A network of tanks that can hold 13 million gallons of rain water have been installed beneath the city centre to protect Birmingham from flooding.

Sluices to the underground chambers will be opened if roads, offices and shopping centres are in danger of being deluged.

The tanks will safeguard the area around Birmingham’s Eastside development area which will be transformed from urban wasteland into hotels, a city centre park and a technology quarter.

It could also be home to a terminus for trains if plans for a high speed rail line get the go ahead.

To put the scale of the £500,000 mammoth plumbing project – which began this week – into context, the tanks will be able to hold the same volume of water as 22 Olympic-sized swimming pools.

Council chiefs say that they will only need to open the floodgates as a last resort if Birmingham experiences freak rainfall levels which occur just once in every 100 years.

David Lloyd, programme manager for the project, said: “In a few years, the area will be covered with a lot of concrete that will mean rain water washes straight off and could overwhelm drains and flood plains around the River Rea and River Cole.

“The systems we currently have in place can’t hold enough water for new guidelines.

“The tanks would only need to be used in a truly spectacular spell of rain, the like of which we haven’t seen for a long time.”

The tanks are formed from a series of large pipes, each 2.5 metres or 8ft diameter. They will be sunk five metres below the surface of the earth at a site just off Curzon Street.

Contractors took delivery of the pipes from a specialist contractor on Monday and work is expected to take about three weeks to complete.

Workmen were given the all-clear after a bomb-squad more used to working in war-torn Iraq visited the site last month to check for unexploded Second World War devices.