How long till Inverness floods?
April 2007
SANDBAGS: There have been two flood alerts recently, when the council has laid sandbags to raise the top of the river bank at the most vulnerable points around Greig Street Bridge.
by Jake Williams
A year after Hurricane Katrina made a mess of New Orleans, it is more or less forgotten here in Scotland, except by folk who have relations there. There has been plenty spectacular stuff in the news, but it is fading from our memories.
But recently, I got a message from my friend Chris Brown who lives there. I had wondered if he was alive after the disaster, but I suppose he had more urgent business than writing to me. His letter is interesting reading. When the flood happened, he had to walk a few miles from his house to get to higher ground. At least the water was warmish. But he also knew that in places the force of water in the drains had pushed up the manhole covers, and they were open and deep. He would be in trouble if he stepped into one, carrying a heavy rucksack of stuff he had taken from the house, so he walked the whole way, through waist-deep water, pushing his bike in front of him.
I try to ignore the most horrible stuff in the news, but there’s something fascinating about natural disasters. I wonder when, and where it will happen in Scotland? There are some Scottish towns that have always been liable to floods. Elgin. Jedburgh. Perth. But Inverness is my pick for The One To Watch. It has a few factors that could combine at some time to create a really serious situation suddenly.
Inverness is right at the junction where three big bodies of water are constantly interacting. The river Ness has a catchment area of 700 square miles, and it all flows through the middle of the town. The Moray Firth ebbs and flows and it is funnel-shaped. The Beauly Firth reaches 10 miles inland, and as the mudflats fill and empty with the tides, all the water has to surge through the narrows between South and North Kessock.
In February 1989 the railway bridge that crosses the Ness near the harbour was washed away in a spate. Scotrail re-built it, then they and the Harbour Management Board spent a few years suing each other over whose fault it was. Everybody was surprised, and put it down to exceptional circumstances, but the weather and the tide were not much worse than what would be considered ‘normal’.
Estimates of the likelihood of another occurrence like that have varied, but my bet is on sooner rather than later, especially with the New Orleans experience. There are half a dozen factors that could add up to give what gambling folk call an accumulator: the Big One comes when a number of not-all-that-rare occurrences all coincide.
When there has been heavy rain the river Ness rushes through the town in spate.
A sudden spring thaw in the hills above Loch Ness can bring millions of extra gallons of water down the river.
The lower mile or so of the river is tidal. That does not mean that it is salt water, even at high tide. It just means that at times when the tide is high the river water has to queue up to get out to the sea, instead of tumbling down the wee rapids just upstream from the harbour.
When the wind is from the North-East, it pushes the sea into the mouth of the river, and makes the waves bigger. This is not likely to coincide with a sudden thaw, which would probably be accompanied by a west wind.
At the full moon, the high tide is higher than normal, which holds the river back; then the next low tide is extra low, so the extra water really rushes down past the harbour.
And every planet, not just the moon, has some tiny effect on the tides. Now and again there is an extra-high, high tide, when the moon lines up with some planet that normally has negligible effect on the tides.
Any of these factors is normal, they happen from time to time. And two or three of them might even occur at the same time. There have been two flood alerts in the last six months, when the council has laid sandbags to raise the top of the river bank by nine inches or so at the most vulnerable points around the Greig Street bridge. In September 2006, the sandbags were out because an extra-high tide was predicted, as the full moon coincided with the autumn equinox. Nothing happened, as the weather was warm and dry. Then in January 2007, there were warnings because of heavy rain, but the tides were normal and again the crisis passed off uneventfully.
But there is one other factor that promises to be a big contribution to the Big Flood, whenever that may happen, next week or in a hundred years time: the changes the humans are making to the firth. Just the same as they have done in New Orleans. Narrowing the river and especially the bit where it meets the sea. Building raised banks along the shore and the riverside: clearing whatever is left of the useless, messy, inconvenient, boggy, low-lying areas that are not dry land, but are not proper beach either.
Back to Hurricane Katrina…
There were towns along the coast that were not flooded as badly as New Orleans. Partly that’s because of the big river, but I am told that the pressure for development around the big city had encouraged more clearing of the natural vegetation, then further along the coast, and that left it vulnerable to influx of the water that the swamps could have absorbed.
Just like all along the shore at the Longman, where in summer 2006 they cleared a band of pines in the shadow of the Kessock Bridge, chipped them and dug out the roots for another half-acre of Business Park.
The difference between the map of the area in the 1950s, and the latest version from Google Earth, is striking. The Longman Industrial Estate has appeared, built on 50 years worth of domestic rubbish, bordered by some boulders which, in an alarming escalation in the last few years, are now heaped up into a rough seawall, a couple of feet higher than the new Waterfront Business Park that they are meant to protect. When they were making the place, the boulders were just an edging, like a hem, to defend the soft fill from the sea.
The New Orleans experience shows that they work well for a while, but as soon as water starts getting over or round or through them, they keep the water in where they were meant to be keeping it out. And when water does get over the seawall, it is now going downhill as it spreads inland so its force is greater, and the flood can come really suddenly.
The new octagonal building that’s appeared at Craigton Point, under the north end of the bridge, narrows that bit of the firth by one percent. Not much, but it could all add up.
The foundations of the bridge itself form two substantial islands that the tides have to flow round. The tides have gone out and in there for 100,000 years or so, and they intend to continue. If they have to get through a narrower gap than they’re used to, then the water will have to go faster. The stony beaches have been built up by silt and stones carried by the river and the firths, being dropped when the speed is not enough to keep on rolling the stuff along.
I do not know the critical water speed, but the sea might one day start taking all this material away again, to form beaches and spits and shingle and mudflats somewhere along the coast: maybe Whiteness Point, near Nairn, will start to grow again after being fairly stable for a century, at the expense of bits of Inverness getting swamped by the sea.
The most reckless of all is the new improvement to the harbour – a substantial breakwater which narrows the last big bend in the river before it reaches the sea. Who designs this stuff? And who appoints the ‘planners’ who uncritically allow the pending disaster to build up?
Here is what I think it would take to flood most of Inverness between The Longman and Clachnaharry.
One year, there is a full moon at the spring equinox (21 March). There has been some snow, and a sudden thaw coincides with torrential rain. Then, as the flood is making its way through the town, the mild west wind swings round to come from the north-east, and strengthens. The waves build up, and some come over the seawall into the industrial estate, at the same time as the river bursts its banks at Greig Street.
It might never happen.
JAKE WILLIAMS is a teacher, naturalist and folk musician with an extraordinary repertoire of songs.
This is an article from the April 2007 edition of Leopard Magazine. To read much more like this every month, see our subscription details.