Flow data collected from over twenty metered sites in Detroit, Michigan are used to determine the source of flows fi:om 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 event'l. As a result of model simulations, relationships were developed to represent time-to-dly 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.
Combined sewer flow data is being collected at a number of sites throughout the Detroit Water & Sewerage Department (DWSD) collection system. The collected data is being used to prepare an analysis to determine flows generated in various areas within the collection system. To establish data selection criteria, a regional sewer model was used to determine the time that would be required for the system to return to dry weather flow (DWF) conditions after specific wet weather events.As a result of model simulations, relationships were developed to represent time 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.
The City of Detroit has 77 combined sewer overflow (CSO) outfalls vvithin its sewer collection system. The City's National Pollutant Discharge Elimination System (NPDES) permit for these outfalls mandates that the public must be notified of any CSO events. H1e notification method developed for the City uses a continuous SWMM model for determining the occurrence and time of overflow. These results are submitted to the state agency for compliance with the state regulatory requirements. This notification method was approved by the state as an interim reporting method until an instrumentation project currently under way is completed. 20.1 Introduction A schematic of the greater Detroit regional sewer system's tributary area is shown in Figure 20.1. The shadings in the schematic represent various sewer districts within the system. The regional system serves 250 square miles (646 km 2) of combined sewers and 630 square miles (1628 km 2) of separate sewers. The regional system includes over 140 combined sewer overflow (CSO) outfalls. The City of Detroit has 77 outfalls within its portion of the regional sewer collection system.
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