KEY POINTS:
Hundreds of people gathered on the banks of the River Severn yesterday to witness one of Britain's most spectacular tidal phenomena.
The Severn Bore - a tide wave that occurs in the lower reaches of the river upstream of the Port of Sharpness at the southern terminus of
the Gloucester and Sharpness Canal - surged along the river in Gloucestershire and Worcestershire where it was witnessed by gatherings at Minsterworth, Stonebench and Overbridge.
The waves, which were also seen on Wednesday, were the first "four-star bores" this year, though an unfavourable wind prevented them meeting predictions of the highest for months.
The Severn Estuary receives the second-highest tide anywhere in the world (only the Bay of Fundy in Canada is greater) and the differences between the lowest and highest tide in one day can be more than 14.5 metres. The high or spring tides occur on several days in each lunar cycle throughout the spring and autumn.
Despite warnings from the local harbour authority, Gloucester Harbour Trustees, the tide (a self-reinforcing solitary wave or soliton, as it is known to scientists) has long since attracted surfers and yesterday was no different, with enthusiasts anticipating the kind of tide which enabled Steve King, a local railway engineer, to record a world record for the longest surf last year.
Though the river did not quite meet expectations it was, as usual, funnelled up the estuary into a wave that travelled rapidly upstream against the river current.
Anticipation of the bore was all the greater because of the near absence of them this year. There have been only two four-star bores in this season, compared to 13 in the equivalent period last year.
"For a bore to form, a considerable rise in tide is needed in a converging channel with a rising riverbed, forming a funnel shape," an Environment Agency spokesman said. "The size of the bore can be affected by wind direction, height of the incoming tide and freshwater moving downstream. It has been known to reach two metres in height and its average speed is 16km/h.
- INDEPENDENT
Swell idea
* The Severn Bore is a tide wave that occurs in the lower reaches of the River Severn.
* For a bore to form, a considerable rise in tide is needed in a converging channel with a rising riverbed.
* The size of the bore can be affected by wind direction, the height of the incoming tide and freshwater moving downstream.
* The Severn Bore has been known to reach 2m in height and it to travel at an average speed of 16km/h.
