Tidal flat morphodynamic processes of the Yangtze Estuary and their engineering implications

The intertidal flats are classified as "attached bar", "spit" and "isolated bar" in relation to the land, and "broad flat", "sharp bank" and "eroded c liff" according to the shape of the cross-shore profile. Tidal currents on the flat are basically back and forth along the river channel banks but gyr atory on the seaward side of the Chongming Island. The flow velocity on the intertidal flat is gradually reduced with increasing elevation. The river discharge strengthens ebb flows and modifies current asymmetry especially o n the lower flat in neap tide, although hydrodynamics over the tidal flat i s tide-dominated. The wave height on the tidal flat is normally limited to a few decimeters although it changes with water depth, slope and wind. Susp ended sediment concentration over the tidal flat is typically hundreds to t housands of mg / 1. Although the delta has grown rapidly in history, the ra te of growth is different in different periods. A maximum advancing rate of 330 m / a was recently found in the central part of the river month toward s the sea. In view of the natural conditions, reclamation of higher interti dal flat (above the mean tidal level) in advancing coasts is suggested, whi ch would leave broad wetlands for wild lives. In addition, some possible in fluences of coastal engineering projects and the future natural backgrounds of engineering under reduction in riverine sediment supply and sea level r ise are addressed.