Watershed & Sewershed Modeling

Urban runoff and its conveyance through sewer systems are critical factors that guide urban watershed management. Municipalities are increasingly challenged with regulatory requirements for combined sewer overflows (CSOs), sanitary sewer overflows (SSOs), stormwater, wet weather capture at treatment plants, and total maximum daily loads (TMDLs). Hydrologic losses such as infiltration and impervious surfaces determine the surface runoff generated in separate systems from an urban area. Similarly, the sewer system elements such as pipes, regulators, pumps, outfalls, and tide gates determine the amount of runoff that will be conveyed to the treatment plant in combined sewer systems. Understanding the urban runoff and sewer system elements help to characterize the existing sewer network, and also in assessing the impacts of future land-use practices and improvements resulting from best management practices (BMPs) and sewer rehabilitation programs.

Our experience in rainfall-runoff characterization and combined, sanitary, and stormwater sewer system modeling is extensive. We have assisted numerous municipalities in developing simple to complex runoff and sewer system network models for characterizing existing conditions and designing abatement programs. Calibration and confirmation of these models is often a daunting task and our strong expertise in the areas of monitoring program design, data analysis, selection of storm conditions suitable for calibration and confirmation, and development of quality control and uncertainty analysis procedures results in the development of consistent, effective, and robust modeling tools.

Our project experience and expertise includes:

• Design of rehabilitation and BMP programs to meet EPA's CSO abatement requirements
• Evaluation of design flows at treatment plants and outfalls for capture of floatables and solids
• Feasibility assessments of real-time control of flows within sewer systems to maximize treatment
• Development of percent capture of wet weather at treatment plants for reporting to regulatory agencies
• Development of pollutant loads for TMDL evaluations

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