Short History of Belfast’s Mourne Water Supply


(Prepared by W R Darby at the request of the South Belfast Historical Society)



As Belfast grew throughout the 18th and 19th centuries the demand for clean water constantly outpaced the supply.  Initially the supply was from the springs in and around the early settlement, but by 1795 it was clear that matters had to be better regulated and in that year the control of the water supply in the town was vested in the Charitable Society.


With a continuing increase in population and demand from the increased economic activity, the Belfast Water Act 1840 was passed and the newly constituted Commissioners became responsible for supply to a population at that time of over 70,000.


In spite of the vigorous programme of works and the bringing into service of more streams and springs in and around the town, by 1852 there was a shortfall of almost one million gallons per day with the position worsening as the population and activity continued to grow at an unprecedented rate.  There followed a series of Parliamentary Acts (1865, 1874, 1879 and 1889), which expanded the system to include reservoirs as far out as Woodburn (above Carrickfergus) as well as increased storage within Belfast.


With the granting of the Belfast City charter in 1888 the boundary was greatly extended from Greencastle to Shaw’s Bridge and Wolfhill to Knock and the Water Board was redesignated as Belfast City and District Water Commissioners. The Stoneyford Works (above Lisburn) were authorised by Parliamentary powers obtained in 1884 to cope with this expansion of the city into higher surrounding areas.


By 1891 the further increase in population led to the appointment of Mr Luke Livingstone Macassey MICE to survey and report on the available sources.  This resulted in the decision to proceed with the Mourne scheme as he had recommended and statutory powers were obtained under the Belfast Water Act of 1893.


It is interesting to note that Lough Neagh, which is now such an important  water source for the entire area, was at that time considered to be “entirely unsuitable” and impossible of being rendered suitable for town supply by ordinary sand filtration. That view was reported by Macassey from an analysis carried out by Mr Robert Barklie FCS.


Macassey declared the Mourne catchment as “beyond suspicion” and “the water soft and pure and possesses a bright appearance”.  Another bonus was that the Mourne scheme could proceed by instalments so that the supply could be piped to Belfast before any Mourne reservoir was built.


Water intakes were constructed on the Kilkeel and Annalong rivers together with a conduit, pipeline and tunnels to take the water to a new open service reservoir at Knockbracken capable of storing 100 million gallons.   Macassey had estimated correctly that the Mourne scheme would be capable of supplying Belfast with 30 million gallons per day.  With the completion of this first stage, Mourne water became available to Belfast in 1901 at a rate of 10 million gallons per day.


By 1910 it had become apparent that the increase in demand called for Stage 2, which was the construction of the Silent Valley reservoir and an increase in the capacity of the pipeline to 20 million gallons per day.  Preparations were well advanced when war broke out in 1914, and it was not until 1923 that construction began on the reservoir, with the cutting of the first sod by Edward Carson (by then Lord Carson of Duncairn).


Construction of the reservoir embankment proved very difficult and stretched the technology of the time to the limit.  Earlier test borings had suggested bedrock at 50 feet, but this proved only to be large boulders in a glacial moraine and bedrock was some 150 feet or more below the valley floor.  This greater depth in water-saturated ground could only be worked in by the use of cast iron shafts with men working in compressed air compartments to keep out the watery silt.  The “cut-off “ trench required to seal the dam wall was excavated down 32 feet into the solid rock to finish some 212 feet below the original river bed, with that phase being completed in 1929 after six frustrating years.  Completion of the reservoir was now straightforward and the water first reached designed top water level in September 1932.  It is reported that there were eight fatalities during the construction, which took ten years rather than the six originally contracted.  The reservoir was finally completed at a reported cost of £1,350,000 and was officially opened on 24th May 1933 by the Duke of Abercorn, Governor of Northern Ireland.


So, with a storage capacity of 3,000 million gallons at the Silent Valley and delivery capacity of 20 million gallons per day to the Belfast area, it was not until after WW2 that further works were called for and Stage 3 was started.


For stage 3 the original Macassey plan to build a second reservoir in the Annalong valley was abandoned and a two and a half mile tunnel was constructed in the period 1950 to 1952 under Slieve Bignian.  This allowed the bulk of the flow in the Annalong river to be routed into the Silent Valley reservoir and enabled much fuller use to be made of the 9,000 acre Mourne catchment area.  It was not, however, until the 1957 completion of the Ben Crom reservoir above the Silent Valley that the full potential was achieved.  This last reservoir added another 1700 million gallons to the storage capacity at the catchment.



Macassey predicted the Mourne works would provide for Belfast’s needs to the end of the 20th century, but by 1960 the Water Commissioners were supplying an unpredicted 540,000 consumers in the Belfast area.  As the Belfast area continued to grow and industry developed, particularly the man-made fibre industries, a new major water source was required.  This was to be the earlier maligned Lough Neagh, which with modern pumping and treatment methods satisfactorily provided initially 10 million gallons per day with a potential for a trebling of that output.  The first phase became operational in 1968 and has been much enlarged since then.  Following the decline in the man-made fibre industries, there was a slowing in growth of demand for water and some of the major schemes planned in the 1970’s and 1980’s were not required.  As demand increases it is likely that once again Lough Neagh will be used to meet it.


Mention must also be made of the construction of the famous Mourne Wall which surrounds and protects the catchment area.  Construction of this 22 mile long wall began in 1904 and took 18 years to complete.  It provided work for many in the area with construction being carried out in the early Spring to late Autumn throughout that period.  It is truly a wonderful piece of work and is a very useful navigational aid for people enjoying the Mournes, particularly when the mist descends.


William R Darby

2 November 2010.

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