Wales

Wales faces the Bristol Channel on its south coast — and the Bristol Channel is one of the most extreme tidal environments on Earth. The estuary funnel narrows and shallows as it runs northeast from the open Atlantic toward the Severn Bridge and beyond, amplifying the incoming tidal wave to a degree that puts Cardiff and Newport in the same tidal league as Mont-Saint-Michel in Normandy and the Bay of Fundy in Canada. Spring tidal range at Cardiff reaches 12 to 14 metres. That is not a typo. It means that at low water springs, the entire foreshore — hundreds of metres of mudflat in places — is exposed, and by high water those same flats are buried under enough water to float a container ship. The tidal signal here is the defining feature of the coast, shaping everything from Cardiff Bay's impounded barrage to the intertidal ecology of the Severn Estuary SSSI, one of the most productive bird habitats in the UK. North Wales is a different proposition — the Irish Sea coast at Llandudno and Colwyn Bay still has a substantial range of 4 to 5 metres at springs, semidiurnal and consistent, but the extreme amplification of the Severn Estuary is absent. Pembrokeshire on the southwest corner of Wales, fronting the open Celtic Sea, has spring ranges of 5 to 7 metres at places like Milford Haven, with significant tidal diamond currents in the Haven's deepwater channel that has made it the UK's largest energy port. The Pembrokeshire Marine National Park, the only coastal national park in Wales, surrounds some of the most dramatic cliff and sea-stack scenery in Britain. The Gower Peninsula, immediately west of Swansea, holds Rhossili Bay — repeatedly rated among the best beaches in the UK — where the massive spring range means the beach alternates between a vast sand flat at low tide and a narrow strip beneath vertical dune cliffs at high. It is a beach that requires a tide table, not just a weather app. The Environment Agency of Wales (now Natural Resources Wales) and the National Tidal and Sea Level Facility maintain gauge stations at Cardiff, Barmouth, and other Welsh ports; the UKHO publishes the official tide tables for Welsh waters in Admiralty Tide Tables volume 1.