IT was good to see that some really quite extensive academic work on coastal erosion along Scotland was being referred to in The National, ahead of COP26 (Map bid to protect coasts, Aug 27).
However, the complicated, interactive nature of coastal erosion deserved far more detail for readers, and hopefully this will be attended to prior to COP26, not least to make readers more aware of both the economic and environmental costs of either defending the shoreline(s) or managing the retreat from them.
The article mentioned Montrose on the east coast, which has been subject to erosion of protective sand dunes for some time, and in the past large quantities of riprap have been carefully placed as a counter measure to such erosion of the dune shoreline.
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Put simply, the size, angularity, weight and overall thickness of any carefully placed random riprap protection will be directly dependent upon the average sea water level and its height above the beach level, and the height of the waves (crest to trough).
So, how has climate change affected the wave heights to date, the surges which raise the average sea water level at the time of wave impact, and the littoral drift by which means the beach is transported incrementally, variably, but persistently along the coastline?
Now the question of how much allowance must be made for increased sea level generally due to climate change, and allowance for greater surge heights, and greater littoral drift and further lowering of the beach, and over what period, must be addressed.
Nature ensures that any human intervention has an effect elsewhere up or down the coast, and any engineer will advise that whilst harnessing the forces of nature can be expensive, they are not usually as expensive as actually restraining the forces of nature.
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But so far that’s the easy bit, because hard solid defences on the shoreline become even more difficult to implement without dealing with close offshore water depths. Then we get to the really awkward bits, the estuaries, which for argument’s sake let’s extend to the upper tidal limit on connecting rivers. These often allow a funnelling of wave and sea energy up the estuary which often sites a city or similar on its banks.
These estuaries often have had some discrete flood defences installed or planned, and include for some planned sea level rise – 300mm for example – and statistically considered predicted surge. Specific and isolated locations can be economically defended from direct tidal flooding, but if a greater sea level rise is to be taken account of, the defences often change in nature and expense, and crucially are subject to a massive extension along the banks of both the estuary and rivers.
To put this simply, a limited sea level rise can be cost-effective at discrete locations along the estuary, but a significant rise above this level of increase starts to make the installation of a cross-estuary tidal barrier possibly as cost-effective, as other benefits often accrue, but this can also raise other issues of adverse effects.
There was an amount of £12 million noted in the article, which in no way suggests the huge costs of restraining nature or indeed retreating from it. Nor was there any connection to how Scotland could, and if it should, “rewild” the inshore three-mile limit, and whether the littoral drift could be positively amended by such activity, as part of an overall flood defence strategy.
Whether such activities include for the revamping of smaller fishing harbour facilities along the coast is not clear, but At a rough estimate I would suggest that earmarking the UK funding for the UK replacement ferry service bridge between Scotland and Northern Ireland would be a good starting point. For the avoidance of doubt that’s the bridge that would traverse the UK munitions dump in the Beaufort Dyke.
If Scotland is to be an independent EU nation state, these matters need to be addressed, and soon – possibly in outline as soon as before May 4 2022, and/or indyref2.
Stephen Tingle
Greater Glasgow
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