The influence of major water conservancy projects on the geological environment of channel and shoreline in the middle and lower reaches of the Yangtze River

Based on the analysis of historical underwater topography and water level data, field measurement, laboratory test and comprehensive evaluation, the influence of major water conservancy projects on the channels and shorelines of the middle and lower reaches of the Yangtze River is studied. Some new progresses have been made. Firstly, a multi-mode sensor system was innovatively constructed to integrate the measurements of land and underwater hydrodynamic, sedimentary and geomorphic characteristics and data acquisition. Secondly, it was found that the main channel of the Yangtze River experienced strong erosion, arc collapse, and strip collapse. Thirdly, the hanging sand and bed sand were coarsened. The resistance of the river bed dropped, which caused the forming of the erosion type chain bead sand wave. The main piers of the Yangtze River Bridge were subjected to serious erosion. Finally, the tidal limit obviously moved up, and the geomorphology of the river changed significantly. On this basis, it is suggested that the investigation, monitoring and mechanism analysis should be strengthened on main river channel, high and steep slope along the bank, the estuary where the tributaries join the main stream, bank collapsing, cross-river bridge pier scour and so on. These results are of great significance to the protection and restoration of the bank and beach of the Yangtze River, the waterway regulation, the coastal flood control, and the maintenance of the piers of the Yangtze River Bridge.