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Multiple Watershed Scales Approach for Placement of BMPs in SUSTAIN
Citation:
LAI, DENNIS, J. Zhen, J. Riverson, K. Alvi, AND L. Shoemaker. Multiple Watershed Scales Approach for Placement of BMPs in SUSTAIN. Presented at World Environmental & Water Resources Congress, Kansas City, MO, May 17 - 21, 2009.
Impact/Purpose:
To inform the public.
Description:
Watershed and stormwater managers need modeling tools to evaluate how best to address environmental quality restoration and protection needs in urban and developing areas. Significant investments are needed to protect and restore water quality, address total maximum daily loads (TMDLs), and evaluate and design sustainable stormwater management systems. A number of stormwater control strategies, commonly known as best management practices (BMPs) or low-impact developments (LIDs), are used to options help create more sustainable development that manages stormwater while minimizing downstream effects. Efforts have been underway by the U.S. Environmental Protection Agency since 2003 to develop a decision-support system for placement of BMPs at strategic locations in urban watersheds. This system is called the System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN). The tool is designed for use by experienced watershed and stormwater practitioners to develop, evaluate, and select optimal BMP options for various watershed scales based on cost and effectiveness. The beta version of SUSTAIN is to be released in early 2009. One dominant technical requirement for SUSTAIN is the ability to place management practices at multiple scales. This is because placement of BMPs at different spatial levels, i.e., on-site, sub-regional, and regional, affects the overall cost-effectiveness of the stormwater control system. In an urban setting, the on-site scale can be exemplified by building lots or neighborhoods with a drainage area in the range of 10-100 acres. LID technologies are normally applied on this scale. Other BMPs collect runoff at hydrologic junctions further downstream, at a level typically associated with the township scale with a drainage area of approximately 100-5,000 acres. At the larger regional scale, the benefits of management are often measured by impacts to receiving streams, lakes or other larger water bodies. The regional scale usually represents a watershed on a county level with a drainage area greater than 5,000 acres. Management plans often need to evaluate the cumulative benefit of management practices at multiple scales on downstream water quality in river, lakes, or estuaries. Detailed simulation can be performed at the site scale or small watershed scale to evaluate the impacts of various combinations for practices and treatment trains on localized water quantity and quality. For evaluation and placement at a larger scale watershed, there can be hundreds or thousands of individual management practices. To manage the complexity of larger watershed scale applications, SUSTAIN uses a tiered approach to evaluate both individual and multiple-nested watersheds. In addition, for distributed BMPs located in residential parcels of a new development or an existing neighborhood, SUSTAIN uses a “lumped” approach to aggregate BMPs, representing infiltration and storage processes. This paper will describe the procedures for performing a tiered evaluation of BMPs at various spatial scales and aggregation of distributed BMPs. It will illustrate framework features and performances through selected examples that are typical of the conditions and scenarios of watershed stormwater management where SUSTAIN is best applied.
