How a UK river serves as a natural lab for flood defence research

When you visit a lab, you don’t usually need to dodge sheep or muddy your shoes, but this lab is far from the norm. I am walking through farmland about 30 kilometers from Edinburgh, England. The air is clear and you can hear the babbling of the river as you approach.

I was guided by Mr. Chris Spray of the University of Dundee, England, to see this stretch of river known as Eddleston Water. Spray and his team began his study of the river in 2009, and since then a series of real-world experiments have been conducted on the river. They call it the ‘natural laboratory’ of river science.

Overlooking the ladle going in and out of the river in search of prey, Spray said the institute was originally set up to mitigate the flood risk facing Peebles, a town of 9,000 in the Eddleston waters. said it was.

Rather than building artificial dams, Spray and his colleagues wanted to find ways to reduce flood risk using nature-based solutions such as planting trees. More importantly, they also wanted to know how effective these methods really are. “Models are great, but we need real-world data to fully understand all the different factors that can influence these results,” says Spray.

Such methods, also known as natural flood management (NFM), are gaining attention. The UK government plans to double the number of UK flood mitigation and coastal erosion projects using NFM from 60 to 120. NFM is relatively rare, Spray said.

One of the big questions in hydrology is what happens when you bend a river, known as re-meandering. Many of Britain’s rivers have been artificially straightened to make room for roads and railways, which we now know also increases the risk of flooding. The idea is that by meandering the river again, it will be able to hold more water and avoid flooding.

But Spray’s team found that, at least in the Eddleston waters, repeated meandering alone doesn’t seem to have a significant impact on flood risk. This is because the floodplains surrounding the new winding rivers are not very large and cannot effectively store the water flooded by the excess rain. But that doesn’t mean there are no benefits, Spray says that river bends have huge benefits for ecological diversity.

For example, the researchers found an increase in the number of salmon spawning grounds where the river meander was resumed. That’s one reason the ladle is trying its luck in the river today, Spray says.

If you look closely at a river, you can see that the water flows in different ways. Water flows much faster in the bends, contains more oxygen, and can be home to a greater variety of insects. These parts of the river simply look more alive than the unrestored parts.

The researchers also studied a leaky dam, which was simply a wooden log placed across a river. In normal river flow, water passes under the logs, but as river levels rise, dams cumulatively slow the flow of water.

Spray showed me one of the dozen log dams lying along the river. Although they look messy and look more like rubble than human-laid objects, Spray says these haphazard logs probably had the greatest impact on Peebles’ flooding of any intervention ever tried. said. “You may not believe it when you see it, but it is a very easy and simple solution to reduce the risk of flooding.”

The research team not only investigated flood risk, but also quantified the financial benefits of the intervention. “Money talks,” says Spray. The researchers say NFM has helped him avoid £950,000 worth of flood damage in the decade since the first intervention was introduced in 2012. But far beyond this are the ecological benefits to the region, such as improved carbon storage and improved water quality. The team values ​​this at around £4.2m. “This is natural flood management that simply cannot be done by building flood defenses,” Spray says.

But nature’s lab comes with its own set of problems. Lab experiments aren’t perfect science, Spray says, and are often a compromise with dozens of landowners in the area. Spray said the team’s effort was scaled back from ideal because re-meandering would require a lot of space and farmers might have other plans for the land. “If landlords don’t want it to happen, it won’t happen,” he says. “We never force our luck.”

This also presents an even bigger problem with NFM. For the scheme to work across Britain, river professionals will need to develop closer relationships with landowners, Mr Spray said. But that is easier said than done and takes time. “We’ve been here for over ten years,” he says. “It took a hard fight to win the trust.”

One solution would be to pay landlords a fee to use the NFM, which the UK government is planning as part of its post-Brexit agricultural reforms, although details have yet to be made public. Spray hopes this will help spark interest in his team’s research. “But these techniques only work with the cooperation of the farmers. They have to be commensurate with their efforts,” he says.