Impact of floods
We often associate floods with disaster and damage. Many Australian communities experience trauma and loss through floods. For example, floods around Lismore in New South Wales during 2022 showed the devastating impact of such events.
Flooding is also a natural process in Australia, the second-driest continent. It can help sustain our ecosystems and economy.
How floods support ecosystems
Floodwaters spill out onto massive coastal areas known as river deltas. Floodwater carries fine sediment, with valuable nutrients and minerals, turning flood plains, deltas and river areas into rich, fertile lands.
The floods:
- fill billabongs and wetlands
- replenish water bodies
- contribute to the life cycle of plants and animals, including in marine environments
- support agriculture – for example, bananas grow in Carnarvon, cotton in St George, rice in Griffith and stone fruit in Swan Hill.
The Queensland floods in 2019 are another dramatic example of how floods can both destroy and renew. Homes were lost and much of the state's cattle industry wiped out, with devastating impacts. As flood levels subsided and water drained to the south-west, the water also brought life and economic benefits to drought-affected areas.
Video: Queensland floods: the water journey to Kati Thanda–Lake Eyre
A second rain system in late March brought even more water, extending across vast flood plains and eventually flowing into Kati Thanda-Lake Eyre, many weeks after the rain first fell. So the water we see down below us has travelled maybe 1000 kilometres. Sometimes at a slow walk, sometimes perhaps at a slow jog depending on how narrow the channels are.
And a massive lake surrounded by tens of thousands of kilometres of desert. Just a big area of water in the middle of Australia. So it’s a huge basin that all this water is draining into. About 17% of the total size of Australia, the water is just draining down into this lowest part of the continent. It's just gone bang and it's growing like crazy.
We've increased our employment, we've increased the number of aircraft, and what we're seeing is a 600-fold increase in the number of four-wheel drives coming through, and actually experiencing Lake Eyre on their way up to the rock.
Beautiful, absolutely stunning. It's amazing, how big it is. You can just see forever. It's also the Simpson Desert and the lake just right next to each other, is pretty amazing.
So this is fantastic news for the graziers, for the wildlife and even for the river itself, for the fish and the bird life that rely on that flow.
We were looking at destocking, starting to destock, and we just sort of started, when that rain fell up north. And as bad as it was, it was good for us, you know.
Every flood is different hey, and that’s what them old fellas said when I first come into this country, 'every flood is different'. How it flows, where they spread out you know, how much feed they grow. And takes a fair while to get down here, like it's only walking pace. You've got to wait for it to come, you've got to wait for it to rise, you've got to wait for it to drop, you've got to wait for the feed to grow. So it is a fair waiting game. Like floods do us good, more than bad, you know?
This is the Warburton River. You can see the way it tracks in a very snake like fashion, though the desert county. Very dry everywhere else, but the Warburton still has water in it. The Warburton River is one of the rivers which goes into Lake Eyre, not always water in the Warburton River, but certainly brings life back to this region when the water does flow. So you can see there's trees, and right at the moment there's bird life, pelicans, and certainly fish in the river at the moment as well. Quite deep here, you can see how the river has carved out channels in the desert country basically. So you look to the horizon, and there is nothing as far as the eye can see except some small shrubs, bushes and dune country. With this oasis I guess of trees and life in the Warburton River.
The lake is incredible, having gone out there 100's of times, I think it's something all Australians should come out here and experience, it's like looking at an inland ocean.
In this year 2019, about 80% of northern Kati-Thanda filled. But that water should also last right though winter, and into spring. By the time we get into summer, there is probably not going to be a whole lot of water left.
Usually when we think about floods, we associate them with destruction and devastation. But for the Channel country, flooding brings life to the outback helping vegetation and wildlife flourish. We haven't seen this amount of water since 2011. With it comes a wave of tourists and an economic boost to towns and communities.
Huge downpours of rain brought devastating floods to parts of northern Queensland and the Northern Territory early in 2019. This water made a slow journey southwest, filling the Georgina, Diamantina and Warburton rivers and flooding desert towns.
A second rain system in late March brought more water, extending across vast flood plains and eventually flowing into Kati Thanda–Lake Eyre many weeks after it fell. So how did the water end up in Australia's largest lake?
January–February rain
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 right across the state.
A phenomenal amount of rain fell. In the seven days to 4 February our rainfall gauge at Townsville Aero recorded 1053 mm, and 1,257 mm in the 10 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. This is the water that made the long journey south.
Ex-tropical cyclone Trevor rain (March)
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. In the week to 30 March, widespread rainfall of 50 mm to more than 200 mm was recorded across parts of the Georgina/Eyre Creek, Diamantina and Thomson/Barcoo/Cooper catchments in the Northern Territory and Queensland. It caused significant flows in these rivers.
Where the water goes
Australia is divided into drainage divisions and river regions based on topography. Most of the drainage divisions affected by the January–February floods (such as around Townsville) drain to the sea, with the exception being the Lake Eyre Basin – the lowest natural point in the country.
Diamantina catchment
The vast Diamantina River catchment is in southwest Queensland and covers an area of about 119,000 sq km. The river passes through Birdsville before crossing the Queensland–South Australia border 10 km south of this town. From there the water moves into the Goyder Lagoon and flows into the Warburton River for the final 150 km to Kati Thanda–Lake Eyre. The distance the water covers is longer than that though, due to the winding of the river system.
