| The laws of sediment incipient motion on rill erosion is the main content of soil erosion research.Domestic and foreign scholars have done a lot of research about the rill erosion evolution process,occurrence mechanism,critical condition and influencing factors of rill erosion,and have achieved rich results.However,most of these results are based on the study of loess rill erosion.The study of sediment incipient motion on rill erosion of piedmont proluvial fan is relatively less,which has not only important significance for deepening the law of soil erosion,but also can be applied to the prevention and control of geological disasters.In this paper,through the soil erosion test with different flow(1.5L / s,2.4L / s,3.3L / s)and different slope(1 °,3 °,5 °),we have researched the laws of sediment incipient motion on rill erosion of piedmont alluvial fan.The main conclusions are as follows:(1)The average flow velocity and average Reynolds number increases with the increase of flow rate and slope gradient,and the effect of the flow rate on the average flow velocity and average Reynolds number is greater than that of the slope gradient.From the top to toe of the slope,the instantaneous flow velocity increases,but there also has a certain degree of volatility.The Reynolds number of rill runoff first increases and then decreases from the top to toe of the slope and its maximum value generally appears in the middle of the slope.The variety of the Froude number is not obvious with the change of flow rate and slope gradient.The relationship between the average flow velocity and the flow rate and the slope gradient can be expressed by power function.The average shear stress,the average flow power and the average unit energy of cross-section of the rill runoff are increasing with the increase of the flow rate and the slope gradient.The average shear stress of rill runoff decreases from the top of the slope down,and the maximum value generally appears at the top of the slope;The average flow power is basically stable in different position of slope;The average unit energy of cross-section has an increasing trend with the runoff flow from the top to toe of the slope,but it appears a certain degree of volatility.(2)In the process of rill erosion,the sediment concentration of rill runoff first decreases rapidly and then tends to stabilize.The fluctuation of runoff sediment concentration gradually increases with the increase of flow rate and slope gradient during the process of rill erosion,.As the flow rate and slope gradient increases,the average sediment concentration increases.The average sediment concentration of rill runoff has a largest correlation with the average flow power.The relationship between the average sediment concentration and the average runoff shear force and the average runoff shear force can be expressed by exponential function.The relationship between the average sediment concentration and the unit energy of cross-section can be expressed by linear function.The soil erosion rate increases with the increase of flow rate and slope gradient,and has the highest correlation with the average flow power.The relationship between soil erosion rate and the average runoff shear force,the average flow power and the average unit energy of cross-section can be expressed by exponential function.The average sediment concentration of the rill runoff and the erosion rate can be expressed as the power function of the flow and slope.(3)Under the small amount starting standard,the grain size in incipient motion is most closely related to erosion d80.The relationship between the grain size in incipient motion and the erosion d80 can be expressed by linear function.The formula of the grain size in incipient motion about non-uniform sand can be obtained through the test.According to the experimental data,the empirical formula of grain size in incipient motion about flow rate and slope is obtained under the test conditions. |
PDF Full Text Request