LONG-TERM COARSENING TREND OF BOTTOM SEDIMENT AT THE LANDWARD LIMIT OF THE YANGTZE ESTUARY UNDER BACKGROUND OF RIVERBED AGGRADATION

摘要

This paper proposes and discusses an interesting phenomenon in riverbed adjustment to a long-term decrease in sediment discharge from upstream. The grain-size (d50) of bottom sediment at Datong, the landward limit of the Yangtze Estuary, shows a steady increasing trend from 1976 to 2004 as a result of persistent decreases in suspended sediment discharge from the Yangtze River into the sea. Such a coarsening process, however, took place under the background of local riverbed aggradation, rather than of local riverbed scouring. The coarsening trend of bottom sediment at Datong is therefore mainly attributed to an increasing supply of coarse-grained sediment from upstream.