had farmers, homeowner, developers 

and many other say that after going through proper training courses they have found LID to be much 

easier then they have seen in the books and have been led to believe. 

—Richard Street, Spotsylvania County, Virginia, Department of Code Compliance, January 2010

8 Figure 3-14. LID cost savings realized in Spotsylvania County, Virginia 

9 2.104.1 Potential Ancillary Benefits of LID/Green Infrastructure 

10 Ancillary benefits are often achieved using LID, and they should be factored into managers’ 

11 consideration of project cost. For example, significant ancillary benefits have been quantified for 

12 green roofs in Cost Benefit Evaluation of Ecoroofs 2008, City of Portland Bureau of 

13 Environmental Services. These benefits are summarized in Figure 3-15. 

14 

Benefits to the public 

• Reduced public costs to manage stormwater 

• Avoided public stormwater infrastructure needs and O&M costs 

• Reduced carbon emissions 
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Chapter 3. Controlling Urban Runoff 70 

• Improved air quality 

• Increased habitat areas 

Benefits to private interests include the following: 

• Reduced stormwater fees 

• Reduced private infrastructure and O&M costs 

• Reduced energy demand and costs 

• Increased roof longevity 

• Increased Floor Area Ratio density bonus potential

The calculated benefits of a hypothetical 40,000 sf green roof include the following: 

• $404,000: the net benefit to the property owner by year 40. 

• $191,421: the net benefit to the public by year 40. 

There is an immediate and long term public benefit. By year five, the benefit is already $101,660.

1 Source: City of Portland Bureau of Environmental Services

2 Figure 3-15. Benefits are quantified for green roofs in Cost Benefit Evaluation of Ecoroofs 2008 

3 Also, a broad range of societal benefits are described in PWD’s A Triple Bottom Line Assessment 

4 of Traditional and Green Infrastructure, Options for Controlling CSO Events in Philadelphia's 

5 Watersheds Final Report, 2009. The categories of benefit accrual resulting from using green 

6 infrastructure stormwater management approaches are the following: 

7 • Recreational Use and Values 

8 • Property Values, as Enhanced by the LID Options 

9 • Heat Stress and Related Premature Fatalities Avoided 

10 • Water Quality and Aquatic Habitat Enhancements and Values 

11 • Wetland Enhancement and Creation 

12 • Poverty Reduction Benefits of Local Green Infrastructure Jobs 

13 • Energy Usage and Related Changes in Carbon and Other Emissions 

14 • Air Quality Pollutant Removal from Added Vegetation

15 2.104.2 Potential Cost Savings of LID/Green Infrastructure 

16 EPA’s report, Reducing Stormwater Costs through Low Impact Development (LID) Strategies 

17 and Practices (EPA 841-F-07-006) compares the projected or known costs of LID practices with 

18 those of conventional development approaches. Traditional approaches to stormwater 

19 management typically use curbs, gutters, and piping. LID-based designs, in contrast, are 

20 designed to use natural drainage features or engineered swales and vegetated contours for runoff 

21 conveyance and treatment. In terms of costs, LID techniques can reduce the amount of materials 

22 needed for paving roads and driveways and for installing curbs and gutters. Other LID 

23 techniques can eliminate or reduce the need for curbs and gutters, thereby reducing infrastructure 

24 costs. Note that in some circumstances LID techniques might result in higher costs because of 

25 more expensive plant material, site preparation, soil amendments, as well as increased project 

26 management costs. Other considerations include land required to implement a management 

27 practice and differences in maintenance requirements.
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Chapter 3. Controlling Urban Runoff 71 

1 Seventeen case studies were evaluated. In general, the case studies demonstrate that LID can 

2 reduce project costs and improve environmental performance. Although not all the benefits of 

3 the projects were monetized, with a few exceptions, LID practices were shown to be fiscally and 

4 environmentally beneficial. In some cases, initial material costs were higher; in most cases, 

5 however, significant savings were realized because of reduced costs for site grading and 

6 preparation, stormwater infrastructure, site paving, and landscaping. Total capital cost savings 

7 ranged from 15 to 80 percent when LID methods were used (Table 3-20). The full report is at 

8 www.epa.gov/nps/lid. 

