The Evolvement Of Eastern Chongming Shoal, Lower Reach Of North Channel And Eastern Hengsha Shoal In Changjiang Estuary

The Changjiang Estuary is a typical medium tidal estuary, which is characterized by three-order bifurcation and four-branch channels discharging into the sea. The North Channel is the north distributary of the second order bifurcation and one of the Changjiang Estuary's main channels into the sea. Eastern Chongming Shoal is on the north side of lower reach of the North Channel, and Eastern Hengsha Shoal is on the other side. Study on channel processes of the North Channel and erosion-accretion processes of tidal flats can offer some reasonable suggestions on exploiture and utilization of the North Channel and tidal flats, as well as the dynamic protections for wetlands.The Eastern Chongming Shoal is one of the main tidal flats in Changjiang estuary. Based on measured and collected data of topography from 1983 to 2003 ,sediment and hydrodynamics, the analysis of this area can give us some conclusions: (1)During 1983 to 2001 the eastern Chongming Shoal deposited and extended considerably, and the area of the tidal flat above 3.5m had increased from 33.6km2 to 98.8km2. (2)An increase of the tidal flat above 0m in area was 4.2 km2, but there was a decline in the average annual deposition rate of the tidal flat above 2.0m.Based on data extracted from topographic charts and obtained through hydrological and sediment surveys in lower reach of the North Channel, the study on the evolution of this area shows that changes of the mouth bars reach in the North Channel was great ,for example, Liuxiao sandy ridge had been enlarged seawards, underwater sandy ridges with length of 17km occurred in the North Channel from the area near the north of HengSha island to 122° 02' E, and the North Channel North Sha developed apparently, which had been situated southeast of the Tuanjiesha floodgate since 1980s.The Eastern Hengsha Shoal is located in the shadow of the Hengsha Island, where the hydrodynamic is relatively weak while sediment is abundant. The 5m isobaths of the shoal has been expanded since 1958, and the area above it increased gradually as well. Due to the construction of Deep Channel Project, the condition of water and sediment changed, which is propitious to deposit more sediment.