Belfast’s sewer network, which dates back to the Victorian era, was suffering as a result of sustained underinvestment coupled with inadequate capacity as a result of the city’s continued expansion.
To address the problem, Northern Ireland Water (NIW) undertook a major Stormwater Management project called The Belfast Sewers Project. The £120 million project aims to improve water quality in both the River Lagan and Blackstaff River while reducing the risk of flooding within the inner city. It also incorporated the rehabilitation and upgrading of the sewer network to ensure compliance with European Union environmental standards.
Belfast is built on an area of complex glacial and fluvio-glacial deposits, which are highly variable. These ground conditions created a number of challenges which required some complex solutions.
Advanced techniques were incorporated into the construction process including major system formwork for the Terminal Pumping Station, Earth Pressure Balance tunnelling methods and sprayed concrete shell techniques for excavations in clay and rock.
A key project landmark occurred in April 2008, with the completion of one of the deepest tunnels.
The Belfast Sewers Project involves work to upgrade the existing sewer networks and the construction of a large diameter drainage tunnel to increase stormwater capacity. A contract to upgrade the sewer network was started in 2005. There are approximately 1,800 km of sewers covering a catchment area of 42 square kilometres. The older central area of Belfast is currently served by two large diameter brick sewers which date back to 1888 and a third concrete sewer which was commissioned in the 1970’s. The tunnelling work is the final part of the Belfast Sewers Project and will provide the required increased capacity in the sewerage system.
The implementation of Belfast Sewers Project will result in the closure of a significant number of the existing combined sewer overflows, which will reduce the pollutant load from the sewerage system on the River Lagan and its tributaries by 85% of present levels. The route of the tunnels was determined by ground conditions, the availability of sites for the tunnel shafts, and other logistical constraints.
A two stage project, the first part concentrates on the sewers, with the following aims:
- To upgrade 500 sewers starting in 2005;
- To use state of the art low dig and no dig technology.
- The second stage of the project looks at stormwater management, with the following facts and aims:
- The construction of some 9.5 km of tunnels ranging from 4.0 metres to 1.8 metres in diameter distributed throughout the city centre area at varying depths.
- The creation of 20 access shafts between 6 and 15 metres in diameter.
- The construction of a 38m wide, 40m deep terminal pumping station; and the addition of a storm tank at the Belfast Wastewater Treatment works.
- The stormwater tunnel system will increase the capacity of Belfast’s sewerage system.
- The project will involve the closure of several existing combined sewer overflows.
- Pollutant load from the sewerage system into the River Lagan and its tributaries will be dramatically reduced.
One of the deepest tunnels was completed in April 2008. The 1,500 metre tunnel, which is four metres in diameter, runs from Whitla Street to a new high-tech terminal pumping station at NI Water’s massive water treatment works Duncrue Street. Capable of holding vast overflows of stormwater – as much as four million gallons – it will reduce the risk of sewer flooding.
This section of tunnel is the longest completed stretch of the Belfast Sewers Project, which when finished will comprise a 9.4km (6 mile) tunnel from Cromac Street to Duncrue Street, with a network of tributary tunnels. The tunnel and pumping station are 40 metres below sea level, the deepest excavation ever in the Belfast area.
The Minister for Regional Development Conor Murphy commented, “The breakthrough is a key milestone in this vital project. The scheme represents a commitment to providing Belfast with a sewerage network that has been designed by the highest industry standards to last well in to the 21st Century. This system will accommodate the expanding city and its drainage needs, significantly reducing the risk of flooding and reducing the risk of pollution to the River Lagan.”
Chris Mellor, Chariman and Chief Executive, NI Water said: “The breakthrough represents another landmark in our journey to a modern and effective sewerage system for Belfast. Northern Ireland Water has a massive programme of water and wastewater infrastructure under way right across the Province. This involves an investment of a million pounds every day in works which will benefit all our 1.7 million uses by providing world quality standards and services. I am delighted that we are well on track to bring such large scale benefits to the city.”
Bill Gowdy, NI Water project sponsor, explained that the tunnel boring machine (TBM) has been operating at a rate of 30 feet per hour since June 2007 and following a naming-tradition on projects of this nature the TBM is called “Lucille”.
He added: “Lucille was specifically selected for this work to ensure that tunnelling on such a large and complex scale could be delivered swiftly, accurately and safely without disturbing surrounding soil.”
Morgan Farrans are the main contractor for this major investment, alongside NI Water’s appointed Project Managers, Atkins. Throughout each stage of this programme a range of advanced technologies to ensure that the initiative runs safely and efficiently have been employed. The programme is due for completion in late 2009/early 2010. •
Christine McKenna, NI Water