9 Table 3-20. Cost comparisons between conventional and LID approaches 

Projecta 

Conventional 

development 

cost LID cost 

Cost 

differenceb

Percent 

differenceb

2nd Avenue SEA Street $868,803 $651,548 $217,255 25% 

Auburn Hills $2,360,385 $1,598,989 $761,396 32% 

Bellingham City Hall $27,600 $5,600 $22,000 80% 

Bellingham Bloedel Donovan Park $52,800 $12,800 $40,000 76% 

Gap Creek $4,620,600 $3,942,100 $678,500 15% 

Garden Valley $324,400 $260,700 $63,700 20% 

Kensington Estates $765,700 $1,502,900 –$737,200 -96% 

Laurel Springs $1,654,021 $1,149,552 $504,469 30% 

Mill Creekc

$12,510 $9,099 $3,411 27% 

Prairie Glen $1,004,848 $599,536 $405,312 40% 

Somerset $2,456,843 $1,671,461 $785,382 32% 

Tellabs Corporate Campus $3,162,160 $2,700,650 $461,510 15% 

Source: Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices,

EPA 841-F-07-006 

Notes:

a. Some of the case study results do not lend themselves to display in the format of this table (Central Park 

Commercial Redesigns, Crown Street, Poplar Street Apartments, Prairie Crossing, Portland Downspout 

Disconnection, and Toronto Green Roofs).

b. Negative values denote increased cost for the LID design over conventional development costs. c Mill Creek 

costs are reported on a per-lot basis. 

10 For CSO communities like Philadelphia that need to reduce stormwater volumes into sewers in 

11 dense, urban areas, LID has been shown to help lower estimated long-term costs of compliance 

12 by reducing the size of the storage tunnels that are built 

13 (http://www.phillywatersheds.org/ltcpu/LTCPU_Complete.pdfhttp://www.phillywatersheds.org/l

14 tcpu/LTCPU_Complete.pdf). That can be made a redevelopment requirement (as in 

15 Philadelphia), to enable implementing the controls over a development horizon time frame. An 

16 additional cost benefit is that there is less need for bond revenue, and less debt service if less 

17 corrective infrastructure can be used. 
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Chapter 3. Controlling Urban Runoff 72 

1 2.104.3 Costs of Water Quality and Coastal Impairments 

2 This guidance document does not provide a literature review of estimated costs of water quality 

3 impairments, but communities should evaluate the damages from such impairments when 

4 determining the true cost of stormwater management. For example, beach closures and shellfish 

5 bed contamination, and loss of fisheries represent significant economic costs to society. An 

6 overview of some of these issues is provided in EPA’s 2000 report Liquid Assets 

7 (http://www.epa.gov/water/liquidassets/execsumm.html). 

8 2.104.4 Costs of Individual Practices 

9 Given the considerations described above, it is clear that comparing the costs of LID practices to 

10 each other, or just to other stormwater management practices, is not the best way to show to the 

11 value of LID practices. In addition to not accounting for these benefits, just stating practice cost 

12 does not show how costs can be optimized by integrating LID features into the landscape, or by 

13 selecting rooftop-to-stream incremental features to filter, treat, retain, capture and use runoff. A 

14 green roof might appear a high cost practice, but in a densely urbanized area it could be the most 

15 economical solution for stormwater management, and given the potential benefits shown in 

16 Figure 3-15, could be a very worthwhile investment in the long term. 

17 Issues that should be considered when estimating capital and O&M costs are the following: 

18 • Because LID practices are relatively new, few examples of comprehensive, full-scale 

19 project costs are readily available. 

20 • Limited literature values for costs often do not provide complete information needed, 

21 such as design/construction/startup information, or level of water quality treatment to be 

22 provided 

23 • Costs are highly site specific, such as if area contractors are familiar with the practices, 

24 and therefore vary considerably. 

25 • O&M will account for much of the ownership cost, so managers should consider the 

26 expected reliability and ease of maintenance when selecting a practice, not just the capital 

27 cost. 

28 • O&M costs attributed to LID practices were found to primarily be for aesthetics (WERF 

29 2005). Many of the activities that would have occurred in regular nonfunctional 

30 landscaping (weed control, litter removal) are reported as LID maintenance. That can 

31 make it difficult to determine how much of the reported cost is actually an additional cost 

32 incurred to ensure that the practice functions. 

