Effects of reforestation on the hydrological function of a small watershed in the Three Gorges Reservoir Area

Abstract

For vegetation communities with hydrological function in the Three Gorges Reservoir Area, the storm event distributed hydrological model Precipitation-Runoff Modeling System (PRMS)-Storm was built based on modular modeling system developed by the US Geological Survey, and was employed to study the effects of forests on peak flows in the Xiangshuixi forest watershed in the Three Gorges Reservoir Area. The results showed that: 1) this simulation study suggested that PRMS-Storm can meet the second level national flood prediction standards of China for simulating storm events of small forest watersheds, and can issue flood forecasting; 2) hydrological functions of different vegetation communities were evaluated, and three simulation scenarios were arranged: mixed conifer-broadleaf forests (scenario 1), broad-leaved forests (scenario 2), and general forests arrangement (scenario 3); 3) the well-arranged forest scenarios can reduce over 20% of surface runoff, result in an increase of over 16% in subsurface flow, and decrease peak flow by 20.8%, 9.6%, and 18.9%, respectively. The reduction of peak flow rates was significant when rainfall peak was higher than 0.8 mm/min, especially for short-term rainfall events. In general, we found that scenarios 1 and 3 were preferable for reducing peak flow rates and volumes in the reforestation practices in the study region, and scenario 1 was better than scenario 3, so the mixed conifer-broadleaf forests had the best hydrological function.