坡面流水深很小，一定条件下呈滚波运动特征，表面张力作用显著。因观测手段限制，现有成果相关结论很不一致，坡面流流态、阻力、描述方法研究仍不完善，受到学术界长期关注。目前基于两相流理论研究坡面流含沙水流问题尚未开展，水沙两相坡面流内部结构及相关参数的高精度量测资料缺乏，数值模拟研究较少。.基于黄土地区降雨及土壤特点，针对不同粗糙度定床坡面，考虑雨强、下渗、含沙量的影响，采用人工模拟降雨、放水（清水、含沙水流）试验，利用PIV技术进行陡坡、缓坡坡面流的3D流动特性研究，同时采用欧拉多相流模型进行具有气水界面的坡面水沙两相流三维数值模拟。观测分析坡面流内部结构特征，研究坡面流流动参数时空分布特征，确定表面张力的大小以及对坡面流流态、紊动机制、流速分布、水流挟沙能力、阻力等特性的影响，研究滚波形成、消失的条件及机理，确定坡面流最佳数值模拟模型、离散方法、参数设置。完善坡面流基本理论和数值模拟方法。

The overland flow is shallow water, moving in roll waves in some condentions, markedly affected by capillary force. The results are inconsistent.，the study on flow states, resistance and description method of overland flow is still imperfect due to the limitations of detection methods and has been concerned about by the academics all the time. At present, the problem of sediment flow in slope is not carried out based on two-phase flow theory. The high-precision measuring instrument data to observe the internal structure and related flow parameters of water-sand two-phase flow are is lacking，the numerical simulation studies are fewer..Based on the feature of rain and soil in loess area, considering the influence of rainfall intensity, infiltration and sediment concentration, through the artificial simulation such as rainfall, dewatering test (clear water, sandy water) Under different roughness bed slope, the PIV(Particle Image Velocimetry) is used to study the 3D flow characteristics of steep hill and gentle slope，meanwhile, the 3D numerical simulation on water-sand two-phase flow was developed using multiphase (Euler) model of ANSYS. The inner structures of the overland flow and its physical features are observed and analyzed, the temporal and spatial distribution characteristics of overland flow parameters are studied, the capillary force value and influence to the characteristics of flow state, turbulence mechanism, velocity distribution, sediment load capacity and resistance are determined，the conditions and mechanism of roll forming and disappearance are studied，the best computation model, discrete method and parameter settings are confirmed for numerical simulation on overland flow. The basic theory and numerical simulation method of overland flow are improved.