长江河口悬沙的运动方式与沉积形态特征分析

The patterns of transportation and morphological features of deposition of suspended sediment in the Changjiang Estuary

长江河口为三级分汊四口入海的中等潮汐强度的三角洲河口。长江河口的悬沙输运有净上移、净下泄、上层下泄而下层上溯、潮滩与主槽之间的泥沙交换及涨潮槽泥沙倒灌落潮槽等五种形式。根据悬沙沉积的不同地点不同沉积形态可分为暗沙、拦门沙、口外水下三角洲以及河口潮滩四种类型。

The data used in this paper are collected during four field surveys, in which measurements at various stations (Fig 1) have been carried out The measurement periods cover December 18-19, 1982 (dry season, spring tide), September 7, 1983 (flood season, spring tide), July 29, 1988 (flood season, spring tide) and December 24, 1988 (dry season, spring tide) Analysis was done by combining the observed data with research results of others According to calculated values of the dominant flow, the Changjiang Estuary can be divided into three types of sections with different characteristics The first is mainly influenced by river flow, or ebb dominant flow section; the second is mainly influenced by tidal flow, or flood dominant flow section; and the third section is dominantly influenced by the density flow In areas with ebb dominant flow, the residual sediments from upper lager to lower layer transport seaward; in areas with flood dominant flow the residual sediments from upper layer to lower layer transport landward; and in reaches with density flow dominated section, the residual sediments transport to the upper layer, which would be carried seaward with the outflowing river water, but in the lower layer it is done in the flood direction Moreover, there are other forms to transport residual suspended sediments: Sediment exchange between channel and tidal flat is caused by horizontal circulation flows Sediment of the North Branch has turned to the South Branch and sediment of the South Passage has turned to the North Passage According to the depositional areas and under water depositional morphology, four types of deposition are :dentified:1)Underwater sandbank formed by diversion of flood and ebb flow; 2)in areas with dense flow dominated section, due to the mixtrue of salt and fresh water formed the turbidity maximum, the mouth bars have the same location as the turbidity maximum; 3)the deposition of the large amount of the suspended sediment is growing into huge submerged delta out of the estuary; 4)and the marshes developed by the horizontal circulation of flow and sediment transport at the channel tidal flat systems