The coastal territories of the Red River, passing through the city of Hanoi (the capital of Vietnam), are developed very dynamically by different types of construction, sand extraction from the river bed and its banks, pumping of water, creation of ponds and agriculture. But these activities are only possible in areas protected against annual floods with a dam. However, in recent years, the intensity of lateral erosion of the river and associated suffocation and landslide processes has become rapidly increasing in both flood and dry seasons. Deformations capture natural river banks and the dam body. The authors analysed the causes and identified mechanisms of these processes taking into account variable climatic, tectonic, hydrological, geological and hydrogeological conditions complicated by economic activities in the coastal zone. The article provides calculations of the stability of banks in different conditions (during and after the flood), which confirms theoretical ideas about the mechanism of the process and coincide with the observations. The greatest contribution to the banks destruction is the variability of the internal friction angle of the sands entering the section of the coastal territory.