The Lagan Weir, completed in 1994, at a cost of £14m
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.
The weir is a series of large 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 led 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.