Polypipe bolsters flood defences at new £2.7m medical centre

Polypipe, the UK’s leading manufacturer of sustainable drainage and water management solutions, has helped to protect a new £2.7 million medical centre from flash floods.

Polypipe supplied its Polystorm and Permavoid geocellular water management systems to the 1,191sqm Churchdown Surgery in Churchdown, Gloucestershire.

Building on the initial design by the contract engineer Rutter Johnson, Polypipe 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.

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.  

As well as this the main Permavoid tank beneath the car park area had a fully welded membrane to the base and sides.

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.”

Neil Bermingham, managing director at NGB (Cheltenham) Ltd, said:

“Having been awarded the full civil engineering and groundworks package, this project provided a perfect opportunity to continue our collaborative relationship with Polypipe.

“Using our installation experience and knowledge of the site, we were able to work with Polypipe and EPG to provide a value-engineered solution to the client that offered cost and construction phase benefits in addition to increased flexibility in future use.

“Having utilised our own in-house CSWIP-qualified geomembrane welding team, we look forward to collaborating with Polypipe and EPG on future contracts.”

The practice, which opened in March 2018 and can serve 20,000 patients, features consulting rooms, nurse treatment areas, a lift, training rooms and a large car park.

However, the semi-rural village is prone to flooding, most notably on July 20, 2007, when a staggering 78mm of rain fell in just 12 hours across the county. Regional news website GloucestershireLive described it as “the worst natural disaster in the county's living memory.”