Tidal bore

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The tidal bore in Upper Cook Inlet, Alaska

A tidal bore (or just bore, or aegir) is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travel up a river or narrow bay against the direction of the current. As such, it is a true tidal wave (not to be confused with a tsunami).

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[edit] The phenomena

Bores occur in relatively few locations worldwide, usually in areas with a large tidal range (typically more than 20 feet (6.1 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 — somewhat like a shock wave — to ‘undular bores’ comprising a smooth wavefront followed by a train of secondary waves (whelps). Large 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. [1]

[edit] Asia

[edit] Australia

[edit] Europe

[edit] United Kingdom

The Trent Aegir seen from West Stockwith, Nottinghamshire, 20 September 2005
The Trent Aegir at Gainsborough, Lincolnshire, 20 September 2005

[edit] France

The phenomenon is generally named un mascaret in French[2] but some other local names are preferred.[1]

[edit] Norway

[edit] North America

Tidal bore on the Petitcodiac River
  • Turnagain arm of Cook Inlet, Alaska. Up to 2 metres (6.6 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:

[edit] South America


[edit] References

[edit] See also

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