Sheffield's rivers, the Don, Sheaf, Porter, Rivelin and Loxley, come off steep ground into the valley floor, and the 2007 floods showed how quickly they rise. New development is usually expected to hold its runoff back towards the greenfield rate, with infiltration considered first and attenuation used where the ground won't take the water.
The Lower Don Valley is old steelworks land, and a formation there can turn up slag, old foundations and buried services. We check the base before we line it and ask for anything that could puncture the membrane to be removed or blinded over.
On a hillside plot in Dore, Ecclesall or Hillsborough that can mean a deep tank set into the slope. In the Lower Don Valley, around Attercliffe and Meadowhall, it more often means a large tank under a yard or car park close to the river.
At Oxspring, near Barnsley, we built two adoptable storage tanks on a housing development: a 183m³ main tank 2.5m deep and a 93m³ offline tank. Both were lined and welded, and the base welds were pressure-tested to 1 bar, marked up and photographed before any crates went in.
Adoptable tanks are inspected before the water company takes them on, so nothing gets covered until it has been proven. We build every tank that way, adoptable or not, and the evidence goes into the handover pack.
The tank's design and sizing belong to your drainage engineer; excavating, forming and backfilling belong to your groundworker. Our part runs from the formation check to the test weld: 300gsm fleece, an impermeable membrane with every joint heat-welded, a crate block with a 95–97% void ratio, and each pipe and the flow control sealed into the wrap.
Crates can come from us or from you. We'll fit whichever crate the design specifies; on a deep tank the loading class and depth of cover decide it, not the brand.
Downstream, Rotherham, Doncaster, Mexborough and Conisbrough share the Don catchment and the same need to keep runoff out of the river in a storm. To the north, Barnsley borough drains partly to the upper Don, where our Oxspring tanks went in, and partly to the Dearne, which joins the Don further down.
We cover all of South Yorkshire from our Tamworth base, along with the rest of the county, and the crew that lines a tank in Rotherham works to the same weld test and handover routine as one in Sheffield city centre.
