Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | JULY 2015 | 15 Project focus S evern Trent has completed an overhaul of the sewer system in Cheltenham which saw 15 individual projects to alleviate sewer flooding in the historic Gloucestershire town. The work, which lasted just under a year and cost around £5M, involved laying more than four miles of new enlarged sewer pipes to increase capacity in the network. There Sewer networks Cheltenham gets £5M sewer faceli Project focus ● Severn Trent tackles sewer flooding in historic town ● 15 individual relief projects in four cluster areas ● Ground conditions presented challenges for no-dig technology Trent in AMP5, a detailed survey and analysis of the network was carried out to establish the causes. However, rather than identifying a specific failing, the survey and hydraulic modelling concluded that the Victorian-era sewers had simply become overloaded over time due to the town's expansion in the last 100 years. "Cheltenham wasn't a typical scheme where we were looking at a single strategic solution which solved the problem of all of the flooded properties in the town," Wayne Ellis, project manager at Severn Trent, explains. "When we first started our investigations, we wanted to establish whether all of the existing problems were linked to the same source or root cause. But this wasn't the case. While the sewers were overloaded, they were in different parts of Cheltenham, with their own localised problems. In each of those locations we were dealing with, there were 150mm or 225mm diameter sewer pipes that were overloaded; while the existing sewers varied in size, it was clear that it was the smaller diameter sewers that were causing the problem." Working with AMP 5 framework partner NMCNomenca, the utility drew up plans for improvements in 15 locations. Most of the projects involved upsizing the network by installing much larger diameter sewer pipes; but others included additional storage (either online gravity storage or offline pump return storage) or additional transfer sewers which took flow from the overloaded pipes to a Cheltenham's Victorian-era sewers had become overloaded as a result of the growth of the town in the last 100 years was also a parallel project costing £750,000 to repair existing sewer pipes through a cured-in-place pipe lining technique. Planning for the project dated back to 2012. At least 45 properties in Cheltenham were vulnerable to either internal or external sewer flooding during times of heavy rainfall, and with tackling sewer flooding a priority for Severn JAMES BROCKETT EDITOR WATER & WASTEWATER TREATMENT

• Cover