The effect of vegetation cover on overland flow velocity can cause changes of characteristics of sediment discharge, but the relationship between coverage changes and the velocity is still unclear under steep slope conditions. Aiming at the shortage of research at home and abroad, this study discussed the relationships between average velocity and coverage rate, slope and discharge systematically on overland flow. Flow velocity was simulated in an experimental flume with varying slope in a large scale of slope gradient ( 5 ° ~ 25 °) , flow discharge (0. 25 ~ 2 L/ s) and coverage rate (0% ~25% ). The result indicated that average velocity of overland flow changes from 0. 15 L/s to 1. 35 L/s. It is closely related to the coverage rate, slope and discharge. With the simulated surface coverage increasing, the water flow consumed more energy to overcome the resistance, so the flow velocity decreased a-long. With the increasing of slope and discharge, gravitational potential energy and kinetic energy of overland flow increased, and the average velocity increased by power function. The statistical regression showed that the dominating influential factor to velocity is coverage rate (45% more or less) , and then slope and discharge. Three factors could be used to simulate the velocity of overland flow (R2 =0. 93). The research is helpful to have further understanding of the character of overland flow on steep slope with coverage by the way of dynamics, and provides theoretical basis of physical modeling of soil erosion.%植被覆盖对坡面流流速的影响,会引起坡面输沙特征的改变,但在陡坡条件下盖度与流速的响应关系尚不明确.针对目前国内外研究的不足,本研究采用变坡实验水槽在较大坡度(5°～ 25°)、流量(0.25 ～2 L/s)和盖度(0％～25％)范围内,系统研究了坡面流平均流速与盖度、坡度、流量之间的关系.结果表明:坡面流流速在0.15～ 1.35 m/s内变化,流速与盖度、坡度和流量关系密切.随着地表模拟盖度的增加,水流克服覆盖物的阻碍作用而消耗的能量越多,水流流速随之减小.随着坡度和流量的增加,坡面流重力势能与水流动能增加,因此流速随坡度和流量呈幂函数增加.通过统计回归发现,盖度对流速的影响最大,占45％左右,坡度和流量次之.三个因子可以较好模拟陡坡、定床条件下水流流速(R2 =0.93).研究结果有助于认识陡坡地表覆盖下坡面流的水动力学特性,为建立土壤侵蚀过程模型提供理论基础.
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