Wonder of the World —— Why is the tidal water of Qiantang River the largest on the 15th day of the eighth lunar month?

Category: social/cultural >> festivals and holidays

Analysis:

zdxb.zju.edu/article/show_article_one.php? article _ id = 1968

Qian Jiangchao, the miracle of the world

Since ancient times, Qian Jiangchao has been called the miracle of the world. Whenever the spring tide comes, the waves are rough and magnificent, and the sound of the tide shakes the ground, such as thousands of troops and horses, and the river rolls, which really tends to "cross the river and destroy the mountains." The tidal head is generally 1-2 meters high, and the highest is more than 5 meters. It pushes upstream at a speed of 5-7 meters per second, sweeping and spectacular. Zhang Yu, a writer in the Ming Dynasty, once wrote such a poem for him: "The Luosha River (Qiantang River) is at the beginning of August, and the mountains and seas are vast. Liu Ao rolled up the Milky Way and Ma Benteng crossed the snow. "

Tidal bore is a natural phenomenon.

Ancient science was backward and could not explain this spectacular natural phenomenon, which was considered as "the entrance and exit of sea urchins" and "the change of dragons". According to legend, during the Spring and Autumn Period and the Warring States Period, Wu Zixu, a general of the State of Wu, was repeatedly persuaded to kill Gou Jian, the king of Yue, and was given a sword by the king of Wu, who whipped him 300 times and threw him into the Qiantang River. Wu's resentment lingered and suddenly turned into a raging storm, seeking revenge on the prince of Wu. Since then, the Qianjiang tide has ebbed and flowed.

The legend of Wu Zixu's irrigation into the Tao is because the ancients could not explain the natural phenomenon of tidal bore, out of sympathy for Wu Zixu. From the perspective of modern science, the ocean tides on the earth are periodic movements formed by the gravitational force of celestial bodies (mainly the moon and the earth) and the centrifugal force generated by the earth's rotation. On the first and fifteenth day of the lunar calendar, the earth, the sun and the moon are almost in a straight line, and the gravity of the sun and the moon is very strong, which is easy to form a spring tide. Before and after the Mid-Autumn Festival, not only are their positions just close to a straight line, but this is also the time when the earth is closer to the sun in a year, so the autumn tide is larger, which is also a common natural phenomenon.

Why is Qian Jiangchao so big?

There are many rivers with tidal bore in the world, such as the Amazon River in South America, the Colorado River in North America, the Seine River in France and the Severn River in Britain. However, the intensity and spectacular phenomenon of tidal bore in Qiantang River are incomparable to other rivers except Amazon River. Although the tidal bore intensity of the Amazon River is comparable to that of the Qiantang River, the estuary of the Qiantang River oscillates frequently and the tidal bore scene changes greatly. Therefore, Qian Jiangchao can be said to be the best and unparalleled.

Why is the tide in Qiantang River particularly turbulent and huge? The trumpet-shaped estuary is one of the reasons. The width of the outer channel of Hangzhou Bay is about 100 km, but it shrinks sharply inward. When it reaches Haiyan Ganpu, the mouth of Qiantang River, which is 90km away from the mouth of the bay, the width is only 20km, while the width of the river in Hangzhou is only about 1 km. When a large number of tides rush into a narrow river, the water surface will rise rapidly. Because there is more sediment deposition at the bottom of the river here, the tidal wave entering the estuary meets the sandbar, the water depth decreases, the resistance increases, the front slope becomes steeper and the back slope becomes slower accordingly. When the front slope is steep to a certain extent, the front water surface rises obviously, thus forming tidal bore and even turning over waves.

However, there are many rivers in the world that enter the sea, which are large outside and narrow inside, deep outside and shallow inside. Why don't they surge like the Qiantang River tide? It turns out that the appearance of * * * is also related to the river velocity. At high tide, its direction is opposite to that of the river. Around the Mid-Autumn Festival, the velocity of Qiantang River estuary is almost equal to that of tide. When rivers with equal strength collide with tides, a huge tidal gap will be aroused. In addition, in the coastal areas of northern Zhejiang, southeast wind or east wind often blows at the turn of summer and autumn, and the wind direction is generally consistent with the tidal direction, which also encourages its momentum. In a word, the formation of the spring tide in Qiantang River is influenced by astronomical and geographical factors (including estuary shape, riverbed landform, hydrology, climate, etc.). ).

