人工模拟降雨下细沟与细沟间流速的沿程分布

Study on rill and interrill flow velocity along hillslopes with simulated rainfall

径流流速不仅是坡面径流的重要水动力学特性，而且是计算其他水力特性及侵蚀产沙的重要参数，本文目的在于研究坡面细沟流和细沟间薄层水流流速沿坡面的变化过程，比较细沟和细沟间径流流速的差别。实验选取1m、2．5m、4m、5．5m、7m、8．5m和10m共7个坡长的小区（均为5。），装填粉壤土，采用历时2h、总雨量121mm的变雨强人工模拟降雨，在固定的降雨时段用染色法测量不同坡段细沟和细沟间的径流流速，每个坡长进行干、湿运行降雨各1场，两者间隔24h。结果表明：（1）在各坡长上，细沟间薄层水流流速小于相应坡段细沟内的径流速度，细沟间流速变化于0．03～0．1m／s，而细沟内流速的变化范围为0．15～0．45m／s，整个坡面平均细沟流速是细沟间流速的2～4倍。（2）细沟和细沟间流速是距坡顶距离L的幂函数，对于细沟流速，L的指数为0．409～0．420，对于细沟间流速，L的指数为0．175～0．218。（3）平均来说，各坡长细沟流速为湿运行大于干运行，且随着距坡顶距离增加，湿运行细沟流速增加较快；而细沟间流速正好相反。本文揭示了细沟和细沟间流速沿坡面变化的基本特征及其差异，有助于深入认识细沟、细沟间侵蚀机理的差异。

Flow velocity is not only an important hydraulic property of overland flow, but also an indispensable index to calculate other hydraulic parameters. The purpose of this paper is to investigate the spatial distribution of rill and interrill flow velocity along the hillslope. Simulated rainfall and 7 plots （5 degrees steepness） with the lengths of 1, 2.5, 4, 5.5, 7, 8.5 and 10 m, repectively, were employed. The tested soil was a silty loam, sampled from Yanqing County, Beijing. For each slope length, the experiment consisted of two identical rainfall events （dry run and wet run）, timed apart about 24 hours. Each rainfall lasted 2 hours with varied rainfall intensity （27-142 mm/h） and a total rainfall of 121 mm. Flow velocities in rill and interrill area were measured with dying tracing at dif- ferent slope positions between 60 and 70 min of each rainfall. The results showed that the interrill flow velocity, on plots of all slope lengths and for both dry and wet runs, varied from 0. 03 to 0.1 m/s, whereas the rill flow velocity ranged between 0.15 and 0.45 m/s. The latter was 2 to 4 times of the former. Both rill and interrill flow velocity were power functions of L, the distance downward from the upper end of the plot, and the exponents of L for rill were larger than those for interrill, being 0. 409-0. 420 and 0. 175-0. 218, re- spectively, which was clue to the concentration of flow into rills along the slope. Addition- ally, the rill velocity in wet run was higher and accelerated faster than that in dry run, whereas it was opposite for interrill flow velocity, which may be attributed to the fact that more water was delivered into rills and the rills were stabler and smoother in wet run. The results are helpful in understanding the processes and mechanism of rill and interrill erosion.