33 • O&M costs for maintaining bioretention might not be any different from the current 

34 maintenance costs for nonfunctional landscaping, in fact, they could be lower because 

35 bioretention would receive more rainwater and require less watering 

36 • LID practices are primarily uses of conventional construction techniques that can be 

37 readily estimated using local contractor quotes and industry guides such as Reed 

38 Construction Data (R.S. Means), as is done for conventional construction. 

39 • A wide range of potential cost outcomes is reported, such as 
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Chapter 3. Controlling Urban Runoff 73 

1 − Cost savings using LID is widely reported from minimizing conventional piped 

2 infrastructure and ponds, and simply using land and landscaping functionally 

3 − Higher cost in dense, urban environments where cistern systems or green roofs might 

4 be costly, but necessary because of land limitations. 

5 − Limited cost savings or additional costs because the local codes require installing 

6 minimum-sized piped systems regardless of LID design. This could be from an 

7 archaic code or for ensuring flood control or other site-specific issues.

8 • LID approaches often have other cost benefits that should be included in a consideration 

9 of the total value of a practice, such as: reduced downstream piping/culvert costs, or 

10 potentially lower O&M costs. 

11 Estimates of stormwater management practice costs have been prepared by several entities and 

12 reflect the variability that is inherent in site-specific design and construction. 

13 The determination of the most cost-effective practice is site-specific, depending on the 

14 availability of land, the local costs of labor and materials, and level of treatment required. The 

15 costs of individual practices are provided in the practice Fact Sheets in Section 6. General cost 

16 ranges and cost estimating approaches for LID and other stormwater management practices have 

17 been documented in the literature and are repeated here. References are provided in Table 3-21. 

18 Table 3-21. Sources of general cost ranges and cost estimating approaches for LID practices 

USEPA. Stormwater Best Management Practices Design Guide, Office of Research and Development, 

EPA/600/R-04/121, Volumes 1-3 (121, 121A, 121B), September 2004. 

USEPA. The Use of Best Management Practices (BMPs) in Urban Watersheds, Office of Research and 

Development, EPA/600/R-04/184, September 2004. 

Center for Watershed Protection. Urban Subwatershed Restoration Manual Series, 2007

(http://www.cwp.org/Store/usrm.htm) 

Water Environment Research Federation. Performance and Whole-Life Costs of Sustainable Urban 

Drainage Systems, 01-CTS-21T, 2005 

Water Environment Research Federation. Decentralized Stormwater Controls for Urban Retrofit and 

Combined Sewer Overflow Reduction, Phase II, 2009. 

Wiess, Peter T., et al. The Cost and Effectiveness of Stormwater Management Practices, Minnesota 

Department of Transportation, MN/RC – 2005-23 

19 

20 However, to supplement existing information sources, some recent examples are summarized in 

21 Table 3-22, and some specific recent cost information from those sources is provided here. 

22 Table 3-22. Sources of recent cost information for LID practices—capital, O&M, life cycle 

Source Key items 

USEPA. Reducing Stormwater Costs through Low-Impact 

Development, Publication Number EPA 841-F-07-006, December 

2007 

Savings of 15% to 80% found for 

LID subdivisions compared to 

conventional subdivision drainage 

practices. 

ECONorthwest. The Economics of Low-Impact Development: A 

Literature Review, November 2007 

Case studies of LID costs and 

economic benefits 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 74 

Source Key items 

Natural Resources Defense Council. Rooftops to Rivers: Green 

Strategies for Controlling Stormwater and Combined Sewer 

Overflows; NRDC 2006. 

www.nrdc.org/water/pollution/rooftops/contents.asp

Policy guide for decision makers 

for LID; nine case studies of 

successfully used green 

techniques 

Fact Sheets in Section 6 Cost considerations associated 

with each practice presented. 

City of Portland, Oregon, Bureau of Environmental Services, 

Sustainable Stormwater Management Pages, 

www.portlandonline.com/bes/index.cfm?c=34598

Extensive examples of green roofs 

and green streets, as well as other 

sustainable stormwater practices 

Water Environment Research Federation. WERF Cost Tool, 2009. 

Free spreadsheet tool developed as part of Performance and 

Whole Life Cost of Best Management Practices and Sustainable 

Urban Drainage Systems (2005). Water Environment Research 

Federation. 

www.werf.org/AM/Template.cfm?Section=Stormwater3

Provides estimates based on 

literature values. Intended for 

modification as needed for user 

project data. Calculates life cycle 

cost. Contains literature review by 

practice. 

