Impacts of urban drainage systems on stormwater hydrology: Rocky Branch Watershed, Columbia, South Carolina

Abstract

AbstractIncreases in impervious surfaces and land‐use changes associated with urbanization have long been the focus of urban hydrological research. However, studies and calculations that consider impervious surfaces alone do not encompass all factors that influence urban hydrologic response, as alternative urban structures may have a substantial effect on stormflow. This study examines several descriptors to improve estimations of hydrologic impacts of urbanization in small watersheds. Configurations of drainage densities that include storm sewers were computed for the highly urbanized Rocky Branch Watershed. Storm sewer configurations resulted in an approximate tripling of the drainage density. In addition, rainfall and stormflow data were analyzed to compare the hydrologic response of two subcatchments with varying percentages of impervious areas and drainage densities. The subcatchment with a higher percentage of impervious area produced significantly (p < .01) higher runoff volumes with an average runoff coefficient of 0.446, while the subcatchment with higher storm sewer densities displayed significantly shorter lag times of 9 min. In this case, the percentage of impervious area increased the volume of runoff but, storm sewer densities accelerated hydrologic responses, suggesting that hydrologically relevant metrics should be considered to accurate assess flood risk alternatives.