Belfast Tidal Flood Alleviation Scheme

Belfast is at risk of flooding from a number of sources including tidal, fluvial and surface water.

Belfast Tidal flood alleviation scheme image

Scheme Summary

  • Cost:                £18m
  • Length:            From Belfast Harbour to Stranmillis Weir
  • Type:               Various permanent and temporary flood defences
  • Status:             Outline Design

Key Dates

  • December 2017 - Appointment of Design Consultant Atkins

Scheme Aim

The principal aim of the Belfast Tidal project is to identify a scheme of works that will provide a long term approach to tidal flood risk management for Belfast. The study area is from Belfast Lough to Stranmillis Weir, which is the extent of tidal influence on the River Lagan.

Scheme Background

Belfast is at risk of flooding from a number of sources including tidal (the sea), fluvial (rivers) and surface water as a result of heavy rainfall. Tidal flood risk is of most concern, with approximately 560 residential and 460 non-residential properties currently at risk from a significant tidal event. DfI Rivers design standard for sea defences is to protect to the 1 in 200 year level with an appropriate increase in level (freeboard) to allow for uncertainties.

The impact of climate change causing sea level rise will increase the number of properties at risk to over 3400 (2640 Residential and 770 Commercial) by 2065 and over 7900 (6050 Residential and 1860 Commercial) by 2115.

As much of the city centre is between 1m to 2m below extreme tide levels, an extreme event would cause serious disruption to commerce, the transportation network, and the social fabric of the city. Any significant depth of tidal flooding within the city centre is likely to drain slowly as the capacity of the drainage network is exceeded. This also raises the likelihood of contamination as tidal flooding overwhelms and mixes with foul sewage and other contaminants. Flooding of the city centre is likely to cause major disruption for several days or even weeks, with increased clean-up and recovery consequences.

Flooding to the city centre in a 1 in 200 year event is estimated to affect an area in excess of 2km2 and will extend to the west as far as York Street, City Hall, and Adelaide Street and as far south as Ormeau Avenue.

 The highest tidal surges recorded within Belfast Harbour have occurred within the past 20 years, most recently in early January 2014. This “near miss” flooding event, concerns over the numbers of “near misses” within a relatively short time period (the 5 highest tidal surges have been recorded since 1994), and the opportunity to build in a “flood risk element” to the York Street Interchange project are reasons why the Belfast Tidal flood risk study was commissioned by DfI Rivers.    

Scheme Description

The proposed scheme extends from Belfast Harbour to Stranmillis Weir and will comprise a number of different forms of both permanent and temporary flood defences. The line and type of these flood defences varies and will be subject to negotiations with a range of stakeholders as well as landowners such as Belfast City Council, the Department for Communities and the Belfast Harbour Commissioners along with private landowners. The height of the defences will also vary in relation to the surrounding ground level but will be of a consistent level in relation to the height above average sea level (Ordnance Datum).

Scheme Benefits

The negative effects which can be caused by flooding are extensive and listed in the scheme detail below.  However to demonstrate the scale of the economic benefits an extract from the feasibility report is included below.

Using standard flood damage analysis, over the 100 year life of the scheme the level of flood risk is estimated to cause damages valued today at approximately £250m. This value excludes the additional impacts as a consequence of long duration flooding and surcharge of the foul sewer system in the commercial centre of Belfast. It also excludes the impact on the local economy as a result of unproductive employment and loss of access which is estimated at an additional £87m (in accordance with economic national appraisal guidance).

Scheme Documents

Examples of images of flood defence can be found on the:


December 2017 - Atkins have been appointed to take forward the outline design and procure a “Design and Build” Contractor.  

May 2018 – To take account of changes to Climate Change Policy the Belfast Tidal FAS Project Team have updated the design parameters.

August 2018 – Environmental Notice published and publicly displayed.

October 2018 - The updated scheme was approved by the Drainage Council.

January 2019 - The updated scheme was approved by the Department of Finance.

February 2019 - The Deputy Secretary and Directors Group approved the updated estimate, gave (internal) Gateway 3 approval and confirmed the availability of capital funding.

August 2019 - The Tender Process is underway.

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