长江澄通河段河床冲淤对流域减沙的响应

River bed erosion and deposition responses to sediment reduction in the Chengtong reach of the Yangtze River

为研究潮汐河道不同区段在流域来沙减少条件下的冲淤响应机制,以长江澄通河段为例,根据水动力特性将其划分为江阴—天生港和天生港—徐六泾两段,结合1950—2014年的水沙资料及2005—2014年的地形资料,比较两段冲淤对流域减沙的响应差异。结果表明:上游江阴—天生港段对流域减沙敏感,较快地由淤积转为冲刷;下游天生港—徐六泾段1998—2004年期间受洪季平均径流流量减小、潮汐顶托作用相对增大的影响,冲刷速率为减小趋势,2004年以后受洪季平均径流流量增大、潮汐顶托作用相对减小及流域来沙持续减少的共同影响,冲刷速率为增大趋势。使得潮汐动力对天生港—徐六泾段由促淤变为促冲的临界洪季平均径流流量为36 000 m3/s,该径流流量也是使得潮汐顶托作用在江阴—天生港段由不显著变为显著的临界流量。目前,流域减沙已加剧澄通河段整体的冲刷。

To examine the erosion and deposition response mechanisms to river basin sediment reduction in different areas of a tidal reach,this study investigates the Chengtong reach of the Yangtze River.The reach is first divided into two sections based on their hydrodynamic characteristics,namely the Jiangyin—Tianshenggang section and the Tianshenggang—Xuliujing section.Then,the differences between the two sections＇ erosion and deposition responses to river basin sediment reduction are compared by using and integrating hydrological and sedimentological data during 1950—2014 and topographic data during 2005—2014.The results demonstrate that the upstream Jiangyin—Tianshenggang section is sensitive to river basin sediment reduction and switches from deposition to erosion relatively quickly.The downstream Tianshenggang—Xuliujing section was affected by the reduced wet-season average runoff and the enhanced uplift action by tide during 1998—2004;thus,the erosion rate decreased.After 2004,the wet-season average runoff increased while the uplift action by tide weakened,and sediment from the river basin further reduced.These changes jointly led to an increase in the erosion rate.The critical wet-season average runoff,at which tidal dynamics no longer promote deposition and instead cause erosion in the Tianshenggang—Xuliujing section,is 36 000 m3/s.This is also the critical runoff threshold at which the insignificant uplift action by tide in the Jiangyin—Tianshenggang section becomes significant.At present,river basin sediment reduction has intensified the erosion of the entire Chengtong reach.