Abstract

The Detroit Water & Sewerage Department (DWSD) collection system and WWTP serves the majority in Southeastern Michigan, This collection system has been modeled in detail since 1987. The primary model used for these evaluations has been the US EPA Stormwater Management Model (SWMM). While this model provides significant capability, the combined sewer evaluations per-formed for this area have required modifications both to the methods used to prepare the model and changes to the calculations performed by the model. This chapter highlights the changes that have been made to the model to provide an appropriate evaluation of the collection system performance.

Many of the new features added to the SWMM model have been driven by the need to evaluate different methods to control combined sewer overflows. Some changes were required by the sheer scope of the modeled area and by the complexity of the collection and treatment system.

The changes made include better methods to simulate flow routing; improved algorithms to simulate dry weather flow (DWF), rainfall dependent inflow/infiltration (RDI/I), and their seasonal variation; better methods to evaluate regulators, outfalls, and storage; and finally, better formats used to present the output to fairly evaluate the different options considered. Many of these updates to the model will be useful for other projects that may not have the large scope of this project.

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