Tide is a natural phenomenon in coastal areas, which refers to the periodic movement of seawater under the tidal force of celestial bodies (mainly the moon and the sun).
Traditionally, the vertical fluctuation of sea surface is called tide, and the horizontal flow of sea water is called tidal current. In order to express the moment of tide, human ancestors called the rising tide in the morning and the rising tide in the evening as sunseekers, collectively called tides. This is the origin of the name Chao.
The extended definition of the word tide is similar to the tidal phenomenon, which is used to describe things that fluctuate and move, and is mostly used in biased phrases, such as tidal lane, tidal family, tidal passenger flow, etc.
World famous tide
The tidal bore in Qiantang River is one of the three largest tidal bore in the world, which is caused by the centrifugal effect of celestial gravity and the earth's rotation, as well as the special topography of the bell mouth of Hangzhou Bay. Qiantang River estuary is wide outside and narrow inside, showing obvious trumpet shape. The river at the mouth of the river is 100 km wide, and the deeper it goes, the narrower it becomes. When it reached Yan Guan Town, Haining, the river suddenly dropped to only 3 kilometers wide.
The surge of Qiantang River and the tide of Yangtze River, which is more than 600 kilometers inland. Mainly because the tidal current is formed upstream along the channel where the river enters the sea. Tide flows into the triangle bay, the tidal level accumulates and the tidal range increases.
The tidal current comes in, and the tidal end stands steeply, splashing like a high-speed vertical water wall. The front has not been dredged, and the waves behind it have caught up again. The waves are higher than each other, which is very spectacular, forming a spectacular scene of "the sky is full of turbid waves, and the rivers are overturned and the mountains are destroyed".