Stormwater Management: Best Management Practices

Stormwater Best Management Practices (BMPs) are techniques that will best manage stormwater quantity and quality on a site, based on unique site conditions, and planning and engineering requirements.

BMPs involves site development design that incorporates the most suitable techniques, or combination of techniques to best manage the anticipated stormwater flow and quality based on an evaluation of site conditions and planning requirements. While a combination or system of BMPs should be included in site designs for the most effective stormwater management, it is preferable that the overall site design be based upon the protection of existing natural resources and hydrological features, with these features incorporated into the overall site design with little or no disruption.

Traditional BMPs are effective in temporarily detaining flood waters, by releasing runoff over an extended period of time to adjacent properties and streams, and have provided some level of water quality treatment. However, while they reduce the flood peak, they may increase the duration of elevated water surfaces as the detained water is released over time. Additionally, the stormwater carries increased pollutant loads, particularly in the immediate aftermath of a storm event, that require additional water quality treatment to protect stream water quality and aquatic habitats.

Advances in stormwater management have led to a natural hydrology site design process. This process first incorporates the existing natural resources and hydrological features into the overall site design with little or no disruption to these features, and then incorporates low-impact BMPs around them, and only then proceeds to incorporate standard BMPs if they are still required. This approach minimizes disturbance of land area, natural features and site hydrology, preserves concentrations of open space, woodlands and environmentally sensitive features, and incorporates landscape-based BMPs low impact development techniques to minimize the usage of traditional structural stormwater facilities.

Stormwater BMPs are applicable for every landscape. Urban landscapes, such as boroughs, frequently experience severe stormwater runoff impacts due to the density of development and high percentage of impervious surfaces that produce increased runoff. BMPs should be incorporated into new developments in urbanized areas, and these areas should also be evaluated for retrofits to correct existing stormwater runoff problems.

Rural landscapes may also consider agricultural BMPs (often referred to as conservation practices) which are frequently defined in soil and water conservation plans developed for individual farms. Guidance and oversight of these plans and practices are provided to farmers by the Chester County Conservation District (CCCD), Natural Resources Conservation Service (NRCS), and cooperative extension agencies. CCCD also reviews and implements the erosion and sediment control program for construction sites (under the National Pollutant Discharge Elimination System, or NPDES) for Chester County.

Chester County municipalities must implement stormwater management by adopting the approved Countywide Act 167 Ordinance, or equivalent standards, as a separate stand-alone stormwater management ordinance. Additionally, technical evaluation and design guidance documents may be recommended or provided to assist designers in understanding state-of-the-art options and their performance, design, maintenance, and cost aspects. Within the ordinance or accompanying guidance documents, a hierarchy of types of BMPs can be established to encourage the use of those practices that best suit the conditions and needs of the municipality. For example, BMPs that reduce the volume of runoff and enhance groundwater recharge of stormwater may be defined as highest priority (given suitable site conditions) while traditional detention ponds maybe defined as lower priority.

The list of accepted BMP practices continues to expand as new practices are proven effective.


BMPsImplementation of stormwater management BMPs provides the following advantages:


The following limitations are associated with stormwater management BMPs:

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Watersheds, An Integrated Water Resources Plan for Chester County and Its Watersheds, was adopted in 2002 as the water resources component of Landscapes. The County-wide Act 167 Stormwater Management Plan, which will be adopted in 2012, is comprised of the Watersheds Plan with an Act 167 Addendum. The Addendum will include a Model Ordinance and Standards Matrix for stormwater management related to land disturbance, Christina Basin MS4 TMDL Implementation Strategy, Act 167 Plan consistency requirements for state financed projects, and additional documentation required to fulfill the Act 167 plan requirements.

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