Photos by Kier
Nestled next to Poole Harbour on the UK’s Dorset coast lies Arne Moors, a site of special scientific interest famed for its diverse and rare wildlife.
It is also the scene of a coastal adaptation project, with a £44m construction contract, to transform 150ha of low-lying grassland into a new diverse wetland. It’s an ambitious project, conceived to compensate for the loss of vital intertidal coastal habitats damaged by rising sea levels.
On paper, Arne Moors defies convention. Unique environments protected by international and national legislation don’t usually see any form of development, but here a three-year construction project aims to create new habitats on a large scale.
A key part of the project is the construction of 4,300m of new tidal embankments, set 500m further inland than the current fixed sea defences. Starting this autumn, the old embankments will be breached in three places – allowing the tide to flood into 78ha of land the size of 96 football pitches, creating vast new saltmarshes.
To compensate for the losses in other habitats within the site, a new 15ha freshwater environment, which involved the relocation of 6ha of turf, and two shallow saline lagoons have also been created. Once complete Arne Moors will open to the public as a nature reserve run by the Royal Society for the Protection of Birds (RSPB).
The Arne Moors project is both complex and unique. “Habitat creation projects like this come around once or twice in a career,” explains Neil Watson, coastal engineer and project executive with the Environment Agency. Its roots go back to the late 1990s when the Environment Agency started to look at changing shorelines in the Poole Harbour area. Its intertidal habitats, mudflats, saltmarshes and reed beds, were at risk from ‘coastal squeeze’, becoming trapped between rising sea levels and fixed sea defences.
“The agency has to provide suitable compensatory areas,” says Watson. “We knew we had to produce at least 44ha of intertidal habitat by 2030.” Fast forward to 2026 and it has been working with Arne Moors landowners the RSPB and Natural England on the project for a nearly a decade. Construction began in 2023 and, once complete, is expected to create enough intertidal habitats to enable development of new defences where needed for another 40 years.
Home to an array of wildlife
In terms of habitats, there are few places like Arne Moors. It is currently designated as a wetland of international importance, a site of special scientific interest and a special area of conservation for its rare mix of plants and animals. It’s home to water voles, sand lizards and adders, with more than 135 different bird species recorded on or flying over the site. “There are so many layers of complexity,” says Watson. “I always say this project is 80% ecology constraints and 20% civil engineering.”
Due to its protections, construction can only take place during the months of April and October. The team, which includes construction partner Kier, must work around different breeding seasons and create appropriate relocation habitats for wildlife before works can take place. Matt Phillips, senior project manager at Kier, says his team had more ecologists than engineers in the beginning “because we had to learn and understand the habitat”.
He says that once landscapes start to be changed wildlife is very quick to see new opportunities, with both Canadian geese and deer flocking to the site to eat newly planted vegetation. “What this highlights is the lack of suitable habitats in the UK,” Phillips adds.
Wildlife isn’t the only challenge. Arne Moors has a varied geological history, making ground conditions hard to predict. That coupled with managing water ingress, meant the project had to be adapted in some parts. Rachel Bennett MRICS, Kier’s managing quantity surveyor on the project says there were a lot of things “out of their control”. “We had to work to understand the impact as soon as possible,” she says.
“It involved a lot of working collaboratively between us the client, our suppliers and the other stakeholders.” Bennett adds that it’s been impressive to watch the site progress over the last three years. “A lot of people think of construction projects as damaging wildlife but that’s not the case here.”
But Arne Moors has not been without a vocal opposition, including from within the local community. Fears have been raised about the size of the site, an increased risk of flooding, noise, construction traffic, and congestion once the new nature reserve opens.
On balancing commercial needs of the project with compliance, Bennett says: "We made sure that the suppliers we wanted to use understood what we had to do and what our limitations were, like noise levels. And that was all covered in the subcontracts to get that compliance passed down the supply chain."
Watson says there have been valid concerns, but at times the agency has struggled to deal with misconceptions, some of which are still being voiced. Kier’s Phillips says the project was deliberately made “outward facing” so people could see the construction, learn about the habitat and the local amenities being created.
Despite its complexity, Phillips describes it as “the project that keeps on giving”. “You could never sit back and relax because there’s always something else that comes in and surprises us,” he says. In the ruts of an excavator the team discovered an incredibly rare plant, a three-lobed water crowfoot. They’ve also undertaken extensive seed collection for the millennium seed bank at Kew Gardens.
The team has helped to expand our knowledge of wildlife, tracking the adaptive nature of water voles and tagging a number of adders to monitor their movements. A flux tower has also been installed on the site that will measure how the saltmarsh stores carbon.
A recent study by Manchester Metropolitan University suggested one restored saltmarsh can store as much carbon in four years as a million new trees grown over 10 years. And while the project has been ongoing an archaeological team has discovered a 3,000-year-old Bronze Age wooden spade and a working pottery kiln, believed to be 2,000 years old.
Watson says the digs have given them so much more understanding of how the landscape has evolved over time, when it was once forested and why there’s peat and clay. “It’s always been a landscape that’s changed and the archaeological message has been the crossover between us and the community.” He adds that for him there’s a people legacy too. “A lot of the workforce has come from within 20 miles, and it’s been nice to offer something back.”
Kier’s Phillips says the project has been unique: “There won’t be another Arne Moors.” He adds that it will only truly begin its new chapter once they leave, when the embankments are breached and the tide comes in twice a day.
