More floods

The floods across eastern Australia have worsened since my last post.  South-east Queensland saw devastating loss of lives in and around Toowoomba during flash flooding there on January 9.  Not far away, in the catchments above Brisbane, 300 mm of rain fell on January 10 and 11 pushing an already full Wivenhoe Dam deep into its reserve flood storage capacity.  Emergency dam releases to the Brisbane River from January 11, combined with heavy local rains and stream flows, saw the lower lying suburbs of Brisbane under water for the first time since 1974.

Even the state of Victoria, over a 1000 kilometres to the south, has experienced widespread flooding as a deep tropical trough dropped heavy rainfall right across eastern Australia.  This is even more remarkable when you consider that Victoria is normally very dry throughout the summer (December-February), being in a strong winter rainfall climatic zone, unlike Queensland which is in our summer rainfall area.

Some flood figures for the records:

  • Approx. 25 major river systems in Queensland, and 15 in Victoria have been or are currently carrying major flood flows. A further 10 major river systems in New South Wales and 5 in Tasmania are flooding currently at anything from moderate to major levels, and several other major rivers in SE NSW were in flood in December.
  • In the Queensland floods, areas of land flooded are being cited variously as the size of France + Germany or Texas + California. In Victoria and Tasmania, the flooding, though severe, covers much smaller total areas and does not involve any capital city-scale population densities.
  • 415 mm of rain fell at Mount Nebo, above Brisbane, in a three day period from January 10-12.  This compares to rainfall of 995 mm at the same place over three days during the 1974 floods (Jan 25-27).
  • Brisbane’s Wivenhoe Dam has a total storage capacity of 2.6 million megalitres —  it is considered 100% full for supply purposes at 1.15 million megalitres, and has an additional flood buffer of 1.45 million megalitres .
  • 645,000 megalitres was released from Wivenhoe Dam on January 11, about a third of the dam’s storage at the time
  • Larger floods have been recorded in Brisbane, including in 1974 which was the biggest twentieth century flood, with several big floods being recorded in the nineteenth century in 1841, 1857, 1864, 1867, 1887 and 1893 (must have been a very wet half-century indeed)
  • Inglewood, in the normally summer-parched north-west of Victoria, recorded 191 mm of rain in four days from January 11-14
  • Various estimates of the total cost of the Australian floods have been proffered by economists with figures as high as $20 billion being quoted.

Unfortunately, Australia has not been on its own in suffering tragic human and economic losses from floods in recent weeks.  Hundreds of lives have been lost in flash flooding and mudslides in Brazil, the Philippines and Sri Lanka.

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