坡度和植被盖度对河岸坡面侵蚀产沙特征的影响

Effect of Slope Gradient and Vegetation Cover on Sediment Yielding Characteristics of the Riparian Slope

坡度和植被盖度是影响坡面土壤侵蚀的重要因子,探讨坡面土壤侵蚀产沙对坡度和植被盖度的响应,对坡面土壤侵蚀产沙的预测和调控具有重要意义。研究基于野外模拟径流冲刷试验,分析了不同坡度(5°、10°、15°、20°)和植被盖度(0、15%、30%)条件下坡面径流系数、泥沙量、时段径流含沙量和侵蚀泥沙粒径组成的变化过程,并运用双因素方差分析和相对贡献指数阐明黄河下游河岸坡面侵蚀产沙特征对坡度和植被盖度交互作用的响应。结果表明:不同植被盖度下坡面径流系数随冲刷历时增加而增加,在冲刷历时前5 min增幅较快,之后增幅变慢并趋于平缓;坡面径流含沙量随冲刷历时呈逐渐下降趋势,随后趋于平缓。坡度小于15°时,不同植被盖度之间的径流系数和时段径流含沙量差异较为明显,坡度大于15°后差异减小。侵蚀产生的泥沙量随冲刷历时和坡度的增加而增加;在同一坡度上,植被覆盖越低,侵蚀产生泥沙量越大。侵蚀泥沙的主要富集粒级中,Dx(10)以粉粒为主,Dx(50)以粗粉粒和极细砂粒为主,Dx(90)以极细砂粒和细砂粒为主。双因素方差分析表明,坡度对河岸坡面侵蚀产生的径流系数、产沙量和径流含沙量均有极显著影响(P<0.001),植被盖度对产沙量和径流系数有极显著影响(P<0.001),而坡度和植被盖度的交互作用仅对径流系数有显著影响(P<0.01),同时相对贡献指数表明,在坡度和植被盖度对坡面侵蚀产沙的交互作用中,植被盖度的作用随坡度的增加逐渐减弱,而坡度的作用逐渐增强,并成为影响坡面水土流失的主导因素。

Slope gradient and vegetation cover are important factors affecting slope soil erosion process,thus exploring the response of sediment yielding characteristics to slope gradient and vegetation cover is of great significance to predicate sediment yielding in soil erosion process.In this study,based on the field runoff scouring experiments on the riparian slope of the lower reaches of the Yellow River,the changing processes of runoff coefficient,sediment yielding,runoff sediment concentration,and sediment particle size composition under different slope gradients（5°,10°,15°,20°） and vegetation covers（0,15%,30%） were analyzed,and the response of sediment yielding characteristics to the interaction effect of slope gradients and vegetation covers on riparian slope were revealed by using the double factor variance analysis and the relative contribution index.The results showed that runoff coefficient under different vegetation covers increased with duration of scouring time,therein,it increased quickly during the first five minutes and then slowed down and became leveling off.The runoff sediment concentration showed decreasing trend with the increase of scouring time and then began to leveling off.On the slope of less than 15°,the differences of runoff coefficient and runoff sediment concentration between different vegetation covers were obvious,while there were less difference on the slope of more than 15°.The sediment yielding increased with the scouring time and slope gradient.On the same slope gradient,the lower the vegetation cover was,the greater the sediment yielding.The sediment particles were mainly made up of silt,coarse powder grains and very fine sand,and very fine sand and fine sand,which accounted for10%,50%,and 90% of the total volume,respectively.The double factor variance analysis showed that slope gradient exhibited the extremely significant effect on the runoff coefficient,sediment yielding,and runoff sediment concentration on the riparian slope（P0.001）,and the vegetation coverage exhibited the extremely significant effect on the slope erosion sediment yield and flow runoff coefficient within the prescribed time（P0.001）.However,the interaction between slope gradient and vegetation cover showed the significant effect only on the runoff coefficient within the prescribed time（P0.01）.Meanwhile,the relative contribution index showed that in the interaction of slope gradient and vegetation cover,the effect of vegetation cover weakened gradually with increasing slope gradient,while the role of slope gradient enhanced gradually and became the dominant factor influencing soil and water loss.