Can beavers help reduce flood peaks?

There is growing interest in how beavers, with their natural ability to build dams and divert water, could help manage flooding © C. Scrimgeour, H. Devey
There is growing interest in how beavers, with their natural ability to build dams and divert water, could help manage flooding

A Lancaster University hydrologist is measuring how two beavers are diverting water onto a flood plain to help inform natural flood management research.

When Dr Nick Chappell heard about a project to introduce beavers onto a tributary of the River Lowther in Cumbria, he saw the opportunity to get valuable new data for a research project on floodplains that he is leading.

The research is informing how natural flood management measures on floodplains – such as building structures, breaching river banks or digging swales to hold back water – can reduce flood risk. Funded by the Environment Agency, it is part of a £40,000 project to quantify floodplain functioning, and linked to Lancaster’s £1.2m NERC-funded project modelling the effectiveness of natural flood management interventions at catchment scales.

Dr Chappell said: “Models are only as good as the measurements of hydrological change on which they are based.

“Very few observations of floodplain functioning are available on which to base models of natural flood management. Our project is using real data from real pilot sites to inform our models.”

There is growing interest in how beavers, with their natural ability to build dams and divert water, could help manage flooding. Dr Chappell realised the Lowther beavers provided a great opportunity for another pilot site.

He approached the Lowther Estate to ask if he could set up a monitoring station before the beavers arrived: they agreed.

‘While there has been monitoring of beaver sites in the UK before, this is the first time a site has been monitored from before the beavers are introduced, providing a better picture of the impact they are having on water flow and storage.

‘It all comes down to the volume of water, how much water can the beavers divert onto the flood plain and store there. What we want to do is to reduce the peak of significant flood events.’

Dr Chappell set up his monitoring station just after lockdown began, with two beavers – Dragonfly and Glen – being introduced into the secret woodland location later in the year.

Lowther Estate had already made preparations for the beavers’ arrival, creating a pond and building a small ‘lodge’ near to the stream to give them a head start.

“The beavers got to work quickly, building their own extension to the lodge, deepening the outflow, and eventually creating a 10m wide dam, the first in Cumbria for more than 400 years, which immediately began to divert water onto the flood plain.”

Dr Chappell’s equipment has been monitoring the streamflow every five minutes, along with the diversions to the flood plain, which he’s using to estimate the volume of water captured. Cameras have also been installed, which provide a visual record of the beavers’ activities and a way of checking the volume estimates.

So are beavers our secret weapon against flooding? He is impressed with the pace of Dragonfly and Glen’s activities but doesn’t want to exaggerate their effects.

“They are a great thing, and they attract people’s interest in nature-based solutions, but there are only two of them, so they are not going to stop flooding in flood-affected communities downstream by themselves. It’s now clear that beavers and other natural flood management interventions do work very locally, but you have to do loads and loads of them across even small catchments to have an impact. We need to get 10,000 metres cubed of water captured temporarily in flood events for every one square kilometre of catchment for real reductions in risk.

“For communities who are flooded by small streams, these sorts of interventions can make a difference and quickly. But to protect somewhere far downstream like Carlisle is going to take decades, needing all the tools in the box, not just green infrastructure, and it is going to cost a lot of money.

“But there are all sorts of other positives in having the beavers, such as putting woody debris back into streams and improving aquatic ecology: there are benefits in terms of water quality, as the water traps behind dams, it settles out unnatural levels of phosphorus and other harmful substances for river life.”

Heather Devey, from the Cumbria Beaver Group, has been visiting and filming the site regularly, noticing all the small dams and ponds and little waterways they have created.

“It has been absolutely incredible to see the impacts the two beavers have had. They’ve created more dams, they’re holding more water back in the landscape, they are flushing it out onto the flood plain and they’ve created more wet woodland. Wetland habitat is so important and it’s going to benefit a huge diversity of species come spring.”

The big test for the Cumbria beavers will be when there is next a major flood in the area. When a flood wave hits the dam, will the dam divert it, especially if it already has a lot of water behind it.

These are the sort of questions Dr Chappell hopes that his monitoring station will help to answer, and that beavers will become part of the arsenal of tools that we can use to protect communities against flood risk in the future.

The Cumbria Beaver Group is a partnership made up of Cumbria Wildlife Trust, RSPB, Lowther Estate and Eden Rivers Trust.

See rare footage of Dragonfly, the female beaver, in daylight, and some night time footage of one of the beavers at work on a tree. Plus the latest video report on how the two beavers are changing the landscape.

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