New tunnels bypass historic aqueduct
The tunnel boring machine begins work at Bleddfa

Severn Trent Water has completed the first of three huge multi-million pound bypass tunnels being built to reinforce water supplies for Birmingham.

The Elan Valley Aqueduct (EVA) has been bringing water to the homes and businesses of Birmingham and the surrounding area for over 100 years. However, after so many years of service, the need for regular maintenance and refurbishment is becoming ever more frequent and so the time has come to provide extra support for the EVA to make sure that it can continue to provide service for another 100 years. To meet this aim Severn Trent Water has embarked on a £300 million flagship programme – the Birmingham Resilience Project.

Paul Dennison, programme manager for Severn Trent, explains: “At the moment, the EVA is the sole source of supply into Birmingham, and storage at our treatment works at Frankley means we can only turn it off for a few days at a time for maintenance. To allow us to turn it off for longer periods, an alternative water supply for the city is being built.”

Pipeline progress

Work began in March on a new pipeline from Lickhill, near Stourport-on-Severn, 25 kilometres into the existing water treatment works in Birmingham.

However, before the pipeline could be completed, checks on the existing aqueduct showed that, in three places along its route, Bleddfa, Nantmel and Knighton, there was work that needed to be done first.

As Severn Trent cannot shut down the aqueduct, the company has had to come up with alternative solutions. Three new tunnels are being built one after another to bypass sections of the existing aqueduct, to which they are being connected at either end.

Giant tunnels

“Each of the multi-million pound projects is huge in its own right, and the machine used to cut the new tunnels is over three metres in diameter,” said Dennison. “A launch ceremony was held in May 2016 to celebrate the arrival and launch of the tunnel boring machine which then spent the next six months underground digging the 1.8 kilometre-long tunnel. The machine broke out successfully in December 2016 – right on target, completing the first tunnel.”

Severn Trent have been working on the project with their contract partner, BNM Alliance, at Bleddfa since October 2015. In March this year, the team prepared for the transfer of flows from the 100-year-old aqueduct at Bleddfa into the newly constructed tunnel. Dennison explained: “We planned the work to coincide with a scheduled shut-down of the EVA, when flow through the aqueduct is suspended for five days to allow inspection and maintenance.”

The new tunnel was flooded by removing the barriers from each end, resulting in the flow being shared between the old aqueduct and the new tunnel. The water was diverted into the new tunnel by placing a series of specially shaped concrete blocks into the aqueduct – gradually turning the flows from the old to the new. The roof slab sections were then replaced and the two working areas were backfilled.

“This is a fantastic achievement by all the team to complete the flow transfer in such a short space of time – just three days,” said Dennison.” We expect everything to be fully back to normal by the end of August at our site at Bleddfa village, and a month later at our site near Monaughty.”

Tunnel two

All the tunnelling equipment from Bleddfa was then transferred to the second site at Nantmel, ready for tunnel number two. The TBM, named the ‘Nantmel Supermole’ by local schoolchildren was ceremoniously relaunched on 5 May, ready to spend five months underground digging the one-kilometre-long Nantmel tunnel.