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Hold back the River: Can Cornish beavers prevent floods?

Posted: Monday 12th June 2017 by CornwallBeaverProject

Flow monitoring equipment set up at Woodland Valley

A lot of discussion surrounding beaver reintroduction is focused on the possibility that these animals can reduce the impact of local flooding events. Peter Cooper writes about how the Cornish project hopes to bring more answers to this question.

Have you noticed that our winters seem to be getting remembered not so much for frost or snow anymore, but for being a bit of a wash-out? Of course in Cornwall we don’t see much of the former weather at the best of times, but on a national scale, winters as a whole are getting warmer and wetter.

This in turn is likely to lead to an increase in serious flood events, and perhaps this was best epitomised by the storms of January-February 2014. While Cornwall was cut off from the national train lines when the sea smashed the rail line at Dawlish, mass flooding events were estimated to have cost the UK over £1 billion.

With each passing winter, and each flooded community, the calls to do something different to alleviate this increasing frequency of soaked-out living rooms grow louder. Natural flood management techniques are beginning to take priority in flood defence planning. Natural flood management aims to hold water back in river catchments, slowing the flow and keeping it out of properties. The government has pledged £15 million towards this, and would include work such as tree planting, restoring blanket bogs, and allowing river courses to naturally re-align.

As we scramble to figure out the best ways to work with the land to lessen the impact of flooding, perhaps the most intriguing method comes from – and given you’re reading this particular blog, you guessed it – beavers. To many, this may seem something of a contradiction. Surely an animal that builds a dam would just exacerbate flooding problems?

Undoubtedly, if a dam was built close to land use, be it farmland, private property or the like, this can happen on a very local scale (though experience in Europe shows there are ways of resolving this through mitigation). However, it’s all a matter of location, and upstream dams may actually prove very useful indeed.

Thanks to recent research just up-country (ie. Devon), Professor Richard Brazier and his team from the University of Exeter and the Devon Wildlife Trust have been studying an enclosed group of beavers in a very similar set-up to our Cornish project. What was once a very small stream has turned into a series of 13 ponds over 5 years, transforming a small wooded ditch into a wetland mosaic. The interest to flood defence comes from the fact that when dammed by beavers, these catchments become great sponges in the landscape and exhibit a significant effect on water movement.

Published research from Brazier’s team shows that the Devon dams hold back far more water than would otherwise be possible without the beavers’ engineering work. Crucially, they slow the flow of water leaving the site, reducing the chance of flash floods occurring. And when rain is lacking, they act as slow-release storage units that then replenish the flow (Puttock et al 2017).

Unfortunately these effects were only measured after the beavers had been released - how would water have behaved before they were present? This is a question we’re hoping to help answer at Woodland Valley Farm as hydrological monitoring started over a year ago. It is crucial to grasp a firm understanding of the relationship between beavers and flood management, and therefore we’re very pleased to be working with Richard Brazier’s research group to monitor both the before and after effects of beavers on water flow; a project which could have national as well as local implications.

For over a year, the team from Exeter have had specialised telemetry equipment installed at the site which monitors the flow of water as it enters and leaves the area, and will continue to do so for at least the next 5 years while the animals are doing their thing. Ladock, the village just downstream of the project, was among those places badly hit in the 2014 storms by flooding, so there is specific interest to see if any tangible effect can be detected. It will be fascinating to see whether the work of Cornwall’s first beavers in 500 years will be able to play some part not only in rejuvenating the environment, but actually providing a service to the local community.

References:

Puttock, A. et al 2017. Eurasian beaver activity increases water storage, attenuates flow and mitigates diffuse pollution from intensively-managed grasslands. Sci. Total Enviro. 576, 430-443.

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