WET News

JULY 2015 WET NEWS 9 projEcT SpEcS • Project cost £2.7M • A 1.4m diameter new pipe constructed under water by specially trained divers • Replace and upgrade the bottom outlet facilities such that the reservoir can be drawn down at a rate of no less than 1m per day • Plug the existing bottom outlet and fill the existing outlet tunnel to protect against internal erosion Y orkshire Water has completed an ambitious pipeline project at its Eccup reservoir using specially trained divers, as part of a £2.7M investment scheme to improve safety. Engineering specialist, Mott MacDonald Bentley (MMB) carried out the work to replace the existing pipework that runs under the embankment of the reservoir. Lee Laherty, Yorkshire Water project manager, says: "This was a huge scheme; the pipe we installed was 1.4 metres in diameter and part of the new pipe had to be constructed under water by specially trained divers." Eccup reservoir was constructed in 1885 and supplies water to the Headingley water treatment works. The reservoir is an impounding reservoir located on Eccup Beck. The embankment dam of the reservoir was constructed in 1885 and incorporates many of the characteristics of a Victorian "Pennine" type structure. Eccup reservoir has a small direct catchment and is used as an "en-route" storage reservoir (ESR) by Yorkshire Water. Focus The following recommendations were made by the Qualified Civil Engineer (QCE) in the interests of safety under the Reservoirs Act 1975: • Replace and upgrade the bottom outlet facilities to such that the reservoir can be drawn down at a rate of no less than 1m per day • Plug the existing bottom outlet and fill the existing outlet tunnel to protect against internal erosion. During the investigation stage, the main focus of the team was to consider options that could meet the draw down requirements specified within the QCE recommendations. The final review of options concluded that a siphon pipe arrangement was the best option to take forward into the detailed design stage of the project. Underwater solutions for Eccup reservoir • Work to improve safety at Yorkshire Water's Eccup Reservoir presented a huge technical challenge for all involved throughout design, construction and commissioning phases. Dean Stiles explains. ONSITE PiPEWoRk inStALLAtion NEED To KNoW 1 Benefits of core team working to quickly resolve any design and third-party issues as they arise 2 Benefits of early engagement with affected third parties to ensure a successful outcome 3 Upfront liaison with all interested parties including several commis- sioning meetings well in advance of the test ensured that it was a closely monitored and controlled operation 4 this work has helped facilitate future tests by setting a robust and acceptable baseline procedure THE VErDIcT • Despite the complexity of the work and the large degree of manual labour, the work was carried out to an excellent standard of construction • For Mott MacDonald Bentley, the key to success was the collaborative partnership adopted through all parties at all levels Complexity of the work meant there was a high degree of manual labour TEcHKNoW • the pipework was constructed from both ends of the siphon, met in the middle of the embankment with pin point accuracy, well within the required tolerances allowed • Part of the siphon had to be constructed underwater using a specialist diving team • Divers worked a long reach excavator to construct the pipe supports • Divers worked closely with MMB to float the pre-welded section of pipe into position • the siphon had to pass through the embankment introducing the potential for significant differential settlement "this was a huge scheme; the pipe we installed was 1.4 metres in diameter and part of the new pipe had to be constructed under water by specially trained divers" Lee Laherty, project manager, Yorkshire Water Yorkshire Water's £2.7m pipeline project at Eccup reservoir used specially trained divers Operational constr- aints meant Eccup could not be completely drawn down to facilitate the installation of the upstream leg of the siphon. This was therefore installed underwater with the assistance of a specialist diving team.

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