Dynamic changes of soil erosion in a typical disturbance zone of China's Three Gorges Reservoir

The water level fluctuation region in China's Three Gorges Reservoir (TGR) represents a disturbance zone that experiences cyclic exposure and inundation due to reservoir operations. This area has also been subjected to long periods of flooding and wave-induced scouring. Thus, soil erosion in the disturbance zone has greatly intensified since the reservoir was first filled in 2006. In this study, soil erosion rates along nine transects in the mainstream disturbance zone (MDZ) and three transects in a tributary disturbance zone (TDZ) were continuously measured between 2008 and 2016 using erosion pins. The results showed that the average erosion rate in the MDZ was 32 mm yr−1, which was more than six times greater than that in the TDZ. Spatially, the soil erosion rates in the MDZ displayed higher variability than those in the TDZ. The highest rate was found for the altitude range of 170-175 m in the MDZ, and the rates in the altitude ranges decreased in the order of 145-150 m, 160-165 m, and 165-170 m. However, the spatial variation of soil erosion rates in the TDZ was less significant than that in the MDZ. Furthermore, soil erosion rates in the MDZ displayed a small decreasing trend over the first six years and a much greater decreasing trend in the following three years. In contrast, these rates decreased significantly and continuously from 2008 to 2016 in the TDZ. The mean reduction rate of soil erosion in the MDZ was statistically higher than that in the TDZ. The annual average value of soil erosion rate reduction from all transects in the MDZ was 4.1 mm yr−1, whereas it was only 1.7 mm yr−1 in the TDZ. Changes in hydrological regime, vegetation cover, and slope gradient were the main factors that governed the spatial and temporal patterns of soil erosion in the disturbance zone of the TGR.