Why is the tide in Qiantang River the highest during the Mid-Autumn Festival?

Qiantang Tide is one of the three largest tidal bores in the world. It is the centrifugal effect of celestial gravity and the rotation of the earth, and is also related to the trumpet-shaped mouth of the Qiantang River. The Qiantang River is a large tidal flat, which is rare in the world. The tide here changes greatly and the water depth changes at any time. Why is the tide of the Qiantang River the largest during the Mid-Autumn Festival? Let's study it together!

Contents of this article

1. Why is the tide of Qiantang River the highest during the Mid-Autumn Festival?

2. Why is there a tide in Qiantang River?

3. How deep is the Qiantang River?

Why is the tide of Qiantang River the highest during the Mid-Autumn Festival?

The tides of Qiantang River actually occur every month or even every day, following the revolution of the moon and the rotation and revolution of the earth. However, the tides are most spectacular around the middle of August of the lunar calendar every year. The rise and fall of tides are affected by the changes in the attraction of the sun and the moon on the earth (especially the attraction on flowing water). According to the law of universal gravitation, we know that the magnitude of attraction has a lot to do with the distance between objects and the relative positions of multiple objects. During the Mid-Autumn Festival, the moon is closest to the earth. Since the moon, the sun and the earth happen to be running on the same straight line, the combined force of the sun and the moon's gravity has the greatest impact on the earth and is likely to pull the tide to the maximum.

Why is there a tide in Qiantang River?

Qiantang Tide is one of the three major tidal bores in the world. It is the centrifugal effect of celestial gravity and the rotation of the earth. It is also related to the trumpet-shaped mouth of Qiantang River. Nearly 500,000 mu of reclaimed land east of Zheshan on the south bank of Qiantang River blocks the mouth of the river like a peninsula, making the section of Qiantang River from Zheshan to the outer 12 kilometers look like a bottle with a big belly and a small mouth. The tide is easy to enter but difficult to retreat. The outer mouth of Hangzhou Bay is 100 kilometers wide, but it is only a few kilometers wide in the outer 12 sections. The riverbed in the eastern section of the river mouth rises suddenly, and the beach is high and the water is shallow. When a large amount of tide surges in from the mouth of Qiantang River, the river surface shrinks rapidly, so the tide has no time to rise evenly, so the back waves push the front waves, layer by layer. Secondly, it is also related to the large amount of sediment under the water of Qiantang River. These sediments block and rub the tide, making the front slope of the tide steeper and the speed slower, thus forming the back waves chasing the front waves, one wave after another. Yanguan Town, Haining, Zhejiang Province is the first scenic spot for watching the tide, so it is also called Haining Tide. In the world, the Qiantang Tide is one of the three major tidal bores in the world, the other three being the Ganges Tide in India, the Amazon Tide in Brazil and the Qiantang Tide in China.

How deep is the Qiantang River?

The bay at the mouth of Qiantang River is trumpet-shaped, with a width of 98 kilometers and a water depth of 8 to 10 meters. More than 90 kilometers to the west, the water surface narrows to 20 kilometers and the water depth is about 4 meters. The water surface is only 2.6 kilometers wide and the water depth is about 1 to 2 meters to Haining. Due to the shrinkage of the terrain and the rise of the riverbed, the tide forms a magnificent tidal bore west of Yanpu, with the highest height of more than 10 meters. The Hangzhou Bay at the mouth of Qiantang River is unstable due to the influence of the tide. Qiantang River is a large tidal flat, which is rare in the world. The tide here changes greatly and the water depth changes at any time. During typhoon season, the water level is even higher. There is also a trench formed by rapids in the Qiantang River, which is also changing at any time, and its depth changes with the seasons. It will also change with the discharge of water from the upstream rivers.