Multi-scale analysis of water-sediment variation characteristics and flood hysteresis patterns in the lower Jialing River
摘要
To reveal the long-term evolution law of water and sediment processes in the Jialing River and support the optimal operation of upstream and downstream water conservancy projects, this study systematically analyzes the characteristics of water and sediment changes in the lower reaches of the Jialing River based on long-term observed hydrological data. Based on the measured runoff and sediment data from 1954 to 2023 at the Beibei Hydrological Station in the lower reaches of the Jialing River, this study systematically characterizes the interannual and intra-annual evolution patterns of water and sediment fluxes using P‑III frequency analysis, double mass curves, and Mann‑Kendall abrupt change tests. Furthermore, hydrological years are classified into wet, normal, and dry categories based on P‑III probability distributions, aiming to support the understanding of water–sediment evolution mechanisms in the downstream reaches. The results show that both annual runoff and sediment load exhibit significant interannual variability. After the 1990s, sediment load decreased by 76.99%, whereas runoff decreased by only 11.93%, indicating a pronounced decoupling between water and sediment processes. The flood season contributes approximately 82%–84% of annual runoff and about 99% of sediment load, highlighting strong seasonal concentration. Statistical tests further confirm that the reduction in sediment load is highly significant (p < 0.01), while the decrease in runoff is comparatively moderate. A generally positive correlation exists between runoff and sediment load, but since 1991 sediment transport under similar water volumes has been significantly lower. When flow discharge (Q) is below 15,000 m3/s, the correlation between discharge and sediment transport rate is relatively strong; when Q exceeds 15,000 m3/s, the correlation weakens due to the combined regulation of the Three Gorges Reservoir and the Caojie Dam. Analysis of 141 storm flood events from 2000 to 2020 reveals diverse hysteresis patterns between discharge and sediment concentration, reflecting the combined control of near‑source scouring and delayed supply from distant sources. In summary, over the past nearly 70 years, the lower Jialing River has experienced a slight decrease in water volume but a dramatic decline in sediment transport, with water and sediment processes becoming more concentrated in the flood season and demonstrating distinct phasing and multi‑source coupled control characteristics. These findings provide an evidence base for high-flow water-sediment prediction and intelligent operation of reservoirs, thereby providing data-driven support for future coordinated operation of the Three Gorges Reservoir and the Caojie Reservoir.