Pennsylvania Handbook of Best Management Practices for Developing Areas

§4. Using BMPs Effectively

§4.1 Objectives of BMPs
§4.2 Components of an Effective BMP Program
§4.2.1 Carefully Prepared Site Layouts and Designs
§4.2.2 Effective Runoff-Control Measures
§4.2.3 Effective Control of Soil Erosion and Sedimentation
§4.3 Obtaining Acceptance for BMPs as Development Practices
§4.3.1 What Developers Should Understand About BMPs
§4.3.2 What Local Officials Should Understand about BMPs

§4.1 Objectives of BMPs

The goal of BMPs is to minimize the adverse effects of development both on and off the site. The philosophy endorsed in this handbook is to preserve sensitive natural features and to develop stormwater systems that are based on BMPs that mimic, as closely as possible, the runoff characteristics of the site in its natural state. These characteristics include:

• Infiltration of the majority of annual rainfall to replenish the water table and provide stable baseflow to streams
• Physical and biological filtration of runoff to provide a clear and pollution free source of runoff to streams and waterbodies
• Moderation of runoff peak velocities to minimize erosion and damage to aquatic habitat in downstream areas

This philosophy stresses preserving natural storage, infiltration, and pollutant-filtering functions where practical. BMPs, such as grass swales, bioretention facilities, permeable pavement, dry wells, and vegetated roof covers, can be blended with preserved features of the natural landscape and with new construction to create a new urban landscape. Oone that is equally as functional and as beautiful as the one it replaces. Ideally, BMPs based on this philosophy will reduce life-cycle costs for stormwater management by minimizing the need for capital improvements to the existing storm drainage systems for conveying, storing, and treating increased runoff volumes and rates.

§4.2 Components of an Effective BMP Program

Comprehensive management programs that use BMPs have the following characteristics:

• Carefully prepared site layouts and designs
• Effective runoff control measures (detention, retention, treatment)
• Effective control of soil erosion and sedimentation during land-disturbing activities

§4.2.1 Carefully Prepared Site Layouts and Designs

Site design has two primary objectives:

• Preserve existing beneficial natural hydrologic functions and pollutant-filtering mechanisms
• Integrate BMPs into the site layout so they conform with existing topographic features, conserve space, and compliment the intended uses of the developed site

Natural features with important hydrologic functions include streams, lakes, wetlands, areas of native vegetation, high-quality woodlands, and natural depressions. These features should be recognized and protected when the site plan is developed. By recognizing and taking advantage of the beneficial properties of the existing terrain features, the scale and complexity of structural BMPs can frequently be reduced.

Protecting natural features is greatly facilitated by flexible development standards and codes that permit planned unit developments and clustering. Where highly degraded natural features are present, the site plan may call for restoring and reconfiguring the site to enhance aesthetic values and natural functions.

The unobtrusive incorporation of BMPs into developments of all kinds requires considering the potential design opportunities at the beginning of the design process. Many choices are available during site design process that have little effect on the return on investment but could substantially influence the hydrologic characteristics of the completed project. These include:

• Building setbacks
• Choice of paving systems
• Minimize contiguous impervious areas
• Pitches of parking lots and other surfaced areas
• Routing and management of roof runoff
• Use of "dead" volumes under patios
• Choice of landscape plants
• Final grading and drainage routing

When selected carefully with the site conditions in mind, BMPs can be incorporated readily into residential, commercial, and industrial developments without interfering with the intended uses of the projects. The deployment of many BMPs can be made virtually invisible to the casual observer. Site designers who incorporate BMPs in their projects will be rewarded by aesthetically pleasing layouts that conserve space, are less prone to runoff-related problems, and are substantially less costly to maintain.

§4.2.2 Effective Runoff-Control Measures

An effective system for draining and controlling stormwater should:

• Safely and economically convey excess runoff through the site.
• Maximize opportunities for attenuating, infiltrating, and filtering surface runoff close to where it is generated.

Table 4.1 summarizes how stormwater BMPs can be adapted to traditional development to protect water resources. Each of the techniques is described in detail in Section 8, "Descriptions of Selected Best Management Practices." The greatest hydrologic and water quality benefits are achieved when BMPs are combined in a logical, integrated stormwater management system. The concept is called the "BMP treatment train," where a combination of BMPs are is used together. In areas that were developed before the present stormwater regulations were in place, BMPs must be retrofitted in the drainage system. Section 8 describes when and how stormwater BMPs can be retrofitted into older developments to remedy existing problems.

§4.2.3 Effective Control of Soil Erosion and Sedimentation

The basic principles of effective soil-erosion and sediment control include:

• Use effective site planning to avoid sensitive areas, minimize the area disturbed, and minimize the time of disturbance.
• Stabilize disturbed soils as soon as possible.
• Filter and trap eroded sediments before they leave the site.
• Control runoff onto and through the construction site and avoid concentrated flows.
• Routinely inspect construction sites and maintain control measures.

Numerous references are available that give guidance for achieving the soil erosion and sediment control measures. The references are listed in Appendix B. A good publication that discusses soil and erosion control for construction sites is the United States Environmental Protection Agency (EPA), Storm Water Management for Industrial Activities (EPA 832-R-92-006, September 1992).

