Thames Water has appointed Barhale to deliver a £12.5 million programme of statutory tunnel inspection and maintenance across key infrastructure, including the Thames Water Ring Main (TWRM) and North London Abstraction and New River Zone raw water assets.
Image: Barhale’s inspection and maintenance programme will include Stanwell shaft
The projects, awarded under the AMP8 Tunnels and Aqueducts programme, will also include the production tunnels within Thames Water’s treatment works, bringing the total length of tunnels under inspection to almost 48 kilometres.
On the TWRM, civil engineering, infrastructure and tunnelling specialist Barhale will use mainly man entry with some limited Remotely Operated Vehicles (ROV) to inspect 12 sections of the tunnel at depths of up to 65m, representing around 20% of the asset’s extent.
At the North London Abstraction and New River Zone, Barhale will carry out 24 inspections concentrated around the Lee Valley reservoir complex. The varying diameter tunnels are buried up to 50m deep and range from 30m to 5,450m in length. The overall length to be inspected in the Lee Valley area is 24.9km.
ROV, CCTV and sonar surveys will be conducted where in person inspection of the tunnels is not possible.
The tunnels will be accessed from existing shafts. Works will be carried out under Confined Space Working conditions and will include clearing sludge, silt, stones and invasive species – particularly mussel concentrations which impact flows. It is estimated that 3,120 tonnes of waste will be removed.
Barhale will complete minor repairs, including mortar repairs, leak sealing and resin injection and replace or repair access furniture such as ladders, landing platforms and covers. Specialist diving teams will complete repairs to inlet screens, eel screens and carry out external shaft repairs. Major repair requirements will be identified and taken forward for appropriate action.
The final inspections will be conducted by Thames Water Reservoir Engineering teams.
Barhale will also replace nine large diameter valves under the programme.
The programme presents numerous environmental considerations with several of the Lee Valley projects located in Sites of Special Scientific Interest (SSSI) and Ramsar-designated locations. Walthamstow Wetlands is a conservation area accessible to the public and work is planned to protect existing bat and newt populations in the tunnels.
“This programme involves complex work in confined spaces and live water environments,” said Steve Best, Senior Project Manager at Barhale. “We have developed inspection and isolation processes with Thames Water over more than 20 years, and they are designed to keep our teams safe while maintaining reliable operation of the network.
“We are proud of our safety record and continue to improve how we manage risk through the introduction of a new confined space working training regime. It imposes new site entry controls and will see all operatives qualified to the highest level.
“Our double isolation protocol, developed with Thames Water, also ensures that there is an additional layer of protection for teams working near live tunnel sections.”
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