Formation conditions and initial site of tidal bore in the north branch of Yangtze River estuary

The occurrence of tidal bore at the Qinglong Harbor,located at north branch of Yangtze River estuary is explored by hydraulic jump theory based on observed data.The tidal current velocity higher than the propagation velocity of tidal wave is the main cause of the formation of tidal bore and the converging river channel and submerged sand bars are the necessary conditions.The tidal influx volume larger than 1.5×10 8 m 3 at the Qinglong Harbor or the volume larger than 18×10 8m 3 at the river mouth are the sufficient conditions for bore forming.Furthermore,the formulas for calculating the tidal influx volume and tide range,which are varying along the river,are established.Under the condition of influx volume reaches 20×10 8m 3,the tidal bore will occur when the tidal wave propagates upward and reaches the Lingdian Harbor which is 50km upstream from the river mouth.It is concluded that the Lingdian Harbor is the inital site of the tidal bore.