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跌坑是坡面土壤特性和薄层水流动力的耦合作用形成,而跌坑对坡面漫流的集中导致了水流流速、流深和切应力的变化,进一步塑造了侵蚀坡面形态导致跌坑贯穿发生细沟;目前关于跌坑与水动力耦合作用的研究相对较少。采用人工模拟降雨试验方法,分析了跌坑对径流特征的影响,定义了径流集中度Kc,回归调查了径流集中后切应力与跌坑贯穿下切速率的关系。结果表明:紫色土曼宁糙度系数随雨强增大而减小,漫流区坡面曼宁糙度系数变化介于0.014～0.026,沟道曼宁糙度系数变化介于0.008～0.015;薄层水流流速和流深顺坡增大,在跌坑处集中后流速剧增,雨强越大流速越大、流深越小;径流切应力顺坡增大,跌坑集中薄层水流而切应力剧增导致跌坑贯穿;试验紫色土可蚀性参数Ke为0.144s/m,跌坑贯穿的临界切应力为2.48Pa。
The fall of a pit is formed by the coupling of the soil properties of the slope and the thin-layer water flow motive force, and the concentration of the falling pit on the slope surface leads to the change of the flow velocity, the flow depth and the shear stress, further shapes the erosion slope shape, Rinsing occurs. At present, there are relatively few studies on the coupling effect of falling pit and hydrodynamic force. The effects of falling pits on runoff characteristics were analyzed by artificial simulated rainfall test. The concentration of runoff Kc was defined. The regression was used to investigate the relationship between the shear stress after runoff concentration and the rate of undercutting. The results show that the Mann - Nün roughness coefficient of purple soil decreases with the increase of rainfall intensity, the mann - ning roughness coefficient varies from 0.014 to 0.026 on the slope of diffusional zone, and varies from 0.008 to 0.015 on the channel. The flow velocity and depth of layer flow along the slope increased, and the flow velocity increased sharply after concentration at the drop pit. The larger the rainfall intensity, the larger the flow velocity and the smaller the flow depth. The runoff shear stress increased along the slope, The sharp increase of stress led to the fall through of the pit. The erodibility parameter Ke of test purple soil was 0.144s / m, and the critical shear stress of drop pits was 2.48Pa.