An Experimental Study On The Development Process Of Gully Head Erosion On Slopes And Its Relationship With The Response Of Erosion And Sediment Production

As one of the most serious areas of soil erosion on the Loess Plateau,the biggest problems faced by the Loess Plateau area are different degrees of gully head advancement due to retrograde erosion of gully channels,undercutting of gully bottoms,collapse of gully walls,landslides and slides,expansion of gully banks,gradual shrinkage and fragmentation of the loess plateau,resulting in the destruction of a large amount of farmland and roads on the loess plateau,seriously damaging agricultural and transport resources and posing a great threat to the safety of urban dwellings.The loess plateau area is dominated by hydraulic erosion,with runoff mainly originating from the loess surface and sediment mainly from the ditches.Therefore,it is necessary to further study the development of gully channels and erosion processes under the retrospective erosion of fine gullies.In the past,there have been more studies on large-scale anadromous erosion by means of field surveys and remote sensing interpretation,but few studies on the anadromous erosion process and morphological characteristics of fine gullies have been reported,which is not conducive to revealing the anadromous erosion mechanism in essence.In order to reveal the coupling effect of hydraulic characteristics,gully morphology and micro-geomorphological features on the erosion of sand production in the fine gullies of loess plateau,we adopt the indoor runoff simulation and scouring test method,combined with 3D laser scanning technology and GIS technology,to study the influence of soil texture,gully head height and water discharge flow on the erosion of sand production in the fine gullies of loess plateau.The aim is to reveal the coupling effect of hydrodynamic properties,fine gully morphology and micro-geomorphological features on the response mechanism of erosion and sand production characteristics,and to provide scientific basis and technical support for the control of slope erosion and the protection of anadromous erosion gullies in high loess gully areas.The main results are as follows,(1)The erosion power dissipation law of the gully head anadromous erosion process is revealed.The loess Reynolds number,runoff shear,runoff power,drag coefficient and runoff power all increase as a power function with the ephemeris of flow production;the loess Froude number decreases as a power function with the ephemeris of flow production.The kinetic energy of loess surface increased with the increase of gully head height and release flow.Among them,the effect of release flow on loess kinetic energy is significant,with the increase of release flow,loess kinetic energy increased by 32.67～112.94%,and when the concentrated runoff flows through the gully bed,the kinetic energy decreases by 1.51～34.69%,and the runoff kinetic energy of chalky loam is less than that of loamy sandy soil,which is consuming more energy to complete the gully head undercut.The energy consumption of the system tended to increase with the increase of ditch head height and water release flow.Among them,the effect of release flow on system energy consumption is more significant,with the increase of release flow,the system runoff potential energy is 0.50～1.01 times larger.At the same time,the contribution rate of energy consumption at the head of the ditch and the height of the head of the ditch were negatively correlated and positively correlated with the release flow,and the contribution rate of energy consumption at the head of the ditch ranged from 43.8%to 86.6%,indicating that the energy consumption at the head of the ditch was the main energy consumption mode under the retrograde erosion of the fine ditch.(2)The mechanism of soil texture and gully head morphological characteristics on the anadromous erosion process was clarified.The higher the height of the gully head and the higher the discharge flow,the more easily the soil is eroded.Among them,the sand production rate of loamy sandy soil is larger than that of chalky sandy loam,and the coefficient of variation of loamy sandy soil is also larger,indicating that its soil erosion process fluctuates more and is more prone to erosion.In contrast,more than 68.8%of the soil erosion in the fine gully erosion process originated from the lower and upper slopes,and the contribution of sand production from the gully head retrospective erosion ranged from 46.21 to 82.71%.In addition,the system erosion sand production rate is significantly correlated with Reynolds number,runoff shear and runoff power,with correlation coefficients greater than 0.85.Meanwhile,the erosion sand production rate increases with the increase of energy consumption,and the correlation between the two is significant exponential function.(3)The evolutionary rules of the head of the gully traceability,gully wall expansion and gully bottom erosion and deposition under fine gully anadromous erosion were clarified and quantified.The distance of anadromous erosion increases linearly with the time of flow production.The height of gully head was negatively correlated with the average rate of anadromous erosion,while it was positively correlated with the release flow,in which the release flow had the greatest influence on the rate of gully head erosion under the slope,and its maximum range of gully head erosion rate was the largest,between 21～57%.Among them,the average rate of retrospective erosion of loamy sandy soil was 1.25～1.99 times higher than that of chalky sandy loam,indicating that loamy sandy soil was more prone to erosion.The closer the distance from the top of the slope,the greater the width of gully head erosion and the smaller the degree of gully wall collapse induced.The average width of head erosion is 1.4～6.6 times and 2.6～26.0 times of the average widening width of fine gully caused by gully wall collapse,and the average depth of head erosion is at least 3.3 and 9.7 times of the height of erosion and deposition depth of the bottom.Therefore,the contribution of gully head erosion to the widening and downcutting depth is significantly higher than the increased or reduced depth of fine gully widening and gully bottom erosion deposition caused by gully wall collapse.(4)Quantify the evolutionary pattern of the transverse and longitudinal cross-sectional morphology of the fine gully channel.The overall cross-sectional morphology of the channel is basically a trapezoidal structure with a wide top and a narrow bottom,with the increase in the length of the runoff process,the cross-sectional morphology of the fine ditch gradually widened,while the depth of the fine ditch channel also increased,to the bottom of the slope evolved into a"wide and deep".The morphology of the fine ditch under the sandy loam soil is more inclined to"narrow and deep",and the morphological indexes of the upper and middle of the slope are wider,and the morphological indexes of the section are close to 0.5,that is,the upper and middle of the slope are more similar to a "V" triangle of equal width and height,and the degree of erosion is smaller.The morphology of fine ditches under loamy sandy soil is more inclined to "wide and shallow",and the range of morphological indexes is larger in the upper and middle part of the slope,i.e.,more than 67%of the cross-sectional morphological indexes are above 0.70,and the morphology of their ditches tends to be more rectangular in cross-section,with a greater degree of erosion.The average depth and erosion intensity of the channel decreased with the increase of erosion length,and the average depth and erosion intensity of the channel under the slope decreased by about 20%compared with those on the slope,and the increase of water release flow could significantly increase the average depth and erosion intensity of the channel.The cut,roughness,undulation and slope of the chalky sandy loam are all 6%～17%larger than those of the loamy sandy loam due to the large undercutting depth.(5)The influence mechanisms of runoff hydraulics characteristics,micro-geomorphic features and fine channel cross-sectional morphology on erosion and sand production were elucidated.The influences of runoff power,topography quantification parameters and fine channel morphology quantification parameters on erosion sand production were 52.1%,19.9%and 28.0%,respectively,and the influences of erosion intensity were 59.4%,16.1%and 24.5%,respectively,for the chalky sandy loam soil.Only the loamy sandy soil had a significant positive relationship between runoff power on erosion sand production and erosion intensity,i.e.,its factor influence rate was extremely significant.The influence rates of runoff power,average gully depth and topography combined quantified parameters on erosion sand production were 70.09～75.0%,9.54～11.39%and 17.17～17.83%,respectively,and on erosion intensity were 70.09～73.52%,9.50～11.14%and 16.98～18.78%,respectively,for different gully head types.