长江口新桥水道动力地貌变化过程研究

Morphodynamic Evolution of the Xinqiao Channel in the Changjiang River Estuary

利用1958—2020年实测地形数据与长江入海水沙数据,分析长江口南支最大的涨潮槽——新桥水道动力地貌变化及其驱动机制。结果表明:新桥水道在1958—2020年间的地貌演变可以分为3个阶段:第一阶段(1958—1997年)新桥水道受控于径流、潮流的耦合作用而经历“冲刷-淤积”的周期性变化,其中河槽主要展现上、下游迁移及河槽收缩交替等特征;第二阶段(1997—2003年)因1998和1999年大洪水造成新桥水道冲刷,新桥水道河槽向上游拓展延伸,河道拓宽明显;第三阶段(2003—2020年)则受人类活动干预和扁担沙北移及径流、潮流耦合作用,新桥水道向下游迁移束窄,并逐渐形成以河道上段为淤积中心的地貌演化格局。此外,随着东风西沙水库构建,拦蓄了部分应进入新桥水道的水体,致使河槽上段落潮动力减弱而加剧河槽淤积,导致新桥水道进一步淤浅。

Flood channel is one of the important geomorphological types that exits in the estuaries worldwide.However,due to runoff-tide interaction and intensive human activities,the geomorphology of flood channel has undergone rapid variation,which is directly related to the port site selection,channel management and river regime stability.Based on the bathymetric data,hydrology and sediment records over the past 62 years,this study analyzed the morphodynamic evolution processes of the Xinqiao Channel,the largest flood channel in the South Branch of Changjiang Estuary,and its driving mechanism.The results show that the development of the Xinqiao Channel during 1958-2020 can be divided into the following three stages.In the first stage(1958-1997),the channel experienced cycle of“erosion-deposition”with upstream and downstream movement,and exhibited wideness and shrinkage characteristics,controlled by the coupling effect of runoff and tide.In the second stage(1997-2003),the channel was further suffered from erosion,extended upstream and got widely due to the impacts from the 1998 flood and 1999 flood.In the third stage(2003-2020),due to human intervention,the northward movement of the Biandan Shoal,and runoff-tide interaction,the Xinqiao Channel moved downstream and presented shrinkage with the sedimentation center located at the upper section.In addition,the construction of the Dongfengxisha Reservoir intercepted part of the water that previously entered into Xinqiao Channel and thereby weakened the ebb tide and accelerated channel accretion,resulting in the further shallowing of the Xinqiao Channel.