流量和坡度对植被水流水动力学特性的影响

Discharge and Slope on Hydraulic Characteristics of Overland Flow Under Vegetated Coverage

为深入揭示植被覆盖下坡面流阻力的内在规律,系统研究了植被覆盖度为32.32%时6个坡度和12个流量组合下坡面流的流动特性。结果表明:坡面流速随流量的增大而增大,该覆盖度下流态指数值接近1;坡面流从层流变化成过渡流,最后发展成紊流状态,但植被覆盖下坡面流的层流状态与明渠定义的不同;阻力系数随流量的增大而增大,流量是影响阻力的主要因素,而坡度对其影响可以忽略;阻力系数随平均水深和壅降差的增大而增大,壅降差不仅能代表水深对阻力系数的影响,而且能反映植被前壅水和后尾水旋涡的形成程度。

Containing the cases of 6 different slope gradients and 12 different discharges, the experiments of overland sheet flow were conduc-ted under the condition of 32.32% of vegetation coverage. The results indicate the following inherent laws of flow regime and resistance char-acteristics. First,flow velocity increases with flow discharges,and the larger value of flow index is close to 1,when vegetation coverage is high. Second,the flow regime transfers from laminar flow into transitional flow and then ends up in turbulent flow. However,the laminar flow regime of overland sheet flow with effects of vegetation is different from that of open channel. Third, resistance coefficient increases with flow discharges,and the major factor affecting the resistance is flow discharge but not slope gradient whose effect can be ignored. Finally,resist- ance coefficient increases with mean depth and the difference of the depth of previous and tail water. The depth of previous and tail water notonly can represent the influence of water depth on the drag coefficient, but also can reflect higher depth and the formation of the tail watervortex before and after the vegetation.