Intercepting Weir

The Department's description

Exterior description and setting

A vertical reinforced-concrete weir across a tributary on the upper section of the Annalong River. Its purpose is to divert some of this water through a south-west running underground conduit to a small reservoir at the intake to the Slieve Bignian tunnel (HB16/01/041). Excess water spilled over the top of the weir, the height of which is fixed. At the top end of this structure is a set of vertical sluices set between concrete abutments. When closed, the water was diverted away from the weir, through a culvert on the left bank to a discharge orifice just beyond the weir. This enabled access to the conduit for maintenance purposes. The sluice gates have now been removed and the bypass is redundant. The banks between the sluices and weir comprise vertical concrete walls. There are concrete footbridges at both ends, each with two horizontal spans and metal two-bar handrails. A small metal pipe also discharges from the bottom of the weir, the flow being regulated by a valve controlled from the footbridge above.

Historical information

The Slieve Bignian Tunnel scheme, of which this dam is a component, was commenced in 1948 by the Belfast City & DistrictWater Commissioners and completed in 1952. The work was carried out by Messrs A.M. Carmichael Ltd of Edinburgh and theconsulting engineers were Messrs Binnie, Deacon & Gourley of Westminster. The weir is still used by the Water Service for its original purpose.

Primary Sources:
1) Belfast & District Water Commissioners, 'The Mourne Scheme: development of the Silent Valley and AnnalongValley catchments', (1959), pp.25-7.
2) Original drawings of the weir are held by the Water Service at Westland House, Old Westland Rd, Belfast (cat no.2F1).

Criteria for listing: architectural interest

A. Style
D. Plan Form
F. Structural System
J. Setting
K. Group value

Criteria for listing: historic interest

V. Authorship
X. Local Interest
Y. Social, Cultural or Economic Importance

Evaluation

This structure is an integral part of of the Bignian Tunnel complex (HB16/01/041), which in turn is a key element of Belfast's water supply. It therefore has group value and is of significance in terms of the Mourne Scheme.