MANAGING WET WEATHER FLOWS USING REAL TIME CONTROLS FOR THE WASHINGTON, D.C. COMBINED SEWER SYSTEM

A hydraulic model has been developed for the District of Columbia combined sewer system as part of a long-term control plan (LTCP). It is a fully dynamic model and can be used to develop real time rule-based strategies. In addition to other capital alternatives such as storage basins and tunnels, the model has been applied to evaluate existing and potential improvements of real time controls (RTC) for the sewer system. The combined system encompasses about 12,955 acres and includes many complex structures including more than a hundred regulators, eight major pump stations, and a swirl concentrator. In the past, real time control strategies were implemented by constructing inflatable dams at several locations within the system. The dams provide retention of wet weather flows through in-system storage, and help capture first flush pollutant loads by maximizing flow to the pump stations. The model can simulate all the current settings of the inflatable dams and gates, and is capable of simulating many other real time control strategies, including a dam reacting to a distant system variable such as flow and/or water level, and a pump discharging depending on the flow at a single or multiple locations or position of a gate. The model was used to evaluate effectiveness of past controls in reducing combined sewer overflows. The results indicate significant reductions in overflows from some sewersheds because of the dams.