长江下游官洲水道河床演变特性及趋势OA

[Objective]The Guanzhou Waterway,a typical goose-head-shaped braided channel in the lower rea-ches of the Yangtze River,is characterized by complex and dynamic shoals,braided channels,and flow-sediment diversion patterns.This study aims to:(1)analyze recent riverbed evolution characteristics(2003-2023)from multiple perspectives,including boundary conditions,diversion ratios,shoal dynamics,thalweg shifts,and ero-sion-deposition changes;(2)quantify the effects of revetment works,upstream reservoir impoundment,and down-stream confluence processes;(3)predict future evolution trends;and(4)propose targeted measures for river re-gime stability.[Methods]Long-term hydro-morphological datasets were employed,including:(1)topographic surveys derived from 1∶10 000 scale maps from the years 1966,1977,1987,1998,2003,2012,and 2023.These datasets were used to analyze changes in shoal areas(e.g.,Qingjie Shoal,Fusheng Shoal),thalweg posi-tions,and cross-sectional parameters(width,depth,width-depth ratio).(2)Hydrological data,including annual runoff and sediment load at Datong station from 1966 to 2022,were collected to characterize changes in the flow-sediment regime,particularly following the impoundment of the Three Gorges Reservoir in 2003.(3)Engineering records of historical revetment projects(e.g.,Sanyiwei,Guanzhou Shoal)were compiled to assess their effects on channel boundary stability.Quantitative analyses included:(1)statistical comparisons of diversion ratios among branches(Dongjiang,Xinzhong Branch,Nanjiajiang);(2)calculations of erosion and deposition volumes(vol-ume changes in the riverbed below+5 m elevation);and(3)trend analysis of key cross-sections(GZ2#,GZ7#,GZ19#)to identify dominant evolution patterns.[Results](1)River regime stability under revetment works:con-tinuous revetment works since the 1980s have stabilized the overall river regime.The width-depth ratio of key cross-section GZ7# decreased from 1.45 in 1998 to 1.28 in 2023,indicating channel stabilization.The Xinzhong Branch,previously active,became nearly inactive,with its dry-season diversion ratio dropping to approximately 1％in 2023 due to sedimentation at its entrance.(2)Effects of clear water discharge:after 2003,the annual sediment load at Datong station decreased by 68.5％,leading to net erosion in the study reach.From 1998 to 2023,the channel from the Qingjie Shoal inlet to Yangjiatao experienced net erosion of approximately 37.9 million m3,with the channel volume below the+5 m elevation increasing by about 6％from 2003 to 2023.Severe erosion was observed at the left bank of the confluence section and at the head of Qingjie Shoal.(3)Critical evolution trends:the diversion ratio of the Nanjiajiang Branch gradually increased from 15％in the 1980s to 24％in 2023 due to scouring along the left margin of Fusheng Shoal.However,its development was constrained by the nodal control of Huangshiji.The left-bank shoal in the confluence section was expected to continue eroding,threatening downstream stability.[Conclusion]This study highlights the critical role of revetment projects in stabilizing this historically unstable braided channel,while revealing new challenges posed by clear water discharge.Key findings include:(1)up-stream changes,such as the shrinkage of the left branch in the Dongliu Waterway and the increased diversion to the right branch,cause a slight leftward shift of the main channel.After being deflected by Jiyangji,this shift leads to a minor rightward displacement of the diversion point between the left branch and Nanjiajiang.(2)Under the new flow-sediment regime,the reduced sediment load accelerates erosion in unprotected areas(e.g.,the head of Qingjie Shoal and the left bank of the confluence section).Ongoing adjustments at the head of Qingjie Shoal may subtly alter the inflow conditions and diversion ratio of the Nanjiajiang branch.Targeted control measures are pro-posed for three critical zones:(1)the head of Qingjie Shoal,to manage scouring-induced changes in the inflow to the Nanjiajiang branch;(2)the left margin of Fusheng Shoal,to mitigate the enhanced deflection effects from Huangshiji;and(3)the left bank of the confluence section,to prevent downstream channel instability caused by persistent scouring.Enhanced monitoring and data collection in these areas are essential for ensuring future river re-gime stability.