Adaptation mechanism of shear geomorphology in beach and trough interaction zone in the tidal zone of the Yangtze River

Abstract

In recent years, the upward shift of the tidal boundary of the Yangtze River has increased the intensity of shear geomorphic hazards such as bank erosion and bank failure in the middle and lower reaches of the river, but its adaptive process and mechanism to different hydrodynamic mutation zones in the beach and trough interaction zone have not been explored yet. Combining the underwater topography of Sunzhou waterway in Tongling River section, Hechangzhou North waterway and Chengchengzhou waterway in Zhenjiang River section from 1998 to 2019, and unmanned shipborne multibeam bathymetry system and ADCP power geomorphology synchronous observation in frequent nested bank failure section from 2016 to now, we analyze the characteristics of the adaptive characteristics of shear geomorphic adaptation in beach-slot interaction zones in the tidal boundary change section of the Yangtze River and the adaptive mechanism. It is found that: sand waves, scouring troughs, scouring pits, accumulators, nest ponds, nest ridges and other micro-geomorphisms are developed in the beach-trough interaction zone, and the flow direction has obvious zoning characteristics, with the mainstream zone, the mixing zone, and the reflux zone close to the shore from the trough to the shore; large and medium-sized sand waves, scouring troughs, and scouring pits are distributed in the mainstream zone, accumulators, and small-sized sand waves are distributed in the mixing zone, and the nest ponds distributed in the mixing zone and reflux zone are loaded with the nest ridges, and small-sized sand waves, The main stream and reflux zone are the main driving force for the bank failure in the beach and channel interaction zone. A sudden drop in the flow velocity in the mixing zone leads to sediment siltation and the formation of piles, and the sudden change in the hydrodynamic field in the reflux zone increases the intensity, resulting in frequent bank failures. The study can provide theoretical guidance for the risk prevention of beach and trough shear disasters.