Attenuation tank installer in Leeds

Attenuation in the Aire valley

Leeds grew along the Aire, and the river and its becks decide how much surface water a new site can send downstream. The Boxing Day floods of 2015 hit the city centre and Kirkstall hard, and they are part of why drainage conditions on Leeds sites get close scrutiny.

Smaller watercourses matter too. Meanwood Beck, Wyke Beck and the other becks that run through the suburbs to the Aire are where many sites end up discharging, and a tight discharge rate onto one of them means a bigger tank behind it.

Most schemes of any size now need storage that releases water at a controlled rate. A geocellular tank is the usual way to fit that storage under a road, a car park or a yard without giving up land on the surface.

Large housing and logistics schemes

Strategic housing at the East Leeds Extension and in south Leeds, and the distribution sites around the M1, M62 and M621, put large hard surfaces onto what was often open land. That means bigger tanks, more connections and, on housing, tanks a water company may later adopt.

On phased sites we work to the groundworker's programme. They dig and form each excavation; we check it, line it, build the crates, make the pipe connections, then hand it back for backfill. Most tanks go in over days rather than weeks, and each phase gets its own test weld record.

Tight sites and railway land

Not every Leeds job has room to spare. City-centre plots and railway land leave little space around the hole. At York station we built a long attenuation tank in a narrow excavation beside the railway buildings, lined in 0.75mm geomembrane, and the base weld was tested at 1 bar of pressure and logged before any crate was placed. Constrained sites around Leeds get the same treatment.

On a site like that the sequence is planned before we arrive: where the crates are stacked, where the membrane is cut, and which end of the excavation closes first. If a delivery comes up short or something doesn't fit, we tell the site straight away and agree how the tank will be finished, rather than closing it out with a compromise.

What we're responsible for

The drainage design stays with your engineer, and the excavation and backfill stay with your groundworker. This is the part that's ours:

• Materials supplied by us, or crates and membrane you've bought in, fitted either way.
• 300gsm fleece and an impermeable membrane, heat-welded, never taped.
• A crate block at 95–97% void, matching the drawn volume and load rating.
• A recorded test weld before backfill.
• A QA and handover file for building control and any future adopter.