坡面水流流速对贴地植被的响应特性试验研究

Experimental Study on the Response Characteristics of the Velocity of Overland Flow to the Ground Vegetation

坡面上植被对坡面流流速有着显著影响,进而对坡面的输沙特性起着重要作用,而覆盖度是植被影响坡面粗糙度的一个重要因素。以往研究多集中在植被覆盖度相对较小的范围。为进一步探明植被覆盖度与坡面流流速间的相关关系,基于坡面流系列概化变坡水槽试验,采用人工塑料草模拟贴地植被,设置了在0～80%范围之间的9种不同的贴地植被覆盖度、3种不同的坡度(10°、20°、25°)以及6个不同的流量级(0.286～1.058 L/s)条件下的共计162组清水径流试验,对坡面流流速特性进行了定量研究。试验结果表明:随着贴地植被覆盖度的增大,流速沿坡长由增大变为减小;当覆盖度小于30%时,流速受流量的影响较大;当覆盖度大于30%后,流速受流量的影响较小。将植被覆盖度引入坡面流流速计算公式,采用生长模型中常见的e–x表达形式反映植被对坡面粗糙度的影响,对公式中的k进行修正,应用非线性回归的方法对试验数据进行回归分析,确定参数k、a、b、c分别为10.06、–1.71、0.22、0.4,所得公式的计算效果良好(R^2=0.96)。将公式应用于其他文献中提及的实验室水槽试验条件,所得的计算值与文献中的实测值符合较好(R^2=0.73)。公式对实验室试验具有良好的适应性,而其对野外条件的适用性仍有待于进一步检验。

Vegetation has significant effects on overland flow velocity and plays an important role in sediment transportation on a slope.The land coverage is an important factor to affect the roughness of the slope.The previous researches have focused on a relatively small range of vegetation coverage.To reveal the relationship between vegetation coverage and overland flow velocity,a series of flume experiments are carried out by using artificial grass to study quantitatively the characteristics of the overland flow velocity under different vegetation coverage.The experiments are set under the conditions of 9 different vegetation coverage from 0 to 80%,3 slope gradients(10°,20°,25°)and 6 flow discharge(0.286~1.058 L·s^-1),which are 162 groups in total.The result shows that the velocity along the slop changes from increase to decrease with the increase of the vegetation coverage.The discharge has a great effect on velocity when the coverage is less than 30%and has small effect when the coverage is more than 30%.The vegetation coverage is introduced in the velocity formula of overland flow,using the common form e^-x in the growth model to reflect the influence of vegetation on slope roughness.Applying the nonlinear regression to the experiment data,the parameters k,a,b,c are determined as 10.06,–1.71,0.22,0.4 respectively.The formula obtained matches well with the measurement(R^2=0.96).Applying the formula to the lab experiments in other literatures,the results agreed with the experiment data reasonably well(R^2=0.73).It seems that the formula has good adaptability to laboratory tests,although its applicability to field conditions needs further testing.