Remote Sensing Monitoring And Scale Effect Of Soil Erosion In The Three Gorges Reservoir Area

The Three Gorges Reservoir Area located in the Upper Yangtze River is the soil erosion intensity area. It has been the key area of the State Soil and Water Conservation because of the vulnerability of the ecological environment and the importance of ecological security barrier for the middle and lower Yangtze River. Therefore, this research on the soil erosion of the Three Gorges Reservoir Area is significant to control of water and soil loss.In this paper, on the basis of RS and GIS, the soil erosion of Three Gorges Resevoir has been monitored through the application of fractal theory and RUSLE model from qualitative and quantitative aspect. Then its spatial distribution and dynamic changes were analyzed. Soil erosion of the fractal spatial pattern was discussed from different landscape scales. And studying variation of LS factor in the RUSLE model from different scales revealed the scale effect of soil erosion in the Three Gorges Reservoir Area. The results showed that:(1) Qualitative analysis showed that the slight erosion area was more than 50% of the study area, which presented a significant increasing from 2000 to 2009, whereas decreased in other erosion grades. The complexity of spatial pattern in slight and low erosion grades presented decreasing and other grades presented increasing. The stability of spatial pattern was highest with the extreme erosion grade, which values were 0.4892 and 0.4636 in 2000 and 2009 respectively.(2) The result of Quantitative estimate showed that the annual soil erosion amount and the mean soil erosion modulus in the Three Gorges Reservoir Area were 18359.43×104 t·a-1 and 31.85 t·ha-2·a-1 respectively, which belongs to medium erosion. Slight and low erosion grades accounted for about 63.93% of the total area.(3) The spatial distribution of soil erosion in the Three Gorges Reservoir Area showed that Soil erosion intensity had no linear relationship with the altitudinal gradient. Moderate to severe erosion intensity mainly distributed over elevation area from 500 to 1500 meters. The soil erosion intensity showed a significant positive correlation with slop gradient. When slope gradient was larger than 15 degree, the frequency of moderate to severe erosion intensity increased significantly. And extreme erosion intensity was almost occurred at the slope which is larger than 35 degree. However the soil erosion intensity had no obvious relationship with slope aspects. The amount of soil erosion on shady slopes was a little higher than that on sunny slopes, occupying 56.63% of the total erosion amount.(4) At landscape level, the fractal dimension of spatial pattern decreased with increasing elevation, but the stability of spatial pattern increased by increasing elevation. At patch level, slight to moderate erosion intensity had no linear relationship with elevation. However, with the elevation increases, the fractal dimension of high to severe erosion intensity become smaller, the stability become larger. Slight and low erosion grades presented a significant decreasing from 2000 to 2009. The stability of moderate to severe erosion intensity presented decreasing at lower elevation, and presented increasing at higher elevation.(5) With resolution of DEM decreases, the maximum and average of S factor become smaller, the maximum and average of L factor showed linear increasing trend. LS factor has different changes rule based on different topography. The maximum and average of LS factor overall presented linearly increasing in Badong County, which is mountain landscape; however the maximum and average of LS factor presented linearly decreasing in Changshou County, which is hilly landscape.