Stormwater system delivers cost reductions

Sept. 4, 2007 -- Developers of a prestigious new office development in West Cumbria have identified a cost efficient solution to control stormwater runoff in a heavy rainfall area using Hydro's Stormbloc® modular storage system and a Hydro-Brake® Flow Control device.

Contractor Thomas Armstrong (Construction) Ltd, who designed and built the spectacular new three floor West Cumbria House at Lillyhall, Workington, needed to provide stormwater runoff attenuation for the roof and external hard paved areas. They identified significant benefits by taking advantage of the loadbearing properties of Hydro's technology to reduce installation costs.

West Cumbria House is a multi occupancy office building for West Cumbria Development Agency with offices to let to new and expanding companies to help improve the local economy.

The site is located in a 1000 mm-a-year high rainfall area and the stormwater system was required to control runoff from 8000 m² of roof, car park and vehicle yard to meet a discharge limit of 11 liters/sec. The original proposal was for a 500 m³ GRP tank approx. 4 m in diameter by 40 m long, buried under the car park.

Bob Boardman, Project Manager for Thomas Armstrong, commented: "Although relatively inexpensive in capital terms, the original plan required the tank to be installed in concrete for structural support under the car park. This entailed deep excavation into stiff clay to prepare the site then, to sink the tank into the poured concrete, a lengthy process of progressive ballasting it with water. In addition at this depth, the tank would have also required a pump installation to empty it for discharge to the drain invert level with implications for access, maintenance and running costs.

"The alternative we adopted was Hydro's Stormbloc® modular storage system. As Stormbloc® is loadbearing, it needed minimal structural work to install, and could be configured as a much shallower profile storage solution, requiring excavation to only 2 meters for a 500m³ tank which was simpler and safer. This meant less shoring, no concrete and less cartaway and spoil disposal costs. Also, at this shallower depth, attenuation with Hydro-Brake® Flow Control Devices was feasible to match the invert depth for discharge to the storm drain, and a pump was not required, reducing operating and maintenance costs."

The new Stormbloc® Inspect access chamber gives excellent access to the inspection channels built into the Stormbloc® tank, and the Hydro-Brake® Flow Control is un-powered and requires minimal maintenance. Overall, the installation offers a much more attractive solution in terms of design, CDM compliance and ongoing operation and maintenance costs.

By introducing the new Stormbloc® Inspect variable height inspection and access chamber in the Stormbloc® module format, Hydro provides integrated inlet, inspection, maintenance and access as part of the system, minimising additional costs for manholes and installation. The new Stormbloc® Inspect also makes it easier for stormwater attenuation and infiltration systems to meet invert requirements.

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