下荆江熊家洲河段平面形态与河床冲淤变化

Channel’s Morphological Change and Riverbed’s Erosion-Deposition Process of Xiongjiazhou Reach in Lower Jingjiang River

熊家洲河段位于长江中游下荆江尾端,其平面形态从顺直过渡到微弯再逐渐演变成S型,是目前荆江最为弯曲的河段。受水沙条件、河岸边界条件、自然裁弯和人工裁弯等因素影响,局部河势调整频繁。熊家洲凸岸斜槽裁弯形成新河槽,导致主流与支汊成为共生的分汊河势,改变了熊家洲出口段水流条件,进而影响下游七弓岭弯道崩岸速率和河床冲淤。为全面分析熊家洲河段平面形态演变过程和河床冲淤变化,选取枯水期遥感影像数据及沿程代表性断面进行分析。结果表明:熊家洲河段整体向下游蠕动且河道展宽,熊家洲弯道新生河槽呈冲刷扩大趋势,7 a平均展宽70 m;出流沿程断面深槽从左岸向右岸方向发展,熊家洲下游的深泓线偏向右岸;三峡水库建成运行后,深泓线开始贴近七弓岭凸岸,而原深槽回淤形成2个沙洲,经过七弓岭弯顶后逐渐向凹岸偏移,出熊家洲弯道后河道沿程呈现冲刷下切趋势。研究成果对目前该段河势控制工程的实施提供了参考意见,为下一步研究三峡水库运行的河势控制提出了思路。

Xiongjiazhou reach is located at the tail of the lower Jingjiang River in the midstream of Yangtze River.The morphology of Xiongjiazhou reach transited from straight to slightly sinuous and then gradually evolved into S-shape.It is currently the most sinuous segment in the Jingjiang reach.Subjected to incoming water and sediment load,and affected by riverbank boundary conditions as well as natural and artificial cutoffs,Xiongjiazhou reach has undergone frequent local adjustment in terms of river regime.Since the chute cutoff in the convex bank of Xiongjiazhou reach,a new anabranching channel was formed,leading to the coexistence of the main channel and the anabranching channel,which changed the flow conditions at the outlet of the Xiongjiazhou reach and further affected the bank collapse rate and riverbed erosion-deposition process in Qigongling bend.According to remote sensing imagery data and representative sections in dry season,the entire Xiongjiazhou reach has been creeping towards the downstream and the channel has been widened.The newly formed anabranching channel in the Xiongjiazhou bend is experiencing expanded scouring,with an average width of 70 m in seven years.The deep trough along the outflow section develops from the left bank to the right bank,and the thalweg of downstream Xiongjiazhou is deflected to the right bank.After the impoundment of the Three Gorges Reservoir,the thalweg has been moving close to the concave bank of Qigongling bend,whereas the original deep trough was deposited into two bars emerging above water surface.After reaching the apex of Qigongling bend,the thalweg gradually shifted to the concave bank.The results of this research provide reference for the implementation of the river regime control project in this segment,and offer ideas for the next step in the study of river regime control.