Llyn Celyn spillway wins top ICE engineering award
The award‑winning auxiliary spillway at Llyn Celyn showcases innovative design, digital construction and environmental care, bolstering flood safety in Wales.
The Llyn Celyn Reservoir auxiliary spillway project in Gwynedd has been awarded the Institution of Civil Engineers’ George Gibby Award, recognising its pioneering engineering and environmental stewardship.
The scheme, delivered by Welsh Water in partnership with Mott MacDonald Bentley and Natural Resources Wales, upgrades Wales’ largest reservoir by volume with a new auxiliary spillway.
Central to the design are four 4.5‑metre‑high reinforced‑concrete tipping gates – the largest system of its kind in the United Kingdom.
These gates are intended to operate only during exceptionally rare flood events, bolstering the reservoir’s capacity to manage extreme conditions safely.
Construction required a 70‑degree soil‑nailed excavation within the sensitive landscape of Eryri National Park, presenting significant engineering challenges.
To meet these, the team employed advanced digital tools, including detailed geophysical surveys and two‑dimensional hydraulic modelling.
Intelligent machine‑guided construction techniques were used to deliver concrete to the remote site with precision.
Two‑thirds of the spillway was built as a culverted structure, minimising visual impact and preserving the surrounding natural scenery.
Sustainability was woven throughout the project, with design optimisation reducing the volume of construction required and lowering carbon emissions.
Excavated material was reused on‑site, further curbing environmental impact while supporting long‑term resilience.
Karen Morris, Programme Delivery Manager at Welsh Water, said: “Winning this award is a fantastic achievement and a testament to the dedication, expertise and collaborative working of everyone involved in the project.” Safety has been at the heart of the scheme, but we have also worked hard to deliver it in a way that respects the surrounding environment and provides long‑term resilience for communities.
We are extremely proud of what has been achieved alongside our partners, contractors and stakeholders, and we are grateful for the support shown by the local community throughout the project.”
Michael McAree, Design Manager at Mott MacDonald Bentley, added: “We are delighted the Llyn Celyn project has received this recognition.” Its success reflects the strength of our partnership with Welsh Water, the ingenuity of our engineering teams and our shared commitment to delivering safe and sustainable infrastructure.
The innovative spillway design and digital approach used during delivery have set high standards for the sector.”
Stephen Shakespeare, Welsh Water’s Dam Safety Manager, commented: “Winning this award is a proud moment for everyone involved in the Llyn Celyn project and recognises the skill, commitment and collaboration behind this important work.” The scheme has strengthened the long‑term safety and resilience of one of Wales’ most important reservoirs.
The new auxiliary spillway introduces the largest reinforced concrete tipping gate system of its kind in the UK, providing additional capacity to safely manage exceptionally rare flood events and helping to protect communities and the environment for generations to come. What makes this project particularly special is that it combines engineering excellence with environmental stewardship.
Through innovation, sustainable design and close partnership working, we have delivered a major safety enhancement while respecting the unique landscape of Eryri National Park. We are incredibly proud that this achievement has been recognised by ICE Wales Cymru.”
The award highlights the growing emphasis on integrating robust flood‑risk infrastructure with ecological sensitivity across Wales.
Industry observers note that the project sets a benchmark for future reservoir upgrades, demonstrating that high‑performance safety solutions can coexist with landscape preservation.
Welsh Water and its partners plan to monitor the spillway’s performance closely, ensuring that the design delivers the intended safety benefits while maintaining the environmental standards achieved during construction.
Local residents have welcomed the development, citing increased confidence in flood protection and appreciation for the careful handling of the national park’s visual character.
With climate change intensifying weather extremes, the Llyn Celyn auxiliary spillway stands as a timely example of proactive infrastructure adaptation in Wales.