Why did the Brisbane floods occur?

Answer 1

The floods in Brisbane in 2011 started when the Brisbane River broke its banks on 11 January 2011. Prior to that, there had been some periodic flash flooding as a result of excessive rainfall in the preceding months, but the release of massive amounts of water from Wivenhoe Dam led to a flood situation comparable to that of 1974.

The floods in the state of Queensland actually began as early as 10 December 2010 as rivers broke their banks in central Queensland.

Answer 2

Brisbane's most devastating flood prior to 2011 occurred in January 1974.

January 2011 has seen almost equally devastating floods, wit the Brisbane River rising to just a little lower than 1974 heights. It has been more damaging in terms of cost, because there are more people living along the river in 2011.

Answer 3

Four major floods have occurred in Brisbane.

The first was on 14 January 1841. This was the biggest flood of the Brisbane River since records began with the river being approximately 8.6 metres above the high tide mark. There was limited destruction to property as the town was still very young and undeveloped.

The next major flood began on 5 February 1893. These floods came within 7cm of the 1841 levels.

The worst floods in terms of death and loss of property occurred in January 1974 when tropical Cyclone Wanda developed into a rain depression that dumped hundreds of millimetres of rain on an already saturated southeast Queensland. This flood reached a height of 5.5 m. Since the construction of Wivenhoe Dam on the Brisbane River within a few years of this flood, Brisbane was believed to be flood-proof.

This changed when, on 11 January 2011, the Brisbane River again broke its banks. The flood was the result of a La Ninaweather pattern, together with the state being saturated by the rainfall resulting from a cyclone system that hit in the north on Christmas Day 2010.

Wivenhoe Dam, which was designed to prevent any further floods, exceeded 160% capacity, requiring the release of a massive amount of water, comparable to the volume of Sydney harbour.

Answer 4

There have been two major flooding events in Brisbane in the last forty years.

The Brisbane floods of January 1974 affected wide regions of the entire city of Brisbane, as well as parts of Ipswich. Most areas affected were around the city's CBD and in the suburbs directly along the river. To the north and south, most suburbs were free of major flooding.

The Brisbane floods of 2011 also affected the same areas. All suburbs along the river were affected to some degree. Worst affected suburbs included Rocklea, Graceville, Chelmer, the CBD, Taringa, East brisbane, Fig Tree Pocket, Yeronga and Fairfield, just to name a few. The city of Ipswich was inundated as well.

Answer 5

The most recent floods in Brisbane in 2011 started when the Brisbane River began to break its banks in the early afternoon of 11 January 2011. Prior to that, there had been some periodic flash flooding as a result of excessive rainfall in the preceding months, but the release of massive amounts of water from Wivenhoe Dam led to a flood situation comparable to that of 1974.

The floods in the state of Queensland actually began as early as 10 December 2010 as rivers broke their banks in central Queensland.

Answer 6

There were large amounts of rain all over the country at the same time for a long time, the river rose. Also, floods are a naturally occurring part of the Australian environment (as are bushfires) and the latest floods (Jan 2011) were overdue. Brisbane hadn't flooded badly in so many years that the "floodplane" land was sold and devoloped into housing and commercial.

Further information:

Australia had been coming out of an El Niño for some time, which means that many parts of Australia had seen gradually increasing rainfall. The Brisbane River catchment and other nearby catchments were some of the places which received a great deal of rain from the La Nina system that had developed.

Rain continued to fall heavily throughout early January. On 10 January 2011, Toowoomba, a city which sits at an elevation of 700m at the top of the Great Dividing Range, received 150 mm of rain within a 40 minute period. The ground could not hold any more water, and the waters from the escarpment at the top of the range rushed down the mountainside, creating a wall of water, a 7m high inland "tsunami", that went through the city and down the range. This wall of water rushed through the Lockyer Valley catchment to the catchment areas of the main dam that protects the city of Brisbane from flooding, sending its capacity to over 190%. The gates had to be opened, sending the equivalent of two Sydney Harbour's worth of water into the Brisbane River each day. This is why Brisbane and Ipswich flooded. Subsequent inquiries have pointed the finger at senior engineers acting too late to release water from Wivenhoe.

Answer 7

There have been several major floods in Brisbane in recorded history, with the most damage being caused by the floods of 1974 and again in 2011. In these two floods, anywhere that straddled the Brisbane River was affected. Brisbane's CBD was badly hit, with businesses shut down for several weeks while people waited for the floodwaters to subside, and then the cleanup.

Residential areas north along the river from Milton west to Chelmer, Graceville and Oxley, as well as pockets like St Lucia, Brookfield and Moggill were hit badly. On the south side, suburbs such as Yeronga and Yeerongpilly were affected. As well, low-lying areas near Oxley Creek through Rocklea were also very badly affected.

Answer 8

The question does not specify which floods in particular. Four major floods have occurred in Brisbane.

The floods affecting Australia over the summer of 2010-2011 began in parts of Queensland as early as December 10, but did not affect Brisbane until January.

Flooding as a result of an unusually heavy rainfall pattern and the effects of La Nina really began to be felt just after Christmas as major centres like Rockhampton and Bundaberg were inundated. The floods then hit many other towns, until finally on 11 January, the Brisbane River actually began to break its banks. The river peaked three days later, on 14 January.

Prior to this, the term "Brisbane floods" referred to when the city experienced devastating flooding from 25 January 1974. These were the worst floods in terms of death and loss of property and occurred when tropical Cyclone Wanda deepened into a massive rain depression after it crossed the coast, drawing the Monsoonal Trough south, and providing enough extra rainfall to the Brisbane valley to produce widespread and severe flooding. It that dumped hundreds of millimetres of rain on an already saturated southeast Queensland. Since the construction of Wivenhoe Dam on the Brisbane River within a few years of this flood, Brisbane was believed to be flood-proof.

The first major flood in Brisbane, however, was on 14 January 1841. To date, these floods have been the worst, high-level wise, although there was less destruction to property as the town was still very young and undeveloped. Flood levels were reported to be over 8 metres above the mean sea level.

The next major flood began on 5 February 1893. These floods came within 7cm of the 1841 levels.

Answer 9

The massive floods that hit Brisbane in 1974 first began to flood the city on 25 January 1974. They started to abate four days later.