#378 Revisited: Designing Dinorwig – Inside Electric Mountain

Engineering Matters · Oct 22, 2026 · 43m

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…