Experimental Study On Flow Resistance Of Slopes With Different Underlying Surfaces

Slope is the basic unit of drainage area,and its runoff process is also the initial stage of watershed production and convergence.The widely distributed slope topography and the spatial heterogeneity of its soil,underlying surface,and vegetation make the study of slope hydrological processes extremely difficult,especially in watershed hydrological models,where slope hydrological processes are often not fully reflected.The slope flow equation is extremely sensitive to resistance,and the"superposition principle"of slope flow resistance needs further study.In order to explore the effect of slope composition on the hydrodynamic characteristics of overland flow and the verification of the"superposition principle"of slope flow resistance,this paper sets up an indoor fixed-bed scouring test and selects 8 different single-width flows(15,30,45,60,75,90,105,120L/(min·m),5 slopes(3°,6°,9°,12°,15°),on smooth glass slopes,sand slopes,gravel slopes(cover Degree 2.5%,5%,10%,15%,20%),grass slope(coverage 2.5%,5%,10%,15%,20%),and sand+gravel composite slope,sand+grass composite slope,gravel+grass composite slope and sand+gravel+grass composite slope,There are a total of 33 types of underlying surfaces and 1,320 types of treatment on grass-covered composite slopes,gravel+grass-covered composite slopes,sand grains+gravel+grass-covered composite slopes.The experimental study has reached the following conclusions:(1)For a single gravel or grass slope,the greater the coverage,the deeper the runoff depth and the slower the flow rate,the greater the Darcy-Weisbach resistance coefficient.By fitting the resistance coefficient,flow,slope and coverage overall,The available function is f=a·Q~b·s~c·d~e(a,b,c,e are coefficients,the same below),the fitting determination coefficient R~2>0.81;the shear force of radial flow increases with the increase of flow Large,which has a significant and significant relationship with slope and coverage.Through overall fitting of runoff shear force,flow,slope and coverage,the available function is?=a·Q~b·s~c·d~e,and the fitting determination coefficient R~2=0.97.(2)On composite slopes,the presence of gravel increases the surface roughness,and a large Accumulated water area is formed at the front end of the slope.The depth of the slope increases and the contact area between the gravel surface and the water flow is large.Its flow reduction effect is better than grass cover.When the coverage is less than 15%,the gravel slope shows good slow flow effect and blocking effect.When the overall coverage is greater than 15%,the gravel and grass are combined to achieve the optimal slope flow and sand reduction effect.(3)Verification of the"superposition principle"of slope flow resistance found that the relationship between the particle resistance of the slope flow and the morphological resistance and the morphological resistance did not conform to the simple linear superposition relationship,and the interaction between different rough elements on the slope would produce additional Resistance,but the positive and negative effects of its interaction will vary depending on the coverage of the particles and the rough-shaped cells.By linearly fitting different resistances,it can be seen that the coefficient of determination R~2 is low,which does not comply with the"superposition principle".