Dorset

Dorset's coastline holds more geological variety per kilometre than almost anywhere in Britain. The Jurassic Coast, the first stretch of English shoreline to receive UNESCO World Heritage status, runs 155 kilometres from Exmouth to Studland, exposing 185 million years of rock strata in a continuous section. The tidal character is as varied as the geology. Outside Poole Harbour, the English Channel delivers a standard semidiurnal range of 1.5 to 2.0 metres at Swanage and Studland — modest by British standards but enough to shift beach access and sandflat exposure meaningfully across a day. Inside Poole Harbour, everything changes. Poole is one of the largest natural harbours in the world by area — roughly 36 square kilometres of sheltered water connected to the sea through a channel barely 100 metres wide at Sandbanks. That narrow entrance produces a resonance effect: the tidal wave cannot push enough water volume through the gap fast enough to follow the ocean tide outside, so the range inside is flattened to roughly 0.5 metres on springs. The ebb and flow through the Sandbanks channel runs at 3 to 4 knots on springs — strong enough that the chain ferry, crossing continuously between Sandbanks and Shell Bay on the Studland side, is engineered to handle the current. The harbour interior's low range means Holes Bay and Lytchett Bay to the northwest remain viable for dinghy sailing and kayaking across most of the tidal cycle, and the Poole town quay stays accessible at all states. Portland Bill at the southwest tip of the county generates the Portland Race — a tidal overfalls zone where the stream running around the Bill at up to 7 knots on springs meets itself and produces standing waves and short-period steep sea, dangerous in even moderate conditions. Chesil Beach, the 18-kilometre graded-shingle tombolo connecting Portland to the mainland, is the classic Dorset shore-angling venue: steep profile, deep water immediately off the beach, and productive bass and cod catches from September through winter. The Fleet lagoon behind Chesil is another near-enclosed water where tidal range is suppressed by a restricted entrance — a pattern repeated across this coast from Poole to Portland. Authoritative tidal data for Dorset comes from the National Tidal and Sea Level Facility (NTSLF) and the UK Hydrographic Office Admiralty Tide Tables.