坡耕地地表起伏对坡面漫流的影响

为揭示微尺度条件下地表起伏对坡面漫流的影响,通过野外人工模拟降雨试验,在相同降雨历时下,分析了60,90,120mm/h雨强下单凸起、单凹陷2种单式起伏和凹凸相连、凹凸相间2种复式起伏以及对照组5种微地形对坡面漫流的影响。结果表明:(1)3种雨强下,与光滑组相比,凸起、凹陷以及凹凸组合均会延迟地表初始产流时间,具体表现为对照组<凸起组<凹陷组<凹凸相间组<凹凸相连组的趋势;(2)凸起和凹陷的存在均会减小坡面漫流的平均流速,其中凹凸相连坡面平均流速最小;(3)3种雨强下,5种微地形的坡面漫流汇水形态共有3种(树枝状、平行状和羽毛状),其中对照组和凹凸相间组汇水形态均为树枝状;凸起组和凹陷组汇水形态均为羽毛状和树枝状,其中凸起组以羽毛状为主,凹陷组以树枝状为主;凹凸相连组汇水形态以平行状为主,兼有另外2种;(4)3种雨强下,5种微地形的汇流密度与径流频度呈现相同的变化规律,即光滑组和凸起组随着降雨强度增大其汇流密度与径流频度均先减小后增大,凹陷组及凹凸组合组均随雨强增大而增加,且5种微地形的汇流密度与径流频度在90mm/h雨强下的差异性最小。该研究结果揭示了不同起伏类型对坡耕地坡面漫流的影响,有助于进一步深入研究土壤侵蚀机理。

Effect of Surface Land Fluctuation on Overland Flow in Sloping Farmland

In order to reveal the effect of surface land fluctuation on the overland flow under the micro-scale conditions, through the field artificial rainfall simulation experiment, the influence of five micro topography types on the overland flow were analyzed under 60, 90 and 120 mm/h rainfall intensity for 90 min. The five micro topography types were smooth, single mound, single depression, intervals mound and depression, continuous mound and depression. The results showed that:(1) Compared with the smooth group, the single mound, single depression and mixed fluctuation mode all delayed the initial flow generation time, and the time followed the order of smooth group < single mound group < single depression group < intervals mound and depression group < continuous mound and depression group. (2) The existence of mounds and depressions reduced the average flow velocity, among which the average flow velocity of continuous mound and depression group was the smallest. (3) Under the three kinds of rain intensity, there were three kinds of catchment form of overland flow on slope (branch shape, parallel shape and feathery shape) in five kinds of microtopography, among which catchment forms of the smooth group and the intervals mound and depression group were both branch, the catchment forms of the single mound group and the single depression group were feathery and branch, while it was mainly feathery shape in single mound group and branch in single depression group. The catchment forms of the continuous mound and depression group were mainly parallel shape. (4) Under the three kinds of rainfall intensity, the confluence density and runoff frequency showed the same change rule, which was the confluence density and runoff frequency of smooth group and single mound group decreased at first, and then increased with the increasing of rainfall intensity, meanwhile, the confluence density and runoff frequency of single depression group and combination of mound sand depressions groups increased with the increasing of rainfall intensity. The differences in the confluence density and the runoff frequency among the five microtopography were the smallest under the rainfall intensity of 90 mm/h. The results of this study revealed the influence of different surface fluctuation types on the overland flow of sloping farmland, which was helpful to further study the mechanism of soil erosion.