A 1,050-feet long tunnel is being driven under Sheffield’s Brightside Lane as Sheffield Forgemasters’ flood alleviation works reach a pivotal point.

The tunnel will connect two shafts, one more than 40-feet wide and the other more than 15-feet wide, both exceeding 35-feet deep, which have been installed at the engineering company’s site, with the first located on the North side of Brightside Lane and the second closer to the River Don.

Civil engineering specialist, JBA Bentley, is leading the project to intercept the Lower Don Valley’s enclosed Bagley Brook culvert where it enters Sheffield Forgemasters’ site, allowing storm water to overflow from the culvert and be stored for transfer into the River Don.

Gareth Barker, Chief Operating Officer at Sheffield Forgemasters, said: “We have reached a pivotal point in our flood alleviation works as we start driving a tunnel across our site to join two large storm-water shafts.”

Known as the Bagley Brook transfer system, the project will address a known flood-risk when the culvert is unable to channel abnormal volumes of storm water, causing flooding at the Northern part of the Brightside Lane site.

Gareth added: “The brook is contained by an enclosed culvert built in the Victorian era along our northern boundary and flows into the River Don but cannot discharge when the river is in flood, causing it to back up through the drainage system during heavy storm conditions.

“The creation of a large underground catchment system consisting of storage shafts, a cross-site transfer tunnel, and pumping station, will allow us to control large volumes of water at critical periods, to be released back into the river at a controlled flow rate.

“We have installed the tunnelling machine in the River Don shaft and both motorists and pedestrians will not even be aware that the machine is in operation creating a six-feet diameter tunnel directly beneath Brightside Lane to reach the other tank.”

Mark Wood, Contracts Manager at JBA Bentley, said: “JBA Bentley is working to connect the two large rainwater storage shafts on the Brightside Lane site and will subsequently construct a new weir chamber, integrated into the side of the existing Bagley Brook culvert.

“This will allow a large volume of storm water to be redirected from the culvert to a new pumping station which will be located at the side of the River Don.”

A section of flood wall at Sheffield Forgemasters’ boundary with the Don will be repositioned to accommodate a new outfall structure from which the pumping station will discharge storm water back into the river at a rate of 8,000 litres per second.

The flood alleviation works form part of Sheffield Forgemasters’ planning requirements for its new 13,000 tonne Forging Line, which is currently under construction adjacent to the Midland Mainline railway.