Misconceived sea defence measures will destroy 'machair,' says coastal zone expert
(Phys.org)—The traditional crofting way of life is under threat in Scotland's Western Isles because of a fundamental misunderstanding of how Atlantic wave action affects their coastlines, a University of Ulster academic has revealed.
Research published in the latest issue of the leading international journal Geology by Professor Andrew Cooper of the University of Ulster in conjunction with colleagues in the Universities of Aberdeen, Dundee and St Andrew's, has discovered that the beaches and machair of the Uists and Benbecula are an unusual type of "barrier island' that are more typical of coasts like those of the eastern USA.
Barrier islands survive by rolling landwards as sea levels rise and storms buffet the coast. Rather than being lost offshore, sand is conserved and pushed landwards, raising the surface of the islands as they move landwards.
However Professor Cooper is concerned that sea defence measures will prevent that process from taking place and will actually destroy the islands' fragile agricultural ecosystem.
"The great days of exploration and discovery may be over, but in the Western Isles we have discovered a whole new chain of barrier islands very close to home: they've been there all the time, but we had not previously recognised their true nature," he said.
"There is a continuous line of sand along the western coast of the islands - known as machair, a kind of flat sandy plain that is draped over the underlying rock. The machair is the main part of the islands that can be farmed, as the rest is rocky. It's seen as a cultural landscape, tied to the crofting lifestyle.
"When we took a close look at the beaches and machair, we realised that they are actually barrier islands. Barrier islands are long strips of sand with tidal inlets at either end, and they are separated from the mainland by a body of water."
In the Western Isles, Professor Cooper observed, the bodies of water tend to be quite shallow, and the tidal inlets are very small, but when you look at their overall shape, you can see that they are in fact barrier islands.
"It's an unusual setting in which to find barrier islands: normally, you find them on low lying coastal plains, not storm-battered rocky coastlines at nearly 60 degrees north. It is a very unusual set of circumstances that allows them to exist in the west of Scotland."
Recognising that these are in fact barrier islands is vital for their environmental management, he argued.
"Farmers that live and work on them have long thought that the islands are being eroded, with sand being stripped from them and carried out to sea," Professor Cooper said.
"Now, that we understand that they are in fact barrier islands, we know that that kind of erosion is not what is happening at all, Instead of sand being carried out to sea, it is in fact being push landwards – almost like rolling up a carpet. The sand is moving from the front of the barrier island to the back: over time, it gradually rolls in a landward direction.
"Unfortunately, following big storms in 2006, a lot of sea walls have been built along the seaward edge of the islands in the mistaken belief that they will stop erosion – in fact, they are stopping the barrier islands' natural tendency to roll landwards.
"Ironically, by stopping the sand from moving, being flexible, we are destroying the coastal environment. We think that by holding the sand in one place we are protecting the machair, but we're not.
"There is a lot of work that needs to be done in the area for people there to understand how barrier islands work, and to help them understand that for barrier islands, erosion is not a threat – it is the life blood of the islands. Without erosion and landward migration of the sands the islands are going to die. If you just put walls around them they will just get locked in and will eventually be submerged.
"That would spell the end of the crofting lifestyle for the thousands of people who live on the islands."
With this new understanding of how the coasts of the islands work, Professor Cooper hopes new environmental management strategies can be developed that will help – rather than hinder – the survival of the machair and the traditional lifestyles that depend upon it.
Journal information: Geology
Provided by University of Ulster