Bores on the Solway

The tidal bore on the Solway approached “…  with a hoarse and loud roar, and with a brilliance of phenomena and demonstration, incomparably more sublime than if the wide sandy water were densely scoured with the fleetest and the most gorgeously appointed invading army of horsemen; before the first wave can be descried from the shore, a long cloud or bank of spray is seen, as if whirling on an axis, and evanescently zoned and gemmed with mimic rainbows, and the rich tintings of partial refraction, sweeping onwards with the speed of a strong and steady breeze”. Gazeteer for 1848, p679.

So wrote a possible observer in 1848, seemingly carried away with the eloquence of his prose. Fifty years later, George Nielsen described the tidal bore approaching the River Eden “with great speed”; “the wave is white with tumbling foam; a great curve of broken surf follows in its wake; and the white horses of the Solway ride in to the end of their long gallop from the Irish Sea with a deep and angry roar”. And indeed, there are much earlier accounts of people being swept away and drowned by the bores that rushed up the rivers: in February 1216 followers of the Scottish king Alexander II, laden with spoils from pillaging Holme Cultram Abbey, were crossing the ford on the Eden when the incoming tidal bore overtook and drowned 1,900 men.

Red shows rivers mentioned; blue for Silloth, Moricambe and Torduff Point

The first time that I experienced the Solway bore I was actually out in the Firth just to the West of Bowness – standing chest-deep in the water, in a line of haaf-netters (see chapter 8 in The Fresh and the Salt, and the website for more photos), fishing for salmon. Distant Criffel had been blotted out by the rain that was beating in our faces, but a dark line with a wavering white crest appeared on our seaward side, moving upstream towards us and accompanied by a low roar. There was laughter, and a shout of ‘Whose idea was this, then?’, and we all hastily waded for the shore. It was not a large bore, perhaps only 30 centimetres high, but it seemed animate in its purposefulness, pushing on up the Firth. Behind it, the brown water rose quietly up the mudflat and spilled silently, frothy-edged, into the creeks. After the bore had passed, we carried our nets back into the water and resumed our fishing, shifting positions in the line as the incoming tide rose higher.

The second time I saw a bore was at Grune Point at the edge of Moricambe Bay: it’s only in retrospect that I understand what I saw – I was sitting on the edge of the saltmarsh with artist Lionel Playford, and as he sketched we were chatting about the patterns of stillness and turbulence on the water as the tide slowly rose in front of us. A shallow layer of water had covered the mudflats and was calm and glossy, when what seemed merely a low wave less than 10 centimetres high curved around the point and, itself unshowy but silvery, over-rode the smooth surface. It poppled against the saltmarsh’s edge and carried on past us up into the creek.

There are perhaps a dozen estuaries in Britain where a tidal surge, bore or aegir occurs, and even then they are not easy to predict, but the main requirements are that the incoming tide is funnelled into a narrowing estuary; that a big spring tide is due; and there should not have been much rainfall to swell the outflowing rivers. The Severn bore is the most famous, but others include bores at Arnside on the River Kent by Morecambe Bay, and on the Rivers Eden and Nith that empty into the Solway.

On the weekend of October 17th and 18th, 2020,  spring tides with ranges of about 10 metres were predicted, and rainfall had been (unusually) low for Cumbria and Dumfries & Galloway. Alerted by the hashtag #solwaybore, people were already posting photos and videos of various bores on social media: Stuart David captured images of kayakers by Burgh Marsh on the Solway; Paul Crabtree uploaded a video of the bore in the River Eden at the head of the Solway; Kate Parry had been picnicking by the River Wampool, which opens into Moricambe Bay (not at all the same as Morecambe Bay), when she had been surprised by a noisy bore; her phone video was subsequently picked up and shown by the BBC.

On the Sunday I too visited the Wampool and was thrilled to hear and see that bore for myself. The river was low, and a flock of gulls was resting and arguing on a sandbank down-river. Suddenly there was the sound of sighing and shushing, and the gulls flurried up onto the surrounding fields. And then it came – a glinting line of water, rushing inland. It wasn’t a single wave, but a train of several smooth wave-forms chasing the front-runner in orderly fashion. The leader hit the supports of the bridge, and split around them, then its edges swashed and broke noisily along the banks. But all the while the waves kept pace with each other, even as the front poured and rattled over a small shingle bed below the bank.

