Elan Valley Aqueduct – Bleddfa

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The Elan Valley Aqueduct (EVA) was constructed in 1904 to provide drinking water to the city of Birmingham, UK. The aqueduct is operated and maintained by Severn Trent Water.

GHD is playing a key role in helping the Barhale North Midland Construction Alliance (BNMA) construct four sections of new aqueduct, reinforcing sections of the original structure that are showing signs of structural distress. Bleddfa was the first site to be addressed, with a regulatory output date of March 2017.This tight deadline was achieved through a fast track design process undertaken in close collaboration between Severn Trent Water, BNMA and GHD.

At Bleddfa, our team developed detailed civil, structural and geotechnical design for a 1.8km long new 3.05 m internal diameter segmentally lined tunnel plus connection structures and temporary works.

Collaborative approach delivers benefits

We simplified the Tunnel Boring Machine (TBM) launch methodology by combining the TBM drive pit and the connection cofferdam in to one, removing the need for a separate 12 m diameter and 10 m deep secant piled shaft. This also reduced the working area substantially, facilitating planning permission, as well as the requirement for cut and fill operations.

We removed the requirement for internal propping of the EVA structure by developing a method for exposing and wrapping the EVA using a staged excavation method. This also reduced the work required – considerably – during an outage.

In addition, our team liaised with BNMA to develop a method that allowed flows to be turned outside the shutdown of the aqueduct. This maximised the chances of achieving the ODI whilst utilising only one shutdown.

Securing water for the future

Flows were turned into the new tunnel at the end of February in March 2017, helping Severn Trent Water achieve its regulatory objective. The finished project will increase the lifespan of the EVA and improve the resilience of Birmingham’s drinking water supply.



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