Severn Trent has unveiled one of its largest ever storm overflow storage tanks to protect residents from potential flooding - and boost river health by preventing spills.

The 25m deep by 25m wide concrete-lined tank in Stroud, Gloucestershire, has been built in conjunction with partners Galliford Try and has a capacity of 7,400m3 – the equivalent of three Olympic sized swimming pools or over 24,500 bathtubs of water.

The mega-tank is a key part of Severn Trent’s £25 million project to upgrade Stroud’s largely Victorian-built sewer network and also includes installing four miles of new enlarged pipes, as well as separating surface water from the waste network. Four tunnel boring machines were used to install the new sewer pipes under the town to minimise disruption, as well as lining 1km of old brick Victorian sewers with polypropylene to stop groundwater infiltrating and adding more water to the pipes.  

The tank will drastically improve water storage capacity in the area by around 1,300% during heavy rainfall, helping to reduce sewer flooding and spills into rivers and watercourses. It will have cutting edge smart controls that can hold storm water back during severe weather events and return it back to our treatment works when rainfall has subsided.

Severn Trent gave a fascinating glimpse inside and from above the storm overflow storage tank, ahead of a new concrete lid being installed within the next few weeks.

Steph Cawley, Customer Operations Director, said: “This enormous storm water tank is an incredible feat of engineering that will benefit residents for generations to come.

“Much of the Stroud sewer system was built in Victorian times, but 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.”

Chloe Dobbs, 24, is Lead Project Manager on the scheme after joining Severn Trent as an apprentice aged 18.  She said: “I’ve loved the opportunity to work on one of the biggest projects of its kind for Severn Trent. It’s been an amazing experience.

“Customers and the environment have been central to this project. By creating so much extra storage, we are going to prevent future flooding for residents and businesses - and of course reduce potential overflow spills into waterways.”

Severn Trent has previously announced a £450m programme to cut spills from other storm overflows at 900 sites across the Midlands this year alone. Chloe, a former pupil at Ash Green School in Coventry, added: “There are many projects like this taking place across the region – although not quite all on this scale!”

Peter Richardson, Senior Project Manager, Galliford Try, said: “We are delighted to have been working with Severn Trent to deliver this innovative scheme that will bring so much benefit to the community, contributing to a reliable sewer network, protecting homes and businesses from blockages and flooding, and improving river health.

“This is a remarkable engineering project and its success is testament to the close collaboration with our client and supply chain and using new techniques and modern methods of construction and engineering.”

The £25m Stroud scheme will also include the removal of a large sewer pipe that runs through the canal in the town, plus improvements at the Stanley Downton Sewage Treatment works.

Severn Trent’s investment plan for the next five years was one of only two from water companies labelled ‘Outstanding’ by water regulator Ofwat, with £11.8bn of funding so far approved. Severn Trent was recently awarded the highest 4*star rating for Environmental Performance from the Environment Agency for five consecutive years – the only water company in the UK to achieve this.

ENDS