Erosion Characteristics Of Debris Flow In Small Watershed After Earthquake Based On Multi-Source Remote Sensing Technology

The gravity erosion of debris flow after earthquakes is intense,which has significant sediment yield and sediment transport capacity and geomorphological effect.However,quantitative modeling and analysis of debris flow erosion after earthquakes are difficult.In this paper,Niuquangou area of Wenchuan Earthquake is taken as a typical study area,and multi-source remote sensing,GIS technology and statistical analysis method are used to divide the Sediment-producing unit of slope-channel-basin,and D-InSAR and Amplitude Tracking technology are combined to generate high-precision three-dimensional deformation field before and after each debris flow erosion.The characteristics of debris flow erosion after the earthquake are studied from different levels of Sediment-producing units of slope,channel and basin.The sediment transport characteristics and processes of post-earthquake debris flow are quantitatively analyzed,and the relationship between different Sediment-producing units and different influencing factors is studied.The results show that:1)Under the action of three debris flows in 2008-2010,the total erosion of slope is 120.70×10~4m~3,61.56×10~4m~3,68.25×10~4m~3,and the total erosion of channel is 12.65×10~4m~3,4.97×10~4m~3 and9.02×10~4m~3,respectively.The sediment yield of river basin is divided into three parts.79.76×10~4m~3,19.02×10~4m~3 and 24.62×10~4m~3,respectively.Among them,the total erosion of slope,gully and watershed caused by debris flow from May 2008 to December 2008 is greater than the corresponding erosion and sediment yield of debris flow in 2009 and 2010.2)The gravity erosion sediment yield of slope body accounts for more than 50%of the sediment yield of all levels of gullies,and is the main source of sediment in all levels of gullies.The lower the grade of gullies,the greater the contribution rate of sediment of slope body.The sediment yield of slopes is mainly convex,concave and mixed,accounting for more than 85%of the total sediment yield of slopes.The sediment yield of slopes has a positive power function relationship with the area of slopes,and the erosion rate of slopes has a positive power function relationship with the height difference,while it has a negative correlation with the length of slopes and vegetation coverage.3)The gully erosion in the basin is characterized by larger scour than that in the main gully,and the silting area is concentrated in the narrower part of the main gully,the bending part and the debris flow gully mouth.However,there is strong downward cutting erosion in the straight and large drop channel.The amount of channel erosion is positively correlated with the area of the channel.There is no obvious relationship between the erosion rate and the area of the channel,but negatively correlated with the length of the channel,and positively correlated with the elevation difference and the ratio drop of the channel.4)The sediment transport capacity is different in different river basins.The larger the river basin level,the smaller the sediment transport ratio and the weaker the sediment transport capacity.The sediment transport ratio of the first river basin is the lowest 0.23,and the sediment transport ratio of the third river basin is the highest 0.92.The sediment yield characteristics of the river basin are affected by the topographic and geomorphological conditions of the river basin.Among them,the erosion amount of the river basin is positively correlated with the area of the river It is positively correlated with the roundness ratio and vegetation coverage,but sediment yield is controlled by many factors.The research results can provide reference and basis for debris flow disaster prevention and mitigation and sediment control in the basin after the earthquake.