Spelga Dam, Kilkeel Road, Hilltown, Newry, Co Down, BT34 5XL

Spelga Dam is an extensive water infrastructure complex constructed between 1954 and 1957 by the Portadown & Banbridge Regional Waterworks Joint Board, and officially opened on 30 June 1960. Designed by consulting engineers R. Ferguson and S. McIlveen, with J.B. Lakely as engineer and built by contractors John Laing & Son Ltd, the dam sits at the top of the Spelga Pass on the south side of the Hilltown to Kilkeel road in a spectacular mountainous setting. The reservoir it created covers what was formerly the Deer's Meadow, a summer booleying (transhumance grazing) area in the medieval period. A section of the original road was submerged during filling of the reservoir, and a new road was constructed around the north and east sides; a hump-backed rubble-stone bridge, now submerged, can still be seen at times of very low water.

The complex comprises five distinct elements: the dam itself and its associated water channels; the entrance gates and walling; the dam superintendent's house; a garage; and a quarry.

THE DAM

The dam spans the River Bann's narrow and precipitous exit from the Deer's Meadow. It is a mass-concrete gravity dam with a vertical wet face to the east, a steeply pitched dry side to the west, and two straight wings meeting at a central point on the upstream side. Corrugated metal panels have been fixed to the top of the wet face to prevent overspill during stormy conditions at high water.

At the apex of the dam is a small octagonal valve house which projects into the reservoir. It has a flat roof, granite block walls, an entrance door to one face, and windows to five other faces, all with concrete dressings. This tower is approached by a metalled path running along the top of the dam, with metal handrails to each side. It also gives access to an internal inspection gallery running along the base of the dam. There are three draw-off levels in the abstraction pipe.

Symmetrically arranged on either side of the valve house are four banks of triple siphons, a later addition installed between April 1974 and March 1975 by Charles Brand & Co. to a design by Ferguson & McIlveen. These siphons are self-activating and designed to carry off excess floodwater. Their installation arose from a decision in the early 1970s to raise the water level within the existing dam by 38 inches (97 centimetres), increasing reservoir capacity by 22 percent to 733 million gallons (3,327 million litres), in response to anticipated population increases in mid-Down. This raised head meant that the highest possible flood — even a once-in-500-years event — could have overspilled the top of the dam, since the two existing spillways, each 50 feet (152.4 metres) wide, could not be widened without substantial work to the foundations. The solution was to install twelve siphons arranged in four banks of three, located on the outer thirds of the existing spillways. Their overspill level was set 38 inches above the previous spillway level, and the height of the spillway between each pair was increased using adjustable metal sluices. Each siphon is capable of abstracting 9 cubic metres of water per second. Under maximum possible flood conditions, the increased head is only 10 inches (25 centimetres) and will not overspill the rest of the dam. A further ingenious feature is that the siphons' internal profile makes them self-priming, meaning they do not require a vacuum at their discharge end to start the flow. This low-cost system had been used successfully at Eye Brook Reservoir in Leicestershire in 1955, and Spelga was its first use in Ireland. The four banks of triple siphons are of special note in the history of civil engineering for this reason, and the dam is regarded as a rare example of its type.

Between each set of siphons is a vertical metal sluice gate spanned by a concrete footbridge forming part of the walkway across the dam. Each of these sluice gates is also a later addition to the original spillway arrangement. The discharge from each pair of siphons is confined by raised training walls to an open tank at the base of the dry face, known as a "bucket", lined with ashlar granite to minimise erosion. From there the water passes over a vertical weir into a common stilling pool, from which it overspills a second weir into the discharge channel proper. This arrangement confines the overspill so as to prevent undermining of the dam's foundations and to ensure that the energy of the falling water is dissipated before it enters the discharge channel. The scour pipe also discharges from the base of the dam into the common stilling pool. There is a small concrete footbridge over the discharge channel and another across the holding tank on the south side of the channel. All channels in the vicinity of the dam have vertical concrete-rendered walls. There is also a large enclosed concrete cistern immediately below the dam on its south side, and further downstream a small weir and compensation flow recorder.

