Cobbs Creek Watershed Plan: restoring an urban stream

The Darby-Cobbs Watershed Partnership worked with the Philadelphia Water Department (PWD) to complete the Cobbs Creek Watershed Management Plan. The plan lays out the actions needed to achieve measurable progress towards restoring legally required, beneficial uses of the stream, and is designed as an integrated watershed planning effort to address objectives of several programs, including Combined Sewer Overflow (CSO) Long Term Planning, Pennsylvania Storm water Management programs, potential or existing Total Maximum Daily Loads (TMDLs), River Conservation Plans, and Phase II Storm water permits. PWD's Office of Watersheds (OOW) has carried out an extensive sampling and monitoring program to characterize conditions in the watershed. The program was designed to document the condition of aquatic resources and to provide information for the planning process needed to meet regulatory requirements imposed by the Environmental Protection Agency (EPA) and the Pennsylvania Department of Environmental Protection (PADEP). The program includes hydrologic and water quality sampling and analysis, and biological and habitat assessment techniques. The Cobbs Creek Plan also included fluvial geomorphological assessments of the entire length of Cobbs Creek. A SWMM model has been developed for the watershed that can simulate the watershed response to storm water in storm sewers as well as combined sewers. The model was applied to assess current pollutant loading from CSOs and from storm water. The model was adapted to simulate a wide array of CSO controls and storm water BMPs. BMPs included swales, green roofs, infiltration basins, porous pavement, and similar techniques. By simulating BMPs at various levels of implementation, graphs of urban BMP effectiveness in controlling CSOs and storm water were developed and used to assemble cost-effective watershed management alternatives. Implementation of the plan recommendations will follow an innovative path towards three targets. The first target focuses on dry weather water quality conditions and aesthetics of the stream (primarily trash removal). The second target focuses on in-stream and riparian habitat improvement. The third, and most difficult to achieve target, focuses on phased implementation of wet weather water quality improvements.