Huge storm overflow water tank built

The tank can hold three Olympic sized swimming pools of water

A huge underground water tank has been made to protect residents from flooding and sewage spills going into rivers in Stroud.

The storm overflow tank is the largest of its kind in the UK and can hold 7,400m3 of water - the equivalent of three Olympic sized swimming pools.

The colossal concrete-lined tank is a major component of a £25m scheme to upgrade the sewer network in Stroud and help prevent future flooding.

Steph Cawley, director of operations at Severn Trent said: "This is designed to stop rain water getting into the environment before it's been treated and remove sewage spills."

Steph Cawley, director of operations, Severn Trent

The new tank will have cutting edge smart controls that can hold water back during severe weather events and return it back to the treatment works when rainfall has subsided.

Much of Stroud's sewage network dates to Victorian times and the project to upgrade it has involved laying more than 1.7km (1.05 miles) of pipes.

Ms Cawley said: "In the next 12 months it will be completely finished and ready to go but in the next few weeks we will be putting the lid on.

"It's designed for a one in 100 year storm, so we hope it would never get full and ideally it will fill a little bit, we'll have a dry period and then it will fill up again.

The lid of the tank will be going on in the coming weeks

Ms Cawley said: "On a normal day our treatment works have enough capacity to treat everything that comes through, this is really for the storms.

"Last year we had 11 named storms so it would come into its own on those occasions.

"This will help when we have excess rain water to capture it all and store it so that when the rainfall stops we can safely treat it and return it to the environment.

"It's particularly important here because with the topography we have a lot of run off from the land with a lot of excess water in our sewers that we don't want to get into our rivers."

She added the need for the tank had become obvious eight years ago.