Marchlyn Mawr additional stored energy project

Abstract

Marchlyn Mawr is located in North Wales and serves as the upper storage reservoir for the Dinorwig Power Station, which operates a 1728 MW pumped storage scheme. Owing to increasing demands on the existing power generation capabilities within the UK, MWH was commissioned by First Hydro Company to provide a detailed engineering solution that would enable the reservoir level to be raised and provide an additional 1·1 GWh of stored energy within the hydro-electric system. The initial scope of work provided by the Client required raising the reservoir level by 2·5 m. However, detailed flood studies carried out during the feasibility stage demonstrated that by raising the crest by 2·5 m and enlarging the overflow could enable a 3·3 m increase in the operating top water level, thereby increasing the available head for power generation. An insight into the measures taken to satisfy the environmental conditions imposed by the planning application is given, as well as the results of full-scale preconstruction trials that were carried out on site, which resulted in modifications to the final design and construction sequence. The engineering solution involved the construction of a 620 m long retaining wall, raising of the dam crest level using rockfill derived from slate waste, enlargement of the existing overflow structure as well as modifications to appurtenant structures and the extension of the original grout curtain.