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Tidal bores, also known as tidal surges, river bores or aegirs, occur when a shallow river with a narrow sea outlet, situated on a wide, flat estuary, surges upstream against the natural flow of the river's current, causing the incoming tide to form a wave, or a series of waves.
Tidal bores can occur on a daily basis, but they are at their highest during times of very high tides.
High tides occur during the phases of a full moon or new moon, when the gravitational force of both the sun and the moon reinforce one another.
The largest annual tides occur around the times of the Spring Equinox in the month of March and the Autumn Equinox during the month of September. These two annual tides are further reinforced during the period of the full moon or the new moon phases, leading to the highest of all tidal bore waves.
There are only around sixty of these phenomena in the world, eleven of which occur in the United Kingdom, which between them produce tidal bores of varying heights and speeds, one of which is the second largest in the world, that of the River Severn. These eleven British rivers are;
The River Dee, England / Wales
The River Dee has a tidal bore which attains heights of between one to two meters which can travel up to sixteen miles inland from Connar's Quay in Flintshire, Wales, where it's five mile wide estuary narrows to a mile wide channel, sending waves surging through to Chester Weir in the City of Chester in Cheshire, England.
The River Eden, Cumbria, England
This ninety mile long river in Cumbria has a tidal bore which can attain heights of around one meter which travel at speeds of up to nine miles an hour between it's estuary on the Solway Firth in the Irish Sea through to Wetheral Weir in the village of Wetheral in Cumbria.
The River Great Ouse, Cambridgeshire / Norfolk, England
East Anglia's one hundred and forty three mile long, River Great Ouse, has a tidal bore colloquially known as the Wiggenhall Wave. The bore attains a height of around one meter and travels between it's mouth at Kings' Lynn in Norfolk to the Norfolk village of Wiggenhall, a distance of about ten miles.
The River Kent, Cumbria, England
Known as the Arnside Bore, this twenty mile long river has a tidal bore which occurs between it's river mouth on Morecambe Bay through to the Cumbrian village of Arnside, one mile away. The bore can attain a height of up to one foot and takes just over two hours to travel the one mile to Arnside.
The River Lune, Lancashire, England
Small rolling waves of around a meter high have been located on this river between it's mouth at Lancaster on Morecambe Bay in the Irish Sea through to the coastal village of Snatchems, a distance of about three miles.
The River Mersey, Merseyside / Cheshire / Greater Manchester, England
England's seventy mile long, River Mersey, has a tidal bore which attains a height of around five meters and travels at speeds of around eleven miles an hour, between it's mouth on the Irish Sea at Liverpool Bay through to the Cheshire town of Warrington, a distance of about thirty miles.
The River Nith, Dumfries & Galloway, Scotland
This seventy one mile long river located in south west Scotland has a tidal bore which can attain a height of just under one meter. The bore travels at speeds of up to six miles an hour between it's mouth at Kingholm Quay on the Solway Firth through to the village of Glencaple, a distance of about three and a half miles.
The River Parret, Dorset / Somerset, England
This thirty seven mile long river situated in south west England has a tidal bore which can attain heights of up to two meters and speeds of up to six miles an hour as it makes it's way from it's mouth at Bridgwater Bay on the Bristol Channel through to the Somerset market town of Bridgwater, a distance of around three miles.
The River Ribble, Cumbria / Lancashire, England
The River Ribble is tidal from it's estuary on Lancashire's Irish Sea coast through to Fishwick Bottoms, situated between Preston and Walton Le Dale, a distance of around eleven miles, where slow rolling waves of around one meter high can regularly be seen.
The River Severn, England / Wales
The River Severn bore is the world's second largest tidal bore. This mega bore can attain heights of between ten to fourteen meters and travel at speeds of between eight to thirteen miles an hour, The bore is one of only three in the world which can be surfed, due to it's five mile wide estuary on the Bristol Channel narrowing to a mile wide channel as it makes it's way through to Tewkesbury in Gloucestershire, a distance of about twenty five miles.
The River Trent, Midlands / North East England
The Trent Bore, also known as the Trent Aegir, attains a height of between one to two meters and can travel at a speed of about twelve miles an hour, from it's mouth on the seven mile wide, Humber Estuary, through to the Lincolnshire town of Gainsborough, some fifty miles away.
The above tidal bores are magnets for visitors who want to either witness a rare, natural phenomena or for those who want to ride the waves in kayaks or canoes, or in the case of the River Severn, surf the waves.To find out more about river sports on these, and many other British rivers, check out this site - www.ukriversguidebook.co.uk.
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