三峡水库调度运行对白螺矶河段河道发育的影响

Impact of Three Gorges Reservoir Operation on Channel Development of Bailuoji Reach

来水来沙是塑造河床形态的动力和物质基础,三峡水库调度运行对水沙过程的改变导致坝下游河道出现剧烈的冲淤调整。选取长江中游典型顺直分汊段——白螺矶河段,从河道槽蓄量、滩槽冲淤、汊道分流能力变化等多角度分析三峡水库蓄水运用后河道发育特征,结合造床流量以上中洪水持续天数变化,定量计算三峡水库调度运行后流量过程变化对白螺矶河段河道发育的影响。结果表明,近年来,白螺矶河段槽蓄量增大并以枯水河槽冲刷为主,汊道段右汊分流比占优,且枯水分流比呈增大态势,三峡蓄水以来的水沙条件可维持白螺矶河段主汊的发育;与无水库调蓄下流量过程相比,现行调度方式下造床流量以上高水持续时间相对缩短,白螺矶河段冲刷总量偏小且右汊分流比略有降低。研究成果可为三峡水库中小洪水调度运行等提供参考。

Flow and sediment are the driving force and material basis for shaping the riverbed.The process of flow and sediment changed by the operation of Three Gorges Reservoir leads to severe riverbed adjustment downstream of the dam.This paper selects the straight-braided channel-Bailuoji as typical which locates in the middle reaches of the Yangtze River,and analyzes the channel development characteristics from perspectives of channel storage capacity,beach-trough scouring and silting and branch channel diversion capacity variation after the impoundment of the Three Gorges Reservoir.Combined with the change in the duration of floods above the channel forming discharge,the impact of the flow process change on the development of the Bailuoji Reach is quantitatively calculated.The results show that in recent years,the channel storage capacity of the Bailuoji reach has increased and scouring mainly locates in the low-flow channel.The right branch is the main branch and the diversion ratio has increased under the low-discharge.The flow and sediment conditions after the impoundment of the Three Gorges Reservoir can maintain the development of the main branch of the Bailuoji reach.Compared with the flow process without reservoir regulation and storage,the duration of high flow above the channel forming discharge is relatively shortened under the current dispatching mode,the total amount of erosion in the Bailuoji reach is relatively small and the diversion ratio of the right branch is slightly reduced.The research results can provide reference for middle-small flood dispatch of Three Gorges Reservoir.