Impact of Land Cover Change on Surface Runoff in the Walnut Gulch Experimental Watershed

Land cover change alters hydrological response of a watershed and usually results in flooding. This paper studies the effectiveness of porous pavements in reducing the impact of built-up area on surface runoff and peak flow in the Walnut Gulch Experimental Watershed. The built-up area is expanded into high intensity developed surface with 80%-100% imperviousness. The precipitation events between July and October of 2018 (more than 60% of annual rainfall) are used to calibrate the baseline response. Watershed is modeled in Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS), whereas flow routing is performed in Hydrologic Engineering Center-River Analysis System (HEC-RAS). The model is calibrated and validated by using observed discharge hydrograph data at the watershed outlet (location: 31o 43' N, 110o 41' W). The precipitation and runoff observations were obtained from the United States Department of Agriculture (USDA), agricultural research service website. Land cover data was obtained from the United States Geological Survey (USGS) website. Two scenarios were modeled. In the first scenario, built-up area is increased by changing the value of imperviousness to more than 80% in HEC-HMS. In the second scenario, low impact development (LID) is integrated in the model in the form of porous concrete used in the built-up area. Model simulation of the first scenario shows an increased surface runoff volume. Moreover, the lag time between storm peak and discharge peak reduces due to decrease in the infiltration rate. In the second scenario, the surface runoff is significantly reduced due to increased infiltration resulting from LID. The results of this research provide useful insight about potential land cover change impact on the watershed response and can help in land use planning.