Process for selecting Best Management Practices
Designers need to carefully think through many factors to choose the most appropriate, effective and feasible practice(s) at a development site that will best meet local and state stormwater objectives. This page presents a flexible approach to Best Management Practices (BMP) selection that allows a stormwater manager to select those BMPs most able to address an identified problem. Selecting an inappropriate BMP for a site could lead to adverse resource impacts, friction with regulators if a BMP does not work as anticipated, misperceptions about stormwater control success, and wasted time and money. Careful selection of BMPs will prevent negative impacts resulting from installing the wrong BMP at the wrong location. Regulators can similarly use these matrices to check on the efficiency of proposed BMPs.
Using the manual to select BMPs
This Manual uses a “functional components approach” wherein basic BMP components are selected and pieced together to achieve a desired outcome. For example, if a BMP is needed to reduce peak discharge and remove sediment, stormwater ponds can be selected as the BMP and the actual design components are then assembled based upon the material presented in the design guidance for stormwater ponds. In this case, a pond with a specific outflow rate and sufficient water quality storage is designed to meet both functions according to state design criteria. This approach limits the inclusion of numerous individual BMP sheets in favor of categorical sheets with design variations included on each sheet. This should be a more user-friendly way of defining how BMPs can be designed to solve a particular problem.
BMP lists follow a simple-to-more complex treatment train sequence, one that starts with on-site pollution prevention and works upward in complexity to wetland systems. The list of treatment supplements is a compilation of additional measures that could be used to enhance treatment either before or after more complex BMP use.
Information on BMPs can be found in the individual sections for bioretention, filtration (see Swales or Sand filters), infiltration (see Infiltration trench or Infiltration basin), stormwater ponds, stormwater wetlands, trees, green roofs, turf, and permeable pavement. Sections on pollution prevention, better site design/LID, runoff minimization (see Stormwater re-use and rainwater harvesting) and temporary construction runoff control practices include some descriptive language but do not include engineering details. Sections on treatment supplements will similarly not contain detailed engineering, but will describe a process that designers should follow when considering the use of proprietary devices, inserts and chemical/biological treatment.
The beginning stormwater manager or a designer unfamiliar with the many BMPs available might have some questions on which BMP or group of BMPs to include in a treatment scheme. A matrix can be developed to serve as a screening tool to get the user going on BMP selection. The matrix contains a list of BMPs contained in this Manual and a corresponding list of use assessment parameters to help narrow the wide range of potential BMPs for a particular project. A user will need to have some objectives in mind to extract information from the matrix, but once into the matrix, selection of BMPs based on either positive or negative factors will be possible.
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