Western Australia

Western Australia wraps the long Indian Ocean coast from the Northern Territory border at the Kimberley region south through Broome, Karratha, and Geraldton past Perth and Fremantle to Margaret River, Albany, and Esperance on the Southern Ocean coast. The tide signature varies enormously across that range. The Kimberley north coast at Broome and Derby runs some of the largest tidal swings on Earth — mean range at Derby exceeds 11 metres on spring tides because the geometry of King Sound concentrates the open-ocean signal into a resonant funnel. Down the central coast at Geraldton and along the Indian Ocean exposure to Perth the range drops dramatically. Fremantle at the Swan River mouth runs one of the smallest open-ocean tides on Earth: mean range about 0.6 metres, spring tides close to 1.0 and neaps near 0.2. The pattern is mixed semidiurnal but heavily diurnal-leaning at most lunar phases, with many days producing a single clear high and a single clear low rather than two of each. What matters more on the south-west coast is meteorological tide. The Fremantle Doctor — the steady south-west sea breeze that builds through the afternoon from November through April — pushes water against the coast and lifts apparent water level by 20 to 40 centimetres on sustained events. The defining seasonal events are the Rottnest Channel Swim and the Cottesloe surf scene. The Rottnest Channel Swim from Cottesloe Beach across 19.7 kilometres of open Indian Ocean to Rottnest Island has run every February since 1991. Cottesloe Beach hosts the Sculpture by the Sea exhibition every March. The 1987 America's Cup defended at Fremantle on the Indian Ocean course off Rottnest is the only America's Cup ever sailed in southern hemisphere waters. The Australian Bureau of Meteorology and the Department of Transport WA publish the authoritative tide tables.