草被覆盖对坡面流流速影响的人工模拟试验研究

草被覆盖是影响坡面流流速变化过程及特征的重要因素之一。研究草被覆盖下坡面流流速时空分布特征，对揭示草被减蚀作用机理有重要作用。该文通过室内放水冲刷试验研究了黄土丘陵区坡沟系统坡面不同草被覆盖对坡面流流速变化过程及特征的影响。试验中共涉及坡沟系统坡面5种草被覆盖度、3种空间配置和2种放水冲刷流量。研究结果表明：放水流量为3.2 L/min时，坡面草被覆盖对坡面流流速的延缓作用较大；流量为5.2 L/min时作用相对减弱；坡面及沟坡平均流速随坡面草被覆盖度的增加呈指数下降趋势。坡面流流速在坡面的发展有一个坡长范围，试验中，在距坡顶3～4 m处，坡面流流速达到最大；坡面、沟坡各断面流速基本上都随着放水冲刷时间的延长而呈下降趋势。

Experimental study on the effect of different grass coverages on the overland flow velocity

Grass coverage has great influence on the change of overland flow velocity. Studies on the temporal and spatial distribution characteristics in overland flow process with different grass coverage degrees are necessary to better understand and reveal the soil loss reducing mechanism of grass coverage. The objective of this study is to reveal the changeable process and characteristics of overland flow velocity with different grass coverages in the slope-gully system on Loess Hilly Area. Five grass coverage degrees (0, 30%, 50%, 70% and 90%), three spatial distributions of grass (upper, middle and lower) and two water inflow rates (3.2 L/min and 5.2 L/min) were adopted in the experimental soil box. Results showed that the grass coverage had great influence on staying flow velocity at 3.2 L/min inflow rates, which was relatively weak for 5.2 L/min inflow rates. An exponential relationship between the flow velocity and grass coverage degree is observed. The flow velocity increased and reached the maximum on the hillslope within a three or four meters' downslope distance, and the flow velocities of each segment almost all decreased with increasing scouring duration in the scouring experiments.