Bores occur in relatively few locations worldwide, usually in areas with a large tidal range (typically more than 20 feet (6 m) between high and low water), and where incoming tides are funneled into a shallow, narrowing river via a broad bay. The funnel-like shape not only increases the height of the tide, but it can also decrease the duration of the flood tide down to a point where the flood appears as a sudden increase in the water level.
Bores take on various forms, ranging from a single breaking wavefront — effectively a shock wave — to ‘undular bores’ comprising a smooth wavefront followed by a train of solitary waves (solitons). Larger bores can be particularly dangerous for shipping, but also present opportunities for river surfing.
The word bore derives through Old English from the Old Norse word bára, meaning a wave or swell.
Rivers that have been known to exhibit bores include those listed below.
Asia
- Ganges–Brahmaputra, India, Bangladesh
- Indus River, Pakistan
- Qiantang River, China,Tidal bore of Qiantang River which has the world's largest bore, up to 9 meters (30 ft) high, traveling at up to 40 km per hour (25 miles an hour).
- Batang Lupar or Lupar River, near Sri Aman, Malaysia. The tidal bore is locally known as benak.
South America
- Amazon River in Brazil and Orinoco River in Venezuela, up to 4m (12 ft) high, running at up to 25 km/h (15 miles per hour). It is known locally as the pororoca.
- Mearim River in Brazil.
- Araguari River in Brazil.
North America
- Turnagain arm of Cook Inlet, Alaska. Up to 2 meters (6 ft) and 20 km per hour.
Most rivers draining into the upper Bay of Fundy between Nova Scotia and New Brunswick have tidal bores. Notable ones include:
- Petitcodiac River formerly the highest bore in North America at over 2 metres (6 ft) high. It was reduced to little more than a ripple due to causeway construction and extensive siltation.
- Shubenacadie River, also off the Bay of Fundy in Nova Scotia. When the tidal bore approaches, completely drained riverbeds are filled. It has claimed the lives of several tourists that were in the riverbeds when the bore came in. Tourboat operators offer rafting excursions in summer.
- The bore is fastest and tallest in some of the smaller rivers that connect to the Bay including the River Hebert and Maccan River on Cumberland Basin, the St. Croix, Herbert and Kennetcook Rivers in the Minas Basin, and the Salmon River in Truro.
Europe
United Kingdom
- River Dee, Wales / England
- River Mersey
- River Severn, Wales / England up to 2 meters (7 ft) high
- River Trent, (the Aegir) up to 1.5 meters (5 ft) high, England and other tributaries of the Humber Estuary
- River Parrett
- River Welland
- River Kent
- River Great Ouse
- River Ouse, Yorkshire
- River Eden
- River Esk
- River Nith
France
The phenomenon is generally named un mascaret in French but some other local names are preferred.- Seine, locally named la barre, had a significant bore until the 1960s. Since then it has been practically eliminated by dredging.
- Couesnon
- Sélune
- Vilaine, locally named le mascarin
- Dordogne River
- Garonne River
Norway
- Saltstraumen near Bodø, claimed to be the strongest tidal current in the world.
Australia
References
See also
- 1812 New Madrid earthquake (in the US) (causing the Mississippi River to flow backwards)
- Hydraulic jump
- Tidal race
- Tonlé Sap (lake and river system in Cambodia) (where monsoon flooding causes the river to flow backwards)
- Undular bore wave
External links
- Quiantang River Tidal Bore in China, USC Tsunami Research Group
- Amateur video of the "Wiggenhall Wave" tidal bore
- link to Proudman Inst. page
- More than 100, freely available, published research articles on tidal bores, hydraulic jumps and related topics by Professor Hubert Chanson, Department of Civil Engineering, The University of Queensland
- The Tidal Bore of the Seine River, France
- Tidal bores, Mascaret, Pororoca. Myths, Fables and Reality !!!
- Chanson, H. (2005). "Mascaret, Aegir, Pororoca, Tidal Bore. Quid ? Où? Quand? Comment? Pourquoi ?" Journal La Houille Blanche, No. 3, pp. 103-114
This article is licensed under the GNU Free Documentation License.
Last updated on Friday September 26, 2008 at 14:50:31 PDT (GMT -0700)
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