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
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
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