Civil engineering contractor JBA Bentley has started tunnelling work beneath Sheffield’s Brightside Lane as part of flood alleviation measures for the Sheffield Forgemasters site.
The 1,050ft tunnel will connect two shafts already installed at the engineering firm’s premises. The first, on the north side of Brightside Lane, is more than 40ft wide, while the second, positioned closer to the River Don, is more than 15ft wide. Both shafts exceed 35ft in depth.
Once complete, the tunnel will intercept the Lower Don Valley’s enclosed Bagley Brook culvert at the point where it enters the Sheffield Forgemasters site. This will allow storm water to overflow from the culvert during periods of heavy rainfall, with the excess stored before being transferred into the River Don.
Sheffield Forgemasters COO Gareth Barker 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.
“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 a 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-foot-diameter tunnel directly beneath Brightside Lane to reach the other tank.”
The scheme is designed to address a known flood risk. The Bagley Brook culvert can currently struggle to cope with abnormal volumes of stormwater, which has previously caused flooding in the northern part of the Brightside Lane site.
As part of the works, a section of flood wall along Sheffield Forgemasters’ boundary with the River Don will be repositioned. This will accommodate a new outfall structure, from which a 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 the planning requirements attached to Sheffield Forgemasters’ new 13,000t forging line, which is currently under construction adjacent to the Midland Mainline railway.
JBA Bentley contracts manager Mark Wood 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 stormwater to be redirected from the culvert to a new pumping station, which will be located at the side of the River Don.”
