SEDIMENTATION IN THE YELLOW-RIVER DELTA, PART-I - FLOW AND SUSPENDED SEDIMENT STRUCTURE IN THE UPPER DISTRIBUTARY AND THE ESTUARY

A 44-year data record measured by Lijin Hydraulic Station on the Yello w River shows that sediment concentration has been increasing while ri ver discharge has been decreasing into the delta since the 1970s. Thes e changes are important because flood waters of the Yellow River, whic h are heavily laden with sediment, must be used to supply Dongying Cit y and Shengli Oil Company which are located on the delta. Based on the analyses of data of velocity, sediment concentration, salinity and se diment grain size from four cross-section measurements at Lijin Statio n and one 8-vessel simultaneous measurement cruise in the estuary, str uctural characteristics of the river flow and suspended sediments thro ughout the upper distributary and the estuary have been studied and di scussed. Results show that when sediment concentrations of the Yellow River exceed 100 kg/m(3) in the lower layer of the river flow during t he hood period, the river flow structure does not coincide with the lo garithmic law of wall and becomes vertically layered, and the vertical distributions of suspended sediment do not,coincide with the diffusio n law. The channel length influenced by the tide wave is less than 15 km and there is no tidal intrusion flow; only weak osmosis of salinity occurs inside the river mouth during the flood period of the Yellow R iver. Simultaneous 8-vessel measurements and simulation using the meth od of Preissman show that there is a tidal sensitive zone inside the r iver mouth bar with a length of 6-7 km, when the discharge is as large as 1100 m(3)/s, and an area of very active sedimentation. The tidal s ensitive region near the river mouth becomes a low-velocity zone that traps a large amount of river sediment which rapidly forms a 'plastic' bed at flood tide, and a high-velocity zone with a strong hydrodynami c action to erode the new bed and transport the sediments into the sea at ebb tide. (C) 1998 Elsevier Science B.V. All rights reserved.