A £3m flood alleviation scheme has been completed in Bristol safeguarding 32 properties from flooding. Wessex Water has constructed two below ground storm storage tanks in St Paul's, Bristol, which will enable the local sewerage network to cope with a sudden increase in flows during storm conditions.

The tanks have a diameter of 12.5m and a depth of 15m. Combined they can hold up to 2,000,000 litres of sewage – nearly enough to fill an Olympic-sized swimming pool.

Andrew Smith, from Wessex Water, said the completion of the scheme - finished on time and below budget – had resulted in all 32 properties being removed from the flood register.

He said: “Before the storage tanks were installed the area’s 150-year-old Victorian brick sewers were unable to cope with the sewage flow during storm conditions, causing flooding at a number of properties in the area.

“Homes in Albany Road and Grosvenor Road which were affected by the flooding have now been safeguarded thanks to this vast increase in the capacity of the local sewerage system.”

The improvements have given the areas in St Paul’s protection against a one in 50 year flood, which means properties will be safeguarded during some of the most intense periods of rainfall.

Approximately 5,000 tonnes of rock was excavated during this scheme, which required both machinery and workers to be lowered into the tanks using a 50 tonne crane.  Workers also had to negotiate challenging conditions during the project, moving heavy machinery to and from the site through narrow, heavily parked roads while ensuring minimal disruption to residents.

The tanks were sealed with a pre-cast concrete cover, requiring the use of a 200 tonne mobile crane before the areas were reinstated, restoring them to their former glory.

“Despite the technically challenging nature of the works, the significant constraints imposed by the location and the restricted working area, the scheme was completed successfully,” said Mr Smith.

The scheme is the third major flood alleviation project completed in Bristol by Wessex Water this year. Recently a £9m tunnel under the streets of city centre was completed and a large wildlife pond in Henbury was created to store surface water during times of intense rainfall.