We are excited to share the first results from essential safety investigations at Rudyard Lake, carried out under the Reservoirs Act 1975.
Recent work has focused on the spillway and outlet tunnel systems, helping to build a clearer understanding of the condition of the area. This included targeted testing of the spillway masonry and a combination of non-intrusive survey techniques and water sampling around the tunning.
These Measures in the Interest of Safety (MIOS) focus on the condition and performance of the spillway and outlet culvert which form two key parts of the reservoir’s infrastructure.
This marks the first opportunity to share what we have found so far as part of the wider Rudyard Lake water improvement project, offering fresh insight into how the reservoir is performing and what steps we will take next to keep it safe for the future.
Rudyard Lake spillway stability
Between early 2025 and May 2026, we carried out a series of investigations at Rudyard Lake, including ground testing, computational fluid dynamics modelling, and pull-out testing on the spillway masonry blocks.
The purpose of this testing was to see how well the spillway holds up under extreme conditions. To do this, we set a clear benchmark that if any of the masonry blocks moved more than 0.1 mm under pressure, it would be considered a failure of the spillway.
The good news is that none of the masonry blocks came close to this failure benchmark, with the largest recorded movement being well within safe limits at 0.1 mm.
This shows the spillway masonry is performing strongly, even when tested against extreme flood scenarios like the Probable Maximum Flood and very rare 1 in 10,000-year events.
That said, inspections have highlighted some wear and tear over time. So, as a next step, we will be moving forward with targeted repairs and repointing of the spillway masonry lining to keep everything in top condition.
Reservoir tunnel and shaft leakage
Between November 2025 and April 2026, we carried out geophysical surveys and water sampling to better understand leakage around the tunnel and access shaft at Rudyard Lake.
The main takeaway of these surveys is that the leak at the tunnel headwall is coming from the reservoir itself and not from natural groundwater. Water samples closely matched reservoir water, suggesting it’s escaping through small gaps or cracks in the tunnel lining.
Our surveys back this up, highlighting areas behind the tunnel wall where moisture or voids may be allowing water to pass through.
In the access shaft, we also found leakage, although the source of this one is less clear and is likely a mix of reservoir water and rainwater getting in.
We will be carrying out targeted works to reduce these leaks and keep everything in good condition. These proposed works include:
- Clearing the feeder channel so all leaks can be clearly seen and monitored
- Repairing and repointing masonry, and replacing any damaged blocks
- Including the access shaft in these repairs to reduce risk while works are underway
Next steps
In the coming months, we’ll be engaging directly with local people, interested stakeholders and providing regular updates on the project’s project, including the feasibility studies and the wider works to the feeders.
