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Project Focus: Cheltenham gets £5M sewer facelift

Severn Trent's renewal of the sewers in the historic Gloucestershire town involved 15 individual projects to tackle sewer flooding


Ward Councillor and Deputy Mayor of Cheltenham Chris Ryder: “Many local families had been badly affected with terrible consequences to their homes during the floods of 2007, so residents and businesses were pleased that the work was carried out so efficiently and effectively. They were tidy and considerate when working outside homes and shops and always kept us informed.”

Severn Trent project manager Wayne Ellis: “It’s been a massive project and investment for us, but an essential one. As anyone who has experienced sewer flooding will tell you, it’s a horrible thing to happen, and it’s our job to stop it. Our new sewers now mean that hundreds of our customers are now better protected from the risk of sewer flooding.”

by James Brockett

Severn 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 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 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 less burdened part of the network. Contractor Lang O’Rourke took care of the water main diversion work necessary as part of the project.

Programming challenge

Work began in June 2014. Programming the work posed a particular challenge - with lengthy road closures in such a densely populated area likely to cause disruption – so the projects were split into four batches by geographical area, and staggered accordingly. Much care was put into stakeholder management, with information distributed via a dedicated website and social media, an ‘In your street’ mobile phone app (newly developed by Severn Trent) as well as through leaflet drops and open days.

Even so, parking became a particular issue for residents during the projects. With much of the work taking place in narrow streets with terraced houses and little off-street parking, Severn Trent took the decision – with the agreement of the local authority - to implement their own residents’ parking scheme in space that they left available for on-street parking. However, it ran into trouble when ineligible cars started using the spaces, frustrating residents and in some cases delaying the work taking place.

“With all of this work we do have hiccups and bumps along the way, but it’s about how you deal with those hiccups and bumps when they arrive,” says Ellis. “I think one of the issues we did have was around that parking scheme that we introduced, but we met with the residents and made sure we implemented and policed it properly, and overall the feedback we then had was very positive, both from our customers and the local key stakeholders.”

Another challenge encountered was that, in an effort to minimise disruption and ensure work could be completed more efficiently, some of the projects were set to use trenchless, directional drilling methodology. However, poor ground conditions made this impractical, with the project team unable to achieve the gradients required for gravity solutions to work. There was no option but to pause and redesign this element of the work, rescheduling it for later in the process. However, this will not put the company off using such no-dig solutions in future, says Ellis.

“I think no-dig offers a very good solution in a lot of cases - it’s far less disruptive to customers and road users, it’s quicker, and more environmentally friendly because you haven’t got all of that excavated material to take to tip. But the ground conditions and the site has got to be right for that methodology. So it won’t put us off, we just need to ensure that when we choose no-dig solutions in future we fully understand the ground conditions and that they are right for what we’ve got.”

Stakeholder engagement success

The sewer repair element of the project, through cured-in place pipe lining, was targeted on sewers that were nearing the end of their design life, those that had suffered collapses or blockages in the past, and those that had the highest consequences of failure in future according to the hydraulic model.
The end of the main works phase of the project came when Roman Road was reopened to traffic in May 2014. While the issues experienced meant that the original aim of completing in March was not possible, the project was brought in on budget and the customers that were at risk of sewer flooding have now been protected.

“Bearing in mind that we didn’t actually start construction work until June 2014, we completed a lot of work in what was a relatively short period of time, managing the impact on customers, business and traffic management too,” concludes Ellis. “I think our stakeholder engagement was a success: right at the outset we understood and recognised the impact that all of this work was going to have on Cheltenham, started a process of engaging with key stakeholders, and maintained that engagement through the life of the project.
“We made a commitment as part of our sewer flooding programme for our AMP5 business plan to solve internal and external flooding problems across our region and Cheltenham contributed to this. Now in AMP6, we’ve got a business plan objective to reduce sewer flooding incidents so there will be more work like this over the next five years.”

Topic: Sewer Networks , Trenchless
Tags: sewers , flooding


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