An Equivalent Rainfall Technique to Identify Dry Weather Flow Data for City of Detroit Flow Balance Analysis
Flow data collected from over twenty metered sites in Detroit, Michigan are used to determine the source of flows from districts tributary to the Detroit Water & Sewerage Department (DWSD) collection system through a flow balance analysis. Criteria developed for selecting data include precipitation, snowmelt, and basin dewatering. The Greater Detroit Regional Sewer System (GDRSS) model, a hydraulic and hydrologic model of Detroit's sewer collection system, was used to refine the rainfall-based criteria. Specifically, it was used to determine the time required for the system to return to dry weather flow (DWF) conditions after one or a series of rainfall events. As a result of model simulations, relationships were developed to represent time-to-dry as a function of the rainfall amount of single- or multiple-day rainfall events. These relationships are a key component of the overall data selection for the flow balance, and provide an objective approach to characterizing DWF in the DWSD collection system.
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