Sedimentation in the Yellow River delta, part I: flow and suspended sediment structure in the upper distributary and the estuary

Abstract

A 44-year data record measured by Lijin Hydraulic Station on the Yellow River shows that sediment concentration has been increasing while river discharge has been decreasing into the delta since the 1970s. These changes are important because flood waters of the Yellow River, which are heavily laden with sediment, must be used to supply Dongying City and Shengli Oil Company which are located on the delta. Based on the analyses of data of velocity, sediment concentration, salinity and sediment grain size from four cross-section measurements at Lijin Station and one 8-vessel simultaneous measurement cruise in the estuary, structural characteristics of the river flow and suspended sediments throughout the upper distributary and the estuary have been studied and discussed. Results show that when sediment concentrations of the Yellow River exceed 100 kg/m 3 in the lower layer of the river flow during the flood period, the river flow structure does not coincide with the logarithmic law of wall and becomes vertically layered, and the vertical distributions of suspended sediment do not coincide with the diffusion 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 River. Simultaneous 8-vessel measurements and simulation using the method of Preissman show that there is a tidal sensitive zone inside the river 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 sensitive 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 hydrodynamic action to erode the new bed and transport the sediments into the sea at ebb tide.