We can restart our computers with a simple ctrl-alt-delete, but how easy is it to do a full reset on a river? A year on from the completion of a three-year project on the National Trust’s Holnicote estate in Somerset, scientists say they’ve proven it can be done – and with impressive, lasting results.
In what was the UK’s first large-scale attempt to reset a river by reconnecting its waters with the surrounding floodplain, a 1.2km managed section of the river Aller was deepened and filled in. It transformed the area and created seven hectares – the equivalent of over 10 football pitches – of waterscapes and wetlands, which those behind the project say are vital for slowing water flow, storing carbon and providing homes for wildlife.
Almost immediately after completion in September 2023 the landscape was put to the test, during England’s wettest 18-month period on record. The newly rebooted area helped to slow the flow of water after several periods of heavy rainfall, helping to protect communities downstream from flooding.
“Trying any new technique is of course challenging but we need to be bold in order to tackle the climate and nature crisis,” said Ben Eardley, project manager at the National Trust. “We had just the worst winter you can imagine post restoration in terms of the number of storms and sheer volume of rain.
“But despite record-breaking conditions with high flowing water levels, the site responded really well …demonstrating the value of the restoration in providing resilience to hydrological extremes.”
Researchers from various universities worked alongside the National Trust on the project, monitoring water flow, water quality and changes to habitat.
“Ground water levels rose dramatically across the site, in some places by over a metre,” explained Dr Richard Mason from Umeå University in Sweden. “This allows the site to act as a large sponge or filter in the river catchment.”
He said the site had moved from a “very simple, static system with little opportunity for wildlife” to one with “significant dynamic complexity”, describing it as an “explosion in life”.
“Put simply, the system has moved from a very tidy area with little for wildlife to a messy complex jumble of waterscapes and diverse habitats that is full to the brim with a huge variety of plants and animals.”
Monitoring of the site has indicated improved water quality and reduced cloudiness, improving the habitat for fish and reducing the impacts of pollution from agriculture. The aquatic habitat has increased, researchers say, by almost 1,800%, with greater diversity ay of wetland habitat types.
Trying any new technique is of course challenging but we need to be bold in order to tackle the climate and nature crisis
“The speed with which the site developed into a diverse patchwork of habitats has been a real surprise,” noted Mason. “After only a few months, the river was already adjusting, creating deep pools, fast riffles [shallow places in rivers where water flows quickly past rocks], and a mosaic of wetlands, which will all support different plants and animals.”
The technique used is known as ‘Stage 0’ river restoration, and was first pioneered in Oregon, US. Rivers there to have received the Stage 0 treatment, including Fivemile-Bell Creeks, have proved to be more resilient to the impact of wildfires due to extreme periods of heat and drought, and have provided wildlife with areas of refuge. Experts say the technique only suits particular sites with certain characteristics, but is capable of reversing centuries of historic managed drainage.
Back at the UK site, fish now have access to a lot more space, which means more food, more shelter and the ability to move and survive if one part of the river is disturbed, for example at times of flooding.
“It’s an exciting time for river restoration,” said Mason, “and this novel technique has real potential for transforming our riverscapes,. What we learn from our detailed monitoring at this site will help river restoration techniques globally. I’m excited to see how the site continues to develop.”
A newly rich landscape for wildlife
Many species are now thriving as a result of the project, those behind it say. “The site has gone bananas in terms of the amount of wildlife and lush vegetation growth that we’ve seen,” enthused Jack Siviter, National Trust ranger at Holnicote.
“There is a huge variety of plants and trees starting to shoot up across the wetlands such as greater tussock sedge, which can grow to over two metres tall. Thanks to the increased wetted area we’ve seen loads of water-loving creatures like wild waterfowl, water voles, eels, lamprey, grass snake, trout, and birds such as red kite, buzzard, kestrel, sparrow hawk, swallow, swift and sand martin.”
The system has moved from a very tidy area with little for wildlife to a messy complex jumble of waterscapes
One particular species the team is monitoring as indicating a healthy wetland is the water vole, which there was limited evidence of at the site in 2023. Recent surveys by Derek Gow Consultancy have shown a dense population in the central area, with scattered signs of them moving throughout the new wetland.
“The new habitat is expansive, connected, and has started growing up wonderfully. With an abundance of their favourite food plants and a link to the surrounding water vole populations, they’ve ended up with a little slice of vole heaven,” said Hazel Reading, ecologist at Derek Gow Consultancy.
“Although 12 months in we can only really say it’s a foothold for now, I wouldn’t be surprised to see a big increase in their population in coming years.”
Matt Pang, catchment co-ordinator at the Environment Agency, a partner in the project and funder of part of the scheme, put the scheme’s success in the following words: “Less flood risk, more wildlife, plus some rare species – the results are mindblowing and we can’t wait to see what the coming years bring.”
Main image: James Beck and National Trust Images