Northern Ireland

Northern Ireland's coastline runs from Carlingford Lough on the Irish border in the south, up along the County Down coast, around the mouth of Belfast Lough, north along County Antrim to the Causeway Coast, and west to Lough Foyle on the Derry border. The tidal character varies considerably around that perimeter, but the dominant feature of the eastern coast is the sea lough system: enclosed or semi-enclosed inlets where the semidiurnal tidal signal drives complex current patterns through narrow entrances. Belfast Lough is a classic drowned river valley opening northeast into the North Channel between Northern Ireland and Scotland. The mean spring range in the lough runs to about 3.0 to 3.4 metres — enough to noticeably transform the character of the foreshore between states of the tide, exposing the mudflats at the lough head that are designated as Special Protection Areas for overwintering waders and wildfowl. The real tidal spectacle in Northern Ireland is at Strangford Lough, 30 kilometres south of Belfast. Strangford is one of the largest sea loughs in the British Isles — 150 square kilometres of shallow water connected to the Irish Sea by the Narrows, a 600-metre-wide channel that must pass all of that water in and out on each tidal cycle. The physics of that constraint produce some of the strongest tidal streams anywhere in the UK or Ireland: currents in the Narrows reach 7 to 8 knots on big spring tides. SeaGen, the world's first commercial tidal stream generator, operated in the Narrows from 2008 to 2019, extracting energy from those currents. The Causeway Coast in the north — the Giant's Causeway, Carrick-a-Rede rope bridge, Whitepark Bay — sees Atlantic swell exposure and a range of 3 to 4 metres at springs. The basalt columns of the Giant's Causeway are partly intertidal, and low-tide access reveals formations that are submerged on every high water. The UKHO publishes Admiralty tide tables for Northern Ireland; NITHC and harbour authorities maintain local gauges at Belfast and Larne.