Wilstone Reservoir

A bit about Wilstone Reservoir-

Wilstone Reservoir is the largest of the four Tring Reservoirs in Hertfordshire. Built in 1802 to supply water to the Wendover Arm of the Grand Union Canal. It is now a designated Site of Special Scientific Interest (SSSI) renowned for birdwatching. Following major embankment strengthening works by the Canal & River Trust, the car park and scenic crest footpath have fully reopened with improved walking surfaces.

• Location: Tring, Hertfordshire (just off the B489)
• Size: 119 acres.
• Management: Managed by the Herts and Middlesex Wildlife Trust in conjunction with the Canal & River Trust.

• Birdwatching: Recognised as one of the best birdwatching spots in southern England. The reedbeds and open water attract a wide variety of resident and migratory species, including marsh harriers, bitterns, and breeding common terns.
• Walking: The area is famous for the Wilstone Reservoir Circular route. The upgraded dam crest path connects with nearby farmland and the Wendover Arm of the Grand Union Canal, making for a pleasant 2 to 3.5-mile stroll.
• Facilities & Access: The recently upgraded car park is located along the B489. You can find local visitor reviews, accessibility tips, and trail details on Free Time with the Kids or check Facebook for community updates and recent sightings.

Wilstone Reservoir improvement works-

The £6 million project to strengthen Wilstone Reservoir began in early 2025 and includes embankment repairs, culvert works, access improvements and habitat improvements.

• Access clearance and a temporary track were completed before the main works began.
• Piling started in summer 2025 to strengthen the embankments, with footpath diversions put in place and later closures to the car park and nearby road.
• By autumn, piling was nearing completion and work moved on to the collector drains, culvert repairs and resurfacing the embankment-top footpath.
• During late 2025, the nearby road gradually reopened, temporary stone was removed for reuse, and steps from the car park were replaced.
• In early 2026, work continued on the culvert, footpaths, car park surfacing and new seating areas along the south-west embankment.
• Most of the footpath and the car park were due to reopen in early April 2026, although a small section at the north-east end remained closed while culvert work finished.
• Main construction was expected to finish in spring 2026, with a short return visit later in the year to install a prefabricated culvert liner.
• Biodiversity improvements, including reed bed work and hedge planting, were planned after the engineering works.

Wilstone Reservoir forms part of the Tring Reservoirs Nature Reserve, a Site of Special Scientific Interest (SSSI) protected for its nationally significant populations of breeding and wintering birds. Originally constructed to supply water to the Grand Union Canal, the reservoirs have since become a well-known birdwatching destination in southern England.

The Tring Reservoirs Nature Reserve comprises four distinct lakes that were originally built to supply water to the Grand Union Canal.

The four reservoirs are:

• Startop’s End (or Startops)
• Marsworth
• Tringford
• Wilstone

Wilstone is the largest of the four reservoirs at Tring. It is up to 5.5m deep and has the capacity to hold over 1M mega litres of water. Together, its two 5m wide embankments that stretch for 1,350m, and range in height from 2m to 8m.

Following a 10-year statutory safety inspection, Canal & River Trust identified some seepage through the reservoir dam embankments in Hertfordshire. Ground investigations also revealed that the dam’s clay core had degraded.

The reservoir remained full of water while the works were carried out, so there was no disturbance to the fish in the reservoir. It also continued to feed water into the canal, and the water level continued to reduce gradually over the summer in the usual way.

There was still enough water for wintering wildfowl, while these works were being done, common terns and other species that rely on the reservoir, were not affected. Water levels were not altered artificially during the bird breeding season, so nests didn’t face any risk of flooding.

As normal, the reservoir will refill during the winter, outside the bird breeding season, so nests will not be affected. No permanent impact on the SSSI or on the wetland habitats, plants and wildlife is expected. The works do not require the water level to fall below its normal operating range, which is around two metres below weir level.

People Involved-

• Main Civil Engineering and contractor for the 6 million embankment strengthening project was KIER Infrastructure.
• Supported by SPI Piling Ltd, for the installation of the steel sheet piles.
• Canal and River Trust.

SPI Piling Ltd, were responsible for the piling work package, being delivered for the Canal & River Trust by its framework partner Kier Infrastructure and specialist contractor SPI Piling Ltd has now completed.

