Modeling Sediment Flux in River Confluences: A Comprehensive Momentum‐Based Study

Abstract The accurate estimation of sediment flux in naturally confluent rivers remains challenging. In this study, we developed a momentum‐sediment model (MSM) that considers the complex structure of confluent rivers to estimate sediment flux. Trend analyses of annual runoff and sediment flux from 1956 to 2022 were conducted at four hydrological stations in the upper reaches of the Yangtze River Basin: Pingshan, Zhutuo, Cuntan, and Yichang. Runoff change was insignificant, whereas the sediment flux decreased significantly at all four stations. The entire time series was divided into five periods: a reference period (P1: 1956–1984) and four changing periods (P2: 1985–1993; P3: 1994–2002; P4: 2003–2012; and P5: 2013–2022). The hydrological time series of the reference period served as the calibration period for constructing the momentum‐sediment models for Zhutuo, Cuntan, and Yichang stations. The MSM expressions were validated in the four changing periods. The momentum‐sediment models for period P1 at Zhutuo and Cuntan stations could be directly applied in periods P2–P5. The MSM for the Yichang station was improved by incorporating the trapping efficiency of the Three Gorges Reservoir. The simulation results of the MSM for sediment flux outperformed the sediment rating curves and linear relationship, particularly for maximum measured values. The applicability of the MSM was validated in the Jialing River, which is characterized by a small basin area, and the Yellow River, which is known for its scarce water and rich sediments. This confirmed that the MSM was insensitive to watershed scale and hydrological conditions.