By the end of February, floodwaters captured by the Diamantina had been steadily moving downstream into the north-east of South Australia with flooding across vast areas of flood plain. On 22 February the Diamantina River gauge at Birdsville peaked at 8.15 m, surpassing the peak river heights of significant floods in 1999, 2000 and 2009 – but falling short of the major 1974 flood where it 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'.
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.
Georgina River and Eyre Creek catchment
This catchment drains an area of more than 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 creeks and rivers. The two main tributaries are 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. The Hamilton rises to the north-east of Boulia and enters the Georgina River below Marion Downs.
The final gauge for this river system is at Glengyle Station. From there it is more than 300 km (as the crow flies) to the Goyder Lagoon. The January–February rain 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.
The rain from ex-tropical cyclone Trevor was much more significant here – the water level reaching 4.9 m early in March. The flow then tracked through the dry desert areas, finally reaching the Goyder Lagoon in early May.
Lake Eyre Basin
Floodwaters drained through the Goyder Lagoon, 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 about 1.2 million sq km of arid and semi-arid central Australia. That's 17% of the continent – nearly five times the size of the UK. It 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. This is the world’s largest internally draining system.
Also Australia's largest lake, Kati Thanda–Lake Eyre covers an area of about 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.
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 continuing to rise rapidly. It peaked at 5.7 m on 12 March. Water began flowing into Kati Thanda–Lake Eyre on 15 March.
Water from ex-tropical cyclone Trevor rain (March)
Water from the Diamantina River moved through the Goyder Lagoon while water from Eyre Creek also contributed to flow downstream of the lagoon. The water level at Poothapoota downstream of the Goyder Lagoon peaked at 5.4 m on 20 May.
How full was the lake?
In early July satellite images showed about 80% of the lake covered, though assessing the fullness of the lake (in terms of capacity) is difficult. This was about the maximum extent of the water and the most extensive cover since 2011.
In the following weeks and months the water cover fluctuated daily with the winds, and slowly reduced due to evaporation.
Goyder Lagoon in the Lake Eyre Basin, May 2019. Credit: Matt Harnetty.
Types of floods
Flooding happens when water extends over what is usually dry land. This can happen when water:
- escapes from a natural watercourse, such as a lake, river or creek
- is released from a reservoir, canal or dam.
There are 2 types of flooding – flash and riverine.
Flash flooding
Flash flooding happens within 6 hours of rain falling. It can happen:
- after a short burst of heavy rain, such as from a thunderstorm
- where the ground is already saturated from earlier rain.
Flash flooding tends to affect a localised area. It can be a serious problem in urban areas if water exceeds the capacity of the drainage system.
Riverine flooding
This happens when rivers break their banks and water covers the surrounding land.
Riverine flooding is mostly caused by heavy rainfall. It can also be caused by king tides, storm surge, snowmelt and dam releases.
Given many Australian rivers are long, riverine floods can happen weeks or months after rain, sometimes hundreds of kilometres away. For example, flood water in the upper Murray River – Australia's longest at more than 2,500 km – may take months to reach the river mouth in South Australia.
In inland parts of Queensland, New South Wales and Western Australia, riverine flooding can affect thousands of square kilometres for weeks or even months at a time.
What causes floods?
Heavy rainfall
The most common cause of flooding is heavy rainfall. Flash flooding can happen shortly after heavy rainfall, in localised areas. Riverine flood peaks are often reached within a few hours or days after rain falling.
King tide
'King tide' is widely used to describe an exceptionally high tide. These tides are a natural and predictable part of the tidal cycle. King tides can increase the impact and extent of riverine flooding. Learn more on our Tides and sea level page.
Storm surge
Coastal flooding is likely during a storm surge – a rise above the normal seawater level along a shore caused by a storm. If storm surge combines with a riverine flood, the area and extent of flooding can increase.
Learn more about storm surge and storm tides on our Tides and sea level page.
Snowmelt
Snow can be thought of as a reservoir of water, waiting for enough warmth to run down the hill. When conditions warm rapidly, snow can melt quickly. This can release too much water for the downstream river channels, causing riverine flooding.
Dam releases
Dams can hold vast amounts of water, but all dams have a capacity. If a dam is close to capacity, dam operators may release water. Sometimes this can cause flooding.
We work closely with dam operators in times of flood to ensure they have the latest weather information. Operators use this information to manage their dams in a way that minimises impacts on communities downstream. Find out about our services for the Water sector.
View of the spillway at Rowallan Dam, part of the Tasmanian Hydro electric system, during flood conditions
Predicting floods
Long before rainfall is recorded on the ground, we:
- assess the potential for flooding
- forecast river heights at certain locations at a given time.
Assessing flood potential
We use 3 main inputs to assess potential for floods.
Forecast rainfall
Forecast rainfall from our meteorologists.
Observations
We collect rainfall and river height data from about 8,000 stations across Australia. These stations are owned and operated by the Bureau and partner organisations. This includes water management agencies and local councils.
Modelling
We use the Australian Water Resources Assessment Landscape model.
This model is run across the entire country every day. It provides an early assessment of how wet or dry soils are and how quickly flooding might happen.
- View this water information on the Australian Water Outlook.
- Find out about our Water research.
When floods are forecast
We simulate how river levels may respond using:
- our knowledge of the catchments
- specialised computer models.
We use this information to:
- alert and warn communities that may be affected
- support the efforts of emergency services.
Learn more about our Flood warning services and our role in supporting Emergency management.