Study on sediment yield characteristics of Xining River basin in Xiangjiaba reservoir area

After the impoundment of the Wudongde, Baihetan, and Xiluodu cascade reservoirs in the lower Jinsha River, sediment inflow from the main stem to the Xiangjiaba reservoir decreased sharply, whereas the tributary sediment contribution increased significantly. To investigate the sediment yield characteristics of major tributaries under the strong sediment-trapping effect of cascade reservoirs, the Xining River Basin was selected as the study area to analyze the sediment yield response to extreme precipitation and determine the annual sediment load threshold. Based on digital elevation model, land use, soil type, and observed hydrometeorological data, a distributed SWAT model was established for hydro-sediment simulation. By combining Pearson Type III frequency analysis with the temporal scaling of a typical annual precipitation process, five extreme precipitation scenarios were designed: the observed maximum annual precipitation and design events with return periods ranging from 100 to 1, 000 years. The results show that the model can satisfactorily reproduce the monthly runoff and sediment processes. The spatial distribution of the sediment yield modulus is characterized by high values in the middle reaches, followed by the upper reaches and then the lower reaches, and the high-value area expands upstream with increasing precipitation return period. Under the five scenarios, the annual sediment loads are 1.10, 2.66, 3.04, 3.37, and 3.55 million tons, respectively; the incremental increase diminishes continuously, indicating a nonlinear response. Based on a fitting analysis of the simulation results and a conservative adjustment, the annual sediment load threshold of the Xining River Basin is estimated to be approximately 4.60 million tons, provided that the underlying surface remains stable and no large-scale sudden geological disasters occur. These findings can provide a reference for sediment inflow assessment and scheduling decisions of the Xiangjiaba reservoir.