Sedimentary and morphological evolution of nearshore coast of Yangtze Estuary in the last 30 years

By analyzing the status quo of tidal flats and nearshore areas, including the sedimentary and morphology with different historical charts and observations of the Yangtze Estuary, the paper discusses the evolutions of nearshore coast of the Yangtze Estuary and its influencing factors in the last 30 years. The results show that: (1) the sediments collected on the tidal flats in the northern part of the Yangtze Estuary changed from coarse to fine, while sediments of the southern part became coarse, especially those near the large construction sites, including the north bank of Eastern Hengsha Shoal, Yangtze River Bridge and East China Sea Bridge; (2) the width of tidal flats in certain parts of the Yangtze Estuary decreased by more than 90%; the morphological characteristics of nearshore profiles were characterized by erosion, including concave and steep slope; the depth of closure (DoC) of Nanhuizui nearshore area from 1978 to 2004 kept at -8 m, while it was scoured by about 1 m because of the bottom erosion in recent 10 years; (3) the erosion characteristic of nearshore area in the Yangtze Estuary resulted mainly from the reduction of basin sediment loads; intensive human activities, including reclamations, Qingcaosha reservoir and bridge constructions resulted in the reduction of tidal flats and the coarsening of sediments; sand ridge migration had a great impact on the nearshore coast of the channels in the Yangtze Estuary.