Experimental Research On The Effect Of Vegetation On Runoff And Sediment Yield Of Gravel Soil Slope

In order to rationally allocate the vegetation and effectively control soil erosion in the Three Gorges Areaon the soil containing gravel slope,at the same time, in order to provide a reliable theoretical basis for the research of soil erosion on slope and the establishment of soil erosion prediction model.To study the effects of vegetation on runoff and sediment yield and hydrodynamic characteristics of gravel soil slope under different slope and rainfall intensity,and runoff plots of different slopes(20°、30°) has been established which was layed of soil containing rock of the Three Gorges area, then configured with different coverage of grass(coverage of 60%、80%and100%)、shrub(coverage of 60%、80%)、combination of grass and shrub(coverage of 60%、100%)were configured,at last artificial simulatedrainfall experiment was conducted under different rainfall intensity(60、90、120mm/h).(1)The runoff of bare slope increase with the slope increases, the sediment yield decreases with the increase of slope.The runoff and sediment yield of vegetation slope varied differently with the increase of slope under different rainfall intensity. The variation of runoff and sediment yield of bare slope with time in the bare slope is rising–decreasing- rising, The variation of runoff and sediment yieldwith time in the vegetation slope is up-stable or rise-drop-stability under 60、90 mm/h of rainfall intensity, in 120mm/h rainfall intensity, The variation of runoff and sediment yield varies with time is rising–decreasing- rising.(2) The regulation mechanism of water and sediment on the grass slope is blocking sand directly, and the slope ofshrubs and combination of grass and shrubsreduce sediment by storaging water,under the heavy rain, the effect of runoff and sediment reduction in the slope ofshrubs and combination of grass and shrubsunder the heavy rainis more obvious than that of the grass slope under the lighe rain. The runoff and sediment yield was negatively correlated with vegetation coverage. The runoff and sediment yield of the bare slope increased with the increasing of the placing time, the runoff and sediment yield of the vegetation slope decreased with the increase of the vegetation growth period.(3)Vegetation-covered slope of interflow is greater than bare slope, the interflow volume increases with the permeability. The infiltration rate obeys to the law of logarithm function, and the intensity of runoff is changed by power function. Between the sediment yied and erosion concentration is a linear function, Cumulative runoff and the cumulative sediment yield meet the power function.(4)Thereduction benefit of the runoff and sediment are the slope of combination of grass and shrub> shrub slope>grass slope,sediment reducing benefit of vegetation is more significant than the runoffreducing benefit.Sediment reducing benefit of different grass slope from high to low order rainfall intensity is 90mm/h >60 mm/h >120 mm/h.The order of the effect of different factors on runoff and sediment reduction benefitis that the intensity of rainfall > vegetation cover > vegetation type > slope.(5)The main control function of the flow velocity on the bare slope is the runoff volume, and the main control function of the flow velocity on the vegetation slope is slope. The average water depth of runoff decreases with the increase of slope gradient. The Re of bare slope increases with the slope gradient, and the Re of vegetation slope increases with the increase of slope under the heavy rain, and the Re number increases or decreases with the increase of slope gradient under the lighe rain. Fr increases with the increase of slope and rainfall intensity.Darcy-weisbach resistance coefficient and Manning roughness coefficient increase with the increase of slopeunder90、120 mm/h of rainfall intensity. The Darcy-weisbach resistance coefficient and Manning roughness coefficient of vegetation slope is much larger than the bare slope.(6)Under different rainfall intensities and different slope conditions,for the different types of slope on the bare slope, herb slope, shrub slope and slope of combination of grass and shrub, The influence of different hydraulic parameters on the average sediment transport rate is different,The correlation degree between the hydraulic parameters is also different.