Whilst the last few years have seen few impressive Severn Bores, Saturday morning's Bore (March 12 2005) is expected to be one of the biggest of the year - a 'four star' bore. The Severn Bore is a spectacular natural phenomenon which attracts sightseers and surfers from near and far. But bores are not unique to the Severn. The bore exists in the Severn because the estuary is just the right shape for funnelling the incoming tides of the Bristol Channel. The flow of water that rushes up the Severn becomes too great for the narrowing, increasingly shallow river to accommodate. When conditions are favourable - low pressure, a strong westerly wind and a high tide following a new or full moon - the surge of water is sufficient to form a wave as much as 2 metres high, with a speed of 14 knots. Highly unusual For topographical and hydrographical conditions to combine in such a way is highly unusual but they do occur elsewhere. The bore on the Severn is the biggest of 8 in the UK but there are thought to be around 60 throughout the world. These include the Seine and Gironde in France; the Indus in India; the Amazon in Brazil and the Knik Arm, Alaska. Anywhere that has an exceptionally large tidal range is favourable for the formation of a bore. The highest tides on earth are to be found in the Bay of Fundy, Nova Scotia. To be more precise, they occur at the eastern end of the Bay in the Minas Basin. Here the tidal range can reach 16 metres, about 3 metres higher than the Bristol Channel. Channel At Cape Split, on the southern side of the Basin, the currents exceed 8 knots and the flow through the 5 kilometre wide channel is said to equal the combined flow of all the streams and rivers on Earth (4 cubic kilometres per hour)! The flow of seawater into the Minas Basin is so great that it causes the surrounding land to tilt slightly. Under such extreme conditions it is not surprising then to learn that tidal bores are found on 5 rivers within the Basin. The biggest bore in the world is to be found in Hangzhou Bay south of Shanghai. The characteristic narrowing, increasingly shallow Bay and large tidal range combine to produce a bore that on the highest tides, can attain a height of over 7 metres and a speed of up to 15 knots. It is said that the roar of the advancing bore can be heard at a distance of more than 20 kilometres. Location To view the bore on Saturday morning's tide you will need to take up your viewing position about 20 minutes before the forecast times. Make sure you are not in a location which will flood should the bore overtop the River. The times and recommended viewing locations are as follows: Minsterworth at 0921; Stonebench at 0936; and Over Bridge at 0956. Article by Richard Angwin 
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We're expecting one of the biggest Severn Bores of the year on Saturday morning. BBC Weatherman Richard Angwin investigates...
