荆江门弯道近期滩槽演变特点及影响因素分析

三峡水库运用改变了下泄水沙条件,坝下游弯曲河型均呈现“凸冲凹淤”演变规律,以致碍航问题日益突出。为研究弯曲河型滩槽演变特点及其成因,以下荆江河段荆江门弯道为例,利用三峡蓄水后近15 a实测地形资料,采用逻辑推理及统计分析方法分析其影响因素并预测了航道变化趋势。结果表明:三峡工程运用后,凸岸边滩年际间呈持续冲刷趋势,冲刷位置不断下移导致河段展宽引起航道条件恶化;在平滩流量(20 000~25 000 m³/s)持续时间＞15 d的年份,凸岸边滩冲刷后退,反之淤长;冲淤幅度与年均来沙量,尤其细沙(d≤0.125 mm)含量密切相关,基本呈同步变化趋势;荆江一期工程实施后,在当前水沙条件下凸岸边滩会继续受冲,形成枯水双槽,航道条件将恶化。水沙过程的改变是弯曲河型滩槽演变的主要原因,遇大水且来沙量较少的年份,荆江门河段很可能出浅碍航,这可为下荆江弯曲河段航道治理提供一定的参考价值。

Recent Evolution Characteristics and Influence Factors of Jingjiangmen Bend Reach

The operation of the Three Gorges Project (TGP) had changed the condition of discharge and sediment. Curved reaches in the Jingjiang River all witnessed erosion in convex bank and deposition in concave bank, detrimental to channel navigation. In order to study the evolution characteristics and influence factors of curved reach, we analyzed the evolution causes and estimated the future changes of Jingjiangmen reach of lower Jingjiang River as an example according to measured topographic data in recent 15 years after the impoundment of TGR via logic reasoning and statistical analysis. Results demonstrated that after the operation of TGP, the convex bank of Jingjiangmen reach showed a trend of continuous scouring year by year, and the position of scouring moved downwards continuously, which deteriorated the channel navigation condition. When the duration of bank-full discharge (20 000~25 000 m³/s) was longer than 15 days in a year, convex bank was scoured and moved backwards, while on the contrary, when the duration of bank-full discharge was shorter than 15 days of the year, the convex bank was silted. The annual variations of convex bank had a good corresponding relationship with sediment concentration, especially fine sand content (d<0.125 mm), synchronously increasing or decreasing. After the first phase implementation project of Jingjiang Reach in 2014, given the discharge and sediment conditions, convex bank wound continue scouring, giving rise to double-groove in dry season and more deteriorated navigation condition. In conclusion, changes in discharge and sediment conditions are the major causes of bend reach evolution. In years of long flood duration with small sediment discharge, Jingjiangmen reach would most likely experience navigation obstruction. These conclusions provide reference for the governance of meandering channels in lower Jingjiangmen reach.