City of Philadelphia. Long Term Control Plan Update, 

Supplemental Documentation, Volume 3, Basis of Cost Opinions, 

September 2009; www.phillywatersheds.org/ltcpu/Vol03_Cost.pdf

Full range of LID costs for new, 

redevelopment, and retrofit. O&M 

costs. Anticipated cost reduction as 

practices become more widely 

used. Retrofit focus. 

North Carolina Coastal Federation. Low Impact Development Pilot 

Study to Reduce Fecal Coliform into Core Sound, Final Report,

Sea Grant Project Number: 07-EP-03, November 2008 

Detailed costs for rain gardens, 

cisterns, conservation landscaping 

and other LID practices. Six 

implemented and 9 planned. 

North Carolina State University (NCSU). Bill Hunt et al. Evaluating 

LID for a Engineering Development in the Lockwood Folly 

Watershed, North Carolina. 

www.nhcgov.com/AgnAndDpt/PLNG/Documents/BrunswickLID.pdf

Demonstrates the cost savings 

achievable using LID in place of 

conventional stormwater treatment.

New York City, Plan NYC, Appendix C, 2008, 

www.nyc.gov/html/planyc2030/html/stormwater/stormwater.shtml

For controls that are high-priority 

for retrofit. 

City of Portland, Bureau of Environmental Services. Cost Benefit 

Evaluation of Ecoroofs 2008. 

www.portlandonline.com/bes/index.cfm?c=50818&a=261053

Quantifies the benefits to owner 

and public of installing green roofs 

PWD. A Triple Bottom Line Assessment of Traditional and Green 

Infrastructure. Options for Controlling CSO Events in 

Philadelphia's Watersheds Final Report, 2009. 

www.phillywatersheds.org/ltcpu/Vol02_TBL.pdf

LID-based, green infrastructure 

approaches provide a wide array of 

important environmental and social 

benefits to the community, and that 

these benefits are not generally 

provided by the more traditional 

alternatives. 

1 

2 Sources of cost data for urban stormwater retrofits, especially roadway retrofits, include the 

3 following: 

4 • Portland, Oregon’s Bureau of Environmental Services; and Seattle, Washington. For 

5 example, Portland notes in its description of its Tabor to the River watershed green6 streets retrofit that resolving the drainage problems it faces using only pipe solutions 

7 would have cost an estimated $144 million, while adding sustainable, green stormwater 

8 management systems reduced the estimated cost to $86 million and enhanced water 
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Chapter 3. Controlling Urban Runoff 75 

1 quality and watershed health 

2 (www.portlandonline.com/bes/index.cfm?c=50500&a=230066). 

3 • Seattle, Washington’s utilities department, Seattle Public Utilities (SPU), has developed 

4 and adopted a green streets design and retrofit approach it calls Natural Drainage Systems 

5 (NDS), started with the completion of the successful SEA Street project in 2001 

6 • (www.seattle.gov/util/About_SPU/Drainage_&_Sewer_System/GreenStormwaterInfrastr

7 ucture/NaturalDrainageProjects/index.htm). As part of the program’s adoption, SPU 

8 conducted a benefit/cost comparison in 2003 between traditional designs and the NDS 

9 design. A summary is provided in Figure 3-16 

10 

11 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 76 

1 

2 Source: www.seattle.gov/util/About_SPU/Drainage_&_Sewer_System/GreenStormwaterInfrastructure/index.htm

3 Figure 3-16. Comparison by Seattle Public Utilities shows lower construction costs for Natural 

4 Drainage Systems than traditional street design 

5 Local governments in the Mid-Atlantic area with cost data include the following: 

6 • Philadelphia, Pennsylvania, Retrofits 

7 • Montgomery County, Maryland, Retrofits 

8 • North Carolina Division of Soil and Water’s Community Conservation Assistance 

9 Program (CCAP)

10 Philadelphia Water Department (PWD). PWD conducted a cost analysis of wet-weather 

11 management approaches as part of its effort to screen and compare green-to-gray technologies in 

12 its Long-Term CSO Control Plan Update (LTCPU). The costs for several of those technologies 

13 are provided here; for additional information and assumptions, see the LTCPU. In general, these 

14 are planning-level estimates, expected to fall in the range of –30 percent to +50 percent for the 

15 Philadelphia area. 

16 These costs were used as the basis for estimating the cost-to-benefits comparison of PWD’s 

17 report A Triple Bottom Line Assessment of Traditional and Green Infrastructure Options for 

