Belfast Sewers


Duration:4 years


Country: Belfast, UK

What did this project achieve?

Upgrade Victorian sewer system to cope with modern day demands

The Belfast sewer system was originally built by Victorian engineers in the 19th century. It was designed as a combined system with both sewage and storm water flowing through the same pipes.

Two centuries later the Victorian system was struggling to cope. Bad weather could mean significant flooding of residential areas due to lack of capacity in the sewer network.

As well as flooding, overflow from the sewers into the river Lagan caused pollution during heavy rainfall.

The Belfast Sewer Project – nicknamed ‘Belfast’s Big Dig’ – aimed to improve the quality of urban life in the city by upgrading waste water infrastructure to the same level as other major cities.


Difference the upgrade has made

Pollution to the river Lagan has reduced. Homes and shops in Belfast are protected from being flooded during storms.

The upgraded sewer system has also played an important, if largely unseen, role in helping urban redevelopment in the city. With less chance of flooding, businesses are more likely to invest.

The project also helped improve water quality in the river.

How the sewer upgrade work was done

‘Belfast’s Big Dig’ took 300 people 4 years to complete. It included the upgrade and repair of old brick sewers and the construction of a new 6 mile storm water tunnel under the city.

The main challenge for project engineers was geology. The ground in the area is made up of saturated alluvial deposits – sand, gravel and clay impacted into rock. Additionally, the water table in Belfast is high. Both these factors made tunnelling difficult.

Engineers used a tunnel boring machine (TBM) nicknamed Lucille to dig the storm water tunnel. Lucille was 90m long and pulled 250 tonnes of support equipment and machinery as it worked its way through the soil.

The TBM’s ripper teeth and roller cutters could power through the toughest of compacted sediment and grind any boulders that got in its way.

Lucille stopped every 1.2m so the tunnel lining could be built behind it. Engineers fitted together 6 pre-cast concrete segments into a 1.2m wide ring with an internal diameter of 4m. A special grout was used to support the lining and stabilise the soil.

A terminal pumping station (TPS) was built at the downstream end of the tunnel. The TPS can pump 4,000 gallons of water per second and was designed to cope with storm water overflowing from the sewer network in the heaviest of rainfalls.


The scheme is designed by the highest industry standards to last well into the 21st Century.

Conor Murphy

Minister of the Department for Regional Development

Fascinating facts

The system’s pumping station is the biggest in Northern Ireland – its capacity of 4m gallons is the same as 7 Olympic size swimming pools.

The storm water tunnel has 19 access shafts and runs at an average depth of 30m.

Jeremy Clarkson and the BBC’s ‘Top Gear’ team used the storm water tunnel to re-enact the classic underground car chase from 1969 movie ‘The Italian Job’ while the Belfast tunnel was under construction. Clarkson swapped a Renault Twingo for the Minis used in the original film.

People who made it happen

  • Storm water tunnel construction: Morgan Est and Farrans Construction
  • Upgrading sewer network: Dawson WAM, McAllister Brothers JV, John Graham (Dromore) Ltd

More about this project

Explore more civil engineering projects

I want to become a civil engineer.

See how your studies lead to a civil engineering career

The job you end up with in civil engineering is likely to link back to what you studied at school, college or university. Here you can see your options at any age.

Studying at school

Up to 16 years

School / college

15-18 years

College / university

18 years +

Change career

Any age