Two centuries of shoreline change in Northern Ireland.

Shoreline change analysis of the entire coast of Northern Ireland was conducted for the period from 1830 to 2021. Even with its 790Km length (including the main offshore islands) the Northern Ireland coastline is remarkably diverse, comprising several notable coastal typologies (cliffs, rocky coasts, sandy beaches, sand dunes, etc.) as well as a number of commercial and industrial activities. Human pressure co-exists with the natural coast and each impacts the other in many ways.

Shorelines were digitised using multiple temporal and spatial datasets (historical maps, aerial photos and orthophotos). The average temporal interval of shorelines ranges from 7.8 to 37 years, depending on location and data availability. The seaward vegetation line was selected as the primary shoreline proxy, whereas cliff edge, rock-water line or anthropogenic structures were chosen subordinately or if deemed more appropriate. Shoreline uncertainty was assessed using various errors inherent from each dataset from which the shoreline was digitised. The ArcMap® tool DSAS 5.0 was used to calculate shoreline rates and distances along 25 m spaced transects covering the entire coastline.

Over the last two centuries the maximum retreat value was highlighted in Lough Foyle between the Roe River mouth and Magilligan Point where the shoreline progressively retreated up to -250 m. The largest shoreline advancement (+3.500 m) was recorded in Belfast following its port expansion.

Sandy coastlines were shown to have the larger natural changes. Magilligan point, after an advancement phase toward its northern extremity between 1830 and 1919, underwent a constant retreat phase that has now extended to its eastern side up. Benone Beach, Castlerock and Portstewart Strand are the only vegetated coastal dune sites along Northern Ireland’s north coast that are advancing in the last 190 years(190-270m) Significant shoreline retreat was recorded at White Rocks (-85 m), Ballycastle (-65 m), Runkerry (-25 m) and White Park Bay (-65 m). In Dundrum Bay, Co. Down, the largest retreat values (-75 m) occurred at Murlough and maximum advancements greater than 200 m at Ballykinler.

The largest shoreline advancements were all attributed to human activities such as land reclamation in the loughs (mainly during the 19^th century), seaward expansions of ports (e.g., Belfast, Bangor, Carrickfergus, Portavogie and Warren Point) or construction of power stations and wastewater treatment areas. Shoreline advancements recorded for the salt marshes of Larne and Foyle Loughs and White Water River mouth also followed human interventions. High rocky coasts, apart from limited rockfalls, were less subject to shoreline changes. The work will contribute to better define coastal cells along the Northern Ireland coastline and inform coastal managers for future development plans of the coast.