长江口南汇边滩短期冲淤变化分析

南汇边滩位于长江口和杭州湾的交汇地带,受长江口和杭州湾北岸两股潮流的控制,近年来由于低潮滩促淤围垦工程导致其水流和泥沙运移、沉积和地貌发生了显著的变化。根据2006—2008年南汇边滩测图及2007年11月—2008年11月每个季度的9个断面测量资料,结合区域内的泥沙沉积特征,探讨南汇边滩对周边涉水围垦工程和流域来水来沙变异做出适应性地貌耦合过程之后的近期冲淤演变规律,着重探讨季节性冲淤特征。结果表明:年度上南汇东滩以淤长为主,南汇南滩以冲刷为主。不同季节南汇边滩冲淤变化过程存在很大差异:平面上,南汇边滩等深线夏、冬季以淤进为主,春、秋季以蚀退为主;垂向上,南汇东滩断面呈春夏秋冲淤交替、冬季淤积的态势,南汇嘴断面呈秋季冲刷、冬夏季淤积的态势,而位于南汇南滩的断面则呈秋冬季冲刷、春夏季淤积态势。南汇东滩沉积物粒径总体上较细,东滩与南滩交汇处的南汇嘴附近中值粒径相对较粗,南汇南滩浅滩沉积物颗粒中值粒径最粗。

Short-term morphological process of the Nanhui mudflat in the Yangtze River estuary

The Nanhui mudflat is located in the intersection area between the Yangtze River estuary and the Hangzhou Bay.It is controlled by two tidal currents from the Yangtze River estuary and the north coast of the Hangzhou Bay.In recent years,the tidal currents,sediment transport,morphological process of the Nanhui mudflat have changed significantly,which is mainly caused by the reclamation project of the low tidal flats.Based on the yearly measured bathymetry data (from 2006 to 2008) and 9 cross-sectional bathymetry data in each season from November 2007 to November 2008,combined with the sediment characteristics,we discuss the features of recent morphological process and interannual change in the Nanhui mudflat after the reclamation project and the hydrologic and sediment variations of the river basin,specially the seasonal scouring and silting characteristics.The results show that the annual erosion and siltation of Nanhui Dongtan is siltation,Nanhui South Beach is erosion.In different seasons of erosion and siltation in the Nanhui shoal,the process is different.In the plane,Nanhui beach isobath in winter and summer is mainly by silting,and in the spring and autumn,it is dominated by erosion.Vertically,the Nanhui Dongtan section in the spring,summer and autumn season is alternation of scouring and silting,it is silt in winter.Nanhui mouth section is scouring in autumn,and silt in winter and summer season.But Nanhui South Beach section is scouring in autumn and winter,silting in spring and summer.The sediment grain size of Nanhui east beach is generally finer.The median diameter of Nanhui mouth near the intersection of east and south beach is relatively coarse,and the median grain size of Nanhui south beach shoal is the coarser.