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 degree=2.5％,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.

Lan Ma;Chengzhong Pan;Jingjing Liu

Key Laboratory of State Administration of Forestry and Grassland on Soil and Water Conservation,School of Soil and Water Conservation,Beijing Forestry University,Beijing,100083,China;Beijing Key Laboratory of Urban Hydrological Cycle and Sponge City Technology,College of Water Sciences,Beijing Normal University,Beijing,100875,China;Soil and Water Conservation Monitoring Center of Haihe Basin of Haihe Water Resources Commission of the Ministry of Water Resources,Tianjin,300170,China

国际水土保持研究（英文）

[1]Lan Ma;Chengzhong Pan;Jingjing Liu-.Overland flow resistance and its components for slope surfaces covered with gravel and grass)[J].国际水土保持研究（英文）,2022(02):273-283

Overland,hillslope,slopeland

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