Astronomical factors: When the sun, the earth and the moon are on the same straight line, the tidal force of celestial bodies is the greatest, and a spring tide appears. (due to friction, it is two to three days behind. Topographic factors: the mouth of the river is large outside and small inside, shaped like a trumpet; Also supported by rivers, the tidal water level rises. Climatic factors: It coincides with summer, and the southeast monsoon adds fuel to the flames.
Extended data:
The cause of spring tide
Time: from August 16 to August 18 in 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 unit mass, or the resultant force of the inertial centrifugal force generated by the earth's movement around the center of mass of the moon (sun) and the moon (sun))
Geographical location: It is related to the trumpet-shaped estuary of Qiantang River. On the south bank of Qiantang River, nearly 500,000 mu of land was reclaimed to the east of Zheshan Mountain, which blocked the estuary like a peninsula, making the section from Zheshan Mountain to the outside of Qiantang River 12 km like a bottle with a small belly, and the tide was easy to enter but difficult to retreat. The outer mouth of Hangzhou Bay is 100 km wide, and it is only a few kilometers wide to the outer 12 sections.
The river bed in the east of the estuary suddenly rose again and the beach was shallow. When a large number of tides flood in from the mouth of Qiantang River, because the river surface shrinks rapidly, it is too late to rise evenly, so the back waves push the front waves and overlap each other. 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.
Wind direction: the 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.
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