Effects of the impervious cover change on runoff and pollutant loadings from a small watershed in South Korea

Abstract

The main objective of this study was to evaluate the performance of the AGNPS (Agricultural Non-point Source Pollution) model in assessing the effects of impervious surface increase of rural area on hydrology and water quality. The Baran watershed, 385ha in size, was selected as the study site, which was a rural watershed experiencing fast increase in impervious surface area along with rapid urbanization. Digital maps extracted from the study site include a digital elevation map (DEM), slope distribution map, channel map, flow direction map, landuse map, soil map, and curve number map. Model parameters related to hydrology and water quality were calibrated and validated by comparing model predictions with the field data collected for 2 years (1999 through 2000). Calibration and validation resulted in R2 values of 0.67-0.91 for all the water quality parameters. The simulated runoff and water quality values also agreed well with the observed data. Some scenarios were used to simulate future impervious surface change by increasing impervious area or decreasing pervious area. Then each scenario was assessed in terms of its effects on hydrology and water quality. The method proposed in this study can be a useful tool for evaluating the effects of the impervious surface change on runoff and pollutant loadings for rural watersheds