坡度对侵蚀产沙及其粒径分布的影响

Effects of Slope Gradient on Yield and Particle Size Distribution of Sediment

利用人工模拟降雨试验,分析北京山区普通褐土在不同坡度条件下的产流产沙状况和侵蚀泥沙的粒径分布规律。结果表明,随着坡度的增大,侵蚀模数呈现先增加后减少的趋势,临界坡度为25°,对应的侵蚀模数为19.7t/hm^2。在研究的5个坡度条件下,侵蚀泥沙都以粉粒为主。当坡度从0增大至30°,<0.002mm的粘粒含量无明显变化;0.002~0.02mm的细粉粒含量先减少后增加;0.02~0.25mm粗粉粒、极细砂粒和细砂粒含量则呈现先增加后减少的趋势。临界坡度为20°,此时细粉粒含量最少,极细砂粒和细砂粒含量最多。与原土相比,侵蚀泥沙在不同粒级存在富集。主要富集粒径随坡度增加先增大后减小。20°坡度时富集粒径最大,为细砂粒(0.1~0.25mm)。

Slope gradient is one of the important factors that affect soil erosion,which not only influences runoff and sediment yield,but also affects the size distribution of sediment particles.Quantitatively evaluating the effects of slope gradient on yield and particle size distribution of sediment is essential for studying water erosion mechanism,calculating nutrient loss,and establishing water erosion model and non-point source pollution model.In the current study,the sediment yield and particle size distribution were analyzed for a typical soil（cinnamon soil）in the mountain area of Beijing at 5different slope gradients,based on rainfall simulation experiments.The results showed that with the increasing slope gradient,sediment yield increased at first and then decreased.The critical slope gradient was 25°,with a sediment yield 19.7t/hm2.For all the 5slope gradient treatments,the eroded sediment was dominated by silt particles.When the slope gradient increased from 0to 30°,no obvious change was observed in the proportion of clay particles（〈0.002mm）,while the percentage of fine silt（0.002—0.02mm）decreased at first and then increased,and the percentages of coarse silt（0.02—0.05mm）,very fine sand（0.05—0.1mm）and fine sand（0.1—0.25mm）increased at first and then decreased.The lowest percentage of fine silt and the highest percentages of very fine sand and fine sand particles were observed at the slope gradient of 20°.Particle enrichment was observed in different particle size classes for different slope gradients,and the size of the most significantly enriched sediment particles increased at first and then decreased with the increasing slope gradient.The largest size was observed at the slope gradient of 20°,which was among 0.1—0.25mm（fine sand）.