Impacts of Parameter Uncertainty and Seasonal Variation on a Regional Model
The most recent release of the City of Detroit regional sewerage collection system SWMM model includes refinements and/or improved characterization of various model parameters such as directly connected impervious area (DCIA), rainfall dependent inflow and infiltration (RDI/I) and dry weather flow (DWF). After these improvements to the model were implemented, the Michigan Department of Environmental Quality (MDEQ) requested that the uncertainty in model parameters and the impacts of this uncertainty on the model results be evaluated. In addition to model parameter uncertainty, the seasonally varying parameters were evaluated to assess the impacts of temporal distribution. A simplified approach to evaluating the temporal distribution in seasonally varying parameters was used by comparing model results of annually averaged conditions and seasonally varying value conditions. The parameter uncertainty impacts analyses were based on a new assessment approach. The results suggest using this approach in lieu of sensitivity analysis. This approach and subsequent results are discussed in this chapter.
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