紫色土坡面跌坑贯穿发生细沟的水动力过程

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〖WTBX〗Kc〖WTBZ〗，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〖WTBX〗Ke〖WTBZ〗为0144 s/m，跌坑贯穿的临界切应力为248 Pa。

HYDRODYNAMIC CONDITION OF RILL DEVELOPMENT ON PURPLE SLOPE LAND

The investigation on the configuration evolvement of rill is the precondition of rill development mechanism research.This study adopts the methods of simulation rainfall and macro-morphology survey to investigate the hydrodynamic condition of rill development on purple soil slope land.When the overflow is concentrated on the drop-pit,the thickness of overflow,velocity of overflow,shear stress of overflow,and kinetic energy of unite width flux increase the multiple,and the Manning coefficient are 3/5,2/5,3/5 and 9/5,respectively.So the concentration degree is defined as.And some simulation tests are conducted to survey the velocity and thickness of runoff.The results show that the coefficient of Manning formula is enlarging with the density of rainfall.The Manning coefficient changes between 0.014 and 0.026 on the overflow region,but on the linear flow the Manning coefficient varies from 0.008 to 0.015.The velocity and thickness of overflow increase slowly with slope length,and then double on the drop-pit.The affection of rainfall density on the velocity of overflow is positive,nevertheless,the action is passive between the rainfall density and thickness of overflow.The shear stress is enlarged on the drop-pit,and the critical shear stress is 2.48 Pa when the purple soil erodibility Ke value is 0.144 s/m.