降雨过程中黄土坡面微地形因子与侵蚀关系研究

Relationship between micro-topography factors of loess slope and erosion under intermittent rainfall

以断续降雨过程中不同阶段的黄土坡面栅格单元地形信息为研究对象,通过12段30 min、60 mm/h雨强的降雨进行模拟降雨试验,对微坡度、微坡向与黄土坡面侵蚀过程、细沟形态演变的相互影响进行研究。研究结果表明:坡面微坡度与微坡向的变化主要集中在降雨初始阶段(0~30 min),后续阶段(30~360 min)变化幅度较小,微坡度和微坡向变化与坡面时段侵蚀量显著正相关。细沟网络形成后,微坡度<15°区间和45°以上区间栅格占比缓慢上升,且主要产生于细沟内部,细沟内部在发育过程中会产生泥沙堆积的平台和坡度较大的陡坎。细沟的发育过程是细沟内径流的剥蚀和边壁不稳定土体的坍塌共同作用的非均匀发育过程,径流的剥蚀和土体的坍塌互相促进,加速了细沟的发育过程,从而造成了侵蚀量的波动。细沟侵蚀过程中坡面微坡向以坡面坡向为主导,坡面坡向栅格占比在30 min后保持不变,而细沟总表面积逐渐增加,说明微坡向与坡面同向的细沟栅格数增加。细沟会产生有一定宽度的沟底,沟道的横截面由“V”形向“U”形过渡。除北向外,其余微坡向栅格数变化与细沟密度、细沟割裂度、细沟复杂度、细沟累计长度和细沟平均宽度显著相关,微坡向栅格数能够较好地反映坡面细沟形态变化。

In this paper,aiming at topographic information of grid units on loess slope at different stages of intermittent rainfall,an artificial simulated rainfall test is carried out with 12 segments of 30 min and intensity of 60 mm/h,and the interaction between micro slope,micro slope direction,erosion process of loess slope and rill shape evolution is studied.The results show that the changes of micro slope gradient and micro slope direction are mainly concentrated in the initial stage of precipitation(0~30 min),while the changes in subsequent stages(30~360 min)are small.The changes of micro slope gradient and micro slope direction are significantly positively correlated with the erosion amount during periods.After the formation of rill network,the proportion of grids in the areas with slope less than 15°and above 45°increases slowly,which mainly occurs in the interior of the rill.The platform of sediment accumulation and steep slope will generate during the development of the rill interior.The development process of rills is a non-uniform development process in which the erosion by runoff in rills and collapse of unstable soil mass at the side walls work together.The erosion of runoff and collapse of soil mass promote each other and accelerate the development process of rills,thus causing fluctuations of erosion amount.During the course of rill erosion,the micro direction of rill is dominated by the gradient direction of slope,and the proportion of gradient grid remains unchanged after 30 min,while the total surface area of rills gradually increases,which indicates that the number of rill grids having the same direction with the slope increased.A bottom of certain width will generate in the rill,and rill section is transformed from V to U shape.Except for the north outward direction,the changes of grid number of rill directions are significantly related to the density of rills,the cleavage degree,the complexity of rills,the accumulated length of rills and the average width of rills.The number of grid of rill direction can better reflect the changes of the form of rills on the slope surface.