Sediment resuspension and implications for turbidity maximum in the Changjiang Estuary

Abstract

A comparative study on the properties and transport of the cohesive sediments in the mouths of the Changjiang Estuary proves that the suspended sediment concentration (SSC) is principally enhanced by the resuspension of bottom sediment in the mouth-bar reach, coupled with the deformed tidal wave and strong tidal current. Salinity intrusion and vertical gravitational circulation lead to the ‘trapping’ of the suspended sediment inflowed from the river and the sea. The turbidity maximum (TM) is therefore delivered by the local resuspension of the accumulated materials and bed erosion. The TM in the Changjiang Estuary is marked not only by its high SSC relative to the adjacent reaches, but also by the high wash-load content. Transport of sediment is very important. Settling velocity of suspended sediment is increased by flocculation. The massive settling during weak current periods often gives rise to the formation of fluid mud. The TM coincides locally with the mouth-bars. The transport of suspended sediment in the TM is analysed by using a splitting method. It is concluded that the contributing factors consist of advective terms and tidal pumping. Advective transport is dominant in the North Channel and tidal pumping predominate in the North Branch and South Passage, and the North Passage is in an intermediate situation.