长江口北支涌潮的形成条件及其初生地探讨

根据2001年4月青龙港出现涌潮时的实测流速和水深，采用水跃原理，简明地揭示了涨潮流速大于潮波传速是北支涌潮的成因。通过影响流速和波速的因素分析，并经实例计算认为：北支的喇叭形河势和水下沙坎是涌潮形成的必要条件；青龙港一潮的进潮量达到1.5亿m3，或北支口门一潮进潮量达到18亿m3是涌潮形成的充分条件。进而据沿程水深和潮汐等有关资料，经对比、试算，建立了沿程变化的进潮量、潮差等计算公式，并计算得到：在口门最大进潮量20.7亿m3的条件下，也只有当潮波上溯到距离口门约50km的灵甸港时，才出现流速大于波速，初生涌潮。由此表明，灵甸港是现今北支涌潮的初生地。

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 m3 at the Qinglong Harbor or the volume larger than 18×10.8m3 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 20×10.8m3,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.