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2012 EPA Research Progress Report

A Tool for Urban Storm Water Management

Storm water overflow presents a big problem in many urban areas. Heavy rains send torrents of water running over pavement, rooftops, and all the other impervious surfaces that cover most city grounds. Not only does this excess water cause superficial flooding of roads and buildings, it also floods city sewer systems. Combined sewer systems that collect municipal sewage and storm water in a single pipe system can overflow during heavy rain resulting in ‘combined sewer overflows’ where sewage and other pollutants overflow into nearby waterways. EPA researchers are developing tools and strategies to help city planners, managers, and others address storm water problems.

EPA’s Storm Water Management Model (SWMM) is widely used for planning, analysis, and design related to storm water runoff, combined sewers, sanitary sewers, and other drainage systems in urban areas. SWMM is a rainfall-runoff simulation model that gives users important information about local water patterns. This helps inform the design and implementation of natural and “green” (rain gardens and barrels) as well as traditional “gray” (pipes) storm water management alternatives. This publicly available model averages 2,000 downloads every month and is often used as a core modeling engine by municipalities.

Screenshot from the Storm Water Management Model Tool.

EPA recently expanded SWMM (version 5) to explicitly model the performance of specific types of low impact development controls, such as porous pavement, bio-retention areas (e.g., rain gardens, and green roofs), infiltration trenches, vegetative swales, and other forms of green infrastructure (see Tapping Green Infrastructure in this report). The updated model allows engineers and planners to accurately represent any combination of low impact controls within a study area to determine their effectiveness in managing storm water and combined sewer overflows.

The development of predictive modeling tools like SWMM for the design of integrated green and gray infrastructure in urban watersheds is intended to improve resource management, criteria development, and regulatory decisions.

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