The Severn Bore

The Severn Bore may sound like the guy in the pub who goes on and on about the River Severn, but that is not what I mean here! It is a natural feature that has become a tourist attraction and an opportunity for surfers to do something that is a bit out of the ordinary.

A bore is literally a tidal wave. Many rivers around the world have bores, which are waves that travel up the river for a certain distance whenever the tide is high enough, but the one on the River Severn in Gloucestershire (England) is particularly pronounced and remarkable.

The River Severn, which is the longest river in Great Britain, reaches the sea at the head of the Bristol Channel. This is the piece of sea that separates Southwest England from South Wales, and it gets narrower the further east it goes. The Channel merges imperceptively into the mouth of the Severn, such that the tidal surge coming up the Channel is funnelled directly into the river.

The funnel effect is in two dimensions. Not only is the river mouth getting narrower (five miles wide at Avonmouth and only a hundred yards at Minsterworth) but the river gets shallower further inland. This means that the body of water being forced upstream against the flow of river water coming down has no choice but to rise up to form a wave.

Another factor that makes the Severn Bore so spectacular is that the tidal range in the Bristol Channel is one of the largest in the world at up to 50 feet (15.5 metres).

The Bore is seen to best effect during the highest tides (spring tides) that occur on five consecutive days each month, twice a day.

The Bore moves upstream at about 8 to 9 kilometres (5 miles) per hour and will take up to two and a half hours to reach its furthest extent near Gloucester, some 34 kilometres (21 miles) from where the Bore usually starts near the village of Awre.

The height of the Bore varies according to the height of the tide and other factors, but a typical Bore is over a metre high in midstream (and higher at the banks).

The Severn Bore is a popular attraction, but it is virtually impossible to see a really good Bore in its ‘natural’ state because it is always highly popular with surfers and canoeists. The challenge is to ride the Bore for as long as possible, and it is sometimes possible to lose the wave at one point but be taken by boat or road to a point further upriver in order to catch it again when it arrives.

© John Welford