BMP Decision Support System for Evaluating Watershed-Based Stormwater Management Alternatives

The proper selection and placement of Best Management Practices (BMPs) is a critical part of the stormwater planning effort. Established urban and newly developing areas must establish cost effective means for restoring existing sites, minimizing impacts to new sites, and provide general site planning for future growth. Prince George's County, Maryland in the Washington D.C. metropolitan area has developed a BMP analysis system to support analysis and decision making for stormwater management planning and design at the watershed level. This system supports watershed hydrologic and water quality analysis, simulation of various innovative BMPs, and selection/placement optimization of suitable BMPs that will achieve the goals, defined by a user. This system helps planners determine which alternatives will yield the greatest benefit by automatically assessing several key site-specific factors. Housed in the ESRI ArcGIS environment, the system provides visualization and GIS processing support for developing networks including sequences of land uses, BMPs, and stream reaches. ArcGIS also serves as an interface for BMP placement, BMP attribute data input, and as a platform for managing the decision optimization component. The system then launches a stand-alone BMP simulation and evaluation module. Since the module is a process based simulation model for BMPs, it provides a technique that is sensitive to local climate and rainfall patterns as well as BMP size, design, and relative placement on the site. The system incorporates a meta-heuristic optimization technique to find the most cost-effective BMP placement and implementation plan that best satisfies a controlled target and fits within a fixed cost budget. A case study application is presented to demonstrate the application of the system. The case study involves a highly urbanized area in the Anacostia River watershed, located within the boundaries of Maryland and the District of Columbia. Several BMPs such as bioretention, green roof, porous paving and rain barrels are proposed, which minimize runoff, improve water quality, and provide water reuse opportunities. The modeling system is used to identify and evaluate various alternatives to determine the most cost-effective types and combinations of BMPs that best minimize the frequency and size of runoff events thereby also reducing the magnitude and frequency of combined sewer overflows to the Anacostia River.