Simulating the Flood Mitigation Efficiencies of Low Impact Development Features in the Little River Watershed (C-7), Miami, Florida

Miami-Dade County, Florida, is a highly urbanized coastal jurisdiction very susceptible to flooding due to numerous natural and anthropological factors such as low topographic relief, high imperviousness, excessive tidal fluctuations, intensive storms, and accelerated sea-level rise. The Little River watershed (C-7), located in northeastern Miami-Dade County, is one of the most flood-prone watersheds in the region. Low impact development (LID) features have been suggested as one potential solution for flood mitigation through enhanced infiltration and storage. LID features help to reduce flood by minimizing the total runoff volume and peak runoff from subwatersheds. To test the effectiveness of LIDs in reducing runoff volume in flood-prone subwatersheds in C-7, we used a calibrated stormwater management model (PCSWMM). We implemented a mixed design approach by incorporating three types of LID features (bioretention cells, infiltration trenches, and rain barrels) in the impervious areas of the flood-prone subwatersheds. We parameterized the LID elements based on their sensitivity to surface infiltration, soil percolation, and storage. We finally simulated the LID features for different flood management alternatives under three storm event scenarios [Hurricane IRMA (~1.5-Yr), 10-Yr, and 25-Yr storm]. The preliminary simulations suggest a potential 20-30% reduction in total runoff volume and 15-25% reduction in peak runoff when LID features represent 25% impervious areas of flood-prone subwatersheds. This ongoing modeling work will help to quantify the contribution of LID features to watershed-scale flood management and watershed restoration.