Simulating the integrated effects of topography and soil properties on runoff generation in hilly forested catchments, South China

Abstract

AbstractEstimation of runoff components associated with catchment topography and soil properties is critical for planning water resources utilization and evaluating hydrological changes due to artificially induced land surface manipulation. In this study, the modified TOPMODEL by Scanlon et al. (2000) was applied to simulate runoff‐generating processes and to separate runoff components in two hilly forested catchments within the Dongjiang Basin of Southeast China. The modified TOPMODEL was improved by integrating an evapotranspiration package with the model algorithms. Influences of catchment topography and soil properties on runoff generation were analysed on the basis of explicit expression of catchment field capacity distribution derived from the topographic index and catchment average field capacity. Study results demonstrate that the model is capable of simulating hydrological processes and separate hydrological components in both hourly and daily time steps. Total runoff generation primarily depends on the effective storage capacity of unsaturated zone. A 50% decrease of the effective storage capacity from 0·22 to 0·11 m over the soil zone leads to a 6·6% increase in total runoff. Topography plays a dominant role in formation of runoff components. When the catchment mean slope increases by 87%, subsurface storm flow could increase by 50% whilst overland flow decreases by 7·5% and baseflow by 6·7%. Vertical changes of soil permeability influence runoff components as well. Decrease of the lower layer hydraulic transmissivity may result in 2–3% increase of overland flow and subsurface storm flow and 5% decrease of baseflow. Copyright © 2009 John Wiley & Sons, Ltd.