Modeling Highway Stormwater Runoff and Groundwater Table Variations with SWMM and GSSHA

Abstract

Hydrologic models are widely used to represent and study water flows in various land uses and environments. This paper presents work done to model stormwater runoff from a highway and forested watershed in Alabama using two models: Gridded Surface/Subsurface Hydrologic Analysis (GSSHA) and Storm Water Management Model (SWMM). Of particular importance in this work is exploring similarities and differences in surface and groundwater modeling results between the two models. SWMM and GSSHA calculated similar precipitation infiltration via the Green-Ampt equation and similar volumes of surface runoff for all events shown here. Comparisons of modeled data to measured streamflow and groundwater table elevation data are made for major storm events in 2013–2014. GSSHA reproduced event streamflow volumes with total sum of absolute residuals (TSAR) error ranges from −4.87 to −0.61 m3/s compared with SWMM flow volume TSAR error ranges from −7.66 to 9.29 m3/s. Both programs performed well in calculating the groundwater table elevation change due to stream bank storage, with sum-square error ranges of 0.0074–0.0206 for GSSHA and 0.0066–0.0249 for SWMM. GSSHA represented spatially varying groundwater table elevations, whereas SWMM calculated the average groundwater table elevation in response to rain events and stream bank storage.