Knockbracken Reservoir, Saintfield Road, Belfast

Knockbracken Reservoir is an extensive waterworks complex on the west side of Saintfield Road, Belfast, comprising a reservoir and its related structures, a river by-pass channel, a scour valve and channel, a water attendant's houses and associated buildings, a chlorination house, and various ancillary buildings.

The complex was originally the principal service reservoir for the Mourne Conduit, which brought water from the Mourne Mountains to Belfast. Advertisements for its construction were placed by the Belfast City and District Water Commissioners in October 1894. The contract was awarded to Messrs Fisher and Le Fanu at a price of £33,444 — the same firm that carried out works at the Mourne end and later built the Silent Valley Reservoir in the 1920s. The reservoir was being puddled in August 1897, completed in February 1900, and opened by Robert McConnell on 2 October 1901. Initially, water was supplied only from the Annalong River, but following completion of the Brackenagh Tunnel in mid-1903, this supply was augmented by the Kilkeel River. The Silent Valley Reservoir came on stream in 1933, followed by Ben Crom Reservoir in 1956. A chlorination plant was added in 1953. Most water from the Mourne Conduit now bypasses this reservoir, feeding directly into the larger of two covered reservoirs at Breda. Knockbracken has continued in use only because increased demand necessitated a continued supply to the smaller of the two Breda reservoirs. The complex will probably be abandoned once the conduit from Newcastle is relaid.

The Reservoir

The reservoir is L-shaped and open. It was formed by excavating the east bank of the Carryduff River and placing a large earthen embankment across the valley at its north end. The inside faces of the reservoir are sloped and pitched on their wet sides with rubble stone.

Water discharges from the Mourne Conduit into the reservoir at its south end, where a concrete-lined recess in the bank is surrounded on three sides by a three-bar metal railing. The water falls over two vertical drops and down an incline into the reservoir. Metal baffle plates across the lower fall and a concrete post at the bottom of the incline break the force of the water and assist its aeration.

Water is abstracted from the reservoir at its north-east end by two vertical cast-iron standpipes, 36 inches in diameter, with valve stocks at the top to control flow. Access to these valves is by a metal footbridge supported on two dressed granite piers, which drawings show to be a facing over concrete. At the north-west end of the reservoir, the bank is broken to accommodate an overspill weir that discharges into the Carryduff River. A footbridge formerly spanned this overflow, but only its cast-iron piers now survive.

River By-Pass Channel

The Carryduff River has been diverted around the west side of the reservoir in an artificial channel. Just before it enters the reservoir grounds, a small cascade weir breaks its flow as the river passes underneath the public road through two cement-lined segmental-headed culverts. There are two concrete-decked metal footbridges over this channel at the reservoir's overspill. The river then cascades down a series of paired steps, at the foot of which the scour channel meets. This section of the channel has vertical random rubble walls, after which the river continues down the valley along its natural course. A short distance south of this complex is a modern lime dosing plant, similar to those at the Silent Valley and Dunmore.

Scour Valve and Channel

On the dry side at the foot of the embankment is a scour channel that falls from east to west and discharges into the Carryduff River channel. It carries the outflow of the reservoir when accumulated silt is being scoured from the abstraction pipes or when the reservoir is being drained. There is a concrete-lined valve control well at its upper end. The channel is piped for a short section from the valve chamber, and part of the bank has random rubble revetments. At its lower end, a series of steps reduces the force of the flow before it meets the river.

Water Attendant's Houses and Related Buildings

The original attendant's house, known as Waterworks Lodge and addressed as 591 Saintfield Road, stands on the east side of the reservoir within a mature planting of conifers. It had been vacant for around six years at the time of survey. The house is a one-and-a-half storey, three-bay dwelling of T-plan, with a one-storey return in an enclosed yard at the rear. The original drawings for the house were signed by Messrs Robert and David Laidlaw of Glasgow, though one Alex Gaill may have been the actual contractor. The building appears to have been completed around 1896. It is similar in design to the water attendants' houses at Silent Valley and Dunnywater, though it has a cement render finish of which no trace is now evident on those comparators. The drawings confirm that the wall render is an original feature.

