The client asked our team to restore and stabilise Heligan’s historic waterway system to improve flood resilience, protect newly reintroduced water voles, and enhance the ecological and visitor experience across the Lost Valley.
Heligan Estate Leat Repair Works
Client Brief
The Lost Gardens of Heligan is a world-renowned botanical garden set on a steep hillside within the Mevagissey catchment. The gardens contain a carefully designed network of waterways that feed a series of ponds throughout the ‘Lost Valley’ and the ‘Jungle’, before finally collecting in a small dipping pond and flowing further down the valley. During a heavy rainfall event, a narrow leat connecting a small lake to the dipping pond failed, causing water to break through the bank. This diverted the flow away from the pond and increased the speed at which water travelled toward Mevagissey.
The Westcountry Rivers Trust is currently delivering a flood-mitigation initiative across Cornwall, also known as Resilient Catchment Communities, with Mevagissey identified as a high-risk coastal village. Partnering with Heligan was a natural fit, and together a plan was formed to reconnect and stabilise the water system.
The THRC Solution
This is where The Habitat Restoration Company became involved. With team members who had previously worked for both Heligan and the Rivers Trust, we understood the sensitivity of the site and the high standards required.
Our solution:
- Construct a natural weir further up the leat to act as an overflow during high-pressure flow events.
- Install a sluice to regulate water levels and activate the weir when necessary.
- Repair and re-clay-line the historic leat bank to prevent future failures.
- Dredge the dipping pond to increase its capacity and slow the rate of water entering the Mevagissey catchment.
This was a highly sensitive project, both due to working within public areas of Heligan and because of the site’s environmental importance, adding to this, water voles were recently released at Heligan. As one of the fastest-declining mammals in Britain, and now red-listed as critically endangered, they have vanished from around 90% of their former range.
To support their recovery, conservation organisations across the UK are implementing extensive habitat restoration and reintroduction programmes. These include improving riverbank vegetation, restoring fragmented wetland networks, and breeding water voles in captivity for release into secure, suitable habitats.
Because the waterways at Heligan are now home to these newly released voles, an ecologist from either the Rivers Trust or Heligan was on site throughout the works, continually surveying and advising to ensure all activity minimised disturbance.
We encourage you to visit The Lost Gardens of Heligan and explore the restored waterways in the ‘Lost Valley’. With a bit of luck, you may even spot a water vole enjoying the benefits of our work.
End result
A complex and sensitive job, working in a historic environment…
- Restored leat system to demonstrate historic functions and enhance visitor engagement on wider estate.
- Aid and improve existing habitats for local rare species populations.
- Maintain a ditch habitat and reduce pressure on constructed pond and culvert down stream.
- Increased local flood storage capacity at Heligan and contribute to mitigating flood risk down steam in Mevagissey.
- Reduction in peak flows, enhanced water quality leaving the site from sediment depositing.
