Project sees ten football pitches of new waterscapes and wetlands
A ‘river restoration technique’ which was first pioneered in America is being hailed as a success for the Holnicote Estate in Somerset following the reconnection of a section of a river to its flood plain.
The three year project has been described as a ‘ctrl alt delete’ for the river and was the first large-scale attempt to reset a UK river to fully reconnect its waters with its surrounding floodplain.
It was achieved by straightening and deepening a section of the River Aller which extended more than one kilometre. The goal was to create seven hectares of waterscapes and wetlands – that’s equivalent to more than ten football pitches!
A priority habitat for nature, wetlands are extremely important to not only slow the flow of water and to hold it during times of drought, but they are also significant for their ability to store carbon and act as homes for wildlife.
Experts say more than 90 per cent of wetland habitat in the UK has been lost in the last 100 years. They add that more than 10 per cent of our freshwater and wetland species are threatened with extinction.
The project was ‘put to the test’ shortly after the project was completed – in the midst of England’s wettest 18-month period on record.
The project team at Holnicote say their work helped to protect local communities downstream by slowing down the flow of water after several heavy rainfall events. It also improved the immediate area for wildlife.
One year on from the creation of the new wetlands on the Holnicote Estate cared for by the National Trust, nature is thriving. Image: View It 360 (provided by The National Trust).
‘We need to be bold’
‘Trying any new technique is of course challenging but we need to be bold in order to tackle the climate and nature crisis,’ says 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 it being record breaking conditions with high flowing water levels, the site responded really well, increasing the ability to store water within the site and lessening downstream storm flows, demonstrating the value of the restoration in providing resilience to hydrological extremes.’
To help the National Trust understand how the site has developed, researchers from several universities have been involved with monitoring water flow, water quality and changes to habitat.
Dr Matthew Johnson from Nottingham University and Dr Richard Mason from Umeå University in Sweden have been working to understand the changes to the water table and development of the river channels and habitats.
‘Ground water levels rose dramatically across the site, in some places by over a metre,’ explains Dr Mason.
‘This allows the site to act as a large sponge or filter in the river catchment, helping to store winter flood water, reducing flood risk downstream and releasing cleaner water more slowly in the drier months to help alleviate drought conditions.’
‘The twists and turns and numerous flow paths that are now present in the floodplain as the water wends its way over the site through thick vegetation, act as a filter to capture sediment eroded from upstream.’
‘Benefitting fish and other aquatic species’
‘The development of habitat to include faster flowing riffles and gravel beds has also been key for benefitting fish and other aquatic species.’
‘The site has moved from a very simple, static system with little opportunity for wildlife to one with significant dynamic complexity which has seen 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.’
Dr Alan Puttock and Professor Richard Brazier from The University of Exeter were able to discuss how teams were able to use drones and sensors to monitor changes in the river flow rates.
They explained that the results found that less water is leaving the site and at a slower rate during the storms. They add that these types of restoration projects can really help downstream communities which are at risk of flooding.
They say the results mean there is the potential for allowing rivers to reset themselves to function naturally by allowing water to find its own pathway across a floodplain.
Other results from the monitoring of the site reveal a reduction in levels of fine sediment further downstream of the site. This improves the habitat for migratory fish and reduces the impacts of pollution from agriculture.
Water quality monitoring showed a reduction in the cloudiness of the water which experts say shows that the site is trapping and storing sediment.
And improvements to water quality may explain why teams noted a significant increase in the ‘aquatic habitat’ of the area where more wildlife have been attracted to the site.
Experts say water quality and clarity has improved in the River Aller in the new area of wetlands created by the river restoration project. Image: View It 360 (provided by The National Trust).
‘Developed into a diverse patchwork of habitats’
‘The speed with which the site developed into a diverse patchwork of habitats has been a real surprise,’ says Dr Richard Mason.
‘After only a few months the river was already adjusting, creating deep pools, fast riffles, and a mosaic of wetlands which will all support different plants and animals.’
‘What amazes me is the amount of wetland habitat created; the river has transformed from a pipe into a sponge.’
‘When you look at the river upstream or downstream it’s still a small stream, a few meters across. It’s the same amount of water, it’s just that it is stored for much longer and it’s great to see how quickly it’s benefiting people and nature.’
‘Connecting rivers to their floodplains is really important for many reasons. At this 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.’
‘Furthermore, access to connected wetland habitats is important to young fish and critically lacking in the UK landscape.’
‘It’s an exciting time for river restoration and this novel technique has real potential for transforming our riverscapes, helping animal and plant life and increasing resilience to climate change.’
‘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.’
Recording the benefits to wildlife
Alongside the various studies, the local team have also been recording the benefits to wildlife.
‘The site has gone bananas in terms of the amount of wildlife and lush vegetation growth that we’ve seen,’ says 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 meters tall. This will provide a rich landscape for wildlife to thrive within.’
‘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 martins, swifts and swallows are all using the site for feeding and nest building, while the birds of prey are using the site for foraging – which is in part due to the rewetting but also the longer sward.’
‘The constant supply of water has also resulted in the site being very green and lush with thousands of wildflowers like wild carrot, providing food for pollinators.’
‘As a consequence, we’ve seen raptors such as kestrels, herons and deer and even barn owls.’
The site has seen such an increase in insect life that at times there have been so many swallows the effect has been a feeding frenzy with hundreds and hundreds of birds swarming to feed on the abundance of food.
Dense population of water voles colonising a central area
‘One of the coolest species we’ve seen is a green sandpiper – which is a great indicator species for healthy, lowland wetland habitat.’
A particular species that the team are monitoring for signs of the site developing to be a healthy wetland habitat is the water vole.
In 2023, there were only limited signs of water voles and only along the edges of the restored section, while the habitat was being established.
However, recent surveys carried out by Derek Gow Consultancy have revealed a dense population colonising a central area, with scattered signs of them moving throughout the new wetland, showing that they are happily exploring their new habitat.
‘The restoration area started as a linear ditch with patches of suitable water vole habitat along it,’ says Hazel Reading, Ecologist at Derek Gow Consultancy
‘This patchiness can limit the voles’ ability to migrate and find the best seasonal food, or even each other, without risking predation.’
‘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.’
‘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!’
Environmental response to restoration exceeded expectations
The Environment Agency were also a partner in the project and funder of part of the scheme.
‘One year on and the environmental response to the River Aller restoration exceed expectations,’ says Matt Pang, Catchment Co-ordinator at the Environment Agency.
‘A rich and diverse wildlife haven has exploded from this back-to-basics, nature-based approach and the wider environment is better for it.’
‘Less flood risk, more wildlife, plus some rare species – the results are mind blowing and we can’t wait to see what the coming years bring.’
The teams say that the project has been made possible thanks to the Interreg 2 Seas Co-Adapt programme and the Environment Agency.
Both organisations have helped fund the project together with the Somerset Rivers Authority (SRA), Green Recovery Challenge Fund and Frugi.
Careful monitoring of this pioneering project will now continue to further understand how the topography develops as well as the ecology of the site.
The project was part of the National Trust’s multi-million-pound Riverlands’ project which was announced in August 2018 and aims to support five river catchment schemes around England and Wales.
