An Investigation of Water Depth and Current Velocity Process in Periodic Inundation Area of East Chongming Tidal Flat, Yangtze Estuary

Abstract

Water depth and current velocity,as the fundamental constituents of hydrodynamics,played an important role in sediment advection,deposition and resuspension on the intertidal flats.A field measurement of water depth,current velocity and flow direction was carried out on the East Chongming tidal flat in the Yangtze Estuary,between April 2002 and January 2003.Measurements of current velocity during semi-diurnal tidal cycles showed different shapes of the time series of velocity between saltmarsh and adjacent mudflat.On the mudflat,in general,the current velocity reached peck value during the flood and ebb phase in single tidal cycle.However,on the saltmarsh,peck current velocity values only appeared during the flood phase,except when marsh vegetation wilting.At the measurement sites,time-velocity asymmetry was significant.A duration period during flood phase was shorter than ebb phase.Current velocity during flood phase,in contrast,was larger than ebb phase.The results indicated flood current dominant in the research area.Marsh vegetation and topographty,which reduced ebb currents,enhanced flood current dominance on the saltmarsh.As a result,there was stable accumulation on the saltmarsh,compared to frequent alternation of erosion and accretion in adjacent mudflat.Overall,under calm weather condition,tidal current process and asymmetry were basic dynamic controls of sediment transport and morphodynamics process on the East Chongming tidal flat.