Thames Water has appointed Barhale to deliver a £12.5m programme of statutory tunnel inspection and maintenance.
The projects, awarded under the AMP8 Tunnels and Aqueducts programme, include the Thames Water Ring Main (TWRM), North London Abstraction and New River Zone raw water assets and the production tunnels within Thames Water’s treatment works. Nearly 48km of tunnels will be inspected.
On the TWRM, 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.
At the North London Abstraction and New River Zone, Barhale will carry out 24 inspections concentrated around the Lee Valley reservoir. The varying diameter tunnels are buried up to 50m deep and range from 30m to 5.45km in length. Overall, 24.9km of tunnels will be inspected in the Lee Valley area.
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 for appropriate action.
The final inspections will be conducted by Thames Water Reservoir Engineering teams.
Barhale will also replace nine large-diameter valves.
The Lee Valley projects are 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 Barhale senior project manager Steve Best. “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 there is an additional layer of protection for teams working near live tunnel sections.”