As part of the improvement work, SPI Piling Ltd, have installed a sheet pile cut-off that will prevent further leakage and safeguard the dam for the future.

The improvements are safety critical works that are required under the Reservoir Act, identified during an inspection in 2021.

SPI Piling Ltd, were invited early in the design and tender process, in order to better meet the objectives of the client. Not only did the client want a solution that simply “did the job” but were extremely keen to ensure that the final solution was one that not only had the correct performance characteristics, but one that could be delivered sustainably!

This early engagement has ensured the following benefits to the scheme:

• Working as a team to develop the bespoke design required for the scheme.
• Enhancing and building a better team-working ethic.
• Introducing best practice and innovations.
• Advice on buildability, sequencing and construction risks.
• Better delivery certainty from the outset.
• Collaborative approach on the selection of specialist plant and equipment in order to deliver the works, effectively.
• Collaborative approach, providing fixity on construction costs and programme.

At the start of this process, SPI Piling Ltd, demonstrated the effectiveness of Steel Sheet Piling as a sustainable solution, not only in terms of the product being supplied into the scheme, but also in terms of local impact during the works in respect of volume of traffic being much less than a concrete solution, but also in terms of project delivery.

Once the design solution was ratified by the client and their team, then SPI Piling Ltd, could get to work, in putting all the great words into practice. Immediately engaging with the supply chain on the biggest concern of all, the steel, Arcelor Mittal was selected to supply their materials based on their commitment to decarbonisation in the manufacture and supply of their off the shelf products.

The sheet piles themselves, were procured by SPI Piling Ltd, from Arcelor Mittal, Europes largest manufacturer of steel sheet piles. Piles from the ArcelorMittal’s EcoSheetPile™ AZ profile range were procured. These elements are manufactured through the Electric Arc Furnace (EAF) route, with relatively low CO2 emissions, compared to the average emissions for the global steel industry which is around 2.3 tonnes of CO2 per tonne of primary steel produced. The production of the EcoSheetPile™ Plus range emits as low as 409 kg CO2-eq. per tonne of steel produced.

This project is leading the way amongst others in understanding the benefits of the circular economy, reducing the wider impact on the environment and local communities by delivering best practice at all stages.

Industry leading choices, moving away from the traditional approach of costs over environment are being made at all levels, driving best practice first and foremost.

Focusing on feeding our vision of continuous improvement, eliminating waste, reducing carbon and reducing cost, the Early Design involvement is key to these successes.

We want our clients to know that it is not simply about “a pile that works”, and that it is very much more than that, and very much centres around maximising the benefits, whilst reducing impacts both socially and environmentally.

Starting early in July 2025, SPI Piling Ltd, began the installation of more than 2,000 piles that measure 7-10m long, through the dam crest at the top of the reservoir’s embankments, which together run for over 1.4km. These were driven into the dam’s underlying Gault Clay strata.

The work was carried out using land-based equipment, with cranes positioned around the perimeter of the reservoir to avoid the need to drain it.

The piles, up to 11m long were installed using the Kowan TOSA Still Worker, a sustainable solution providing remote access to installation and an environmentally friendly noise and vibration free methodology. Critically, and equally important, this method provides for an enhanced safety conscious installation when considering the already degraded structure and the risk that Vibration may have caused to it when installing the new cut off walls.

Other than the large crane jibs, visible for miles in the skyline, the local communities would not have known we were there installing these piles.

With all the upfront considerations, and the added benefit of bringing SPI Piling Ltd, in to provide Early Contractor Involvement the sheet piling element of the project completed 4 weeks Ahead of schedule, proving that if the entire project buys in to sequencing, methodology and material choices, the benefits to the project far outweigh, the conventional choices of cost over quality of services.

Other works following the pile installation works, are nearing completion being undertaken by Kier Infrastructure, including the reservoir’s washout culvert and drainage systems at the toe of the embankment.

We recently attended the opening ceremony to see the substantially completed works alongside the entire stakeholder teams, and were unanimously greeted with strong praise on the facts that the communities nearby were surprised that the piling works that they were advised of were undertaken in such a quiet and controlled manner, and in their words “we didn’t hear a peep”.

We would like to thank Kier Infrastructure for choosing SPI Piling as their Piling Contractor of Choice, and for their collaboration on the project, delivering critical infrastructure for Canal & River Trust.