Effects Of Gravel Contents On Rill Erosion In Colluvial Deposit Slope

Gravel is an important factor affecting soil erosion,but the mechanism of gravel on rill erosion is still not clear.Therefore,this study chose the soil-rock mixture of colluvial deposits as research objects and conducted runoff scouring experiment at four kinds of gravel contents(0,10,30,50% gravel mass ratio)and four flow discharges(2,4,8,12 L/min).The rill morphological characteristics,hydrodynamic characteristics,runoff and sediment yield characteristics and their internal coupling relationship were analysed to investigate the effect of gravel content on rill erosion process on colluvial deposit slopes.The main conclusions are as follows:(1)Rill erosion is mainly downcutting erosion,and develops to narrow and deep.The depth of rill cross section is large on the top of slope,which is similar to the “V” shape,and the erosion is severe.The depth of rill cross section is small on the bottom of slope and the erosion is relatively mild.The rill cutting depth of slope with 10% gravel content is the smallest.The number of drop pits and the shape index of longitudinal section increase with the scouring duration.With the increase of gravel content,the longitudinal shape of rill tends to be complex.(2)All the flow regime in the process of rill erosion is turbulence.The flow pattern is mainly slow flow,and the Froude number decreases with scouring duration.The flow velocity decreases with scouring duration,but the flow depth increases with scouring duration;the flow velocity decreases with the increase of gravel content,but the change trend of water depth with the increase of gravel content is not obvious.The resistance coefficient and Manning's roughness coefficient increase with scouring duration,and resistance coefficient and Manning's roughness coefficient are the largest at the slope with 30% gravel content.The shear stress of the water flow increases with scouring duration,but stream power and unit steam power decrease with scouring duration;the change trend of shear stress and stream power with the increase of gravel content is not obvious,but the unit flow power decreases with the increase of gravel content.(3)The runoff rate,sediment yield rate and sediment concentration fluctuate and decrease with scouring duration.The runoff and sediment yield decrease first and then increase with the increase of gravel content,and the lowest is on the slope of 10% gravel content.(4)The correlation between rill morphology,erosion hydrodynamic parameters and erosion sediment yield is different on different gravel content slopes.Under comprehensive conditions,Reynolds number,flow depth,steam power and sediment yield are significantly correlated with the depth of rill cross section;Froude number,resistance coefficient and Manning roughness coefficient are significantly correlated with the shape index of rill cross section;flow velocity and steam power are significantly correlated with the number of drop pits;Significant correlation is found between sediment concentration and width-depth ratio of rill cross section;Sediment yield rate and unit steam power are extremely correlated,the unit steam power can be used as the best hydrodynamic parameter to simulate sediment yield from rill erosion of the colluvial deposit.