| Overland flow is the source of hydraulic erosion on the slopes of the Loess Plateau,and its hydrodynamic characteristics are highly susceptible to vegetation characteristics,surface soil characteristics,and rainfall.Therefore,in-depth study of the mechanism of slope flow resistance under the interaction of vegetation pattern and coverage has important guiding significance for the study of water erosion on the Loess Plateau.This study explored the impact of vegetation landscape heterogeneity on slope runoff hydrodynamic characteristics through indoor simulated water discharge scouring test,based on tribological mechanics and applied ecology,and established simulated effects under natural conditions,vegetation pattern and coverage The empirical formula of downslope flow resistance provides new ideas for the calculation of downslope flow resistance covered by vegetation patterns,as well as the improvement and enrichment of hydraulics in the extension and practical application of slope flow.(1)Under the cover of random patchy vegetation,in the virtual laminar flow area,the comprehensive resistance coefficient is negatively correlated with the Reynolds number,while in the transitional flow area,the relationship between the two changes at the critical coverage.As the coverage increases,the two The relationship gradually changes from a negative correlation to a positive correlation;the comprehensive resistance coefficient is related to the coverage by an exponential function,and the trend with the submergence is limited by the coverage.Below the critical coverage,the two are negatively correlated overall.Above the critical coverage,the overall resistance coefficient decreases first and then increases as the submergence increases.In addition,based on the principle of equivalence of water flow resistance,comprehensively considering the effects of hydraulic slope,coverage,Reynolds number,and submergence degree,a slope flow resistance calculation model was established.(2)In the five patterns of the same coverage,the effect of slow water flow of vegetation patches on slopes is not very different when the flow is small,and the pattern difference gradually becomes prominent when the flow is large.Under different patterns,the vegetation flow on the slopes belongs to the virtual laminar flow zone and the transitional flow zone;the vegetation patch direction,fragmentation and slope have a significant effect on the vegetation resistance mechanism.As the flow increases,the relationship between the vegetation resistance coefficient and the equivalent Froude number under the belt type gradually changes from a negative correlation to a positive correlation,while the strip type is just the opposite;on the whole,the patch direction is compared to fragmentation The degree has a greater impact on the soil and water conservation of slopes;as for the vegetation zone on slopes,the vegetation zone should be paved along the contour line(that is,the direction perpendicular to the water flow),and the mosaic distribution should be appropriately increased.(3)The research on the mechanism of slope flow resistance under the interaction of pattern and coverage shows that the relationship between the resistance coefficient under the bare slope and Frud number is significantly positively correlated.With the increase of vegetation coverage,the effect of vegetation resistance is prominent,and the relationship between the two gradually changes from positive to negative correlation,and the threshold is near Cr=2.51%;the overall Darcy resistance coefficient is negatively related to the power of the unit water flow;Coefficients and coverage are subject to pattern and slope.The unit flow power is introduced to characterize the slope flow resistance coefficient of vegetation pattern from the perspective of energy and flow pattern.The coefficient of determination of the model is 0.746.Through verification,it is concluded that the model can better calculate the flow resistance in different patterns and has a certain universality. |
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