Large-Scale Analysis of Sewer Capacity to Inform Capital Planning and Design

The city of Philadelphia invests in the renewal of its wastewater and combined sewers to keep the collection system functioning effectively and efficiently. Scenarios that lead to replacement of collection system pipes include pipe failure, capacity limitations, end of design life, etc. In this paper, we describe an ongoing effort to evaluate sewer design peak flow capacity for Philadelphia Water Department’s (PWD) sewer system. Historically, capacity analyses were conducted using record-drawings, measurements, and manual hydrologic and hydraulic calculations. The updated approach described here utilizes a systematic and semi-automated approach to assess sewer capacity. Along with traditional engineering calculations, tools such as geographic information systems (GIS), computer models, and databases are used to implement the updated approach. The process is not fully automated and human intervention is required. We demonstrate the potential of the collection system capacity inventory to support capital planning through investment modeling, and to assist with engineering design. For example, the citywide database of flow capacity can expedite development and analysis of complex hydrologic and hydraulic models. The hydrologic and hydraulic models developed could be then used for evaluating alternatives to meet defined objectives.