坡沟侵蚀产沙关系的模拟试验研究

黄土高原坡面从分水岭到坡脚,径流侵蚀产沙方式和产沙强度等特征表现出明显的垂直分带性。为了揭示造成这种垂直分带性特点的形成机理,本文设计了4m长坡面(坡度为20°)和3m长沟坡(坡度为50°)组成的坡沟系统试验土槽,采用四个不同流量(2.1Lmin-1、3.2Lmin-1、5.2Lmin-1、7.2Lmin-1)的放水冲刷试验,研究了坡面不同来水量、来水含沙量及来水动能对沟坡侵蚀产沙的影响,并建立了坡沟系统侵蚀产沙过程的数学模型。结果表明:坡面放水径流强度、坡面来水含沙量以及坡面来水单位水流功率均影响着沟坡部分侵蚀产沙量的大小。坡面放水径流强度与沟坡侵蚀产沙量之间呈幂函数关系;坡面来水含沙量和坡面来水单位水流功率与沟坡部分的侵蚀产沙量之间呈线性关系。根据单位水流功率的概念,计算得出试验条件下沟坡侵蚀产沙的临界单位水流功率值为0.632。最后,根据改进的Yalin公式及沟坡侵蚀产沙的影响因素,分别建立了坡面和沟坡侵蚀产沙的数学模型,经计算后与实测值进行对比发现结果基本令人满意。

SIMULATION OF SEDIMENT YIELDING IN RELATION TO SLOPE AND GULLY

Runoff erosion formation and sediment yielding intensity on slopes of the Loess Plateau of China show apparent vertical zonation because of the complicated topography and the special climate conditions of the region.To reveal mechanism of the formation of runoff erosion and the characteristic of vertical zonation,an experiment was carried out with a simulated slope-gully system,which was composed of a 4-meter long slope(20°)and a 3-meter long gully slope(50°),and four different fluxes of runoff(2.1 L min^-1,3.2 L min^-1,5.2 L min^-1,and 7.2 L min^-1).Impacts of flux,silt content and impetus of the runoffs on sediment yield were explored.Based on the findings,a mathematical model was established for depicting sediment yielding process in the system.Results show that intensity,silt content and flowing power per unit volume of the runoff flowing down the upper slope were the major factors affecting sediment yield in the gully.Sediment yield in the gully was exponentially related to intensity of the runoff,and linearly to silt content and flowing power per unit volume of the runoff.Based on the concept of flowing power per unit volume,a value defined to be critical to sediment yielding in the gully was figured out to be 0.632.And based on the modified Yalin equation and factors affecting sediment yield,mathematical models were worked out for sediment yield on the slope and in the gully,respectively.Results of the calculation using the models were found to be satisfactorily comparable to the measured ones.