SWMM Application to Combined Sewerage in New Haven

Storm Water Management Model (SWMM) of EPA was calibrated to predict runoff flows in the central portion of the city of New Haven, Conn. The study area is served by combined sewers and overflow structures to divert excess wet weather flow into the adjacent receiving waters. For application of SWMM, the project area was divided into 23 subcatchments and two of them were selected for model calibration. During storm events, the rainfall hyetographs, the runoff hydrographs and combined sewage quality parameters were measured in each of the two subcatchments. Using these data in SWMM calibration and verification of flow quantities was accomplished successfully. However, problems were encountered in the quality calibration. The calibrated model (quantity portion only) was subsequently used to predict runoff flows for the design storm in each of the 23 subcatchments. A two-year storm was selected as design storm from the available 35 yr of rainfall record. Literature values of BOD and SS were used to predict wet weather waste loads.