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

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 30 kilometres outside of Edinburgh, UK. The air is crisp and I can hear a river babbling as I approach.

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. Working with the local environmental charity Tweed Forum, Spray and his team started studying the river in 2009 and it has been home to a series of real-world experiments ever since. They call it a “natural lab” for river science.

As we watch a dipper soaring in and out of the river in search of prey, Spray tells me that the lab was originally set up to cut the flood risk facing Peebles, a town of 9000 people, that sits on Eddleston Water.

Spray and his colleagues wanted to find out how they could cut flood risk using nature-based solutions, such as tree planting, rather than building artificial dams. More importantly, they also wanted to find out how effective these methods really were. “Models are great and all, but it’s only with real-world data that you get a full understanding of all the various factors that can affect these results,” says Spray.

Such methods, also known as natural flood management (NFM), are gaining traction: the UK government plans to double the number of flood reduction and coastal erosion projects in England using NFM from 60 to 120. But, despite this, the evidence base for NFM is relatively sparse, says Spray.

One big question in hydrology is what happens when you make a river bendier, otherwise known as re-meandering. Many of the UK’s rivers were made artificially straight, freeing up room for roads and railways, but we now know this also increases the risk of floods. The idea goes that re-meandering rivers allows them to hold a greater volume of water and so avoid flooding.

Yet Spray’s team has found that, at least in Eddleston Water, re-meandering alone doesn’t appear to have a major effect on flood risk. This is because the floodplain surrounding the newly bendy river isn’t particularly large, so can’t effectively store the water that overflows due to excess rain. But that doesn’t mean there aren’t benefits: a bendier river has a massive benefit for ecological diversity, says Spray.

For example, the team found an increase in the number of spawning habitats for salmon in re-meandered sections of the river. This is one of the reasons why the dipper is trying its luck in the river today, says Spray.

A closer look at the river also reveals the various ways in which the water seems to flow – it is far faster on the bendier bits, which contain more oxygen and can give rise to a greater variety of insect life. These parts of the river simply seem more alive than the unrestored sections.

The researchers have also studied leaky dams, which are simply tree logs placed across a stream. During normal river flow, the water passes under the logs, but when river levels rise the dams cumulatively slow the flow of water.

Spray shows me one of these dams, comprised of a dozen logs lying across a stretch of the river. It looks messy, more like debris than something placed by humans, but Spray says these haphazard logs have probably had the biggest impact on flooding in Peebles of all the interventions they have trialled. “You wouldn’t think it looking at them, but they’re such an easy and straightforward solution to cutting flood risk.”

Beyond looking at flood risk, the team has quantified the monetary gains of its interventions. “Money talks,” says Spray. The researchers say that NFM has helped avoid £950,000 worth of flood damages in the 10 years since the first interventions were installed in 2012. But this is far outweighed by the ecological benefits to the region, such as improved carbon storage and increased water quality, which the team values at around £4.2 million. “This is what natural flood management can do that simply building flood defences cannot,” says Spray.

But natural labs come with 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. Re-meandering takes a lot of space and farmers may have other plans for that land, says Spray, so the team’s efforts have been scaled down from the ideal. “If the landowner doesn’t want it to happen, it doesn’t happen,” he says. “We don’t push our luck.”

That also points to a bigger problem with NFM. For it to work across the UK, river practitioners need to foster 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. “The trust has been hard fought for.”

One solution is to pay landowners to use NFM, something the UK government is planning to do as part of its post-Brexit farming reforms, although the details haven’t yet been published. Spray hopes this will help increase the take-up of his team’s research. “But these techniques only work if you get farmers on board – you need to make it worth their while,” he says.