ASSESSMENT OF LOW IMPACT DEVELOPMENT ON CSO

Low-impact-development (LID) measures have been demonstrated to markedly reduce peak runoff flows from new and existing urban developments. The goal of this project was to derive a reasonable estimate of the maximum potential reduction in CSO volume for the Hamilton County CSO service area addressed in the recent CSO Long Term Control Plan Update through the application of green infrastructure measures. This investigation was designed to provide a reasonable indication of the maximum potential benefits of LID measures and to determine if more comprehensive investigations should be initiated to integrate LID into the CSO Long Term Control Plan.A representative combined sewer overflow (CSO) drainage area, Lick Run (CSO 005) in the Mill Creek watershed was selected for detailed evaluation to determine the maximum potential benefit of LID measures with respect to CSO control. The outcome of the Lick Run assessment is used to extrapolate the potential benefits to other CSO areas based primarily on land use, soil and topographical information providing the District with an understanding of the maximum reasonable potential of LID in reducing CSO.The effectiveness of LID features used in a combined sewer area was shown to be beneficial in reducing that amount of CSO and increasing the level of control. It was also shown that the incremental benefit in CSO control associated with LID features lessens as the level of CSO control increases. The Metropolitan Sewer District of Greater Cincinnati believes a comprehensive green infrastructure will not replace the need for structural controls but will enhance and possibly offset structural program elements providing an improvement in the control of CSO and receiving water quality.