Llyn Celyn improvement work


At Welsh Water we take our responsibility for safely maintaining and operating our dams and reservoirs seriously.

In 2020, a statutory inspection was completed by an independent Panel Engineer. He confirmed that Llyn Celyn reservoir is in a good state, however as expected he made some recommendations to ensure that the reservoir meets the latest UK guidance. The recommendations in his final report are statutory and are enforced by Natural Resources Wales. Welsh Water must respond to them within a defined timescale.

The proposal is to build a new auxiliary spillway to deal with exceptionally high-water levels that are anticipated on average once in every 10,000 years. Work will also be carried out on the existing pipes and valves as part of an upgrade maintenance programme.

Please be assured that this does not mean there is any immediate safety concerns with the dam.

What can you expect?

Since the publication of the Engineer’s report in 2020, various investigations have been carried out on site including ecological and ground investigations, which has enabled our contractors to progress on the design of the new auxiliary spillway.

The proposed plan is to build an auxiliary spillway on the opposite side to the current overflow, near the main car park off the A4212, at the crest of the dam. The plans for the new spillway were shared with the local community in 2021. We anticipate that the full planning permission for the work will be submitted to Snowdonia National Park Authority in Autumn 2022. If permission is granted, work would start in Spring 2023.

Upgrade and maintenance work is also needed on the pipes and valves within the main tower and the tunnel that connect to the powerhouse. This work does not require planning permission. Some of this work has already been carried out but more is now scheduled.

From early September until early November, you will see increased activity at Llyn Celyn. There will be additional plant machinery on site, as well as professional divers. The divers will be working on the main tower structure and will have support boats on Llyn Celyn.

Keeping everyone informed

As a company, we are committed to keeping customers and stakeholders informed of any work we undertake and will be doing the same here at Llyn Celyn. Further details about the design of the auxiliary spillway will be shared with the public as part of the planning process. We are also liaising closely with our regulator Natural Resources Wales, Snowdonia National Park Authority and Gwynedd Council.

If you would like to know more about our work at Llyn Celyn please visit our website here.