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.
Topography
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.
More information
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.