18 Controlling CSO Events in Philadelphia's Watersheds. The report indicates that the benefits from 

19 green infrastructure stormwater management are significant; those findings on benefit valuations 

20 are applicable even to non-CSO communities. To compare the costs of traditional versus green 

21 infrastructure, PWD assessed the capital, O&M, and life cycle costs for several stormwater 

22 management practices. It is important to note that the estimated costs were for facilities that 

23 would theoretically meet Philadelphia’s stormwater ordinance, shown in Figure 3-17, to manage 
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Chapter 3. Controlling Urban Runoff 77 

1 the first inch of runoff from directly connected impervious area, by infiltration possible, unless a 

2 waiver is obtained. 

3 Source: Philadelphia’s Stormwater Manual; http://www.phillyriverinfo.org/WICLibrary/chapter%201.pdf

4 Figure 3-17. Philadelphia Stormwater Manual v2.0—Section 1.1.1 Stormwater Ordinance and 

5 Regulations 

6 Cost estimate ranges from PWD’s Long-Term Control Plan for planning purposes are provided 

7 in Table 3-23 for redevelopment and for retrofit. In the LTCPU, PWD addresses many of the 

8 considerations in evaluating costs, including O&M schedules and costs, and replacement costs. 

9 Table 3-23. Summary of direct construction cost estimates from PWD’s Long-Term Control Plan 

10 Supplemental Documentation, Volume 3 [ENRCCI 7966; RSMEAN 115.2] 

Control Type 

Minimum cost 

($ / impervious 

acre) 

Median cost 

($/impervious 

acre) 

Mean cost 

($ / 

impervious 

acre) 

Max cost 

($ / impervious 

acre) 

Bioretention Retrofit $65,000 $120,000 $160,000 $410,000 

Redevelopment $44,000 $90,000 $110,000 $200,000 

Subsurface Retrofit $65,000 $120,000 $160,000 $410,000 

Infiltration Redevelopment $44,000 $90,000 $110,000 $200,000 

Green Roof Retrofit $430,000 $500,000 $500,000 $570,000 

Redevelopment $200,000 $250,000 $250,000 $290,000 

Porous Retrofit $65,000 $160,000 $160,000 $410,000 

Pavement Redevelopment $44,000 $110,000 $110,000 $200,000 

Street Trees Retrofit $18,000 $18,000 $18,000 $18,000 

Redevelopment $15,000 $15,000 $15,000 $15,000 

Source: Philadelphia LTCP

*From Philadelphia LTCP: Other cities have been experiencing costs in the range of $7–16 per square foot 

($305,000–$700,000 per impervious acre), with a typical range of $10–14 per square foot ($435,000–$610,000 per 

impervious acre). A recent green roof at Temple-Ambler campus was approximately $11 per square foot ($480,000 

per impervious acre). The least expensive green roofs in Chicago, which has the largest-scale program in the U.S., 

are on the order of $6–7 per square foot ($285,000 per impervious acre), and this could be a reasonable estimate of 

what can be achieved in the future with a large-0scale program in Philadelphia.

The Water Quality requirement stipulates management of the first one inch of runoff from all Directly 

Connected Impervious Areas (DCIA) within the limits of earth disturbance. The Water Quality 

requirement is established to (1) recharge the groundwater table and increase stream base flows; 

(2) restore more natural site hydrology; (3) reduce pollution in runoff; and (4) reduce combined sewer

overflows (CSO) from the city’s combined sewer systems. The requirement is similar to water quality 

requirements in surrounding states and in other major cities. 

• The requirement must be met by infiltrating the water quality volume unless infiltration is 

determined to be infeasible (because of contamination, high groundwater table, shallow bed rock, 

poor infiltration rates, etc.) or where it can be demonstrated that infiltration would cause property or 

environmental damage. 

• A waiver from the infiltration requirement must be submitted and approved if infiltration is not 

feasible... (continues)
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Chapter 3. Controlling Urban Runoff 78 

1 

2 In addition to capital cost, PWD estimates the cost decrease that can occur as LID practices 

3 become more of a standard practice. PWD LTCPU estimates that costs will decrease for the 

4 following reasons (PWD 2009): 

5 • Improved site designs will result as designers learn to incorporate the new stormwater 

6 requirements into designs from the beginning. Now, such features are added to a site plan 

7 as an afterthought, resulting in higher design costs. Leaving more functional open space 

8 in the site design for stormwater management is assumed to occur over time, and 

9 designers will learn how to work with the expected site conditions.