The dam is 1,132 feet long, 98 feet high, and 102 feet thick at its base. Some 80,000 cubic yards of concrete were used in its construction. The reservoir covers 148 acres, has a capacity of 600 million gallons, and is fed from a catchment of 1,740 acres. Together with the Board's existing reservoir at Fofanny on the Upper Shimna (opened 1909), the dam can supply 6.5 million gallons per day, with a compensation flow of 0.5 million gallons per day. A new filtration plant was opened in 1960 at Fofannybane to service both the Fofanny and Spelga reservoirs.

The north bank of the reservoir is pitched with granite rubble for a short distance above the dam. Further along the north bank is a public car park containing a prominent plinth of quarry-faced granite blocks, all ribbon-pointed, into which three plaques are set. On the left (when facing the reservoir) is a bronze plaque outlining the dam's construction, including its dimensions and a diagrammatic cross-section. In the centre is a circular polished granite plaque reading "Portadown & Banbridge Regional Waterworks Joint Board 1948" with a depiction of a water fountain. On the right is a second bronze plaque dated 1960 outlining the dam's historical development, recording that the proposal was initiated by the Portadown & Banbridge Joint Water Board in 1946, which was absorbed into the Regional Joint Board in 1948 and comprised Portadown Borough Council, Newry Urban District, Newry No.1 Rural District, Banbridge Rural and Urban Districts, Tandragee Rural District, Dromore Urban District, and Downpatrick Rural District; the dam also supplied the Kilcoo area of Kilkeel Rural District. Construction began in 1954, with concrete pouring commencing in October 1955; water began to flow into the reservoir in August 1957 and overflowed the sill in November of that year. Something was formerly mounted on top of the plinth but has since been removed.

GATES AND WALLING

The top of the dam is accessed by a metalled track from a small parking area on the north side of the reservoir. This area is enclosed by a rubble granite wall coped in concrete, into which is set a pair of steel gates hung from ribbon-pointed granite piers with pyramidal concrete caps. The gates carry raised capital letters reading "Spelga Dam". On the outside face of each pier is a bronze plaque: the left plaque records the laying of the foundation stone by Dame Dehra Parker, Minister of Health and Local Government for Northern Ireland, on 18 May 1956, and lists the members of the Board's Working Committee (chaired by R.J. Morgan JP, OBE), along with the engineer, consulting engineers, contractors, and resident engineer (J.A. Soye). The right plaque records the official opening by N.T. Dickson, Vice-Chairman of the Board, on 30 June 1960, with equivalent details of the committee and officials. Similar but smaller gate piers are found on the roads leading to the superintendent's house and to the garage.

SUPERINTENDENT'S HOUSE

The superintendent's house lies below the dam on the north side. It is a one-storey, four-bay dwelling with a pitched natural slate roof, plain painted bargeboards, two granite block chimneys, and plastic rainwater goods. The walls are finished in painted cement wet dash. The main elevation faces west and has a porch to the third bay from the left; the left cheek of the porch contains the half-door entrance and the other faces a top-hung 1-over-1 double-glazed window. Each remaining bay has a double-glazed window. The right gable has a window to the right. The rear elevation, which faces the dam, is abutted at the right by a wall enclosing a small yard and outhouses, all with small transom lights. There are two windows to the left. The left gable is blank.

GARAGE

Down the slope to the south-west of the house is a one-storey, two-bay garage, with a roof and walls matching those of the house. It has two large tongued-and-grooved sheeted doors to the south wall, blank gables, and a glass-brick window to the north elevation.

QUARRY

A short distance up the slope immediately to the west of the dam is a large quarry from which granite was extracted for use in the concrete during the dam's construction. At the south-western corner of the quarry, up the slope, is a small concrete post on which an alignment sighting instrument was formerly mounted.

The dam has been scheduled as a historic monument under the Historic Monuments and Archaeological Objects (Northern Ireland) Order 1995.