Watershed/Sewershed Modeling

Urban runoff and its conveyance through sewer systems are the critical factors that guide urban watershed management. Municipalities are increasingly challenged with regulatory requirements for combined sewer overflows (CSO), sanitary sewer overflows, 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 systems. Understanding the urban runoff and sewer system elements help in characterizing the existing system, and also in assessing the impacts of future landuse practices and improvements resulting from best management practices (BMPs) and sewer rehabilitation programs.

HydroQual has assisted major municipalities since the 1980s and has developed simple to complex runoff and sewer system 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. HydroQual has also served critical roles in the regulatory aspects of wet weather discharges including the U.S. Environmental Protection Agency’s guidance documents on CSO abatement.

Our experience in rainfall-runoff characterization and sewer system modeling is extensive and we have assisted more than a dozen municipalities including New York City, Passaic Valley Sewerage Commissioners, Washington (DC), and Fort Wayne (IN) in their CSO projects. Our staff have used a range of modeling tools including the Storm Water Management Model (SWMM), EPA SWMM, XP-SWMM, and InfoWorks for characterizing combined, sanitary and stormwater systems. HydroQual’s project experience 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, and development of pollutant loads for TMDL evaluations.