Write a tour guide that introduces the tide of Qiantang River

The Qiantang River is located in Zhejiang Province, my country, and eventually flows into the East China Sea. The tide at its mouth is the Qiantang Tide, which is famous all over the world. Every year, many tourists come to watch this spectacle. Before the arrival of the tide, a tiny white dot first appeared in the distance, and in a blink of an eye it turned into a ray of silver, and accompanied by waves of thunderous tides, the white line rolled in.

With almost no time for people to react, the surging tide has roared in. The peak of the tide is 3-5 meters high. The waves behind are catching up with the waves ahead, one layer after another, like a long white belt, huge. It has the potential to overwhelm mountains and seas. The tide came from far and near, rushing in. The tide pushed forward, roared like thunder, sprayed beads and splashed jade, and was as powerful as a galloping horse. Tide watching began in the Han and Wei dynasties and flourished in the Tang and Song dynasties. After more than 2,000 years, it has become a local custom.

Rule

The appearance of tides is regular, with high tides on the first and fifteenth day of the lunar calendar. At this time, the three celestial bodies of the moon, the earth and the sun are almost in the same straight line, and the tidal forces of the moon and the sun act in almost the same direction. The combined force of the two is the largest, and the sea water rises the highest and sinks the lowest, which is spring tide.

On the eighth and twenty-third day of the lunar month, the positions of the sun, moon, and earth form a right angle. At this time, the combined force of the sun's tidal force and the moon's tidal force is the smallest. At this time, there are two lowest high tides and the highest high tide. The low tide is called a "semidiurnal tide". Usually, this tide occurs every day in most places on the earth.

In some places, the tidal difference between two high tides and two low tides is very large, and the rising and falling times are called "mixed tides". In some places, there is only one high tide and one low tide a day. The interval between high tide and low tide is about 12 hours and 25 minutes, which is called "diurnal tide".

The "Qianjiang Tide" is mainly formed by the special topography of the estuary of Hangzhou Bay. Hangzhou Bay is wide on the outside and narrow on the inside, deep on the outside and shallow on the inside. It is a typical trumpet-shaped bay. The river surface at the mouth of the sea is 100 kilometers wide. Going west to Kanpu, the river surface suddenly shrinks to 20 kilometers. When we arrived at Yanguan Town in Haining, the river was only 3 kilometers wide.

When the tide rises, the wide and deep mouth of the bay swallows a large amount of seawater at once. Because the river surface shrinks rapidly, becomes narrower and shallower, the rising tide does not have time to rise evenly, so the waves behind it push the waves ahead, and each wave changes. Higher than a wave.

When we arrived near Dajia Mountain, we encountered a huge underwater barrier sand bar. The tide rushed up, setting off a towering and astonishing huge wave, forming a steep water wall and forming the first tidal peak. The "Qianjiang Tide" has two tides every day, with an interval of about 12 hours. The first tide is delayed by about 45 minutes every day, forming a regular semi-monthly cycle. The maximum tide head is 3.5 meters, and the tidal range is up to 9 meters.