Resolving flooding issues

Growing populations, ageing assets and the rise in extreme weather events are impacting cities around the world.

This is the case in Newark, a market town in Nottinghamshire in the East Midlands of England, where the community is at risk of sewer flooding. The water and wastewater network operated by water authority Severn Trent requires upgrading.

Challenge

Tim Sawyer, Severn Trent’s Programme Manager explains, “Newark is expanding rapidly, and this is putting pressure on our ageing infrastructure. The existing water and sewer pipes have been serving the community for many years, but they are simply no longer able to cope with the extra demands being placed on them.

“The result is an increased risk of interruptions to our customers’ water supply and, more worryingly, an unacceptable increase in the number of sewer flooding incidents.

“Sewer flooding is one of the worst things that can happen to our customers, and we know that there are around 400 properties currently at risk in the Newark area. This is not acceptable and that’s why we have to do something about it.”

Solution

Severn Trent is undertaking a GBP60 million replacement and upgrade of 20 km (12 miles) of old pipes and tunnels. The work includes a 3 km (1.8 miles) long, 2.85 m (9.35 feet) diameter tunnel from the Crankley Point treatment works with a 1 km (0.62 miles) long, 1.5 m (3.2 feet) diameter tunnel branch in order to cope with increasing demands.

The BNM Alliance consisting of Barhale and North Midland Construction PLC is tasked with delivering this ‘fit for the future’ network. GHD’s Manchester team is partnering with the Alliance to help deliver the project and realise value for money on site.

Since our engagement, Chris Oates, Principal Civil/Structural Engineer, has been on site with the Alliance for two days a week to maximise the benefits of our design options.

One of these options involved walking the Alliance team through our Terminal Pumping Station (TPS) solution using a 3D model and physical model replicating the site conditions. Normally, the stormwater pumps would face outwards, but we proposed a solution with the pumps facing inwards, which meant we could reduce the diameter of the TPS by 25 percent. This has reduced excavation, costs, and risks to nearby railway lines.

We are also producing a Tunnel Operations Management Plan for the operation and maintenance of the tunnels throughout their asset life. This includes operational advice across items including emergency evacuation arrangements and ventilation systems.

Outcomes

Rupert Tagg from the BNM Alliance praised our approach, saying, "We have a great relationship with GHD built on understanding – and then delivering to – our needs. Chris' site-based presence has helped to build those key relationships and by walking through digital and physical models, the team have provided assurance in the value of their design interventions to help us deliver more for our client."

The local community has been supportive of the project with people expressing their satisfaction with the team’s collaborative and citizen-focused approach.