Griff Rhys Jones has the privilege to ride the Severn Bore in his travels around Britain by River – Rivers A Voyage into the Heart of Britain – as seen on BBC.
“A bore is quite simply the sea tide coming up a river. As the incoming tide marches up the shallow estuary, it picks up pace and pressure. By the time it hits the more confined space at Sharpness, where the river has contracted to a mere mile wide, it has begun to lift up. The Severn fills like a saucer and the tide rises with incredible rapidity.”
It is difficult to calculate the number of bores in the world. I have read that there are sixty but also that there are ”over a hundred”. Both accounts concurred, however, on one matter. The Chinese may have the most spectacular, with a wave 20 feet high on the Hang Chou Fe River, but Britain has the biggest number: eight in one account and twenty in the other. I suppose it depends where the oncoming wave counts as a notable phenomenon.
The Severn has the largest of the UK’s tidal bores. According to folk tradition the Severn Bore occurs once a year on Good Friday – but folk were wrong because in fact there are two bores a day on 130 days of the year with the largest occurring around the equinox.
The factors that cause the Severn Bore begin far out at sea when the Atlantic Ocean hits the shallower waters of the continental shelf. The shelf slows the incoming tide and forces the waves up.
This tide then passes through the Severn estuary and into the river itself, where the width and depth of the channel decrease rapidly. This funnels the water into a truncated wave, which can travel up the river for over 25 miles at average speeds of between 8 and 12 mph.
The bore itself regularly attracts spectators but even this can be a dangerous activity. Once the bore passes by, those watching from the banks can enjoy two spectacles. First, the entire river will flow in the opposite direction to the way it should be going. Second, the river level will rise about an hour afterwards forcing spectators to run – or perhaps paddle – for the hills.
For myself I can remember seeing a wave about a foot high travelling up the River Camel opposite our home in Guineaport Road back in the late 50s or very early 60s. My Mum says it must have been in the 1950s when she was standing on the bridge facing towards the sea, looking at the river and generally taking in the view when she saw this wave coming towards the bridge, very small maybe two and a half to three inches tall, right across the river, the island was quite small back then, much much smaller than now. The wave wasn’t turning or curling and was going against the normal flow of the water.
Norman says he thinks he has seen something similar himself on the Camel Estuary. On his boat and coming in around the bend just before the new bridge. As he says the estuary gets rapidly narrower about here which might exaggerate the difference.
2019
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