Simulation of Urban Wet Weather Best Management Practices at the Watershed Scale
While water resources planning on a watershed basis has become the preferred approach on both the Federal and State level, much of the planning and implementation of watershed plans will continue to occur on a more local level. The numerical analyses discussed in this chapter are part of a comprehensive watershed planning program underway in southeastern Pennsylvania. The goal of the Southeastern Pennsylvania Waterways Restoration Program (SPWRP) is to regain the resources in and around streams that were lost due to urbanization, both within the City of Philadelphia and in the surrounding counties.
The regulatory context of watershed planning is complex. The watershed planning approach being developed is intended to meet requirements of five major regulatory programs. These are:
1. the requirements of section 303(d) of the Clean Water Act Amendments to improve water quality on impaired water bodies;
2. the Phase I and Phase II National Pollutant Discharge Elimination System (NPDES) stormwater regulations to control pollution due to discharges from municipal and industrial stormwater systems;
3. Commonwealth of Pennsylvania Act 537 Sewage Facilities Planning to protect and prevent contamination of groundwater and surface water by developing proper sewage disposal plans;
4. Commonwealth of Pennsylvania Storm Water Management Act 167 to address management of stormwater runoff quantity and quality in developing areas; and
5. the U.S. National Combined Sewer Overflow (CSO) Control Policy.
Some of the data collection and analyses are common to more than one program. The SPWRP provided an integrated watershed management approach that effectively met the requirements of each program without duplication of effort.
This chapter presents a case study for the Cobbs Creek watershed, an urban watershed draining approximately 22 square miles (35 km2) in southeastern Pennsylvania. Analysis of available GIS data indicates that approximately 50% of the drainage area is covered by impervious surfaces, including roads, parking lots, and rooftops. About 20% of the total area is served by a combined sewer system, 75% is served by separate storm sewer systems, and 5% is unsewered. Because the watershed is highly developed, the potential for new development is limited. The Cobbs Creek watershed is a complex system that provides ample opportunities to develop and demonstrate a comprehensive watershed management program in an urban environment.
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