Abstract: Few studies have addressed the role of raindrop impact on hydrodynamic mechanism of soil erosion. In this study, rainfall simulation experiments were conducted to evaluate the role of raindrop impact on processes of runoff and sediment yield, flow-hydraulic characteristics, and dynamic mechanism of raindrop impact under three rainfall intensities (50, 75, and 100 mm h−1) at three slope gradients (5°, 7.5°, and 10°). These rainfall intensities and slope gradients were tested under two soil surface conditions: one with raindrop impact and the other without raindrop impact by placing nylon net over a soil pan. Result showed raindrop erosion accounted for 72.3% to 96.2% of the total sediment yield. Furthermore, runoff rate and sediment concentration were greatly reduced during rainfall with the elimination of raindrop impact. The corresponding reduction rates were 1.13% to 84.08% and 48.13% to 96.50%, respectively. After eliminating raindrop impact, hydraulic parameters of flow depth, flow velocity, Reynolds number, and Froude number were markedly reduced, whereas Darcy-Weisbach coefficient was increased 1.40 to 5.31 times; flow velocity was the key hydraulic parameter affecting raindrop erosion. Raindrop impact caused the critical hydrodynamic forces of shear stress, unit stream power, and stream power increase more than two-fold relative to the treatment without raindrop impact. Raindrop erosion rate had a significant linear relationship with the relative increment in unit stream power or stream power induced by raindrop impact. These findings present a new approach for predicting raindrop detachment rate from the point of flow hydraulics and dynamic mechanism of raindrop impact.
1State Key Laboratory of Soil Erosion and Dryland Farming in the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi, China.
2Graduate University of Chinese Academy of Sciences, Beijing, China.
3College of Resources and Environment, Northwest A&F University, Yangling, Shaanxi, China.
Address for correspondence: Prof. Fenli Zheng, State Key Laboratory of Soil Erosion and Dryland Farming in the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling, Shaanxi, 712100, China; E-mail: email@example.com
Received October 25, 2011.
Accepted for publication June 4, 2012.
Financial Disclosures/Conflicts of Interest: This study was supported by National Natural Science Foundation of China, National Basic Research Program of China (grant no. 2007CB407201), and the French Minister of Foreign Affairs through a Hubert Curien grant (PFCC 2009-2010; grant no. 20919ZC).