Causes of spring tide in Qiantang River

1. time: from August 16 to August 18 of the lunar calendar, the sun, the moon and the earth are almost in a straight line, so the tidal force (the difference between the gravity of the moon, the sun or other celestial bodies on the earth and the gravity of the earth's center of mass, or the inertial centrifugal force generated by the earth's movement around the center of mass of the moon (sun) and the moon (sun).

2. Geographical location: It is related to the trumpet-shaped mouth of Qiantang River.

Nearly 500,000 mu of land was reclaimed to the east of Zheshan on the south bank of Qiantang River, which blocked the estuary like a peninsula, making the section from Zheshan to the outside of Qiantang River look like a small belly bottle, and the tide is easy to enter but difficult to retreat.

The outer mouth of Hangzhou Bay is 100 km wide, and the outer 12 section is only a few kilometers wide. The riverbed in the east of the estuary suddenly rises and the beach is shallow. When a large amount of tidal water comes into the mouth of Qiantang River, due to the rapid contraction of the river surface, it is too late for the tidal water to rise evenly, so it is necessary to use the back waves to push the front waves and stack them layer by layer.

Secondly, it is related to the sediment deposition under the Qiantang River, which blocks and rubs the tidal current, making the front slope of the tidal current steep and gentle, thus forming a wave after catching up with the front wave, and one wave overlaps with another.

3. Wind direction: southeast wind is often blown along the coast, and the wind direction is generally consistent with the tidal direction, which is helpful for the tidal direction.

Extended data

Precautions for tide watching:

1, the great power of tidal bore.

The tidal bore in Qiantang River has two climaxes a year, namely the vernal equinox and the autumnal equinox. There are two flood seasons in January, which appear two or three days after the first day and the fifteenth day of the first lunar month. There are two orgasms a day, with an interval of 12 hours. The tidal head of a tidal bore is generally 1-2 meters high and can reach 3 meters, and it advances from downstream to upstream at a speed of about 20 kilometers per hour.

Every year, the tides around August 18 of the lunar calendar are the most spectacular, and special tidal bore such as first-line tide and resurgence can be seen. There is also a dark high tide at ordinary times, which is calm and imperceptible in the distance, but it is overwhelming, hidden and dangerous when it is near.

2. Tide watchers and activists along the river lack understanding of tides, and their safety awareness and vigilance are not high.

Many accidents are caused by people's lack of understanding of the danger of tidal bore in Qianjiang, or their ignorance of this danger, which is highlighted by the fact that many foreigners turn a blind eye to the warning signs and signs beside the entrance doors dedicated to the inspection and maintenance of dikes and ponds, cross at will, and even swim and bathe in the river.

Therefore, tide watchers should enhance their awareness of self-protection and pay attention to the following three points:

(1), fully understand the fluctuation law and habits of tidal water in Qiantang River, especially the harm of tidal water. Water in Qian Jiangchao is not only supplied on the 18th day of the eighth lunar month, but also four days a year. Pay attention to the flood season information of Qiantang River released by the media.

(2) Choose safe areas and lots for tidal observation and activities, pay attention to warning signs and obey the management of managers. Pay attention to the warning signs on the dams along the river and strictly abide by them. To obey the management command of the management personnel, stop in the designated area to watch the tide. Don't cross the fence to the floodplain, groin and other places. Go to play and enjoy the cool. Don't swim or bathe in the river.

(3), master the method of self-help. In the face of danger, don't panic, quickly and orderly retreat to safety, and immediately call for help to the surrounding staff or others. When you leave, don't lose the precious opportunity to save yourself in order to save your property.

In case of falling into the water or being hit by the tide, try to grasp the fixtures around you to prevent them from being swept away by the tide. In case of emergency, people around should take rescue measures quickly and call 1 10 to call the police.

Baidu encyclopedia-Qiantang chamber