1955 Hunter Valley floods

The Hunter Valley Floods (also known as the Maitland Flood) of February 1955 was a major flood on the Hunter River in New South Wales, Australia. They were one of the most devastating natural disasters in Australia's history.

The flood overwhelmed rivers on both sides of the Great Dividing Range, creating an inland sea the size of England and Wales. Worst hit was the inland city of Maitland, which is sited precariously on low-lying land on the Hunter, was completely inundated by floodwaters. A total of 25 lives were claimed during a week of flooding that washed away 58 homes and damaged 103 beyond repair. In Maitland alone, 2180 homes were invaded by water.

Heavy rain owing to the influence of La Niña had been occurring over the catchment of the Hunter River since October 1954 when, on 23 February 1955, an extremely intense monsoonal depression developed over southern Queensland and moved southwards. The very strong and extremely moist northeasterly airflow meant that over the basin of the Hunter and parts of the Darling River, rainfall amounts for a 24‑hour period were the highest since instrumental records began around 1885. Around Coonabarabran, as much as 327 millimetres (over 13 inches) fell in a single day, whilst falls in the upper part of the Hunter Basin the following day were generally around 200 millimetres (8 inches).

With such heavy rain on already very wet ground the Hunter, along with tributaries of the Darling (Castlereagh, Namoi and Macquarie especially) reached levels quite unprecedented since measurements were first taken about 100 years earlier. For instance, the Namoi's discharge, normally only about 25 cubic metres (875 cubic feet) per second, reached a massive 9000 cubic metres (320,000 cubic feet) per second, whilst the Macquarie peaked at around 6100 cubic metres (215,000 cubic feet) per second.

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