The sewer systems in Belfast were built by the Victorians in the 19th century. These large pipes were designed as a combined system with both stormwater and raw sewage. This old joint system struggled to cope with the two centuries of urban growth in Belfast, causing flooding and pollution during heavy rain.

 

There has since been projects to increase the capacity of the system ranging from 30m to 40m below the ground. The most recent of which finished in 2010 and created an additional 9.5km of tunnel under the city at 4m in diameter. The hope is that the new tunnel will be able to protect the city from a 1 in 30 year rainfall event. In addition to this is has reduced the pollutant load being added into the River Lagan by 85%.

 

The sewer system has a terminal pumping station which can pump the water to the Belfast wastewater treatment works in Duncrue Street at a rate of up to 4,000 gallons of water per second. Any excess volume is discharged after screening through a diffuser into the Herdman Shipping Channel.