The house is oriented east–west, with the top of the T at the east and the principal gables facing north and south. The roofs are pitched and covered in natural slate, with ogee cast-iron gutters on projecting eaves. There are plain bargeboards to the gable ends, each with framed apex finials. A yellow brick chimney stands at either end of the main ridge. The walls are finished in lined and painted smooth cement render over a smooth rendered base course. A plain platband runs around the building at cill level on both floors; it is uncertain whether this is of stone or concrete as it has been overpainted. All windows have been sheeted over with plywood or fitted with metal security mesh, with their cills incorporated into the platbands.

The principal facade faces north. At the left is the slightly projecting gable of the left front room. A verandah runs across the facade to the right of this gable. It has a monopitched natural slate roof carried on three round metal columns with decorative cast-iron brackets at the top. The verandah floor is laid in alternating red and white tiles. The main door, now sheeted over with plywood, is at the left end of the verandah and leads into the middle bay of the house. To its right are two 2/2 sliding sash windows. The left gable has two similar windows, with a horizontal drip mould shared by both. At first floor, above the verandah, a gabled dormer rises from the eaves and contains a semicircular-headed window with a run-moulded architrave. An identical window appears in the apex of the main gable at the left.

The east wall has two 2/2 sliding sash windows at ground floor, one to each room, each with a horizontal drip mould continuing the facade mouldings. At first floor there are two gabled dormers, each with a semicircular-headed window, which presumably light a front and a back bedroom. This wall continues to form the perimeter of the yard. Two 4/4 sash windows light a lean-to shed on the inside of the yard.

The south wall was not inspected in detail as no access was gained to the yard. There is a flat-roofed porch at the centre, with a half-landing light above, and a single-storey lean-to shed abutting on either side. At the right is a semicircular-headed window in the gable apex, with no window opening to the upper left side.

The west wall is blank except for a single 2/2 sliding sash window at ground floor. This wall continues to the right to form the perimeter of the yard, along which are two modern wooden windows in what may be original openings.

The yard was originally accessed from the south through a wide opening flanked by square pillars with pyramidal caps; this entrance has been narrowed with concrete blocks and a modern pedestrian door inserted. A large modern door has been inserted in the gable of the lean-to to allow access to a garage.

A short distance south of the lodge is a one-storey building with an enclosed yard, most recently used as a canteen by grounds staff and formerly used to house a horse and trap belonging to the reservoir's water superintendent. The building is oriented with its gables to east and west and the yard to the south. The roof is pitched and covered in natural slate with half-round metal gutters. Plain bargeboards run to both gables, with a framed wooden apex finial to the east-facing gable. The walls are wet-dashed with cement over a smooth rendered base, with smooth-rendered corners and opening trims. The east gable contains two entrances, both now sheeted over with plywood, with a circular window in its apex. The north wall is blank except for a series of metal ventilators. The south gable is blank except for a circular window in its apex. External inspection revealed two wooden doors and two windows along the building's south wall, though the yard was inaccessible. The yard is entered through two high sheet-steel gates flanked by smooth-rendered pillars surmounted by pyramidal concrete caps. The yard wall, coped with concrete, rises at the south to accommodate the natural slate roof of a lean-to shed within the yard.

At the entrance to the grounds is a comparatively modern two-storey brick dwelling, 589 Saintfield Road, now privately owned but formerly the home of the reservoir attendant.

Chlorination House and Miscellaneous Buildings

In the immediate vicinity of the valve well are seven small brick buildings, all with flat concrete roofs and of comparatively recent date, housing flow gauges, valve stocks, and chlorination plant. Also in this area is a relatively modern one-storey dwelling originally built for the chlorination plant attendant. This has since been sold by Water Service and is now in private ownership.

Boundary Wall and Entrance

The grounds are bounded along the main road to the east by a concrete wall comprising rock-faced concrete blocks laid in regular courses with stepped concrete copings. Originally there was a hedge along the road, but this was removed when the road was widened and the present wall built. There is a pair of modern steel gates at the south end of the wall and another opening to the north. Original drawings show the original entrance gate to have been of wrought iron with a flanking screen.