eagre n : a high wave (often dangerous) caused by tidal flow (as by colliding tidal currents or in a narrow estuary) [syn: tidal bore, bore, aegir, eager]
- Rhymes: -iːɡə(r)
- A large wave like an eagre, diverging from its bow, was extending to either bank, swamping the tules and threatening to submerge the lower levees. — Bret Harte, A Protegee of Jack Hamlin's
A tidal bore (or just bore, or eagre) 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).
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.
Rivers that have been known to exhibit bores include those listed below.
- Petitcodiac River in the Bay of Fundy, New Brunswick, Canada, formerly the highest bore in North America, 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, Nova Scotia. When the tidal bore approaches, completely drained riverbeds are filled. The bore is fastest and tallest in some of the smaller rivers that connect to the Bay. It has claimed the lives of several tourists that were in the riverbeds when the bore came in.
- Turnagain arm of Cook Inlet, Alaska. Up to 2 meters (6 ft) and 20 km per hour.
- 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
- 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
eagre in Bengali: জলোচ্ছ্বাস
eagre in German: Gezeitenwelle
eagre in Spanish: Macareo (física)
eagre in French: Mascaret
eagre in Galician: Macareu
eagre in Ido: Baro-fluxo
eagre in Italian: Mascheretto
eagre in Hungarian: Torlóár
eagre in Dutch: Getijdegolf
eagre in Japanese: 海嘯
eagre in Norwegian: Tidevannsbølge
eagre in Norwegian Nynorsk: Tidvassbølgje
eagre in Portuguese: Macaréu
eagre in Russian: Бор (волна)
eagre in Finnish: Vuorovesiporras
eagre in Swedish: Bore (hydrologi)