A UK first for Somerset as Exmoor river floodplain restored
Somerset Rivers Authority is backing the UK’s first large-scale project to reconnect a river to its original floodplain.
Work is underway along part of Exmoor’s River Aller on the National Trust’s Holnicote estate in West Somerset.
The project’s ambition is to create a better, more resilient place for nature and people, using a ‘Stage 0’ restoration approach successfully pioneered in the United States (this approach is described in detail below).
Part of the National Trust’s multi-million-pound Riverlands initiative, the project is being led by the National Trust working together with the EU’s Interreg 2 Seas Co-Adapt programme and the Environment Agency.
The project is being part-funded by Co-Adapt, the Environment Agency, Somerset Rivers Authority (SRA), the Green Recovery Challenge Fund and Frugi.
It follows a successful 2019 pilot on a tributary of the Aller, in the area between Selworthy church and the A39, which was also part-funded by Somerset Rivers Authority.
The initial 2019 trial is now being scaled up to embrace 15 hectares of the main river Aller and its surrounding Exmoor landscape.
The project will benefit wildlife by creating new habitats and rejuvenating the local area.
It will help to tackle the impacts of climate change by holding water in the landscape.
Slowing the flow of water will also help to reduce flooding downstream in places such as Allerford and Bossington.
The ‘Stage 0’ approach to river restoration
The approach being taken is known as ‘Stage 0’ [0 = Zero] after an influential academic analysis by Dr Brian Cluer and Professor Colin Thorne of the way that rivers have evolved over long periods of time. Put very simply, ‘Stage 0’ is the name given to the state of affairs at the beginning of a long cycle when streams and rivers have channels that branch out naturally, before they later get modified into single channels.
Again put very simply, their aim is to restore the kind of natural conditions that might have existed before.
Experiences in the State of Oregon show that when river systems are restored to ‘Stage 0’, natural processes and habitats can be recovered.
In many cases – for example at Fivemile-Bell – this leads to a slower-flowing river system with many smaller channels, pools and riffles, and valuable wetlands that support a much richer diversity of flora and fauna.
‘Stage 0’ restoration sites in the USA have also proved resilient to the impact of fires brought on by recent extreme periods of heat and drought. They have provided wildlife with areas of refuge.
The River Aller project is the first time that ‘Stage 0’ techniques have been used on a large scale in the UK.
Ben Eardley, project manager for the National Trust, said: “We now have a tried and tested method to start reversing the damage done to our rivers.
“‘Stage 0’ floodplain reconnection completely resets natural processes – it’s like the ‘ctrl, alt, delete’ equivalent of a computer reset – and lets the river decide what it wants to be.
“By seeing the river and its surrounding landscape as a whole, we can build resilience and boost biodiversity.”
The first stage of the project has seen shallowly-skimmed areas created through earthworks carefully designed to ‘reset’ the valley bottom and allow for a natural river flow. Around 4,000 tonnes of soil have been moved on site: no material is being brought on to, or taken, off site for this restoration.
600 tonnes of large timbers have been pinned or partially buried into the floodplain so that habitat restoration can be ‘fast-tracked’. These timbers came from non-native tree species clear-felled on the Holnicote estate.
Woody debris helps to slow flows, and develop more hydrological and ecological diversity.
Floodplain wildflower seeds such as ragged robin, devil’s-bit scabious and meadowsweet are being sown this autumn.
In spring 2023, further habitat-enrichment work will include the planting of about 25,000 native trees such as willow, bird cherry and black poplar.
Ben Eardley said: “The river will no longer run along a single channel but form part of a complex waterscape with channels, pools, wetland and marshes.
“This helps slow the river flow to help combat flooding and drought events as well as well as increasing wildlife and tackling the impact of climate change by holding water in the landscape.
“By creating these new wetlands, they will not only hold more water during floods or drought but also effectively store carbon.
“So, the river catchment will be better able to cope with extreme weather events or changes in climate. And it also rejuvenates the surrounding landscape.”
Riverside habitat improvements will help to support more wildlife including aquatic insects such as dragonflies, fish such as brown trout, grass snakes, birds, bats, water voles and otters.
Ben Eardley concluded: “Careful monitoring of this pioneering project will guide future floodplain reconnections in the UK and abroad.
“It’s a nature-based solution that you can literally see in action.”
Councillor Mike Stanton, Chair of Somerset Rivers Authority (SRA), said: “The SRA has part-funded lots of Riverlands activities on the Holnicote estate, including the successful 2019 ‘Stage 0’ pilot. This latest project is the biggest and most exciting yet. It offers Somerset new possibilities for reducing flood risks, improving water quality and creating bigger and better habitats for wildlife.
“We must and will learn from this initiative with respect to other places in Somerset, and other schemes the SRA is funding.”
Somerset Rivers Authority is part funding an extension of the River Aller project upstream at Tivington Farm.
Elements of the ‘Stage 0’ approach to restoration have also already been adopted for SRA-funded projects at Marston Park and Witham Friary near Frome, but it is important to note that ‘Stage 0’ cannot be achieved everywhere if there are topographical constraints or if property or existing infrastructure would be put at risk.
One reason the National Trust has been able to go ahead with the River Aller project is that its Holnicote estate is 12,000 acres, so it owns the necessary space.
The Trust’s team at Holnicote have been working with Professor Colin Thorne, Chair of Physical Geography at Nottingham University, on developing a ‘Stage 0’ approach that will work in the space available.
Professor Thorne said: “Around two dozen streams and rivers in the US State of Oregon have been successfully restored as complex and fully-connected channel-wetland-floodplain systems known as Stage ‘0’, producing remarkable benefits to river health, heritage, wildlife (including key species), sustainability and resilience.
“The outcomes of these restoration projects in Oregon coincide with the aims of the Riverlands project and it is really exciting that the first ‘Stage 0’ restorations in the UK are now being planned and implemented at the Holnicote Estate, as part of the Riverlands project.”
Dr Stewart Clarke, National Trust specialist – Freshwater, Catchments & Estuaries, said: “We are creating the best possible conditions we can for the river to adapt and respond to whatever comes its way in the face of more severe and regular floods and droughts predicted with climate change.
“Wildlife is declining even faster in fresh water than on land or in the sea due to factors such as pollution, centuries of river modification and invasive species. Our efforts here must focus on actively adapting these landscapes to future flood and drought, recognising the floodplain as part of the river and finding the best ways to manage land beside rivers. We are embracing the latest evidence and trying out new techniques, leading the way and working with others in the adoption and promotion of ‘Stage 0’.”
Harry Bowell, Director of Land and Nature at the National Trust said: “This innovative work to explore techniques on how to make our landscapes more resilient to climate change is absolutely critical as we tackle both the nature and climate crisis, over the coming years.
“Working in partnership, and at pace, with bodies like the Environment Agency is exactly what we need to be doing more of as we face into these challenges. This project is a fantastic example of how this can be done through our collaborative efforts.”
Matt Pang, Environment Agency Catchment Coordinator, said: “The Environment Agency is really excited to be involved in the work being delivered by the National Trust across the Holnicote Estate.
“The River Aller Floodplain Reconnection scheme allows us to test the new ‘Stage 0’ river restoration concept at a larger scale. It should achieve a range of outcomes for the environment including increasing habitat diversity and biodiversity, reducing flood risk for downstream communities, and making the river more resilient to the impacts of climate change.
“We hope this project as a whole will significantly contribute towards achieving targets for nature recovery and climate change at a landscape scale, and provide vital evidence towards restoring natural processes in our river systems.”