Engineering methods have advanced considerably since 2009, when a presentation at the EWRI Congress reviewed the state of practice of wet weather flow analysis. Today, massive online datasets and continued software and hardware improvements enable considerably more accurate modeling of urban collection systems than was feasible at that time. As was concluded in the 2009 paper however, “methods used for typical engineering work have advanced quite modestly… 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.” The EPA Stormwater Management Model (SWMM) has maintained its preeminence as the standard for dynamic collection system modeling since the 2000s. Many improvements have been made to the software in the last dozen years, including options for explicit representation of low-impact development practices in 2010, faster simulations via addition of multithreading in 2015 and skipping hydraulic computations during dry weather in 2016, and gutter and catch basin hydraulics in 2021. This paper reviews the state of practice of collection system modeling, considering software availability, functionality, and selection, model complexity, calibration criteria, and simulation methods including design event selection. Protocols for modeling drainage, 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.
