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BORED TO DEATH: rivers that kill

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River Ribble tidal bore in Lancashire, England.
River Ribble tidal bore in Lancashire, England.

By Scott A. Rowan

Yes, you can get bored to death.

Don’t worry, however, you would need to be wading along the shore of a turgid river for it happen, not sitting on the couch at the next family function beside your aunt who tells endless tales of feline folly only she finds fascinating.

A tidal bore is a form of tidal wave that occurs when strong ocean or sea waves push against a river that empties into the larger body of water. Typically referred to simply as bores, these water surges are uncommon and only happen in places where specific geological formations exist that allow the energy of large bodies of water (oceans, seas) to become compressed into a river, temporarily reversing the flow of the river due the massive amount of water flowing upstream.

GEOLOGY OF BORES
Not all rivers along a coastline will experience a bore. There must be several specific land formations under the water for a bore to happen:

• the river/stream must be fairly shallow
• the river’s outlet to the open water must be narrow
• the river’s estuary (where river meets ocean/sea) is wide and flat
• the fluctuations between high and low tide must be large with a minimum difference of approximately 20 feet (6 m)

Tides along coastlines are predictable, but tidal bores are not (which a few exceptions below). The rarity of bores – seeing a tidal wave so large it reverses the flow of a river for a short period of time – can easily lead to death. Though the river level may only rise a few feet, tempting locals to river surf or kayak and amateur photographers to get a great photo: be warned – the energy alone in a bore can drown you, not to mention the amount of submerged debris bores dislodge (trees, rocks, structures, etc.)

RARE BORES

The annual fall tidal bore on the Qiantang River in China is a fatal attraction for adventure seekers every year. In 2015, the Chinese bore was responsible for five missing or killed people.
The annual fall tidal bore on the Qiantang River in China is a fatal attraction for adventure seekers every year. In 2015, the Chinese bore was responsible for five missing or killed people.

Though potentially lethal, bores in China, Brazil, and Alaska that occur on a semi-predictable schedule are the siren call to intrepid kayakers, surfers, and the curious onlookers eager to experience one of Mother Nature’s oddities. For some, however, this treat is one of Mother Nature’s last tricks as the powerful surges still continue to claim lives despite most people knowing the dangers.

Every year, adventure seekers flock to the Qiantang River in Hangzhou, China, site of the world’s largest tidal bore that occurs every fall due to natural conditions. The tapered channel of the Qiantang River forces the bore to compress and, with nowhere else to go but up, the bore can reach heights of 30 feet (9 m). The violence of the Qiantang bore creates a cacophonous roar that can be heard for hours prior to the bore finally appearing, giving residents plenty of time to run to the water see the action. Every year casualties are reported and it isn’t uncommon for witnesses to be killed. In the aftermath of the 2015 Qiantang bore (August 31, 2015), Chinese authorities reported the bore caused one death and that four other people were swept out to sea.

In Brazil, the bore at the mouth of the Amazon River, named the pororoca, is so strong that the Amazon does not have a delta. The surging waters of the pororoca can reach up to 13 feet (4 m), forcing all sediment in the river to empty directly into the Atlantic.

In Sri Aman, Malaysia, tidal bores occur twice daily, and at much smaller heights. Called the benak, these daily bores max out at approximately 5 feet (1.5 m) and have become a popular tourist attraction.

DEATH BY BORE
Near Anchorage, Alaska, an unusual sight can be seen: surfers get gnarly on some rad waves. Every day in the Gulf of Alaska, in an area called the Turnagain Arm, bores occur that can reach up to 10 feet (3 m). Though not known for the violent force the Qiantang River bores possess, experiencing the Turnagain Arm bores can be lethal for the inexperienced. River silt and mud becomes a tarbaby-like trap that kills the curious every year. Onlookers eager for a closer look will often walk out onto the mud flats, only to discover that they cannot move and that nobody can come out to save them or else they will suffer the same fate. When high tide rolls in, the trapped onlooker drowns.

Another unexpected way that bores can cause human death: mauling. Bores, particularly ones in remote areas like Alaska and in the Amazon, kill tons of fish and aquatic animals which attracts countless carnivores – bears, wolves, alligators and other scavengers – all of which can cause onlookers more problems than rising waters or quicksand-like mud.

DEATH TO A BORE

The mascaret tidal bore on the Seine River in France was a destructive force for centuries before a system of manmade water projects including dams and canals eliminated the lethal aspects of the river's swells.
The mascaret tidal bore on the Seine River in France was a destructive force for centuries before a system of manmade water projects including dams and canals eliminated the lethal aspects of the river’s swells.

The Seine River in France is probably the best example of human engineering eliminating the costly and lethal problems caused by bores. For centuries, people and businesses living and working along the Seine River were held hostage to an unpredictable bore, called the mascaret. The mascaret was responsible for hundreds, if not thousands, of ships being sunk by the surprise bore. Throughout the 18th and 19th century, construction of dams, canals, irrigations systems and dredging efforts killed off the mascaret.

 

 

SOURCES:
http://education.nationalgeographic.org/encyclopedia/tidal-bore/

http://www.seafriends.org.nz/oceano/waves2.htm

http://www.dailymail.co.uk/news/peoplesdaily/article-3218143/Run-lives-Dramatic-pictures-spectators-dashing-safety-enormous-tidal-waves-high-30-feet-struck-China.html

 

 

 
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