10 • Lower material costs are expected over time as the practices become more standard. The 

11 materials that at a premium now because they are a specialty item will become routine. 

12 For example, PWD estimates that in the future, porous pavement costs will be 

13 comparable to traditional pavement costs. 

14 • Reduced design costs are expected as more designers become familiar with LID 

15 practices. PWD estimates that designs for LID projects will be on par with more standard 

16 designs.

17 • Reduced perception of risk will result in a lower contingency being applied to cost 

18 estimates.

19 The ranges of cost reduction expected by PWD over time from improved site design and lower 

20 material costs is approximately 20 percent up to about 25 percent.

21 LID Green Street Programs. Green street projects have been implemented for the past several 

22 years in Portland, Oregon, and Seattle, Washington, and other locations. Montgomery County, 

23 Maryland, . Montgomery County has undertaken several green streets projects, and recently 

24 compared the costs of its projects, both estimated and completed, with reported costs from other 

25 jurisdictions, as well as could be interpreted from the literature information provided. There is 

26 limited data available to date, and many factors contribute to the differences in costs reported, so 

27 this data might not be widely applicable. Table 3-24 presents a recent summary of the 

28 Montgomery County evaluation, with information added from Portland on itsPortland’s

29 estimates. 

30 Table 3-24. Summary of green streets costMontgomery County, Maryland, evaluation

Estimated 

level of WQ 

control Total DA

Cost per acre DA 

(in $1,000s) 

Cost per sf BMP SA 

(in $/sf) 

Cost per impervious 

acre DA 

(in $1,000s) 

(acres) design construction design construction design construction 

Bioretention retrofit projects 

Montgomery 

County 

100% 1.1a

$17 $112 $17 $113 $20 $131

100% 0.17bPortland $41 $214 $26 $136 $41 $214

(Areas 

reported as 

impervious 

only) 

100% 0.21c$10 $79 $8 $29 $10 $79

Prince 66% 13.4d$14 $104 $19 $139 $32 $233
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 79 

Estimated 

level of WQ 

control Total DA

Cost per acre DA 

(in $1,000s) 

Cost per sf BMP SA 

(in $/sf) 

Cost per impervious 

acre DA 

(in $1,000s) 

(acres) design construction design construction design construction 

George’s 

County 

86% 1.5e

$72 $92 $99 $126 $217 $276

Swales and Filter Strip Retrofit Projects

Montgomery 

County

16% to 50% 1.1 to 3.7f$33 to 

$75

$26 to $84 $35 to 

$86

$39 to $44 $96 to 

$128

$40 to $143

Caltrans 

Swales 

56% 0.20 to 

2.4g,i

NR $31 to $121 NR $12 to $58 NR $35 to $128

Caltrans Filter 

Strips 

100% 0.49 to 

2.42h,j

NR $23 to $120 NR $12 to $43 NR $35 to $128

Burnsville, MN 

(less 

urbanized)

NR 5.3 j$12 $24 NR NR NR NR

1 Notes:

2 Source: Montgomery County, Maryland, and Portland, Oregon

3 NR = Not Reported; DA = Drainage Area; SA = Surface Area; sf = square foot; Estimated Level of Control = 

4 a. Dennis Ave. Health Center 

b. 12th 5 & Montgomery Ave.; , Portland, OR, Report - only planter & pavers; 

6 ttp://asla.org/awards/2006/06winners/341.htmlttp://asla.org/awards/2006/06winners/341.html

7 c. Green-Siskiyou, OR - curb planters, no subdrain, assume total DA (total impervious DA in report); 

8 http://www.asla.org/awards/2007/07winners/506_nna.htmlhttp://www.asla.org/awards/2007/07winners/506_nna.html

9 d. Route 201 Gateway - roadway median retrofit 

10 e. US Rt. 1 at I-95 Interchange 

11 f. Various projects, combination of completed costs and costs estimated for projects yet to be built 

12 g. Various 2004 projects; include factors that increased the cost for dense urban retrofit (traffic control, etc.) 

13 h. Various 2004 projects; include factors that increased the cost for dense urban retrofit (traffic control, etc.) 

