Queensland floods: the water journey to Kati Thanda-Lake Eyre
19 March 2019
Updated 3 July 2019
In late January and early February, an intense and slow-moving monsoonal low over northern Queensland caused record-breaking rainfall and disastrous flooding. Areas affected included the Townsville region and westwards across large areas. In March, ex-tropical cyclone Trevor brought more rain, over a broad region of central and southwest Queensland and adjacent area of the Northern Territory. Since then there's been a lot of water on the move—we follow its journey to Australia's largest lake, Kati Thanda-Lake Eyre.
A phenomenal amount of rain fell. In the seven days to 4 February 2019 our rainfall gauge at Townsville Aero recorded 1052.8 mm, and 1257 mm in the ten days to 6 February. There were several sites in elevated areas including Paluma, Woolshed, and Upper Bluewater that reported 12-day accumulations of more than 2000 mm! Further west, large areas recorded 300–500 mm including the northern parts of the Diamantina catchment—and it was this water that was about to start a long journey south.
Video: This short video looks back at the Queensland floods
Ex-tropical cyclone Trevor rain (March)
In the week to 30 March, widespread rainfall of 50 mm to more than 200 mm was recorded across parts of the the Georgina/Eyre Creek, Diamantina and Thomson/Barcoo/Cooper catchments in the Northern Territory and Queensland. This rainfall, associated with the remnants of ex-tropical cyclone Trevor, resulted in significant flows in these rivers.
Where the water goes
Australia is divided up into drainage divisions and river regions based on topography. Most of the drainage divisions affected by the floods (such as around Townsville) empty out into the sea, with the exception being the Lake Eyre Basin—the lowest natural point in the country.
Animation: Topographic Drainage Divisions and River Regions
The vast Diamantina River catchment is in southwest Queensland and covers an area of approximately 119 000 sq km. The river passes through the town of Birdsville before crossing the Queensland–South Australia border 10 km south of Birdsville.
By the end of February, floodwaters captured by the Diamantina had been steadily moving downstream into the northeast of South Australia with flooding extending across vast areas of flood plain. On 22 February 2019, the Diamantina River gauge at Birdsville peaked at
8.15 m, surpassing the peak river heights of recent significant floods in 1999, 2000 and 2009—but falling short of the major flood of 1974 where the river peaked at 9.45 m.
By late March, the water had receded in the Diamantina between Birdsville and the Goyder Lagoon, and the vast flood plain was 'greening', following the inundation of the preceding weeks.
However, there was more water to come. Rainfall from ex-tropical cyclone Trevor brought a 'second wave'. The water level at Birdsville measured 2.4 m on 18 April and rose steadily to peak at 7.7 m on 29 April. It has dropped slowly since, was less than 4 m on 20 May and is continuing to fall.
Photo: Birdsville, Queensland, in flood, February 2019. Credit: Birdsville Bakery
Georgina River and Eyre Creek catchment
This catchment drains an area of over 200 000 sq km. It rises to the northwest of Mt Isa with three main tributaries, the Buckley, James and Ranken rivers. Further inflow enters the system from numerous creeks and rivers, the two main tributaries being the Burke and Hamilton rivers. The Burke River drains the area to the north of Boulia and enters the Georgina River about 20 km upstream of Marion Downs, while the Hamilton rises to the northeast of Boulia and enters the Georgina River below Marion Downs.
The final river gauge for this river system is at Glengyle Station, from which it is over 300 km (as the crow flies) to the Goyder Lagoon, just prior to the start of the Warburton River. It is then around 150 km further to Kati Thanda-Lake Eyre, although the actual distance covered by the water is longer, due to the winding of the complex river system.
The January/February rain event resulted in water level at Glengyle reaching about 3.5 m in the latter part of February. However, water didn't progress far past Glengyle. Rain from ex-tropical cyclone Trevor rain was much more significant here. The water level reached 4.9 m early in March. The flow then tracked through the dry desert areas, with some flow finally reaching the Goyder Lagoon in early May.
Lake Eyre Basin
Floodwaters continue to drain through the Goyder Lagoon in South Australia, which forms part of the Lake Eyre Basin. Water flows from the lagoon into the Warburton River on its way to Kati Thanda-Lake Eyre, one of the largest saltwater lakes in the world.
The Lake Eyre Basin region covers approximately 1.2 million sq km of arid and semi-arid central Australia. It represents 17 per cent of the continent and stretches, north to south, from just below Mount Isa in Queensland to Marree in South Australia. From west to east, it extends from Alice Springs in the Northern Territory to Longreach and Blackall in central Queensland. Lake Eyre is the world’s largest internally draining system.
Also Australia's largest lake, Kati Thanda-Lake Eyre covers an area of approximately 9,500 sq km—however it's rare for the lake to completely fill. When the lake is full, it has the same salinity level as the sea, but as it dries up and the water evaporates, salinity increases.
Map: Lake Eyre Basin
Water from January/February rain
By 5 March, the Warburton River gauge at Poothapoota in South Australia (just downstream of the Goyder Lagoon) gave the first indication that the floodwaters were moving through, with the water level jumping 0.8 m in about 30 minutes and then rising rapidly. The water level there peaked at 5.7 m on 12 March.
The first flows into Kati Thanda-Lake Eyre occurred on 15 March. Since then, water has continued to flow along the Warburton Groove into the lake.
Water from ex-tropical cyclone Trevor rain (March)
More water has flowed across the border into South Australia. Water from the Diamantina River moved through the Goyder Lagoon while water from Eyre Creek also contributed to flow downstream of the Goyder Lagoon.
The water level at Poothapoota downstream of the Goyder Lagoon peaked at 5.4 m on 20 May. The water level has been dropping rapidly during June and inflows into Kati Thanda-Lake Eyre are reducing day by day.
In early July satellite images showed about three quarters of the lake covered, though assessing the fullness of the lake (in terms of capacity) is more difficult. This is likely to be about the maximum extent of the water coverage, and probably the most extensive cover since 2011. Over coming weeks and months the water cover will fluctuate daily with the winds, and slowly reduce due to evaporation. However, it is likely that the deeper areas of the lake will retain some water through winter and well into spring.
Image: Lake Eyre, 2 April 2019. Credit: Sue Manniche
A 'green lining'
While Kati Thanda-Lake Eyre hasn't completely filled from this event, even partially filling the lake creates a desert oasis for a variety of birdlife, which breed on the lake's islands and shoreline.
The floodplains of the Diamantina River and other channels in central Australia are also gradually rejuvenating after years of drought.
Image: Goyder Lagoon in the Lake Eyre Basin, May 2019. Credit: Matt Harnetty
But, while the floodwaters are good news for some, it's hard to forget the devastation caused by the heavy rainfall and floods in northern Queensland, where homes were lost and much of the State's cattle industry wiped out.
Our thoughts are with all those affected by these devastating floods, or involved in supporting recovery and reconstruction efforts, which will continue for many months to come.
Animation: Floodwaters moving from Queensland to Kati Thanda-Lake Eyre, 14 February—14 July 2019 (colours enhanced for visibility). Source: Himawari satellite, Japan Meteorological Agency
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