The Effects of Various Low-Impact Development Combinations on Surface Runoff Reduction in the Smith Branch Watershed Using the SWMM Model.

Urbanization across the world has increased the volume of surface runoff along with increasing the frequency of flooding. Measures like low-impact development have been made in order to reduce the volume of surface runoff. While LID measures have been implemented across the world, they have not been studied within the Smith Branch watershed. The purpose of this study was to see the effectiveness of different LID measures on surface runoff reduction in the Smith Branch watershed. Results were recorded from simulations through EPA SWMM (Environmental Protection Agency Stormwater Management Model). It was hypothesized that the combination of green roofs and permeable pavement would be the most effective in surface runoff reduction. This study used a digital elevation model and QGIS (Quantum Geographic Information Systems) to generate subcatchments and their associated parameters. Subcatchments were added to SWMM, coupled with a rain gauge for rainfall data, along with conduits, junctions, and an outfall to represent surface runoff drainage. Once simulations were run, surface runoff volume was recorded. The LID model with only green roofs removed 22.767% of surface runoff, green roofs + vegetated swales removed 27.834% of surface runoff, and green roofs + permeable pavement removed 74.439% of surface runoff. It was found that adding LID to the model would result in the surface runoff volume decreasing. These results suggest that a combination of green roofs and permeable placement should be implemented in the Smith Branch Watershed for surface runoff reduction.