14 i. BMP Retrofit Pilot Program, Final Report, Report ID CTSW - RT - 01 – 050, California Department of 

15 Transportation, January 2004 

16 j. Roadside swales and rain gardens; suburban community retrofits 

17 

18 Coastal North Carolina, Community Conservation Assistance Program (CCAP). Striving to 

19 protect its shellfish resources, LID hasrequirements have been encouragedin place in North 

20 Carolina since 1986. but were strengthened in 2009 including a requirement for new and 

21 redeveloped projects to

•

22 Retain and control approximately 3.6 inches of rainfall, or the one-year, 24-hour storm, 

23 for projects within one-half mile of shellfishing waters.

24 • Retain and control 1.5 inches for projects with greater than 25 percent impervious cover, 

25 for areas outside the one-half mile area

26 As a result, North Carolina has implemented a cost-share program to help start the adoption of 

27 new LID technologies. They developed cost information that they use in the CCAP to estimate 

28 cost-sharing amounts. Table 3-25 provides a summary costs for coastal North Carolina for 2009. 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 80 

1 Table 3-25. LID costs used by the North Carolina Division of Water Quality’s Community Cost 

2 Share Program 

BMP Components Unit type

All areas unit 

cost 

Abandoned well closure Each 

Backyard rain garden SqFt 

 Bioretention excavation SqFt $5.00 

 Bioretention soil amendment -sand SqFt $0.50 

 Bioretention mulch SqFt $0.75 

 Bioretention plants (installed) SqFt $1.50 

Backyard wetland SqFt 

 Wetland excavation SqFt $5.50 

 Wetland plants (installed) SqFt $2.30 

 Wetland outlet structure Each $50.00 

Cisterns Each 

 Cistern 250-1,000 gallons installed Gallon $1.75 

 Cistern 1,000-3,000 galons installed Gallon $1.00 

 Cistern 3,000 gallons installed Gallon 

 Accessories package Each $700.00 

 Cistern foundation SqFt $1.40 

 Concrete pad for cistern SqFt $3.60 

 Shipping charge Each 

Critical area planting SqFt 

 Grading - minimum Job $25.00 

 Grading - light, 1" - 3" avg 100 SqFt $3.90 

 Grading - medium, 3" - 6" avg 100 SqFt $4.82 

 Grading - heavy, 6" - 9" avg 100 SqFt $5.74 

 Grading - extra heavy, 9" - 12" avg 100 SqFt $6.66 

 

Grading - maximum heavy, more than 12" 

avg 100 SqFt $7.58 

 Vegetation (grass) - minimum Job $15.00 

 Vegetation (grass) 100 SqFt $0.75 

 Vegetation (trees/shrubs) SqFt 

 Vegetation - mulch, netting 100 SqFt 

 Vegetation - mulch, small grain straw 100 SqFt $1.28 

 Matting - excelsior, installed SqYd $0.95 

Diversion Feet 

 Excavation SqFt $5.00 

 Vegetation (grass) 100 SqFt $0.75 

 Filter cloth-geotextile fabric SqYd $2.25 

 Filter cloth-pins, metal anchor Each $2.00 

 Vegetation - mulch, netting 100 SqFt 

 Vegetation - mulch, small grain straw 100 SqFt $1.26 

 Matting - excelsior, installed SqYd $0.95 
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 81 

1 

2 Amesbury, Massachusetts Cost Comparison of LID Parking Lot and Conventional Parking 

3 Lot. When evaluating the costs of LID, it is important to do it in comparison to the costs of 

4 alternative stormwater management. The economies of subdivision development with LID 

5 practices have been documented (USEPA 2007). As an example, Table 3-26 presents a detailed 

6 breakdown of a cost comparison for two parking areas estimated in for a project in 

7 Massachusetts, indicating that the LID construction cost was not higher than conventional costs. 

8 For this project, design costs were reported as higher because it was a relatively new type of 

9 design, but lower maintenance costs were reported to be anticipated. 

