递增式连续降雨条件下典型山区坡面径流产沙水动力学特征

山区复杂的下垫面条件导致了山区小流域水文响应过程的复杂性，山区坡面作为山区小流域水文响应的基本单元，研究其不同下垫面条件下径流产沙水动力特征具有重要意义。为明晰山区坡面不同下垫面条件下径流水沙水动力特征，该研究选用官山河小流域作为研究对象，基于室内模拟递增式连续降雨试验方法，研究了坡度、土层厚度分布和土层底部透水性等山区坡面下垫面特性共同作用下的坡面径流产沙水动力学特征。结果表明：1）连续降雨条件下，雷诺数、水流剪切力和径流功率随着产流时间和雨强增加呈现增加趋势，Darcy-Weisbach阻力系数呈降低趋势。2）雨强增加使雷诺数均值和径流功率均值显著增加（P<0.05），设计雨强60、90、120 mm/h时的雷诺数均值、径流功率均值分别比30 mm/h的雷诺数均值、径流功率均值增加了130%、276%、366%和171%、328%、435%；坡度增加使水流剪切力均值和径流功率均值显著增加（P<0.05），坡度15°、25°的水流剪切力均值分别比坡度5°的增加了135%和187%，坡度15°、25°的径流功率均值分别比坡度5°的均值增加了224%和357%；土层厚度分布对阻力系数 均值和土层底部透水的雷诺数均值、径流功率均值有显著影响（P<0.05），土层底部透水性仅对土层厚度分布为上薄下厚的雷诺数均值和水流剪切力均值有显著影响（P<0.05）。3）雨强是影响坡面产流产沙水动力特征的主导因素，对雷诺数的方差贡献率高达83.11%，水流剪切力主要受到雨强和坡度的影响，累计贡献率达67.64%，径流功率主要受到雨强和坡度的影响，累计贡献率达80.58%。在单一雨强条件下，坡度和土层厚度分布是影响水动力参数的主要因素，土层厚度分布和坡度的交互作用、土层底部透水性和土层厚度分布的交互作用对水动力参数也有一定影响。因此，在研究坡面产流产沙规律时，除考虑雨强和坡度外，还应兼顾考虑土层厚度分布和土层底部透水性及其交互作用的影响。该研究结果可为山区坡面复杂下垫面条件下的坡面产流产沙机理提供一定的理论支撑，并为改进山区小流域水文过程分布式模拟提供参数率定依据。

Hydrodynamic characteristics of runoff and sediment yield on the slopes in typical mountainous areas under incremental and continuous rainfall conditions

Underlying surface has led to the complex hydrological response of watersheds in small mountainous areas. Among them, the slope can be the basic unit of hydrological response. It is of great significance to explore the hydrodynamic features of runoff under different conditions of underlying surface on mountainous slopes. In this study, the underlying surface of the slope was selected in the typical mountain areas, the Guanshan River watershed. Multiple simulated rainfall experiments were conducted in the laboratory. A systematic investigation was made to clarify the runoff and erosion hydrodynamic features of the soil slope under different slope gradients, soil thickness distribution, and soil base permeability. The results showed that: 1) The Reynolds number, shear stress, and runoff power increased with the increase of rainfall intensity, whereas, the Darcy-Weisbach resistance coefficient decreased. The rain intensity initiated a significant increase in the mean values of Reynolds number and runoff power (P<0.05). The mean values of Reynolds number and runoff power at the rain intensity of 60, 90, and 120 mm/h increased by 130%-435%, compared with the mean values of 30 mm/h. Slope gradients shared significant positive effects on the mean shear stress and mean runoff power (P<0.05). The mean shear stress for the 15 and 25 slope gradients treatments increased 135% and 187%, respectively, compared with the 5 slope gradients treatment; The mean runoff power increased 224% and 357%, respectively. The thickness of the soil layer had significant effects on the mean Darcy-Weisbach resistance coefficient, mean Reynolds number and mean runoff power under a permeable soil base. The permeability of the soil base also exhibited a significant effect on the mean Reynolds number and the mean shear stress, when the thickness of the soil layer was thin at the top. The hydrodynamic features depended mainly on the rainfall intensity. The variance contributions to the Reynolds number reached 83.11%. The dominant influencing factors on shear stress and runoff power were the rainfall intensity and slope gradients. The sum of both variance contributions to shear stress and runoff power reached 67.64%, and 80.58%, respectively. Slope and soil thickness were the main influencing factors on the hydrodynamic parameters under a single rainfall intensity, followed by the interactions between soil thickness and slope gradients. The bottom permeability and soil thickness also presented some influence on the hydrodynamic parameters. Therefore, it is very necessary to consider the soil bottom permeability, soil thickness, and their interaction on hydrodynamic features, rainfall intensity, and slope gradients. The findings can provide some theoretical support to determine the influence of runoff and sediment yields on the complex slope surface. Some parameters can also be offered to simulate the hydrological process in small mountainous watersheds.