Quantitative study on the mitigation of soil erosion by comprehensive ecological and geotechnical debris flow treatment measures in small basins:A case study of the Sangong River Basin
In order to assess quantitatively the impact of debris flow control projects on soil erosion in small basins,this paper takes the Sangong River Basin in the upper reaches of Tianchi Lake as the research object.Based on field investigation data,a topographic map overlay,and remote sensing interpretation data,we calculate the soil erosion rate of the basin in two periods(1971~2003 and 2008~2020).We also use Google Earth Engine to compute the change of vegetation coverage in this basin over the study years,the impact of comprehensive ecological and geotechnical debris flow treatment measures carried out in this scenic spot on the soil erosion and ecology of the basin are thus uncovered.Our main results were:(1)the average vegetation cover of Sangong River Basin increased by 11.34%after the debris flow treatment,where areas with high vegetation cover increased by 16.93%,and the vegetation cover of the debris flow gullies and river valleys increased significantly.(2)The average erosion rate of Sangong River Basin from 1971 to 2003 was 0.34 mm/a,which was 131%higher than the average erosion rate of the North Tianshan Mountain Basin in the same period.This erosion rate was caused by deterioration of basin ecology due to the outbreak of flash floods and debris flows triggered by human factors such as overgrazing and indiscriminate logging.(3)After the basin was regulated by ecological and geotechnical engineering projects(2008~2020),the average erosion rate reduced to 15%(0.051 mm/a)of that before treatment.which was only 34%of the average erosion rate of the same period in the mountain basin of the North Tianshan region.