Severn Trent unveils 25m deep storm overflow tank

The Stroud Sewer Strategy project has delivered a 7,400m3 capacity concrete-lined tank built with partners Galliford Try.

The mega tank is part of Severn Trent’s £25m project to upgrade Stroud’s largely Victorian-built sewer network and includes installing four miles of enlarged pipes, plus separating surface water from the waste network.

Four tunnel boring machines were used to install the new sewer pipes under the Gloucestershire town, as well as lining 1km of old brick Victorian sewers with polypropylene to stop groundwater infiltrating and adding more water to the pipes.  

According to Severn Trent, the tank will improve water storage capacity in the area by around 1,300 per cent during heavy rainfall, helping to reduce sewer flooding and spills into rivers and watercourses. Its ‘smart controls’ will hold storm water back during severe weather events and return it back to the water company’s treatment works when rainfall has subsided.

Severn Trent added that a new concrete lid will be installed on the overflow storage tank in the coming weeks.

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In a statement, Steph Cawley, customer operations director, said: “With a growing population and climate change - with some of the wettest months on record being experienced - we now have more demand than ever on our network.

“Solutions like this mean when there is heavy rainfall we can store the water and then, when it stops raining, we can safely treat it and return it to the rivers, which means we will have less spills into watercourses like the River Frome.

“This work will also provide people living in Stroud with a more reliable sewer network by creating more storage and larger sewer pipes, helping to protect homes and businesses from blockages and flooding.”

The £25m Stroud scheme also includes the removal of a large sewer pipe that runs through the canal in the town, plus improvements at the Stanley Downton Sewage Treatment works. In July 2024 Severn Trent announced a £450m programme to cut spills from other storm overflows at 900 sites across the Midlands.