Abstract:
The comparative analyses of the synchronous tidal data obtained from 31 tidal level stations located at the Zhejiang coast and the Yangtze River estuary show that there is a good consistency and obvious regulation of the tidal variation in this area. The spring and neap tides both occur once in a half a month tidal cycle, and the high and low tides occur twice in a lunar day, so the tidal variation process presents the semidiurnal tidal characteristics. In the estuary, the ebb tide duration is longer than the flood tide one, and the ebb tide duration becomes longer from the estuary to the upstream. In the nearshore shallow water from the Yangtze River estuary to the Damutu tidal level station located at the middle coast of Zhejiang Province, the ebb tide duration is also longer than the flood tide one. The flood and ebb tide durations are almost equal at the stations of Dongji and Dachen islands of the Zhejiang coast. Along the south coast of Zhejiang Province, the flood tide duration of Songmen, Pishan island, Kanmen and Dongtou stations is a little longer than the ebb tide one, but it shows an opposite characteristic of Nanji island, Pipamen and Xiaguan stations. In the nearshore shallow water from the Yangtze River estuary down to Xiaguan, there is a trend that the tidal range distribution gradually increases from the north to the south. In the estuary, the maximum and mean high tidal levels become larger from the estuary to the upstream. And the maximum and average tidal levels become larger from the north to the south; however, the distribution characteristics of the minimum and mean low tidal levels are opposite in the nearshore shallow water zone.