Abstract:
Shoal-channel system is a common estuarine geomorphic unit. Its evolution process directly dominates the channel stability and tidal flat utilization. Based on historical bathymetric chart, Landsat remote sensing images, fluvial water and sediment discharge records and the discharge diversion ratio, the shoal-channel evolution process of upper reach of the North Branch during 1992—2022 is explored. The results show that Chongtou Shoal and Xinyue Shoal exhibit an average annual siltation of 0.32 km
2 and 0.25 km
2, respectively, with over 50% of siltation occurring between 2000-2003. The channel of Chongtou Shoal experienced significant erosion during 2000—2008, with the volume enlarging by over 50%; while the channel of Xinyue Shoal changed relatively small. Landward sediment transport from the sea to the North Branch driven by tidal current supports siltation of Chongtou Shoal and Xinyue Shoal, while fluvial sediment supply has a slight contribution; The curved channel pattern around Qinglong Port and tidal surge are responsible for the Xinyue Shoal siltation, During the flood season, the ebb and flow of tidal currents are responsible for the Chongtou Shoal siltation, and due to Coriolis force and shoal expansion, flood current flows to the north and generates flood channel in dry season, North Branch thus is featured by "channel erosion and shoal siltation" .