Stirling University study shows dams mitigate flooding by acting like a sponge, storing and then slowly releasing water.
A population of beavers in Scotland that was blamed for flooding may actually be preventing it, a study has shown.
Dams built by beavers in eastern Scotland act like a sponge, experts say, and mitigate flooding by storing and then slowly releasing water.
The presence of the reintroduced animals also benefits the wider environment by improving biodiversity and lowering levels of agricultural pollutants, according to the study published in the journal Freshwater Biology this week.
The research comes after residents in Alyth blamed beavers for flash flooding in July last year, saying some of the debris washed through the village in Perthshire showed signs of being chewed by animals upstream. But in October, experts said beavers were not responsible and the flooding had been caused by heavy rain and a high flow in the river.
Now academics from Stirling University have studied streams draining from 13 hectares (32 acres) of farmland, and compared areas where beavers were known to be active against those where they were absent. In the 10 dams built by the beavers, the series of interconnected pools created by the animals was up to seven times richer in organic matter and had 20 times more aquatic plant life. The number of species in the surrounding area increased by 28%, the study showed.
Agricultural pollutants were also reduced as a result of the beavers, according to the report, with concentrations of phosphorus halved and nitrate levels reduced by 43% compared with areas where there were no beavers.
Dr Nigel Willby, of Stirling University’s school of natural sciences, said: “Beavers have been previously incorrectly blamed for flooding, particularly near Alyth where our study was conducted. However, all the beaver dams remained standing upstream of the floods during July and more recent flooding.
“Our work points to the fact that by having the beaver dams present on a stream, the floods are locally mitigated, as these dams store and slowly release water, unlike undammed, straight streams where water flows without obstacle.”
The researchers said ecosystem engineering by beavers in the form of dam-building might offer a natural mechanism for restoring degraded streams, but had to be weighed against the potential for occasional negative impacts on land use or fisheries.
Andrew Bauer, the deputy director of policy for the farmers’ union NFU Scotland, said: “Statistically, it was always likely that there would be small pockets of land where the environmental benefit might outweigh the considerable problems being caused.
“There is no indication where the 13 hectares mentioned in this case are, but any benefits seen in localised areas will need to be viewed by the environment minister against the damage being done to productive farmland, longstanding flood banks and established woodland on large parts of Tayside.”Naturalists confirmed last year that more than 150 beavers are living and breeding successfully in the wild in the southern Highlands after escaping from nearby private collections. Ecologists called a reintroduction scheme at Knapdale in Argyll an “outstanding success” after four pairs produced 14 young in five years.
Last year, Natural England agreed to allow wild beavers living in Devon to remain at large after a campaign by conservationists.