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Gravel movement creates a varied river bed with deep pools, shallows and exposed areas of gravel. These provide habitats for fish and other species under drought, normal and flood conditions.
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Female salmon, prior to spawning, in the River Dee.
“The other thing to bear in mind,” explained Angus Tree, a freshwater adviser
with SNH, “is that when change happens in one area, it’s likely to have knock-on effects for some distance both downstream and upstream. “Unforeseen and unwanted side effects often occur some distance from the area where the river engineering is taking place. That may be costly for both neighbouring landowners and the natural heritage.” Scotland’s gravel bed rivers are certainly a significant feature in the landscape. Many are virtually household names and some are known the world over, particularly for the quality of their salmon fishing. They range in size and energy, depending on where they are and the local climate and underlying geology. Short, steep rivers, such as the Kerry and Nevis, flow to the west coast. Larger, more varied ones, such as the Dee and Tay, flow to the east.
“... battling against nature instead of trying to work with it will become increasingly futile.”
No matter what size they are, each of these rivers supports wildlife that’s specially adapted to an ever-changing environment. The Atlantic salmon, for instance, depends on clean gravel with plenty of oxygen for its eggs to incubate. And the complex lifecycle of the freshwater pearl mussel requires not only a healthy salmon or trout population, but also clean gravel with lots of oxygen in which to develop and live. “There have been some big impacts on Scotland’s gravel bed rivers through people altering them to try to provide flood defences,” added Angus. “Land managers have widened and deepened rivers by removing gravel to accommodate higher flows, they’ve straightened them to increase the speed with which they carry water, and they’ve built up banks to protect roads and buildings on floodplains.
“But if you remove gravel, for whatever purpose, it changes the shape of a
river’s channel, and you may end up with unexpected and sometimes alarming results. And climate change predictions of more frequent and larger floods suggest that battling against nature instead of trying to work with it will become increasingly futile.”
If you’d like to find out more about river management, then SNH and the Scottish Environment Protection Agency (SEPA) now have a number of publications on the subject. These are available through their websites and include SEPA’s Good Practice Guide – Sediment Management and Floods, Dredging and River Changes, as well as SNH’s Gravel Working in the River Tay System – A Code of Good Practice.
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www.snh.gov.uk
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