Articles & Case Studies


Posted: Wednesday 14th October 2009

INNOVATIVE THINKING helped to find a sustainable drainage solution to a major Cumbrian road project. A space-saving solution to controlling surface water in a high rainfall area has been provided by situating a Hydro Stormbloc® storage attenuation tank in the centre of a new roundabout.

The ‘hard’ SUDS option developed by Hyder Consulting reduced environmental impact and flood risk at the site, part of the Highway Agency’s A595 Parton to Lillyhall improvement plan. By contrast, the alternative to provide a suitably-sized stormwater wetland at the location was ruled out due to lack of available land.

”We had considered a number of options for the stormwater control. Wetlands used elsewhere on the route would occupy too much room in this location, as would storage pipes. As the land in the middle of the roundabout was available, we considered a 2 m deep pond there, but the possibility that a vehicle might end up in it was not acceptable,” explains Alan Cope Senior Drainage Engineer at Hyder Consulting.

The new 35 metre diameter roundabout is located at the junction of the A595 and 596, and provides access to the developing Lillyhall Industrial Estate. By combining the installation of the 271m3 Stormbloc® storage tank with the roundabout, the project was able to provide the surface water control required for a 1 in 100 year event, within the Highway Agency’s safety parameters, without extra land requirement.

“Hydro’s Stormbloc® was selected as it is a loadbearing modular block system which can be installed in a very shallow void, so is very cost effective,” continues Alan . “It can easily be landscaped over, without additional loadbearing construction, and is simple to handle on site.

“Installation of a tank might have had maintenance problems with silting but, because Hydro’s Stormbloc® has extensive inspection and jetting channels, the Highways Agency were happy to accept it; Stormbloc®’s load bearing capability would also be much safer in case of vehicle intrusion.”

The Stormbloc® installation includes two Stormbloc® Inspect access chambers, allowing for periodic inspection of the storage, and is combined with a spillage intercept trap; discharge is via a Hydro-Brake® flow control device at 5 litres/second into the existing drainage network, the limit for a 1 in 100 year event. The Stormbloc® tank is wrapped in geotextile over carefully selected aggregates and an impervious geomembrane completes the tank.

“It’s an excellent demonstration of how so-called ‘hard’ SUDS solutions work alongside ‘soft’ solutions,” adds Alan Cope. “Elsewhere, along the Parton to Lillyhall improvement scheme on the A595, there are three stormwater attenuation ponds/ wetlands. Each solution is valid in its context.”

Hydro’s Stormbloc® is a modular system which provides a 95% void ratio, and requires only shallow excavation; its load bearing characteristics allow landscaping or vehicle loading above it. In addition, Stormbloc® features access for CCTV inspection and water jetting through patented tunnels, and offers low maintenance requirements.

Tel: 01275 878371,
Fax: 01275 874979,

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