In late 1973 the UK’s Central Electricity Generating Board gained parliamentary approval to build the largest and most difficult pumped storage hydroelectric power station in its history. It was the largest civil engineering contract ever awarded by the government and became the biggest construction project in Europe. Engineering teams had to burrow 750m deep into the Cambrian slate of Elidir Fawr mountain at Dinorwig, North Wales to create the underground power station and a 16km labyrinth of tunnels up to 10.5m in diameter linking upper and lower reservoirs. 

It’s scale and complexity pushed the limits of design and construction with engineers developing state of the art practices for rock reinforcement and concrete design and pioneering new construction methods. As the station celebrates 40 years of operation and looks ahead to a bright future as a battery for renewable energy, we speak with the people that planned, designed and constructed electric mountain hearing stories that have never been told before.

Guests

Kin Almond, supervising civil engineer, James Williamson & Partners 

John Armstrong, station manager Dinorwig and Ffestiniog, First Hydro

James Arthur – senior engineer, James Williamson & Partners

John Cowie – associate, James Williamson & Partners 

Chris Roberts, commissioning engineer, Central Electricity Generating Board (CEGB)

Dyfrig Roberts – assistant engineer, James Williamson & Partners

Robin Thomas – civil engineering technician, James Williamson & Partners 

Ian Waite – project surveyor, James Williamson & Partners 

Musical recording of “Tydi a Roddaist” used with the permission of the Caernarfon male voice choir who performed in the excavated machine hall in 1979.

Partner

Mott MacDonald is a global engineering, management and development consultancy focussed on improving society by considering social outcomes and relentlessly focussing on excellence and digital innovation. James Williamson & Partners became part of Mott MacDonald in 1990.