§4.3 Obtaining Acceptance for BMPs as Development Practices

Many of the BMPs described in the handbook have been recommended by water-resource planners and engineers for the past 10 or more years, yet the BMPs have not become common development practice in Pennsylvania. The numerous stakeholders in urban drainage cite a number of reasons for the historic failure to implement BMPs, for example:

• Many engineers and landscape architects have not been trained in nontraditional BMP approaches and consequently are reluctant to include them in site designs.
• Many municipal officials have not been convinced of the benefits, either locally or regionally, of alternative drainage and site design practices and other BMPs.
• The opposition of a vocal minority of residents to occasional ponding and other drainage "nuisances" discourages official acceptance of natural drainage practices.
• Concerns about water quality typically are given less emphasis than concerns about flooding and drainage in the adoption of local development controls.
• The voluntary nature of state BMP programs has minimized the urgency to implement local programs.

Most of the objections to BMPs, and the concerns underlying each, are readily addressed by more thoroughly understanding their technologies, costs, benefits, and tradeoffs.

The paragraphs below briefly summarize the understanding that must be communicated to the nontechnical stakeholders in urban drainage management. Arguments for refuting common objections from developers and local officials to implementing BMPs are presented.

Readers of this handbook should use the section as an information source from which to build the materials or arguments for educating relevant stakeholders.

§4.3.1 What Developers Should Understand About BMPs

Developers need to understand:

• The market factors affected by BMPs
• The costs, and the cost savings, of BMPs
• The technology transfer limitations to BMPs

The Market Factors Affected by BMPs

Several market factors are mandating that BMPs be incorporated into design if the resultant development is to be marketable. The market factors are:

• Green thinking
• Permitting requirements
• Liability concerns

Green thinking is shorthand for the public’s embracing of the environmental movement. As a result of green thinking, the public, particularly the more well-to-do and educated, places a higher value on products that are environmentally friendly. A development that exhibits features that are obviously environmentally friendly–e.g., protected wetlands, natural habitats, green spaces–will have a marketing edge over a less-sensitive development. The market effect of BMPs in Pennsylvania has not yet been documented. However, a recent New England study indicated similarly valued housing structures commanded higher prices and appreciated more rapidly if in developments with smaller lots traded for more green space and environmental amenities.

With regard to permitting and liability, BMPs minimize the potential for future damages, both off and on the site. In the past, developers have avoided most of the cost and liability of damage by claiming compliance with current practice. The recent increase in awareness of, and legislation for, BMPs makes that defense less viable. If damages can be attributed to a developer’s failure to incorporate BMPs, the developer may be held liable for repairs and mitigation.

The Costs, and Cost Savings, Associated with BMPs

Stormwater must be managed for all developments. By using BMPs, rather than more traditional systems, development and stormwater infrastructure costs can be lowered. Other aspects of the life-cycle cost of stormwater management systems also can be reduced by using BMPs judiciously.

Capital costs can be reduced through BMPs, such as:

• Site designs incorporating clusters and reduced setbacks, resulting in less grading, reduced paving, less landscaping, and lower mitigation costs.
• Vegetated swales are less costly to install than curb and gutter, catch basins, and underground storm sewers.
• Directing flow to vegetated filter strips or infiltration devices to reduce runoff rates and volumes can reduce the size (and cost) of downstream conveyance and storage devices (storm sewers, culverts, and detention basins).
• Using upstream detention basins to reduce peak runoff rates can reduce the size (and cost) of major drainageways and storm sewers.

How Developers Are Affected by BMP Technology Transfer Limitations

Most developers rely on their planning and engineering professionals to address site design and drainage questions. Developers, however, should be aware that engineering curricula traditionally has not addressed urban stormwater BMPs. In fact, existing curricula often present a bias towards "structural" solutions, such as storm sewers and lined channels, even when "softer" approaches are more appropriate. Most planners and engineers have had minimal exposure to newer BMP technologies in their academic careers, or through continuing education, and consequently may be poorly equipped to evaluate applicability, costs, or benefits. Consequently, developers must consciously seek professionals with specialized training or experience in innovative site design and urban stormwater BMPs.

§4.3.2 What Local Officials Should Understand About BMPs

Local officials need to fully understand the tradeoffs in selecting BMP alternatives. Many of the objections raised by local officials can be readily offset by specific BMP advantages if the tradeoffs are understood and compared. Table 4.2 lists commonly cited concerns and tradeoffs associated with incorporating BMPs into urban drainage plans. In order for local officials to fully embrace BMP alternatives, several specific concerns must be addressed.

Local officials and the public must understand, and ultimately embrace, the water quality benefits of BMPs, both locally and regionally. They must realize that effective BMP programs can improve the appearance and quality of lakes, streams, wetlands, and detention basins, resulting in improved property values and recreational opportunities. They also must understand that BMPs that protect water quality also benefit flood control.

Local officials responsible for adopting ordinances and codes must recognize the true costs of including stormwater BMPs. The officials must understand that communities with reasonable, but high, standards for new development can both attract desirable development and maintain a high quality of life. They must be committed to educating their constituents about the advantages of BMPs. In particular, officials must be prepared to respond to inevitable concerns or complaints from citizens about temporarily ponded water or other "nuisance" conditions.

The maintenance costs of BMP systems should be compared to the overall lifetime costs of competing conventional facilities. Although some individual BMPs may be more expensive to maintain than traditional approaches (e.g., swales vs. storm sewers), well-constructed BMP systems should be less expensive in the long run. For example, BMPs will reduce downstream sediment loads, thereby reducing the need for sediment removal from waterways and ponds. BMPs that stabilize runoff rates will minimize downstream bank erosion and repair costs of bank stabilization.