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METHODS FOR OPTIMIZING URBAN WET-WEATHER CONTROL SYSTEM
Citation:
HEANEY, J. P. AND J. G. LEE. METHODS FOR OPTIMIZING URBAN WET-WEATHER CONTROL SYSTEM . U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-06/034, 2006.
Impact/Purpose:
to inform the public
Description:
To minimize impacts of urban nonpoint source pollution and associated costs of control (storage and treatment) associated with wet-weather flows (WWFs), stormwater runoff volumes and pollutant loads must be reduced. A number of control strategies, so-called “best management practices” (BMPs) are being used to mitigate runoff volumes and associated nonpoint source (diffuse) pollution due to WWFs. They include ponds, bioretention facilities, infiltration trenches, grass swales, filter strips, dry wells, and cisterns. Another control option is popularly termed “low impact development” (LID) – or hydrologic source control – and strives to retain a site’s pre-development hydrologic regime, reducing WWF and the associated nonpoint source pollution and treatment needs.
Methods are needed to evaluate these BMPs, their effectiveness in attenuating flow and pollutants, and to optimize their cost/performance since most models only partially simulate BMP processes. Enhanced simulation capabilities will help planners derive the least-cost combination for effectively treating WWFs. There is a confusing array of options for analyzing hydrologic regimes and planning for LID. Integrating available BMP and LID processes into one model is highly desirable.
This report describes a methodology that integrates simulation (“what–if” analysis) and optimization (“what’s–best” analysis) for evaluating which of the myriad of alternative wet-weather controls deserves the title of “best”. The optimization analysis integrates process simulation, cost-effectiveness analysis, performance specification, and optimization methods to find this “best” solution. All of this analysis is done using a spreadsheet platform. Following a general review of optimization methods and previous applications to wet-weather control optimization, a series of spreadsheet based tools are described. An improved method for spatial analysis to get a more accurate representation of land use is described. Then, a spreadsheet-based method for analyzing precipitation records to partition them into storm events or to develop intensity-duration-frequency curves is presented. Next, simple methods for estimating infiltration and performing flow routing are described. Influent pollutant loads may be described simply as event mean concentrations (EMCs) or by treatability studies. Next, a spreadsheet version of the STORM model for continuous simulations is presented, followed by an update on the cost of wet-weather controls. Then, a primer on optimization methods describes the ease of using these techniques in a spreadsheet environment. Application of these tools to optimize storm sewer design is presented next. Lastly, an integrated stormwater management optimization model that combines land use optimization and a storage-release system is outlined.
The effort documented in this report is linked to a parallel effort at Oregon State University titled: BMP Modeling Concepts and Simulation. This work analyzes several current modeling methods to evaluate BMP performance with the intention of facilitating integration of improved BMP modeling methods into the EPA’s Storm Water Management Model (SWMM). Several other models are examined as part of this study. Options for enhancement of SWMM’s LID simulation capabilities are also presented. Two extensive case studies in Portland, Oregon help to clarify current SWMM capabilities and needs for enhancement.