State of the Practice of Wet Weather Flow Analysis

Engineers analyze wet weather flow in collection systems using a variety of computer tools and analytical techniques. Tools and data available for performing these analyses have greatly advanced since software for this purpose was first standardized in the 1970s. The practicing engineer today has access to GIS-based modeling software, high-resolution land cover and elevation datasets, and enormous hydrologic databases. Methods used for typical engineering work have advanced quite modestly by comparison. Furthermore, there is little standardization of how analyses of drain, combined sewer, and sanitary sewer collection systems are carried out, despite considerable commonalities among their wet weather performance. This paper reviews the state of the practice of collection system modeling, considering software availability and selection, model complexity, calibration criteria, and simulation methods. Urban modeling protocols for drain, combined, and sanitary sewer systems are discussed. Uniform approaches for model calibration are suggested. Finally, the paper identifies research and development needs where the state of the practice is limited by current technology.