A Model Framework to Support Integrated Watershed Planning

The numerical analyses discussed in this paper 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. This paper presents a case study for the Tookany-Tacony-Frankford (TTF) watershed, an urban watershed in southeastern Pennsylvania. Because the watershed is highly developed, the potential for new development is limited. The watershed is a complex system that provides ample opportunities to develop and demonstrate a comprehensive watershed management program in an urban environment. The foundation of the current study is a comprehensive hydrologic and hydraulic model of the watershed including a sub-model of the combined sewer system (EXTRAN) and its tributary area (RUNOFF), and a RUNOFF representation of the drainage area tributary to the areas served by separate storm sewer systems. The stream system itself is modeled using EXTRAN, with open channels representing the natural stream cross sections. The RUNOFF and EXTRAN models of the combined sewered areas were developed and calibrated as part of the City of Philadelphia's CSO permit compliance program. The watershed-wide model calibration for this work was based upon continuous simulation model comparisons with historic observed daily streamflow. Simulated and monitored event volumes were compared and hydrologic parameters were adjusted to obtain a reasonable match across a range of storms. The resulting model simulates rainfall-runoff processes, flow in the sewer system, and flow in open channels. It was used to evaluate the technical merits of a number of watershed management alternatives, ranging from stormwater best management practices to CSO control measures to stream and habitat restoration.