Impact of water level change on sedimentary characteristics of distributary channel in Poyang Lake delta

Key words:  Poyang Lake delta  water level change  distributary channel  sedimentary characteristics

Abstract:

To study the impact of water level change on the sedimentary characteristics of distributary channel in Poyang Lake delta, this research applied methods of modern sedimentary investigation, mining profile, and grain size analysis to delta plain distributary channels in Ganjiang middle branch delta and Xinjiang delta front. The results suggest that there are two types of sedimentary units in the distributary channels in Ganjiang middle branch delta:lag deposit and point-bar; and three types in the distributary channels of Xinjiang delta front:tadpole-shaped sand ridge, linear low-lying sand, banded channel sand, respectively. When water level rises, sediments mainly deposit onshore back to the source in delta distributary channel; meanwhile, point bar receives sediments and develops water rising wedge-shaped sand. Sediments mainly prograde towards the basin, and delta develops at low water level. When water level declines, point bar develops water falling lateral sand. When water level rises, delta front distributary channel develops tadpole-shaped sand ridge,which is subsequently transformed into banded channel sand by waves on both sides of the river; when water level declines, delta front distributary channel develops banded channel sand. Affected by water level change, sand in the distributary channel shows a heterogeneous distribution in both the plane and vertical profiles, while sand in the delta front distributary channel has typical in plane zoning features.