Lagan Weir

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Lagan Weir during a falling tide

Lagan Weir in Belfast; other landmarks pictured are the Belfast Customs House, the M2 motorway bridge and, reflected in the Royal Mail building, the Samson and Goliath cranes of Harland & Wolff

The Lagan Weir, completed in 1994, at a cost of £14m, is located across the Lagan between the Queen Elizabeth Bridge and the M3 bridge (completed around the same time) in Belfast, Northern Ireland. The Lagan Weir was jointly funded by the Corporation and the European Commission it was constructed by Charles Brand Ltd and designed by Ferguson and McIlveen.

The weir is a series of massive steel barriers which are raised as the tide retreats to keep the river at an artificially constant level. This improvement to the sewerage system combined with massive dredging of the river by mechanical excavators, and installation of an underwater aeration system, has lead to a marked improvement in water quality and the environment around the river.

The objective of the structure is to keep the level of the river artificially constant, as it is a tidal river the level of the water varied by up to three metres between high and low tide. This exposed mudflats which were unsightly and emitted a strong odour, particularly in the summer months. The transformation of the riverside by the construction of the weir has been a catalyst for development along the riverside. Another part of the project is the “Lagan Lookout” centre which explains the history and function of the weir as well as the history of the Lagan itself.