What works are planned at Wilstone Reservoir?
Following a 10-year statutory safety inspection, the Canal & River Trust is planning to strengthen the clay core embankments of Wilstone Reservoir, near Tring in Hertfordshire. Improvements will also be made to the reservoir’s washout culvert and drainage systems at the toe of the embankment.
Over two thousand 11-metre long sheet piles will be driven into the reservoir’s embankments, which together run for 1,350 metres. The work will be carried out using land-based equipment, with cranes positioned around the perimeter of the reservoir to avoid the need to drain the reservoir.
Why are these works necessary?
These are statutory safety works required under the Reservoir Act, identified during an inspection in 2021.
Who is carrying out the work?
The engineering work will be undertaken by our engineering contractor Kier.
How much will it cost and who is paying for it?
The cost of the works is estimated to be over £6 million and the work is being paid for by Canal & River Trust. The Trust cares for 71 large reservoirs, some of the oldest in the country and among the oldest of their type in the world. There’s more information about our reservoirs on our Reservoir Works and Water Resources webpage
How long will it take?
The project will take around 15 months, with site preparation and vegetation works starting mid-January, and the main construction phase starting in May 2025 and ending March 2026.
Will any footpaths be closed?
We’ll need to close the footpaths and the car park at Wilstone Reservoir. The footpaths around the other three reservoirs at Tring will remain open, and the car park at Startop’s End Reservoir, next to the Water’s Edge Cafe will remain open.
Will any roads be closed?
The project team is actively working to avoid or minimise any lane closures, but it’s possible we’ll need to close some local roads during part of the main construction phase in August.
Will any wildlife be affected by the works?
Wilstone Reservoir is part of the Tring Reservoirs Nature Reserve SSSI, designated for their nationally important assemblage of breeding and wintering birds. Originally built to supply water to the Grand Union Canal, the reservoirs are now one of the best birdwatching spots in southern England.
We’re planning to use a silent/press piling machine for most of the work to minimise disruption to wildlife and local people. Hammer piling will be restricted to the minimum necessary (up to seven weeks) and noise barriers will be set up to limit disturbance to wildlife. All piling works required are at the reservoir's northern end, away from the most sensitive reedbed habitat for nesting birds at the reservoir's southern end.
The reservoir will remain in water, so there will be no need for a fish rescue. During the construction works, the reservoir will continue to supply water to the canal, and the water level in the reservoir will slowly reduce throughout the summer, as is usual.
There will still be water for the wintering wildfowl, common terns and other birds and animals that rely on the reservoir. And there will be no unnatural changes in water level during the bird breeding season that could put bird nests at risk of being flooded.
The refill of the reservoir will occur, as is usual, during the winter months, outside of the bird breeding season, ensuring there will be no damage to bird nests. It is unlikely that there will be any lasting effect on the SSSI designation and associated wetland habitats, plants and fauna that are reliant on maintenance of water levels. The construction works do not require the reservoir level to be reduced beyond its normal operational range, which is approximately two metres below weir level.
Will any trees be cut down?
Unfortunately we do need to reduce the height of around 635 metres of hedgerow and fell nine small/medium sized trees to create access space for construction plant and materials. All vegetation works will be completed outside of the bird breeding season (by end of Feb 2025), and checks for wildlife will be done before the start of works.
Once the works are completed, a series of biodiversity improvements are planned to mitigate the habitat loss, including reed bed enhancements, tree planting within the Wilstone Reservoir nature reserve area and gap planting in the reservoir’s hedgerows. This planting will add a mix of British native plants in keeping with the local area, such as Hawthorn, Blackthorn, Crab Apple, Dog Rose, Common Dogwood, Red Dogwood, Field Maple, Guelder Rose, Hazel, Spindle, Sweet Briar Rose and Wayfaring Tree.
A 15 metre buffer strip of reedbed will be cut back to deter nesting birds within an area that could experience disturbance from piling and crest raising works and other machinery noise. This strimming work will be done in February before the nesting season.
What will the working hours be?
The standard working hours for construction activity will apply 08:00 to 18:00hrs Mondays to Fridays and 09:00 to 13:00hrs on Saturdays with no construction on Sundays or Bank Holidays.
Will the works affect water supplies to the Grand Union Canal?
The works have been programmed to take place across the summer and autumn months in a way that means the reservoir can still be used to supply the canal with water as normal and refill during the winter of 2025/26.
When was Wilstone Reservoir first built and why?
Wilstone Reservoir was built in 1802 to supply water to the Wendover Arm of the Grand Union Canal.
How large is Wilstone Reservoir?
At 119 acres (48 hectares) Wilstone is the largest of the four reservoirs at Tring. It is up to 18 feet (5.5 metres) deep and has the capacity to hold over one million mega litres of water (enough to fill over 300,000 Olympic sized swimming pools). Together, its two five-metre wide embankments stretch for 1,350 metres, and range in height from two to eight metres,
How many reservoirs are there at Tring?
The four individual reservoirs in the Tring Reservoirs Nature Reserve are Startop’s End, Marsworth, Tringford and Wilstone.
There’s more information about visiting Tring Reservoirs here Tring (Marsworth)
Who manages Tring Reservoirs?
The Herts & Middlesex Wildlife Trust leases and manages the Tring Reservoirs, and the Canal & River Trust maintains operational responsibilities for the four reservoirs.
Who do I contact if I have a question about the works?
If you have any questions about the works, contact the Canal & River Trust on 0303 040 4040 or visit ways to contact us page.
