基于LiDAR观测的长江河口南汇南滩近期动力地貌研究

The Nanhui tidal flat is an important reserve of land resources in the Changjiang (Yangtze) River estuary, in which the morphodynamic processes reflect directly the relative strength between the river and sea forces. Based on high-resolution monthly point cloud data in spring tide period from April 2016 to May 2017 and the associated hydrological and sediment records, we studied the geomorphological evolution of the tidal flat. The tidal flat could be divided into three zones, namely, upper, middle, and lower zone in terms of the mean high and low water levels of neap tide. The main results are followed. (1) The Nanhui tidal flat stretches seaward overall during the observation period with a vertical deposition rate of 10cm. The land area of the middle flat zone increased while those of the upper and lower flat zones decreased in trend. (2) The geomorphological evolution of the flat varied seasonally with weak erosion in summer and autumn, and strong deposition in winter and spring. Meanwhile, apparent spatial differences were detected along the tidal flat. A scouring zone in the depth between 10 cm and 80 cm runs through the middle of the upper flat zone and the west side of the middle flat zone. A strong silt range (20-85cm) occurred along the vegetation area of the upper zone. In addition, a large scale of weak siltation (5-30cm) appeared in the middle-eastern part of the tidal flat. (3) The Nanhui tidal flat did not suffer erosion with the large decrease of riverine sediment, indicating that its morphodynamic processes were affected mainly by the local hydrodynamic condition and suspended sediment concentration. Moreover, the longitudinal zoning of erosion-deposition could be explained by the regional seawall-induced variation of flow direction.