Study on the effect of river inflow on estuarine turbidity maximum in the North Passage of the Yangtze Estuary

The Yangtze Estuary is a giant multi-channel bifurcated river-tide system, which is affected by medium-intensity tides (mainly semilunar tides) and obvious seasonal variation of riverine inflow, and its hyrodynamic-morphological conditions are very complex. In this research, the response of discharge to the dynamic characteristics of water and sediment in the maximum turbidity area (North Passage) of the Yangtze Estuary is studied. The research results show that the increasing of discharge means the increasing of hydrodynamics, which first of all has two consequences: one is the enhancement of sediment resuspension capacity, the other is the increase of transport capacity; in addition, in the maximum turbidity area of the estuary, because of the river effect, there is often an increase in estuarine circulation, and the change of discharge also means that the transport capacity from the bottom to land also changes. The measured data and mathematical model jointly show that the larger the discharge is, the greater the sediment concentration of the beach with low velocity will be, however in the main flow area, due to the triple effects of the increase of discharge, the sediment concentration in the maximum turbidity area does not increase in one direction. Sediment concentration in the maximum turbidity area reaches the maximum under the discharge of 30, 000-40, 000 m³/s. This study clarifies the sediment suspension state of the estuary under different discharge conditions, which could provide a reference for the development and utilization of soil and water resources, ecological environment protection and waterway dredging maintenance in the Yangtze Estuary.