By 1910 the ever-increasing demand for water was putting pressure on the Commissioners to implement stage two of Macassey’s Mourne Scheme – the building of the Silent Valley Reservoir with a capacity of 3,000 million gallons. Unfortunately, the talented engineer who devised this remarkable scheme with great foresight, never lived to see its completion, having passed away two years earlier in 1908.
The Commissioners’ own Chief Engineer, Mr F.W. McCullough and his team prepared the design and contract drawings for the new impounding reservoir which were in an advanced stage when war was declared in 1914.
It was 1922 before tenders were invited and the contract was eventually awarded in 1923 to Messrs. S. Pearson and Sons for just over one million pounds, a sum later renegotiated to £983,250. The first sod on the construction of Silent Valley was cut by Lord Carson on 10th October 1923 and within weeks ‘Watertown’ as it is known today, was emerging. Houses and hutments were built to accommodate the engineers, supervisors and workmen. The site had its own hospital and police station and there were shops, a canteen and a cinema for recreational use. The ‘town’ had its own coal-fired power station, which also provided the first street lighting in Ireland.
The infrastructure was further supported by a purpose-built railway constructed between the Silent Valley site and Annalong Harbour, a distance of 4.5 miles. In addition to carrying heavy plant and machinery, the track was also used to convey over one million tonnes of material and many hundreds of workmen.
2,000 men worked at the Valley from 1923 to 1933 – sadly eight lost their lives during construction work. For the men from Mourne, the Silent Valley contract was a godsend, for the only available work at that time was in the stone quarries or the fishing boats. The job-hungry men of Mourne walked incredible distances to get to work in Watertown, with many crossing the mountains twice a day.
The construction of the reservoir was a stringent test to engineer and labourer alike. Due to the geology of the valley floor, a 212 feet deep cut-off trench had to be constructed to eliminate the risk of water pressure uplifting and moving the dam. An ingenious method of construction using air locks and compressed air (35psi) kept the water out of the excavations. These extremely arduous conditions restricted the workforce to only the fittest of men and a limited working day.
Where the trench was more than a 100ft deep, the walls were supported by special cast iron segments. Once excavated, the trench was filled with concrete. All of the concrete was mixed by hand and on some days up to 100 tonnes were poured. As one of the greatest civil engineering achievements ever, the Silent Valley Reservoir was opened on 24th May 1933 by the Duke of Abercorn. The final cost of the scheme was £1.35 million.