The 24th IAHR-APD Congress (24th IAHR-APD Congress)

136 / 2024-02-19 12:58:17

Evaluation index and trend of the stability of fluvial mid-channel bars in the Jingjiang Reach

Comprehensive stability index；Mid-channel bars；TGR operation；Jingjiang Reach

Due to the lack of high-precision underwater topographic surveys and detailed hydrological and sediment data, our understandings of discriminating method and descriptive index for the stability and development trend of mid-channel bars in alluvial rivers remain incomplete. Based on the characteristic values of bar width（B_s）, water surface width（B_w）, bed sand median particle size（D₅₀）, channel water slope（J）, water depth（H）, average bar top elevation（Z₁）, mean elevation of deep pool（Z₂）, a comprehensive stability index（S_c）of mid-channel bars is proposed. We used this indicator to evaluate the stability and development trend of mid-channel bars in Jingjiang Reach. The results showed that before the operation of the Three Gorges Reservoir（TGR）, the comprehensive stability of mid-channel islands increased and enhanced significantly, and remained in a fully developed state, caused by lateral and vertical accretion of sediment. After the TGR operation, the comprehensive stability of mid-channel islands increased slightly, attributed to the effects of weakened lateral stability and enhanced vertical stability. Before the TGR operation,, the comprehensive stability of central bars showed a slight increase or small change trend, but after the TGR operation, the comprehensive stability of central bars showed a significant decline trend. This is mainly because changes in flow and sediment regimes caused continuous erosion of central bars, reducing the lateral, longitudinal and vertical stability of central bars. It can provide theoretical basis for riverbed evolution, bank stability and channel management of large alluvial rivers.