The leading edge spreads across the shingle

As with that Solway bore, the front pulled the tide behind it so that the water reached up the banks in minutes. Comparing the height against the bridge supports before and after the bore passed, nearly two metres of height had been gained in 10 minutes.nd the current, brown with sediment, raced on upstream, with lumps of tree-trunks and timber swirling on its back (see videos on the website). Brown foam spun in eddies below the bank and the sound now was of rushing, splashing water. How far inland did it travel? I wish I knew where its energy had fizzled out. It would be a fine thing to fly in a gyroplane on a day when a Solway bore was expected, and to watch the Upper Solway fill and spill into the rivers.

I’d naïvely thought that the bores would happen shortly after the tide turned, but this is not the case – and when you look at the map and see the areas that the Upper Solway includes, it begins to make more sense that the bores often occur much later in the tidal cycle, sometimes just before predicted high tide. To confuse predictions even further, the tidal cycle in the Upper Firth is far from cyclical – the ebb takes a disproportionately long period compared with the flow.

At Torduff Point on the Scottish side, for example, there are only 2-3 hours between low and high water – the left-hand side of the curve is very steep; the rest of the nearly six-hour cycle is taken up with the ebb. But at Carsethorn on the mouth of the Nith, and at Silloth on the west side of Grune Point, the six-hour cycle is fairly standard. (Note that the vertical scales are different for the two graphs below; these graphs, and those for other tidal predictions can be found here.)

To imagine the Upper Solway basin filling up evenly, like water in a bath, is wrong: there are the river channels, the sandbanks, the vast disc of Moricambe Bay, the friction created by the shallows and the scaurs, the hollows and channels around Port Carlisle …. I’ve waited at Grune Point during the big spring tide, waited for the tide to flood, knowing the time of low water at Silloth – and slowly, very slowly, a glimmer appears in a distant channel nearer the Scottish side; after two-and-a-half hours the sandy and muddy expanse of Moricambe Bay is still exposed, even though it’s only ‘just around the corner’ from Silloth. Then suddenly, after about three hours, the tide arrives, and rapidly fills the bay, bubbling and hissing at the edges of the sculpted mudflats and the small cliff-edges of the saltmarsh. And still it continues to flood in, until at least an hour-and-a half past Silloth’s high water time.

It is at that late stage that the dammed-up pressure of the tide suddenly overcomes the force of the outgoing fresh water from the rivers – and breaks through. So the bore on the Wampool exploded up-river at about the same time that high water was due at Torduff Point; the bore on the Eden – further to the North-East, also roared up-river at about the same time.

And as that bolus of water pushes up the river it forces the river’s flow to temporarily reverse; the turbulence at the edges sweeps up the sediment; sometimes the bottom of the leading edge is slowed by friction against the river bed so that the peak of the wave topples over into an aerated white crest. The dynamics of every bore, even in the same river, are always different, dependent on the relative flows of fresh and salt, the heights and the weather. It would be so easy to become addicted to looking for bores, to become a ‘bore bore’ …

Here are links to videos and blogs about the bores:

Stuart David on Twitter: the bore at Burgh Marsh, October 2020

Paul Crabtree: the Eden bore, October 2020 https://www.youtube.com/watch?v=YVxOV49RC5w&feature=emb_logo

Caerlaverock wetlands centre, the Nith bore: https://www.caerlaverock.org.uk/bored-of-isolationdifferent-perspectives-on-the-bore/

The Wampool bore: October 2020 https://thefreshandthesalt.co.uk/chapter-eight/

Mirjam Glessmer, The Arnside bore: https://mirjamglessmer.com/2019/07/31/tidal-bore-in-arnside/

Michael Berry, the Severn (and other) bores: https://michaelberryphysics.files.wordpress.com/2013/06/berry478.pdf 

Tide tables for Torduff Point: https://tides.willyweather.co.uk/dg/dumfries-and-galloway/channel-of-river-esk—-torduff-point.html

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