Front row for big bore
People watch a tidal bore heading up the Qiantang River in Hangzhou, Zhejiang province, on Aug 18. The annual peak for watching the phenomenon, known as the Qiantang Tide, usually falls around the Mid-Autumn Festival - occuring next month this year - but monthly tidal bores also attract visitors from across China. [Photo by Dong Xuming for China Daily]
The Qiantang River tidal bore is as famous as the ones on the Ganges in India and the Amazon in Brazil.
The river, originating in the border region of Anhui and Jiangxi provinces, runs for 459 kilometers through the coastal Zhejiang province, passing through the provincial capital Hangzhou before flowing into the East China Sea via the Hangzhou Bay.
The river is the southern terminus of the ancient Grand Canal that links five major rivers in China from north to south, and enables water-borne traffic to travel inland from Hangzhou as far north as Beijing.
While the Hangzhou Bay at the mouth of the Qiantang is about 100 km wide, the river narrows to a mere 2-3 km at one point - its Yanguan section. And as the tidal waters are blocked by the narrow river passage, pressure builds up from behind until a tidal bore is formed, creating a high water wall.
In addition, the presence of a submerged sandbar at the mouth of the river acts like a springboard for the tide, sending the crest of the bore higher.
Also, combined with the gravitational pull of the celestial bodies and the centrifugal force produced by the rotation of the Earth, tidal waves are created for the first five days and in the middle of every month according to the lunar calendar, which adds up to about 120 days a year.
