Water & Wastewater Treatment

WWT May 2017

Water & Wastewater Treatment Magazine

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Page 16 of 47

Project focus Pipes and pipelines Going with the flow in the Elan Valley Project focus T he Elan Valley Aqueduct (EVA) has been bringing water to the city of Birmingham for more than a century. The 119km-long aqueduct is one of the last great civil engineering achievements of the Victorian era. Opened in 1904 by Victoria's son, King Edward VII, the aqueduct today carries 320 million litres of fresh water to Birmingham from mid- Wales every day – roughly twice the volume it carried a century ago. The EVA is one of Severn Trent's most significant assets, but aŠer more than 100 years of service, the work is needed – a task which could get underway before the new alternative pipe is in place. The three new sections, at Bleddfa, Knighton and Nantmel, are being tunnelled alongside the existing aqueduct and the flow of water diverted into the new sections allowing the old tunnel to be sealed off. Proactive maintenance The contract for this phase was awarded to BNM Alliance, a joint venture between Barhale and North Midland Construction which has just completed the 1.8km-long Bleddfa diversion, the first of the three sections to be replaced. "There was no risk of imminent failure in the aqueduct," says Richard Holloway, the BNM Alliance site manager at Bleddfa. "These replacements are proactive maintenance." The new tunnels are being bored with an earth pressure balance tunnel boring machine (TBM) which requires a large, 15m deep launch pit. The transition, first from the existing conduit into the new tunnel and then back to the original conduit again, has been carefully designed to avoid slowing the flow of water down the aqueduct. The entire EVA, from mid-Wales to Birmingham, is gravity- fed – there are no pumping stations – and so interruptions and obstacles must be avoided at all costs. Precast concrete manufacturer Kijlstra has been instrumental in the design and production of the critical tunnel sections that divert the flows into and out of the new tunnel. "The contract was split between upstream and downstream projects," explains Kijlstra's production manager Rupert Treadaway. "Each contained large U-channel elements in which we placed bespoke benching elements with continually changing profiles for a gradual transition from a square section to a rounded one to minimise any effect on the flow." AŠer each flat-bottomed culvert section was installed the appropriate benching element was cemented in place and then cover slabs placed on top to close the conduit. Custom- designed diversion blocks were installed to divert the water from the existing stream into the new layout without having to shut down the water flow. Although the diversion is only about 20m long, its design required painstaking calculation, says Rupert. "We worked very closely with 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. This led to the Birmingham Resilience Project (BRP), a scheme to safeguard the EVA and protect Birmingham's water supply. At around £300M, the BRP is the biggest infrastructure project in Severn Trent's history. One of the first phases in the BRP is to replace three sections, totalling 4.6km, of the EVA where Bleddfa is the first of three diversions involved in the EVA project ● Elan Valley Aqueduct renewed as part of £300M Severn Trent project ● Three sections totalling 4.6km tunnelled alongside existing aqueduct ● Bespoke precast concrete units chosen for swi and accurate installation www.wwtonline.co.uk | WWT | MAY 2017 | 17

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