基于实测资料的钱塘江涌潮水动力学特性研究

A study on the hydrodynamic characteristics of the Qiantang tidal bore based on field data

基于近年来钱塘江河口三次涌潮观测资料,系统分析了钱塘江涌潮的水动力学特性,计算了涌潮到达时刻的Froude数,结果显示可用Froude数判别涌潮形态,并建立了计算涌潮潮头陡度的解析公式,复演了涌潮到达时潮头陡度急剧增加的过程。研究表明:涌潮的沿程潮位、涨落潮历时和流速等特性受河口沙坎地形影响明显;流速的垂线分布大潮期间在潮到后一小时内以抛物线分布为主,其余时间以对数分布为主,而在中小潮时涨、落潮阶段均以对数分布为主;垂向流速比纵向流速小一个量级,当涌潮到达时刻急剧增大;潮头高度与当地潮差存在良好的正相关关系。

Based on the several field measurements of tidal bore on the Qiantang Estuary in recent years,the hydrodynamic characteristics of the tidal bore have been researched.The distributions of tidal levels,flood and ebb durations and current velocities along the river were influenced distinctly by the large sandbar of the estuary.During spring tide the vertical profiles of current velocities were parabolic at the bore arrival and this lasted for one hour,and then the vertical profiles turned to be logarithmic.During neap and middle tides,velocity vertical profiles were logarithmic at both flood and ebb tides.The vertical velocities were smaller by one order of magnitude than those of horizontal velocities,when the bore arrived,the vertical velocity increased obviously.The heights of the bore fronts have positive relationship with local tidal ranges.The Froude numbers at the bore arrival were calculated and the results showed that the Froude number could be used to justify the forms of the tidal bore.Furthermore,an analytic formula was built to analyze the gradient of the water surface of the bore front,by which the water surface changes during the tidal bore passing by were reproduced.