Instrument Sighting Tower, Donard Forest, Drinnahilly, Newcastle, Co Down

Instrument Sighting Tower, Donard Forest

This is an instrument sighting tower constructed as part of the Mourne Water Scheme and is probably a unique survival in Northern Ireland. The tower is situated just inside the tree line a short distance south-west of Drinnahilly summit, positioned on the line of the Mourne Conduit which is here tunneled under the mountainside.

The structure comprises a square tower measuring 4.95 metres at the base and approximately 10 metres high. Four slightly tapering walls are built of random Silurian rubble with squared granite rubble quoins and concrete coping at the top. The walls have been heavily repointed in cement. An entrance at the west end of the south wall is now infilled with concrete blocks. There are two openings: a single opening on the left side of the west wall towards the top, and another higher up on the north wall. Both openings have single granite heads with no cills and retain wooden frames, which may originally have been shuttered rather than glazed.

Inside the tower stands a square tapering random rubble pillar rising from the ground and surmounted by a concrete pillar which projects approximately 1 metre above the wall line of the building. This would probably have supported a telescope mounted on a horizontal axis and capable of being turned in a vertical plane. A hemispherical metal frame with eight curved legs rises over this pillar from the wall head. The legs meet at the top in a circular ring which formerly stabilised a projecting semaphore pole. This frame may have been for protecting the sighting instrument, though there is no indication of how it was originally covered. A contractor's drawing shows that the sighting instrument was mounted on a metal plate on top of the concrete pillar and protected by a glazed wooden frame.

The tower was constructed in connection with the Mourne Conduit, which brought water to Belfast from the Annalong and Kilkeel rivers. The construction of this section was advertised by the Belfast City & District Water Commissioners in March 1896. The contract was awarded to H & J Martin of Belfast and involved the construction of a 3445-metre long concrete-lined tunnel under Millstone and Thomas Mountains on the north-eastern slopes of Slieve Donard. The aligning of the tunnel necessitated the erection of instrument sighting towers at each end of its intended route — one here at the Tullybranigan end at the highest point on the surface and 178 metres over the tunnel, and another on Millstone Mountain of which no trace survives. There was also a third near the main road at the Ballagh end, from which sightings were taken into the tunnel as it was being constructed. The tunnel was completed during the summer of 1901 and water flowed to the service reservoir at Knockbracken in October of the same year.