The Severn Bore – UK, and the Araguari Pororoca – Brazil

It’s not long ago that I talked about the tidal bore in Cook Inlet, Alaska, but there is another one in Europe which is equally worth a mention – the Severn Bore.

This is one of Britain’s  truly spectacular natural phenomena and it happens several times a year. The large surge wave can be seen in the estuary of the River Severn, where the tidal range is the 2nd highest in the world – as much as 50 feet (approx. 15.4m).

You will see from my article last month that I claimed, with great confidence, that the Turnagain Arm tidal bore in Cook Inlet was the second highest tidal swing in the world, but perhaps I am wrong… opinions would be welcome please! However, the facts I got about the Alaska Bore suggest that their tidal swing can be as much as 35 feet – which would give the Severn Bore plenty of room to manoeuvre into second place.

Back to good old England and their mighty wave…

the Severn Bore, a tidal bore or bore tide, in the Severn Estuary, UK

The Severn Bore

The Severn Bore is actually one of 8 in the UK – but it is most certainly the largest. The shape of the Severn estuary is ideal for the creation of this spectacular boretide – it funnels the water into an increasingly narrow channel as the tide rises, thus forming the large wave. The river’s course takes it past Avonmouth where it is approximately 5 miles wide, then past Beachley and Aust, then Lydney and Sharpness where it is approximately 1 mile wide, and soon the river is down to a width of a few hundred yards. By the time the river reaches Minsterworth it is less than a hundred yards across, and remains this width all the way to Gloucester.

As the river narrows so does the depth change, it becomes more and more shallow particularly near Bristol which some feel is the point where the phenomena begins. The narrowing of the river and the diminishing depth accentuates the funnel shape. Therefore as the incoming tide travels up the estuary, it is routed into an ever decreasing channel and so the wave is formed. It is not really recognisable as a true wave until it approaches the first major bends well inland of Sharpness.

Altogether, it’s over twenty miles of wave with changing conditions and shape all the way. If the tide is big enough, someone  somewhere will get a wave. The smaller the tide the more fickle the wave becomes. It is also worth bearing in mind that when a tide is given a no “star rating” there can still sometimes be a few sections that will work. Depends on how keen you are!

Generally speaking, high river means good surfing from Newnham up to the Severn Bore Inn. Low river level is good news for the Inn to the weir. It can be up to 2 metres (6.6 ft) high.

There was a fear that a barrage would be built across the estuary in an attempt to harness the power of the tide and use it for creating electricity for the UK – 5% of the UK’s electricity consumption would be produced here claimed supporters of the plan…

The Severn Estuary Barrage which would ruin the bore tide or tidal bore in the Severn Estuary

The Severn Estuary Barrage - shelved for the moment

…  The feasibility report found it would be difficult to attract private investment and the project represented “high risk”. Moreover “it was expensive and I was not convinced it was the right way forward. Other low carbon options, like new nuclear power stations, seemed to make more sense. I am pleased that the Energy Secretary has also reached this conclusion,” said MP for the Forest of Dean Mark Harper.

As you can imagine, Environmentalists and seekers of surf were delighted too.

I am able to give you here an estimate of dates for 2011’s bore tide on the Estuary courtesy of the  Severn Bore site, but for the exact times of the occurrence please go directly to their site, remembering that the bore can arrive up to 20 mins. early or 30 mins. late depending on prevailing weather conditions.

  • February: 19th – 22nd
  • March: 20th – 22nd
  • April: 18th – 20th
  • May: –
  • June: –
  • July: –
  • August: 30th – 31st
  • September: 27th – 30th
  • October: 27th – 29th
  • November:  –
  • December: –

For the months where no bores are shown it means that no tides exceed 9.0 m at Sharpness and therefore no bores occur.

The bores happen both day and night and usually the tides of the equinox are the largest.

As you can imagine, and witness the video – surfing the Severn boretide is a very popular outing and it can get pretty crowded. However, surfing at night is not for everyone, just the regulars and it’s a pretty unique experience… although more popular in the summer months!

And we’ll end with another bore tide on another continent… South America this time, and the River Araguari in Brazil.

This rumbling bore tide, called the Araguari Pororoca, happens 3-4 days a month, twice a day at high tide, for 3-5 months a year. It is a boretide that has its origin deep in the heart of the Amazon Rainforest: the Araguari flows from the Tumucumaque mountain range 350km (218 miles) inland and flows south out into the Atlantic Ocean just north of the mouth of the Amazon by which stage many tributary waters have been collected along the way.

It starts working at 1.0m-1.5m (3ft-5ft) and holds up to 5m (16 ft) and over, running at 13 mph (21 kms). It is a totally epic wave for experienced surfers. Fast and powerful, you can test your surfing skills for about 500m.

Surfing through the jungle is a whole new experience – just watch out for those snakes!

While we’re in the vicinity of the Amazon and discussing tidal bores, I came across two interesting facts: the bore is the reason the Amazon does not have a protruding delta; the ocean rapidly carries away the vast volume of silt carried by the Amazon, making it impossible for a delta to grow past the shoreline.

And the other extraordinary fact: If the Pará river and the Marajó island ocean frontage are included as the mouth of the Amazon then the Amazon estuary is some 325 kilometres (202 miles) wide. By this criterion, the Amazon is wider at its mouth than the entire length of the River Thames in England!!! WOW!

If you want to surf this tidal bore be aware that it’s not that easy to get to which makes it even more of a challenge. You might witness local villagers watching this natural phenomenon in awe but you won’t see many of them, or anyone else, surfing the wave. An extreme vacation I think…

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