Heligan Estate: Repairing a Historic Leat to Slow Water Towards Mevagissey

Working in a Historic and Sensitive Site

The leat was both a historic feature and part of Heligan’s managed water system. That meant the repair had to be practical, but it also had to sit properly within the character of the gardens.

The site was open to the public while the works were taking place, so access, safety and presentation all mattered. The footpath was temporarily closed and diverted while we moved machinery and materials into position, then reopened as soon as the main machinery was off the path and we were working down in the leat itself.

There was also an ecological watching brief throughout the works because water voles had recently been released into the wider waterway system at Heligan. That added another layer of care to the job. We were working around live water, within important habitat, and in a public garden where disturbance needed to be kept as low as possible.

Getting Machinery Into Position

One of the hardest parts of the job was simply getting the right equipment into the right place.

The leat was narrow and awkward to access, so a mini excavator had to be lifted into position using a larger excavator. From there, most of the more detailed work was done with hand tools, a dumper truck, and a lot of careful manual work.

This was not the sort of job where you could just drive machinery in and start digging. Every movement had to be thought through: where the machine could sit, how materials could be brought in, how the public route could be protected, and how we could avoid unnecessary damage to the surrounding garden and wetland habitat.

The weather made things harder. Conditions were poor throughout, and severe flooding arrived almost immediately after the works were finished. In one sense, it was not ideal. In another, it meant the repaired system was tested straight away.

Repairing the Leat and Rebuilding the Bank

The failed section of leat was repaired using externally sourced puddling clay, coir rolls, coir matting, and natural site-won materials to rebuild and stabilise the banks.

The clay lining was puddled by hand. It is slow work, but it was the right approach for this setting. The aim was to create a watertight repair that still felt appropriate within the historic garden landscape, rather than introducing a hard, engineered-looking solution.

Upstream of the main repair, we created a temporary barrier and diversion so the work area could be managed safely. Timber and steel plates, straw bales, signage and public barriers were used to control water, protect the work area and keep visitors safely away from the active site.

The bank was then rebuilt and finished using the clay, coir and site-won material so the leat could once again carry water along its intended route.

Sluice, Overflow and Natural Weir

A new sluice was installed to help regulate water levels within the system.

The sluice was built from a steel frame with solid oak timber sleepers and concreted into position. It was designed to give better control over water movement and allow the system to respond during higher-flow events.

Further upstream, we also constructed a natural weir using stone won from site, clay, coir matting and other available natural materials. The purpose of the weir was to act as an overflow during periods of higher pressure, helping to manage water without forcing everything through one narrow point.

This was the balance of the project: repair the historic leat, but also make the water system more resilient than it had been before.

Dredging the Dipping Pond

The dipping pond had also become silted, reducing its capacity to hold water.

Using an excavator, we dredged the pond and placed the material in a pre-determined excavated area below the pond. Getting the excavator into position was one of the more awkward parts of the job, but increasing the pond capacity was important.

The restored pond now has more ability to hold water before it continues downstream. That helps reduce pressure on the leat, the pond system and the culvert further down the valley.