Study On Soil Erosion Characteristics In Typical Gully Land Consolidation Project Area In The Loess Area

The ecological environment of the Loess Plateau is fragile,and it is the region with the most serious soil erosion in the world.In order to improve the ecological environment and protect people’s livehood,the Gully Land Consolidation（GLC）project,which is on the basis of the“Grain for Green”（GFG）project,has been firstly taken in Yan’an city.However,in the process of the GLC project,the landforms and land use pattern were changed,which has changed the soil erosion characteristics of the region.It is of great significance to study the characteristics of soil erosion in the GLC project area for the later soil erosion control.In order to fully understand the characteristics of soil erosion in the GLC project area,this thesis takes the demonstration area of the GLC project including Gutun Watershed and Ansai Nangou as examples to study the characteristics of soil erosion in the watershed scale,gully scale and slope scale.Firstly,on the watershed scale,based on the rainfall data,soil attribute data,digital elevation model（DEM）data and land use data of the Gutun watershed,the characteristics of soil erosion are analyzed based on RUSLE model through the extraction and calculation of each erosion factor.Then,on the basis of watershed scale,select the consolidated gully and unconsolidated gully with severe erosion as the research object.Two phases（2018/11-2019/09）of digital surface model（DSM）data are obtained based on UAV photogrammetry technology,and the difference of DSM data is used to analyze the soil erosion characteristics of gully scale.In the slope scale,a high cut-slope in Ansai Nangou is selected as the research object.Based on the three-dimensional laser scanning technology,two phases（2018/11-2019/09）of 3D point cloud data are obtained,and its erosion characteristics are analyzed through the establishment and difference of 3D model.Finally,based on the characteristics of soil erosion on the watershed scale,gully scale and slope scale,the comprehensive prevention and control suggestions are put forward.Through the research,the main conclusions of this thesis are as follows:（1）In 2018,the average soil erosion modulus of Gutun watershed was 2423.57t·km^-2·a^-1,which belongs to mild erosion,and the total amount of erosion is 101741.47t.Soil erosion was mainly slight erosion and mild erosion,accounting for 71.19%of the total area of the watershed.The soil erosion degree increased from gully head to gully mouth,and the erosion near gully mouth was the most serious.The relationship among elevation,slope,aspect,land use type and soil erosion is as follows:Soil erosion mainly occurs in the area with elevation of 950～1100m,and the proportion of erosion amount is as high as 71.88%.The soil erosion degree decreased with the increase of elevation;Soil erosion mainly occurs in the slope zone of>35°,and the proportion of soil erosion is as high as 50.08%.The soil erosion degree increases with the increase of slope;The soil erosion degree on different aspects is characterized by sunny slope>semi-shady slope>semi-sunny slope>shady slope;The soil erosion degree of different land use types is characterized by bare land>ordinary road surface>industrial and mining land>grassland>cultivated land>unused cultivated land>shrub land>forest land>water area,residential area and hardened road surface.（2）In the gully area,the area of elevation reduction accounts for 26.78%of the gully area,and the elevation reduction is mainly-0.3～0m,accounting for 86.31%of the elevation reduction area.The erosion areas of the consolidated gully and unconsolidated gully are mainly distributed in the hillslope erosion area,accounting for87.44%of the total erosion area of the gully area.The degree of gully erosion in the consolidated gully and unconsolidated gully is increasing from the head to the mouth of the gully.And the degree of gully erosion of the consolidated gully is weaker than that of the unconsolidated gully.The relationship between elevation,slope and soil erosion is shown as:Soil erosion mainly occurs in the 1000～1050m elevation zone,and the erosion volume accounts for 43.45%of the total erosion volume of the gully area.The erosion degree of the 1000～1050m and>1100m elevation zones is the most serious,and this conclusion is a supplement to the erosion characteristics of the specific gully area under the watershed scale;Soil erosion mainly occurs in the slope zone of>35°,accounting for 45.99%of the total erosion volume of gully area,and the soil erosion degree increases with the increase of slope.（3）In the slope scale,the total volume of slope erosion is 129.2 m3.The erosion degree of the whole cut-slope is more and more serious from the top to the foot of the slope,and the soil erosion mainly occurs on two slopes near the foot of the slope,and its erosion volume accounts for 58.81%of the total erosion volume of the whole slope.It is found that the soil erosion on the slope is affected by water gathering area,slope height,soil type and drainage channel.The specific performance is as follows:the water gathering area will aggravate the soil erosion degree on the slope surface,and the erosion degree of the area under the water gathering area is extremely serious;the higher the slope height is,the more serious the soil erosion degree is;the ancient paleosol is more vulnerable to erosion,which will aggravate the soil erosion degree on the slope surface;the drainage channel above the slope has little impact on soil erosion,but the drainage channel below the slope will obviously aggravate the erosion degree of the slope.（4）According to the characteristics of soil erosion on the scale of watershed,gully area and slope,this paper puts forward the suggestions for comprehensive prevention and control of soil erosion on different scales in typical GLC project area in the Loess area.On the watershed scale,it is suggested to improve the ecological control measures and engineering control measures,and strengthen the ecological awareness.On the gully area,it is suggested to combine the treatment of gully with the treatment of slope,with the treatment of slope as the main measure.On the scale of slope,it is suggested to optimize the design scheme of drainage channel,develop eco-slope protection materials and strengthen the ecological control of slope.