Evolution and driving mechanism of sediment transport characteristics in the Xihanshui River Basin

The Xihanshui River Basin is a key sediment-producing area in the Jialing River Basin. The evolution of its sediment transport directly affects the ecological security of the upper Yangtze River and the sedimentation of the Three Gorges Reservoir. Clarifying its long-term evolution pattern and driving mechanism is of great significance for the implementation of the Yangtze River Protection Strategy. Based on 61 years of continuous observational data (1965–2025) from the Shanjiaba Hydrological Station, this study adopted statistical analysis methods, the double mass curve method, and six types of mutation point detection methods (Mann–Kendall, Pettitt, etc.) for cross-validation. A sediment-discharge power function model was constructed, combined with GIS spatial analysis (RUSLE model), to quantitatively analyze the characteristics of sediment variation, mutation patterns, and the contribution rates of climate change and human activities to sediment reduction, thereby providing a scientific basis for watershed ecological governance. The results show that: ① Over the past 61 years, the annual sediment discharge of the basin has shown a significant downward trend, decreasing sharply from 23.26 million tons/year during 1965–1990 to 6.09 million tons/year during 1991–2025, reaching a historical minimum of 0.29 million tons in 2016; ② The sediment transport rate exhibits a strong power-law relationship with discharge, with the flood season (July–September) contributing 76.8% of the annual sediment discharge; ③ The abrupt change point of sediment discharge around 1990 coincides with the initiation of the “Changzhi” Soil and Water Conservation Project. Subsequently, the superimposed effect of projects such as the Grain-for-Green Project further intensified the decreasing trend of sediment discharge. The proportion of high-vegetation-coverage area in the basin increased from 15% in 1980 to 78.9% in 2020, and the contribution rate of human activities to sediment reduction exceeds 74%; ④ When sediment discharge falls below the natural background value for a long period, it may lead to riverbed incision, and vigilance is needed against the rebound of soil erosion under extreme rainfall scenarios. This study confirms that large-scale soil and water conservation projects are the core driving force behind the sharp reduction of sediment in the Xihanshui River Basin. In the future, it is necessary to optimize cascade reservoir operation and riverbank protection, and to strengthen ecological restoration in steep slope areas. The results provide key scientific references for ecological governance, cascade reservoir operation, and the optimization of soil and water conservation projects in sediment-producing areas of the upper Yangtze River.