The Brisbane 2011 Floods Essay

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Brisbane Catchment
South East Queensland consists of 14 major river catchments and sub-catchments. The Brisbane River catchment has an area of almost 14,000km2 making it the largest catchment in the area. The Brisbane River is also the longest river in south east Queensland at 309km. The catchment includes several small dams and two large dams; Somerset and Wivenhoe. The Wivenhoe aimed to prevent future flooding and was completed in 1984. Figure 1 shows the Brisbane River catchment including the associated rivers and creeks that feed into the river.

Flooding
January 2011, South East Queensland experienced two major floods that had a significant impact on many communities throughout coastal Queensland. January 10th the city of
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For the case of the Brisbane River flooding it was termed a “dam release flood” by hydrologist appointed by the Insurance Council of Australia. A dam release flood is defined as a flood caused by rapid release of large volume of water from a dam. This can typically be seen as an emergency response to an incoming flood. If the release is sufficiently large it can flood the receiving waterways.

Rainfall Event
In 2010, eastern Australia experienced an extremely wet spring (September to November) receiving rainfall in the 600 to 1,200 mm range. With the excessive rainfall prior to the rainfall in early January, meant that the catchment was saturated. Following the wet spring came one of the four strongest La Nina events since 1900. Historically for eastern Australia, strong La Nina events are often associated with extreme rainfall and widespread flooding (BoM 2011, pg. 2). Southeast Queensland and northeast New South Wales experiences a very heavy rainfall exceeding 200 mm between the 10th and the 12th of January.

Bureau of Meteorology has released a Special Climate Statement pertaining to the weather, rainfall and flooding that occurred over the period November 2010 to January 2011 (BoM, 2011). The following extracts are quoted from this Special Climate Statement.

“10 to 12 January. An upper-level low combined with a humid easterly flow to bring very heavy rain to southeast Queensland and northeast New South Wales. The heaviest falls were in

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