摘要
Overland flow resistance plays an important role in predicting hillslope hydrological and erosion pro-cesses on hillslopes.Soil surfaces covered with grass and/or gravel may increase hydraulic resistance to overland flow,but there is little information on the determination on these resistance components in a composite slopeland.In this study,the smooth and sand-bed surfaces covered with different gravel or/and grass(cover degree¼2.5%,5%,10%,15%,20%)under five slope gradients(3,6,9,12,15)were subjected to inflows to investigate the hydraulic resistance and validate the sum law of resistance components.The results showed that,the overland flow mainly belonged to transition or turbulent and supercritical flow regime with 150<Re<2050 and 0.4<Fr<6.9.As the gravel or grass cover increased,Darcy-Weisbach resistance coefficient(f)significantly increased.The resistance can be well predicted by flow discharge,gravel or grass cover using a power equation.The flow discharge had a greater influence on flow resistance than gravel or grass cover,and the impact of flow discharge weakened with the increasing bed slopes.The total resistance was generally greater than the sum of resistance components,and there existed a positive additional resistance for the composite surfaces.The additional resistance accounted for 37.4%,4.2%and 16.6%to the total resistance for the sand surfaces covered with gravel,grass and both of them,respectively.These results can help to understand the rainfall-runoff processes and improve the design of soil and water conservation measures in the rocky and mountainous areas.
基金
the National Natural Science Foundation of China Project(Grants 51779004,41530858,42077059)
China National Science and Technology Major Project of Water Pollution Control and Treatment(2018ZX07101005-04).
