Rill Erosion Processes On Steep Loess Slopes

Soil erosion is one of the major global environmental problems,which is severely restricting the sustainable development of global society and economy.In recent years,due to spoil and slag accumulation body of engineering construction,terraces,trenches and subgrade excavation,a large number of steep slopes(?25 °)have been formed.Bare steep slopes are easily eroded after being hit by raindrops and runoff,and have become a new source of sand production.There are few reports on the research of rill erosion on steep slopes,so that it is difficult to form a complete understanding of rill erosion.In order to ascertain the process mechanism of the rill erosion on the steep slope,it can more accurately reveal the influence mechanism of the formation of the rill on the steep loess slope,and provide a theoretical basis for the prevention and prediction of the rill erosion on the steep slope.Therefore,the loess soil of loess plateau are used to study the rill morphological characteristics,runoff and sediment characteristics and hydraulic parameter characteristics of rill development and evolution on steep slopes(?25°)with the combination of flume scouring and artificial simulated rainfall experiments.The main conclusions are as follows:(1)Evolution characteristics of rill erosion on the steep loess slope:The development process of rill erosion on steep loess slopes is roughly divided into four stages: splash erosion and surface erosion,rill formation,rill development,and rill collapse.In addition,the rill development stage is divided into the development stage of primary rill and the development stage of second gully;the rill collapse stage is divided into two categories: the rill width suddenly decreases and the width of the rill keeps increasing.The length increases as the runoff duration increases,but the increasing rate gradually decreases.As a whole,the rill width increases during the runoff,and it fluctuates greatly during the 20 to 40 minutes of the runoff.Under the entire slope condition,the source erosion rate increases with the increase of rainfall intensity.The rill dissection degree increases with the increase of rain intensity;it first increases,then decreases,and then increases again with the increase of the slope;and gradually increases with the increase of runoff duration,the regression analysis model of rill dissection degree and runoff duration is quadratic function equation y = ax2 + bx + c(P <0.01,R2 = 0.989).(2)Characteristics of runoff rate and sediment rate of rill erosion on the steep loess slope:The runoff rate and sediment rate are relatively stable throughout the test,then they increase slightly with the increase of runoff duration and show stable fluctuations.When the slope is constant,the runoff rate increases linearly with the increase of flow rate;under the small slope(25° and 30°)and large flow(2.0 and 2.5L/min),the linear relationship between the runoff rate and the flow is not extremely significant,the slope has no significant effect on the runoff rate.The rate of sediment rate increases linearly with the increase of the flow,the effect of slope on the sediment rate is not very significant;the variation law of the sediment rate under the conditions of the entire test is 0.6 <1.0 <1.5 2.0 <2.5 L / min.(3)The hydraulic characteristics of rill erosion on the steep loess slope:The velocity decreases first,then keeps smooth and steady as scouring time.The Reynolds number of the flow varies between 199.996 and 873.482 in the erosion process,it is affected mainly by flow discharge and there is a linear relationship between the Reynolds number and flow discharge.The Froude number of the flow is larger than 1 in the whole experiments,which indicates that the rill flow belongs to the supercritical flow condition.Meanwhile,the Froude number of rill flow is in a reciprocal decreased relationship with flow.Darcy-weisbach resistance coefficient(f)is positively related to flow and is in a power function relationship with the Reynolds number.(4)Study the erosion mechanism of rill erosion on steep slopes based on data denoising:The signal-to-noise ratio(S/N)in Taguchi design is used to conduct the data(runoff and sediment of rill erosion and the hydraulic characteristics)denoising for the dependent variables in the tests and the differences between the data before and after denoising are analyzed by studying the significance,contribution rate and fitting degree of influence factors on observed dependent variables in order to determine the applicability of this data denoising method to soil erosion tests.The results show that the main influencing factors of runoff rate,sediment rate,velocity,the Reynolds number,the Froude number,the Darcy-weisbach resistance coefficient could be identified well.However,for the data after denoising,the values of significance testing(P)of the influencing factors were bigger,increasing the contribution rate of the influence factor to the observed variable,reducing the contribution rate of the error,and reducing the absolute error and relative error between the predicted value and the measured value.However,the difference between the evaluation indicators(coefficient of determination?Nash-Sutcliffe efficiency coefficient and the relative root-mean-square error)before and after the data denoising is not very large indicates that the error(noise)of the original data is small enough to ensure the accuracy of the test results and more accurately clarify the mechanism of the erosion of the rill erosion on the steep slope loess slope.