Tidal Bores: An Introduction

Hangzhou is one of China’s great metropolises, harboring 9.2 million citizens and a rich cultural history. Located in Zhejiang Province, just south of Shanghai and at the end of the Grand Canal, the city has served as China’s capital at several points in history: in the Wuyue Kingdom (907–978) and in the Southern Song dynasty (1126–1276; then known as Lin’an).

While noted for its cultural and historical significance, Hangzhou has yet another claim to fame: Hangzhou Bay, fed by the Qiantang River, is home to the world’s largest tidal bore (towering as high as 10 meters).

The Qiantang River is the largest in Zhejiang Province, but its estuary at the East China Sea is tremendously wide: 100km at its shallow opening into the sea. This narrows to around 20km by the time tidal forces reach Ganpu, a town further up the bay from Hangzhou. In the absence of other forces, such as typhoons, the tidal bores are most prominent between Wenjiayan and Ganpu.

This funnel shape is precisely what allows the tidal bore to grow. According to National Geographic, tidal bores form when a shallow river opens up to a larger body of water in a wide estuary, as is the case with the Qiantang. For tidal bores to form, a wide tidal range—6 meters or more—needs to be present.

The thundering “Silver Dragon,” as the Hangzhou Bay tidal bore is known, can be heard for quite some time before reaching spectators. In its path opposite to the river current, the tidal bore stirs up sediment and even vegetation with a vortex near the riverbed, causing the water to have a brownish appearance. This process also brings salt water into the river. Generally, slightly smaller waves follow one large initial crest.

This phenomenon is most celebrated around the autumnal equinox, when some of the largest waves can be seen. The city of Hangzhou claims that the best viewing can be done during the Mid-Autumn Festival, the 15th day of the 8th lunar month (October 4th for 2017). The 18th (October 7th) has the largest waves, but the city also claims that sizable waves occur between the 1st to 5th and 15th to 18th of each lunar month.

The Silver Dragon has a long cultural and folkloric tradition surrounding it, with the tradition of viewing the bores dating back to the Han Dynasty (202 BCE–8 BCE; 23 CE–220 CE). This activity also enjoyed great popularity in the years of the Tang and Song dynasties (618–1279 CE).

While being a sight to see for two millennia, the tidal bores are also a danger to surrounding communities that has been extremely difficult to tame, says E. N. Dolgopolova. Between the 1960s and 1990s, however, major projects were undertaken to increase the amount of usable land around the Qiantang River and Hangzhou Bay. In all, 730 square kilometers were reclaimed.

At the same time, though, the government did not want to eliminate the tidal bore entirely; the tourism potential for the natural phenomenon was also crucial. Fung Mei Sarah Li asserts that the People’s Council took note of the tourism potential for the bores, especially as China opened up to commercial ventures. The first tidal bore festival was held in 1992, and proved so successful that Xiaoshan, a nearby city, too, started capitalizing on the tidal bores. By 2003, 1.1 million visitors came to the festival. This has led to the reconstruction of traditional culture lost during the Maoist era, and many new traditions have been added.

While the society around them has changed, and as Hangzhou Bay and even the tidal bores themselves undergo natural shifts, they persist, constituting an important part of Chinese environmental history. With rising see levels and continued water projects in the region, their relevance is unlikely to decline.