Provision of a surface water attenuation tank with sufficient lateral strength to be located adjacent to an adopted highway.

Brief:
1. Provide detailed structural analysis of tank performance to meet all the adopting authority’s requirements.
2. Within a restricted area, provide sufficient attenuation for a 100 year storm.
3. Configure the tank to accommodate off-line car parking bays.

The challenge facing consulting engineers Capita Symonds was to find a tank manufacturer that could support the proposed scheme with a rigorous structural analysis of its in-situ performance.

By working in close co-operation with project consulting engineers, ACO Design Services were able to provide a full in-situ structural analysis of ACO StormTank. The only UK supplier able to achieve the level of detail required by the adopting authority, ACO StormTank was the only product considered for selection on this landmark regeneration scheme.

Sized to attenuate the surface water run-off that would arise from a 1 in 100 year storm coinciding with a 1 in 200 year high tide – together with a 30% allowance for climate change – the tank would need to withstand the lateral and sheering loads exerted by passing traffic using the new adjacent highway.

The 120 cubic metre ACO StormTank at Centenary Quay has a recessed edge profile along one side to avoid any direct vertical loading from a series of off-line parking bays on the highway.

Configured to attenuate all the water it receives, the tank is encased in an impermeable welded geomembrane which is then wrapped in a protective outer fleece – a combination that achieves a fully watertight and stable installation.

When tidal conditions permit, the tank discharges to the adjacent River Itchen through a conventional non-return valve outlet.

ACO StormTank’s innovative design uses high strength central pillars and side walls to provide load bearing capacity and structural integrity. A completed tank only requires side panels at its perimeter to provide lateral support.

“ACO was the only potential supplier who could provide the quality of information and level of detail we needed to satisfy the adopting highway authority,” says Robert Cooper, Principal Engineer at Capita Symonds.
“The technical assessment compiled by ACO’s Design Services Team formed a vital part of the overall Section 38 submission which was subsequently fully approved.”

The result is a totally barrier free interior void that can be easily accessed, inspected and cleaned. The free flow of storm water entering the tank also avoids having to use expensive pipe manifolds and additional pipework to distribute flow evenly.

Key data