Polypipe has deployed a water management system to help protect a new development in Gloucestershire from flash floods.

The £2.7m Churchdown Surgery was protected with Polystorm and Permavoid geocellular systems.

The company worked with consultant engineering firm EPG, and civil engineer and installer NGB Cheltenham, to review and value-engineer a solution capable of negotiating various onsite challenges, including an extremely high water table.

Using the combined design and installation experience of the team, a mixed product solution was supplied by Polypipe that included a Permavoid system for use beneath a large permeable paving car park and two Polystorm tanks utilising anti-flotation measures on soft landscape areas.

Due to the high water table, a 150mm deep system using 2,614 Permavoid cells delivered 138m3 of stormwater storage beneath the hard landscaping surface. Permavoid was also selected due to its high structural load capacity. Polypipe, EPG and NGB had to tend with a water table that left only 130mm of cover in large hard landscaped areas, which meant a shallow attenuation system was required.

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In addition, 200 Polystorm PSM1a crates were used in soft landscaped areas, which provided a further 40m3 of water storage. Due to the high water table, both Polystorm attenuation tanks installed beneath the landscaped areas surrounding the car park were wrapped in a fully welded impermeable geomembrane. Both systems are designed to cope with and manage sudden heavy rainfall, which has affected the region in the past decade.

To treat oil and capture silt, 35m of Permachannel, Permavoid Biomat and four Permaceptor separators were used to channel the collected stormwater away from the site and into local water networks.

Following consultation with EPG and NGB, Polypipe delivered a customised Permaceptor much larger than the standard model to manage greater amounts of stormwater collected from the overall water management system.

Each modified Permaceptor can treat a larger catchment area over 150sqm and was installed to reduce the amount of Permachannel and Permavoid Biomat cells needed within two isolated permeable car park areas separated from the Permavoid tank.

Phil Williams, consultant engineer at EPG, said: "This project provided objectives that we knew Polypipe could deliver upon. With only 130mm cover on the car park we chose to use Permavoid beneath the car parking bays because of its load bearing capability, and the ability of the system to negotiate the high water table on the site.

"By working with Polypipe's technical experts, we were able to design a system that could provide two levels of oil and silt treatment."

Rosie Cheetham, marketing manager, Polypipe, added: "This is a great example of a collaborative approach delivering a system that will serve a community for years to come.

"Our water management experts worked closely with all parties from the early stages of the design process to develop and deliver a modern, intelligently engineered SuDS solution that was easy to install."

(CM)