Effects of Land Use Change on Hydrologic Response at a Watershed Scale, Arkansas

The population has increased at a fast pace in the last two decades in Arkansas. One direct result from this process is urbanization, especially in northwest Arkansas. Land use and land cover (LULC) had been changed from forests, pastures, and farmland to urbanized areas over a short time span. Increased flood discharge and decreased water quality have been negative side effects of urbanization on the environment. In this study, five watersheds were selected as representative of the entire state. These watersheds were selected to examine the hydrological response to land use change over the last two decades in Arkansas. The curve number, a term used to describe the runoff depth, was calculated for the five watersheds. Out of the five watersheds, the Illinois River watershed experienced the greatest change in land use from 1993-2006, whereas the other four watersheds experienced slight land use change. The land transformation model (LTM) was used to forecast the land use of the Illinois River watershed in the year 2019. Simulated urbanized area in the Illinois River watershed from 1993-2019 increased from 3.7 to 23.6%. The curve number of the Illinois River watershed would increase from 68.9 in 1993 to 72.1 in 2019. The Spring Creek-Osage Creek watershed, a subwatershed in the Illinois River watershed, was selected for detailed evaluation of the hydrologic response attributable to land use change. The storm water management model (SWMM) was used to calculate the flood discharges resulting from different storm events. The simulation results showed that during 1993-2019, the peak flood discharge of the Spring Creek-Osage Creek watershed for the storm return periods 2, 5, 10, 25, 50, and 100 years increased 230, 180, 160, 140, 130, and 110%, respectively, whereas the total flood volume increased 270, 220, 200, 170, 160, and 140%. The results in this study might suggest to small cities like Bethel Heights that it is better to plan the drainage systems for the coming decades before such cities have already sprawled. This study also applies a combined methodology of a regional scale urbanization-flood model, which could be used to improve flood frequency analysis.