10 Table 3-26. Comparison of conventional design vs. bioretention in two parking areas in Amesbury, 

11 Massachusetts 

Bioretention Area 1 Bioretention Area 2 

Island = 51,155 SF (4,867 SF landscape) 

Adjacent to clubhouse = 77,90 SF (19,584 SF 

landscape) 

Quantity 

Unit 

cost Total cost Quantity 

Unit 

cost Total cost 

 Item LID Standard LID Standard LID Standard LID Standard 

Loam (4" 

depth) (CY) NA 59.6 $40 NA $2,384 179 239.4 $40 $7,160 $9,576

Bioretention 

soil mix (24" 

depth) (CY) 360.5 NA $40 $14,421 NA 363 NA $40 $14,520 NA

Seed (SY) 240 541 $4 $960 $2,164 1360.8 1941 $4 $5,443 $7,764

Composted, 

double 

shredded 

hardwood 

mulch (3" 

depth) (CY) 25 0 $28 $700 $0 68 20 $28 $1,904 $560

Trees (EA) 18 18 $518 $9,315 $9,315 45 45 $518 $23,288 $23,288

Shrubs (EA) 61 30 $32 $1,922 $945 216 108 $32 $6,804 $3,402

Perennials 

and grasses 

(EA) 1450 0 $2 $2,900 $0 2068 0 $2 $4,136 $0

Landscape 

 total $30,217 $14,808 total $63,255 $44,590

HDPE Drain 

pipe (12" 

dia) (LF) NA 55.4 $12 NA $648 NA 148 $12 NA $1,732

Catch 

Basins (EA) NA 2

$3,07

5 NA $6,150 NA 4 $3,075 NA $12,300

Water 

Quality Units 

(Stormcepto

r STC 900) 

(EA) NA 1

$8,00

0 NA $8,000 NA 1 $8,000 NA $8,000

Curb 

(Extruded 

Concrete) 

Straight (LF) NA 506.8 $6 NA $2,914 NA 655.5 $6 NA $3,769

Site work

Curb 

(Extruded 

Concrete) 

Radius (LF) NA 45.7 $8 NA $356 NA 78.5 $8 NA $612
3/15/202-22-10 Chesapeake Bay Executive Order Section 502 Guidance — Do Not Cite or Quote — 

Chapter 3. Controlling Urban Runoff 82 

Bioretention Area 1 Bioretention Area 2 

Island = 51,155 SF (4,867 SF landscape) 

Adjacent to clubhouse = 77,90 SF (19,584 SF 

landscape) 

Quantity 

Unit 

cost Total cost Quantity 

Unit 

cost Total cost 

 Item LID Standard LID Standard LID Standard LID Standard 

Wheel Stops 

(EA) 43 NA $66 $2,838 NA 49 NA $66 $3,234 NA

Drain 

Manholes 

(EA) NA NA

$3,32

5 NA NA NA 1 $3,325 NA $3,325

Earthwork 

(CY) NA 183 $5 NA $860 NA 493 $5 NA $2,317

Pipe 

Bedding 

(CY) NA 15.3 $2 NA $36 NA 41.1 $2 NA $96

 total $2,838 $18,964 total $3,234 $32,151

Bioretention Area 1 Bioretention Area 2

total $33,055 $33,772 total $66,489 $76,740

1 Source: Eisenburg, Bethany, Design, Engineering, Installation, and O&M Considerations for Incorporating 

2 Stormwater Low Impact Development (LID) in Urban, Suburban, Rural, and Brownfields Sites, American Society of 

3 Civil Engineers (ASCE), Low Impact Development Conference Proceedings, 2008 

4 

5 2.115 References 

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12 Arendt, R. 1999. Growing Greener: Putting Conservation into Local Plans and Ordinances. 

13 National Lands Trust-American Planning Association-American Society of Landscape 

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15 ASFPM. 2010. Natural and Beneficial Floodplain Functions: Floodplain Management—More 

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18 Casey Trees. 2008. Green Build-out Model. Casey Trees, Washington, D.C. 

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20 February 23, 2010.

21 Center for Watershed Protection. 1998. Better Site Design: A Handbook for Changing 

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23 <http://www.cwp.org/Store/bsd.htm>. Accessed February 23, 2010.
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Chapter 3. Controlling Urban Runoff 83 

1 Center for Watershed Protection. 2003-2008. Urban Subwatershed Restoration Manual Series. 

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7 <http://www.cwp.org/Resource_Library/Center_Docs/SW/pcguidance/Manual/PostConstr

8 uctionManual.pdf>. Accessed February 23, 2010.

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13 Cheng, M.S., C.A. Akinbobola, J. Zhen, J. Riverson, K. Alvi and L. Shoemaker. 2009. BMP 

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17 February 23, 2010.

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21 Chesapeake Bay Program. 2009. Developing Best Management Practice Definitions and

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25 February 23, 2010.

26 City of New York. 2008. Plan NYC, Appendix C. City of New York, New York, NY. 

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