The Mudflat System of China

Abstract

Most of the 2000 km of intertidal mudflat on the Chinese coastline is developed in the mesotidal Bohai Sea, where the Yellow River now discharges, and on its pre-1855 delta 600 km to the south on the Yellow Sea coast. The Yellow River has the largest sediment suspended load of any river in the world, with an average of 24.7 kg of sediment per cubic metre of water at its mouth. Four hundred million tons of sediment are deposited annually in the lower reaches of the river, and 1200 million tons are transported to sea in the surface mud plume. This accumulates either in the deeper waters of Bohai Bay or on the intertidal mudflats. These mudflats are typically 3 km wide, but are up to 18 km wide at the delta. They are divided into four zones: the polygonal zone with mud cracks and sparse vegetation above normal HTL; the inner depositional zone of mud on the higher part of the flat; a central erosional zone; and an outer depositional zone of silt on the lower intertidal flat. Landwards a salt marsh is developed. Seawards the sediment passes from sandy silt at LTL to fine mud (silt and clay) in water depths of 10 m. The historical changes in the course of the Yellow River are well known, and the formation of cheniers on the Bohai Bay coast can be correlated with times when there was little or no fluvial sediment supply. For almost 700 yr prior to 1855, the Yellow River discharged to the Yellow Sea in North Jiangsu. Submarine sand bars reworked by tidal currents from the submerging former delta mouth protect about 200 km of coastline from erosion, and intertidal flats are prograding. Elsewhere in North Jiangsu, coastal retreat is rapid, and in places a modern chenier-like shell beach is developing. The history of development of this entire coastal system is dominated by the Yellow River and anthropogenic modifications of its basin.Key words: sediment, mudflats, Yellow River, Bohai Bay, China