GIS-SWMM based LID Design Evaluation

University of New Orleans investigators are developing a cost-effective network of flow monitoring sensors to calibrate a campus Storm Water Management Model (SWMM). The pre-calibrated model is used as a preliminary tool to measure and study the effectiveness of GI design alternatives on the campus for the 10yr/24hr design event. A geographic information system (GIS) that facilitates large scale, site specific, low impact development (LID) modeling in SWMM is essential in simplifying and defining model development for the LID system. Several SWMM parameters, such as pervious/impervious surface areas, subcatchment width, and surface and subsurface drainage slope, among others, are a function of onsite attributes such as infiltration rate, depression storage, roughness, flow length, etc. With GIS processing, these attributes can be more precisely defined. The LID-GIS becomes a valuable pre-processing input tool for SWMM model development and site LID analysis by properly delineating GIS layers and assigning attributes specific to LID modeling. This study conducts a preliminary evaluation of the effectiveness of LID features in a SWMM model on the UNO Lakefront campus. Five LID systems are designed as an exercise to test the preliminary model and identify nodes of interest for hydraulic analysis. At each node of interest, the effectiveness of the LID at reducing Peak Flow, Mean Total Inflow, Total Inflow Volume, and delayed Time to Peak was tested using the paired t-test for LID effectiveness and the Nash-Sutcliffe Efficiency coefficient (NSE) for evaluation of statistical significance of differences between the baseline model and the LID implementation. One example LID implementation with the addition of a bioretention cell and impervious pavement parking results in a simulated 7% mean peak flow reduction, 14% mean inflow volume reduction, and little change in time to peak. Results like these are then used to evaluate and recommend specific LID design modification alternatives.