New sewer tunnel to spare Belfast repeat of costly flash flooding

The 9.4km structure will deal solely with excess storm waters from existing sewers

DOWN DEEP in Belfast’s newest sewer one couldn’t help humming the Harry Lime theme from the film The Third Man or picturing Michael Caine and the Mini car chase from The Italian Job.

We’re standing 30m under ground at the end of 9.4km of tunnel, much of it 4m in diameter, that stretches in an inverted Y-fashion from central areas of Belfast to the city’s docks at Belfast Lough.

Close by are six massive pumps designed to prevent much of Belfast suffering the flash flooding of recent years that has cost millions of pounds in damage to homes, businesses and roads infrastructure.

Arc lamps cast some light along the tunnel but it’s dark and eerie and it’s impossible not to conjure the image of doomed Harry Lime, played by Orson Welles, running through the sewers of Vienna trying to evade the character played by Joseph Cotten and the chasing pack who want to nab him for his nefarious crimes.

It’s easy to let your imagination run free in an odourless sewer and there is no foul smell because this huge Northern Ireland Water stormwater management project isn’t due to start operating until the end of this year.

The new 9.4km of tunnel has the sole purpose of dealing with the excess storm waters that flow from the existing 1,300km of sewers – much of it dating back to the Victorian 1870s – in heavy rain. The water ends up at the end of the tunnel to be pumped into Belfast Lough from six pumps each capable of dispersing 4,000 gallons a second.

Normal sewage is treated elsewhere in the general docks area and pumped out further up the lough. Hitherto, the current sewers have been unable to cope with storm pressures, resulting in burst manhole covers and heavy flooding in areas of Belfast such as Ormeau Road, Ravenhill Road and Ladas Drive, as well as pollution of the River Lagan.

Project manager Dr Alan Skates of consulting engineers Atkins says the new tunnel can deal with a storm as severe as one might expect over a 30-year period.

The cost of the Northern Ireland Water project, which was carried out by British firm Morgan-Est and local firm Farrans, is £130 million with an additional £30 million spent on upgrading some 500 sewers that were in poor conditions.

By the end of the year, engineers will start opening 10 of 19 new 30m deep shafts which will bring the overflow from the existing sewers to the new tunnel at times to in turn connect to the pumping station. Such overflows are estimated to happen only a few times a year.

There are longer-terms plans for two more similar overflow tunnels to be developed to cater for the east and west of Belfast.

“While the cost of the project may seem high, there will be a long-term beneficial affect,” Dr Skates says. “Not only should this end the costly flooding in parts of Belfast but it should also prevent the overflows that currently end up in the River Lagan.

“We estimate that this will reduce by 80 per cent pollutants from the Belfast sewers going into the Lagan. It’s been a roller- coaster, challenging ride.”

In total 250,000 cubic metres of rock and soil was excavated. More than 270 people were employed at peak and thankfully no one was killed or seriously hurt during what Dr Skates says was “risky and dangerous work”.

Despite the traffic disruption, most Belfast people were oblivious to this massive project.

They will have an opportunity to get a worm’s-eye view of the tunnel later this year or early next year in the next Top Gear series for the BBC, which will feature two Renault Twingos racing through the new state-of-the-art Belfast sewer.

It will all make sense, say the Northern Ireland Water people who invited Top Gear in to film, but only insofar as anything makes sense on Top Gear.