Optimizing green infrastructure practices for the Pond Run watershed in Hamilton, New Jersey

Flooding appears to be a disruptive disaster to human health and property during the progress of urbanization. Due to climate change and urbanization, Green Infrastructure (GI) or Low Impact Development (LID) has become a solution for the increasing volume of rainfall by disconnecting the runoff from the sewer system, extending the water retention time, and reducing the impervious surfaces that contribute to the river. This study is seeking a better understanding of the effectiveness and economic feasibility of green infrastructure. The hypothesis is that sufficient green infrastructure practices will reduce flooding in aspects of water elevation and floodplain width. Based on previous work, five sub-basins within Pond Run Watershed in Hamilton, New Jersey were identified as the priority areas for stormwater runoff mitigation. This study further analyzed the largest sub-basin of those five in aspects of hydrologic and hydraulic characteristics. A total of 45 points along the North Branch of Pond Run are identified as points of interest, where the geometric data of the channel cross-sections are surveyed. The peak discharges at the survey points are modeled with HydroCAD based on land use data from geographic information system (GIS) and field verifications with 1, 2, 5, 10 and 100 year type-III 24-hour-storms. The hydraulic study is modeled with Hydrologic Engineering Centers River Analysis System (HEC-RAS) to predict scenarios under various runoff situations assuming 10%, 20%, 30%, 40% and 50% of imperviousness through the whole sub-basin is disconnected by green infrastructure practices. By comparing the water surface elevation and floodway width under different assumptions, the effectiveness of GI is analyzed. The water elevation and floodway width of the North Branch of Pond Run are reduced by applying green infrastructure under various amounts of storms. However the effectiveness of GI decreases as the amount of water precipitation increases. In addition, the peak runoff volume reduction is correlated with economic feasibility. A few design plans within the subject watershed are given as examples, which will contribute to a better understanding of both the efficiency and the cost-effectiveness of GI and will help the public to make appropriate decisions.M.S.Includes bibliographical referencesby Tianshui Y