Australia experiences extremes in weather which sometimes lead to catastrophic natural disasters at opposite ends of the spectrum, such as droughts and floods. Flooding can completely cut off access to towns, damage buildings and infrastructure and may also lead to lives being lost. It is interesting to note that in a country known for being so dry, every state and territory in Australia has been affected by flood disasters at some point.
How does flooding happen?
When an area receives too much rain, such as when a tropical cyclone occurs, it can be disastrous. The underlying geology of an area can contribute to how runoff from rainfall behaves, such as whether it will soak in quickly or stay on the surface. Areas with high rainfall and soil high in clay will tend to be prone to floods, much more than low rainfall areas or those with sandy, free-draining soils. A PALMS activity investigating how different soil types respond to rainfall can be found here.
As well as the geology and soil type in an area, its topography will also play a role in flooding. Topography is the shape and features of a landscape and includes aspects such as hills and valleys and the height of areas above sea level. People may settle in valleys due to lush native vegetation and rich soil, but this may prove a bad decision in times of high rainfall.
Topography is an important consideration when planning where to place dams used to supply water to nearby populations. The landscape surrounding a dam is ideally sloped to allow natural run-off and collection of rainfall and the location of a dam may be the site of a pre-existing river or stream.
Gordon Dam, Tasmania (Image: JJ Harrison, Wikipedia Commons)
How landscape topography can influence flooding can be investigated by trying the PALMS Flooded Landscape activity demonstrated in this video. The supporting teacher notes can be found here and the student worksheet here.
PALMS Flooded Landscape activity
A land of flooding rains
Areas such as the Kimberly region of Western Australia can be prone to flooding, especially during cyclone season due to the high clay content of the soils. In the first few months of 2018, Broome was badly flooded after several cyclones and tropical storms hit the area, dumping two years’ worth of rain in two months. The town was completely cut off due to the flood waters damaging the major highway accessing the town, leading to supplies running low until repairs could be made.
Both coastal and inland areas of Queensland have suffered disastrous flooding events including the widespread event in the summer of 2010-2011 when even the city of Brisbane was badly affected. This flooding was caused by rain due to a very strong La Niña event which brings wetter conditions to eastern Australia combined with Cyclone Tasha crossing the coast.
With some areas being more prone to floods than others, this must be taken into consideration when planning the location of houses and infrastructure. Several towns in Australia have been relocated after major flood events, as discussed in this article.
Flood marker, Rockhampton, Queensland (Image Mark Marathon, Wikipedia Commons)
Flooding for new life
Floods are not always a disaster and can instead help to bring a burst of life to an area. Khati Thanda-Lake Eyre in South Australia is normally a dry area but every few years, flooding events in Queensland and the Northern Territory feed water into the region’s basins, filling the lake. This encourages thousands of waterbirds to visit the area along with other wildlife and the ecosystem is dramatically transformed. This ABC Behind the News video documents the lakes’ transformation and includes links to further information and activities.
Some further information and resources on floods and other natural disasters can be found at the following web pages:
- The CSIRO Extreme Events web page gives information on current research into events such as floods.
- The Bureau of Meteorology web page gives information on the national flood forecasting and warning service
- The Australian Institute for Disaster Resilience web page offers information on natural disasters and a lesson plan on floods can be found here.
- This ABC Education video looks at how the city of Tokyo is set up to defend against floods.