Modeling Interstate Runoff with a Physics-Based, Spatially Explicit Model (GSSHA) Using High-Resolution DEM Data and Measured Field Data

Abstract

An initial assessment of interstate runoff impacts to a receiving water body yielded approximately 2 years of groundwater, surface water, and streamflow measurements upstream and downstream of a section of an interstate within a rural/forested watershed. It became clear that stormwater runoff is larger downstream of the interstate, but analysis of area-averaged runoff datasets have resulted in a variety of inconclusive findings. In order to better understand the hydrology of the interstate and its associated flow features (medians, ditches, realignment of channels, compacted soils, etc.) a detailed hydrological model (Gridded Surface Subsurface Hydrologic Analysis (GSSHA)) is being set up with high-resolution digital elevation model (DEM) data, soil characteristics, and coupled with measured field data. Research questions include: Do the interstate’s features (ditches, median, soil types) encourage or limit infiltration, flow velocity, and groundwater fluctuations? Of interest is the variation in surface-water groundwater interactions at the interstate stream crossing, as well as interactions within the interstate median, interception of subsurface runoff by ditches, permeability of the interstate subsurface (as compared with the surrounding area), and the runoff-rainfall ratio of the areas. To answer these questions, a resolute, physics-based model (GSSHA) is used to resolve the varying hydrologic features of the interstate. By resolving the interstate runoff features, work in the future may be done including comparing the models effectiveness of predicting land use change impacts to other widely used and available hydrological models (such as Stormwater Management Model (SWMM5)).