River Lagan dredging project

The Department for Communities is the navigation authority for the 4.8km stretch of the River Lagan between Stranmillis Weir and the Harbour Commissioner’s limit on the downstream side of the Lagan Weir. There is a requirement on the Department to maintain a navigable channel through the river – typically this is achieved by maintaining the river bed at a designated level of -1.2m AOD (Above Ordnance Datum)..

In the past, the water quality of the river was poor and at low tide unsightly smelly mud flats were exposed. The bad smell was due to decomposition in the mud releasing gases into the air and this increased during the summer months as the higher temperatures increased decomposition. The banks of the river were overgrown and deserted, wildlife was practically non-existent and there were few fish. Due to these environmental issues, the 'city turned its back on the river' and this was reflected in the decline along its banks with derelict lands and little investment in the area.

Since 1994 however, a programme of dredging works has delivered significant environmental and regeneration benefits for the city. The legacy and continued realisation of these benefits is dependent on further investment in dredging the Impounded River Lagan.

The Department had carried out a series of investigations to consider siltation rates in order to determine the volume of material that had built up since the previous maintenance dredge which was completed in 2011 to assess dredging options to reinstate the -1.2m AOD level.

A contract to the value of approximately £3.9m was subsequently awarded to local firm ABCO Marine Limited. The project began in September 2019 and was concluded in March 2020. Over 55’000m3 of silt was removed and transported by sea for disposal.

Excavated material was loaded into small shuttle barges which, over the course of the contract, made over 3000 trips up and down the length of the river transferring this material to the larger sea going vessel.

The sea going barge made a total of 123 round trips of 6 hours each to the NIEA approved disposal site in the Irish Sea.

In addition to the organic material, some 250 tonnes of manmade rubbish including shopping trolleys, traffic cones and bikes was removed from the river and taken to licensed disposal sites.

Strategic Context

The following strategic objectives contained within regional and local policies are dependent on the River Lagan being maintained:

to enhance the quality of life for the people living in the surrounding areas of the river
to improve the water quality for the benefit of aquatic life, those that use the river for recreational purposes and the general environment of the city
to reduce the risk of flooding in the area; and
to encourage business growth and promote the development of economic infrastructure.

Dredging the Impounded River Lagan to remove sediment build up improves the quality and aesthetics of the river and assists in flood management, critical to ensuring that these strategic objectives are delivered.

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