Runoff and Sediment Characteristics at Multi-scale Nested Small Watersheds in the Central Region of the Three Gorges Reservoir Area under Extreme Rainfall Events
To study the source and type distribution of sediment in the central region of the Three Gorges Reservoir Area,this pa-per utilizes the multi-scale nested small watershed rainfall and sediment characteristics data from 2003 to 2022 collected by Comp-renshensive Safety Monitoring System of Three Gorges—Water and Soil Conservation Monitoring Station in Typical Area of Wan-zhou,Institute of Mountain Hazards and Environment,Chinese Academy of Sciences.By applying the Mann-Kendall rank correla-tion test,the paper conducts an in-depth analysis of the trend changes in sediment discharge within the reservoir area watershed and its relationship with extreme rainfall.The results indicate that:(1)There is a significant increasing trend in the number of rainy days,moderate rain,heavy rain,and rainstorm in the typical small watershed in the central Three Gorges Reservoir area;(2)During the process of converging from tributary gullies to the outlet,some bedload sediment deposition occurs.However,during ex-treme rainfall events,the deposited sediment is reactivated and flows into the downstream,and the sediment on the watershed slope mainly loses in the form of suspended sediment;(3)Due to the impact of human activities,there are significant differences in ero-sion moduli among various tributary gullies and catchments within the nested small watershed,with the maximum erosion modulus being 9.71 times higher than the minimum.Meanwhile,the annual erosion moduli of the small watershed and its nested tributary gullies show increasing trends of varying degrees,reaching a maximum in 2020,a year with frequent extreme precipitation events;(4)Although there is an overall decreasing trend in rainfall in the typical small watershed in the central region of the Three Gorges Reservoir area,the frequent occurrence of extreme rainfall remains a key area for soil erosion prevention and control.Therefore,in response to the frequent extreme rainfall erosion characteristics and the sediment migration patterns within the small watershed,strengthening the exclusion and management of ecological risks for bedload and suspended sediment at their sources in the small watershed,and stabilizing riverbed sediment deposition will effectively reduce the sediment output at the outlet station of the small watershed.
Three Gorges Reservoir areaextreme rainfallsuspended sedimentbedload