Qiantangjiang Guanchao Resort

Qianjiang Tide Watching began in Han and Wei Dynasties, flourished in Tang and Song Dynasties, and lasted for more than two thousand years. The Southern Song Dynasty is scheduled to inspect the navy on the Qiantang River on August 18th of the lunar calendar (the so-called birthday of the tide god), and it has become a habit to watch the tide since then. Su Dongpo praised: "August 18th tide is spectacular. Kunpeng hit the water for 3,000 miles and trained a long drive of 100,000 people. The red flag and green cover gradually disappear, and the black sand and white waves eat each other. When life encounters ancient difficulties, this trip has two benefits. "

The traditional tidal resort is Yan Guan Town in Haining, so it is also called "Haining Tide". Around the Mid-Autumn Festival every year, more than 6,543,800 people gather in this scenic spot with zhenhai tower, Sea Temple and Zhongshan Pavilion, forming a huge crowd and being very lively. There are three good places to watch the tide. First of all, near Yanguan, you can see the "first-line tide" in Yin Tao rolling neatly. Second, in the Babao Gorge to the east of Yan Guan, we can see the collision of two tidal heads in the east and south, which set off a "tidal wave" of ten thousand icebergs and snow peaks thousands of miles away. Thirdly, in the old salt storage in the west of Yan Guan, you can see that after the tide has surged over the T-shaped dam, the waves stand on the wall and rush to the "resurgence" in the sky. Because the tide is retrograde at the speed of 25 kilometers per hour, if you watch the tide three times, you must race with the tide head by the tide-watching car. You can see the tide in Babao first, then enjoy the scenery of the first-line tide in Yan Guan, and finally enjoy the resurgence in the old salt warehouse. Because there are many kinds of tidal bore, the best place to watch tidal bore is uncertain, so we can choose it carefully according to the specific situation.

How to watch Qian Jiangchao?

The tidal bore of Qiantang River has attracted thousands of viewers in Qian Qian with its majestic momentum, changeable pictures and charming scenery. So how can we see Qian Jiangchao? Poets and writers in China have written many descriptions of tidal bore, which can give us a lot of enlightenment. For example, "Longpingsha started in Bai Hong, Yaotai lost its jade cup" and "Ruolian crossed the river", comparing the tidal bore on the horizon to Bai Hong, Yinlian and Sulian. "Stormy waves come like snow", "Furious waves roll frost and snow" and "snow waves travel thousands of miles", comparing tidal bore to frost and snow. "Like a thousand wind horses galloping on a silver saddle, competing for novelty and beauty", the tidal bore is compared to a flying horse.

"If a dragon fights, it is as urgent as snow and hail", and the tidal bore is compared to a dragon. "Tide-colored Milky Way covers the blue sky, and the sunlight column gives a red basin", and the tidal bore is compared to the Milky Way. "When you are suspicious of the sea and the air, drums are drummed on all sides" and "the autumn moon is thousands of miles away, and the sound of a hundred troops is in the middle of the night" are the voices that describe the tidal bore. And compare the sound of tidal bore to "thunder rumbling" Some compare the sound and shape of tidal bore, and the sound and shape correspond, such as "there are thousands of Lei Zhen clouds in the sky, silver horses on the ground" and "thunder at sea, waterfalls across the river". The sound and shape correspond, which makes people feel heard and seen. Another example is "the August tide at the head of the Rakshajiang River engulfs mountains and carries the sea" and "unstoppable and thunderous", which fully shows the momentum of the tidal bore. As can be seen from the above, different metaphors constitute a picture with different images. Qian Jiangchao appreciates it with its own shape, sound and potential, giving people endless aftertaste. So when we look at the tidal bore in Qianjiang, we should not only look at its shape, but also listen to its sound and potential. The combination of form, sound and potential is pleasing to the eye.

Advantages and disadvantages of tidal bore in Qianjiang River

The tidal bore in Qiantang River has a long history, and it has made merits and demerits for thousands of years. Who can comment? The spectacular tidal bore in Qiantang River is unparalleled in the world and has become a tourist project. Tidal bore is rich in tidal energy resources. For example, the average tidal range of Ganpu in the estuary is 5.57 meters, and the maximum tidal range is 8.93 meters, which is the richest tidal energy resource in China's coastal areas. At high tide, a large amount of offshore sediment enters the estuary with the tidal current, and part of it is deposited in the estuary, forming a continuous beach, which is also a resource. However, the tidal bore did bring pain and disaster to the people along the river. "The mighty rivers shed tears for the victims." "The hurricane pulled up trees like a mountain, and the vibration dried up instantly. Thousands of households in the sea, no one floats. " This is the portrayal of the tidal disaster at that time. Whenever a typhoon comes, and when the tide is high, the storm surge is particularly harmful. People along the Yangtze River have waged a long-term and resolute struggle against tidal disasters. Through the efforts of working people in past dynasties, seawalls with a length of 365,438+07 kilometers have been built on both sides of Qianjiang River. It is like an iron wall, resisting the impact of tidal bore and flood, and safeguarding the lives and property of people along the Yangtze River and the safety of farmland.