Research On Response Mechanism Of Rill Flow And Drop Pit Characteristics

Among many erosion modes,rill erosion accounts for more than 70% of the total loss.It contributes greatly to the water and soil loss on the Loess Plateau.Therefore,rill erosion is favored by scholars at home and abroad.Drop pit is a common micro-geomorphic form in rill erosion,and it is a necessary condition to form rills.If there is no drop pit,it will be difficult to form rills.Therefore,by discussing the impact characteristics of drop pit characteristics on rill flow,the study is expected to provide further supplement for the study of influencing factors of rill development and rill flow erosion on slope surface,and at the same time,it is of positive significance to put forward practical and reasonable control methods for rill erosion and to control the current situation of erosion on Loess plateau.Taking Yang Ling soil as the research object,this test carried out indoor water discharge scouring tests under four pit spacing(40,50,60,70cm),three gradients(15,20,25 degrees)and five flow rates(2.4,3.6,4.8,6.0,7.2L/min),and studied the influence of drop pits on hydrodynamic characteristics of rill flow,the shape of longitudinal section of rill and the effect of drop pits on rill water.Research on runoff erosion and sediment yield.The results show that:(1)The average flow rate of rill flow has a good power function correlation with pit spacing,flow rate and slope.Under this test condition,the degree of influence on the average flow rate of rill flow from large to small is: gradient > flow rate > pit spacing.The Froude number of rill flow on the slope surface in this test is more than 1,which indicates that the rill flow pattern is in rapid flow state in this test;this test model The Reynolds number of flow on the enclosure slope ranges from 503.68 to 2718.49,which indicates that the flow of flow is mainly turbulent.(2)When the flow rate is the same,dimensionless parameter L/H has a negative correlation with the preset pit spacing;the development coefficient SP of each test group ranges from 1.010 to 1.067,and SP is positively correlated with the preset pit spacing;Manning roughness coefficient n is positively correlated with dimensionless parameter L/H;dimensionless parameter L/H is linearly correlated with energy dissipation rate delta;Manning roughness coefficient n and energy dissipation rate Delta is negatively correlated with SP.(3)There is a power function relationship between flow sediment concentration and slope,flow rate and pit spacing,and the slope index is larger than the flow index and pit spacing index.It is found that the average sediment concentration and the average velocity are positively correlated.The runoff erosion and sediment yield of loess slope in this test has obvious stages,which can be divided into three stages:the initial stage of rill,the vigorous development stage of rill,and the stable stage of rill.The erosion and sediment yield in the vigorous development stage of lower gully accounts for 56.19?68.33%of the total sediment yield.The variation range of control coefficient under this test is 0.468<K<0.988,and the rill erosion sediment yield without drop pit is larger than that of preset drop pit.Under any slope and discharge conditions,the sediment carrying coefficient of rill flow increases with the increase of pit spacing.When slope and discharge flow are the same,there is a positive correlation between control coefficient and pit spacing.There is a linear function relationship between erosion sediment yield and drop pit development coefficient SP and dimensionless parameter L/H,the former is linear increment and the latter is linear decrement.