Analysis of the changes and formation causes of tidal bore at the north bayou of the Yangtze River estuary in recent years

The tidal bore is getting weak greatly at the Qinlonggang position of the Yangtze River estuary since 2003.The reason is that the reclamation projects make the up and middle river segment to form a bend channel with the small change rate of the river width along the channel.At the same time,the condition of the river depth is meliorated.The occurrence of tidal bore is bated.On the other hand,the reasonable relation between local terrain and the average tide fluctuation rate at Qinlonggang is set up by introducing local terrain index.The research shows that the annual variatiion in the average tide fluctuation rate at Qinlonggang correspond to the course of human activity (e.g.the reclamation projects) and the variation in the local terrain.It also indicates that using whole section index for the tidal bore can not reflect the effect from the local terrain very well.Owing to the variation in the tidal bore at the north bayou of the Yangtze River estuary in recent years affecting the river bed evolution at the bifurcation area of the north and south branches,this research has realistic meaningfor the repairing of the water course and the utilization of the river banks.