Lake Wood is part of Eddleston Water, a stretch of river near Peebles, UK
Colin McLean
When I visit a research lab, I don’t normally expect to have to dodge sheep or get my shoes muddy, but this lab is far from normal. I am walking on farmland about 18 miles outside of Edinburgh, UK. The air is fresh and I hear a river babbling as I get closer.
It is this stretch of river known as Eddleston Water that I have come to see, guided by Chris Spray at the University of Dundee, UK. Spray and his team began studying the river in 2009, and a series of real-world experiments have been conducted since then. They call it a “natural laboratory” for river science.
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As we watch a dipper float in and out of the river in search of prey, Spray tells me that the lab was originally set up to mitigate the flood risk facing Peebles, a town of 9,000 on Eddleston Water.
Spray and his colleagues wanted to know how they could reduce flood risk by using nature-based solutions, such as planting trees, instead of building artificial dams. More importantly, they also wanted to know how effective these methods really were. “Models are great and all, but only with real-world data can you get a full understanding of all the different factors that can affect these results,” says Spray.
Such methods, known as natural flood management (NFM), are gaining popularity: the UK government plans to do so to double the number of flood mitigation and coastal erosion projects in England with NFM ranging from 60 to 120. Nevertheless, the evidence base for NFM is relatively sparse, says Spray.
A big question in hydrology is what happens when you make a river more pliable, also known as re-meandering. Many of Britain’s rivers have been artificially straightened, freeing up space for roads and railways, but we now know that this also increases the risk of flooding. The idea is that by re-meandering rivers, a larger water volume can be retained and floods can thus be prevented.
Still, Spray’s team has found that, at least in Eddleston Water, remeandering alone doesn’t seem to have a major effect on flood risk. This is because the floodplain surrounding the new winding river is not particularly large, so the water that overflows due to excess rain cannot be effectively stored. But that doesn’t mean there aren’t benefits: A more winding river has huge benefits for ecological diversity, says Spray.
For example, the team found an increase in the number of salmon spawning areas in re-meandered parts of the river. This is one of the reasons why the dipper tries its luck in the river today, says Spray.
A closer look at the river also reveals the different ways the water seems to flow – it’s much faster on the more pliable stretches, which contain more oxygen and can give rise to a wider variety of insects. These parts of the river just seem livelier than the unrestored parts.
The researchers also studied leaky dams, which are simply logs placed across a stream. During a normal river flow, the water flows under the logs, but when the river level rises, the dams cumulatively slow the flow of water.
Spray shows me one of these dams, consisting of a dozen logs that span a stretch of the river. It looks messy, more like debris than anything placed by humans, but Spray says these haphazard logs probably had the biggest impact on flooding in Peebles of all the interventions they’ve tried. “You wouldn’t tell it by looking at them, but they’re such an easy and straightforward solution to flood risk reduction.”
In addition to looking at flood risks, the team quantified the financial benefits of its interventions. “Money talks,” says Spray. The researchers say NFM has helped prevent £950,000 worth of flood damage in the 10 years since the first interventions were installed in 2012. But this is more than offset by the environmental benefits to the region, such as improved carbon storage and increased water quality. which values the team at around £4.2 million. “This is what natural flood management can do that building flood defenses alone can’t,” says Spray.
But natural laboratories have their own problems. Spray says the lab’s experiments are often a compromise with the dozens of landowners in the area, rather than perfect science. Winding again takes up a lot of space and farmers may have other plans for that land, Spray says, so the team’s efforts have slimmed down from the ideal. “If the landowner doesn’t want it to happen, it won’t happen,” he says. “We’re not testing our luck.”
That also points to a bigger problem with NFM. To make it work across the UK, river practitioners will need to maintain closer relationships with landowners, says Spray. But that is easier said than done and takes time. “We’ve been here for over a decade,” he says. “We fought hard for confidence.”
One solution is to pay landowners to use NFM, something the UK government plans to do as part of its post-Brexit agrarian reforms, although the details have not yet been published. Spray hopes this will help increase acceptance of his team’s research. “But these techniques only work if you get farmers on board — you have to make it worthwhile,” he says.
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