Hazards, Disasters and Survival
A booklet for Students and the Community
Chapter 3
Flood Hazards and Disasters
WHAT ARE FLOODS?
Floods occur when water covers land which is normally dry. They may result from prolonged or very heavy
rainfall, severe thunderstorms, monsoonal (wet season) rains in the tropics, or tropical
cyclones. Other, less common causes include
snow-melt, dam failure, or storm surge and tsunami - both involving rapid seawater
flooding (see Chapters 7 and 9 respectively).
People who live near rivers, or in low-lying coastal areas, live
with the greatest threat of floods. Periods
of heavy rain, not necessarily in their area, can lead to rises in the water level of
streams and rivers to a point where channels
can no longer hold the volume of water. Alternatively,
for some coastal dwellers, there is the threat from the sea as mentioned above and
explained later.
Common Types of Flooding in Australia
Slow-Onset Floods - Flooding of rivers in the vast
flat areas of central and western NSW and Queensland, as well as parts of Western
Australia, may last for one or more weeks, or even months on some occasions. Floods in these areas can lead to major losses of
livestock and damage to crops as well as extensive damage to rural towns and road and rail
links (see Case Study 2).
Rapid-Onset Floods - Flooding can
occur more quickly in the mountain headwater areas of these larger rivers as well as in
the rivers draining to the coast. The rivers
here are steeper and flow more quickly, with flooding sometimes only lasting for one or
two days. These floods can be potentially
much more damaging and can pose a greater risk to loss of life and property. This is
because there is generally much less time to take preventative action, and a faster, more
dangerous flow of water. This type of
flooding can affect most of our major towns and cities.
Such flooding had a very severe effect on north-eastern Victorian towns of Benalla,
Shepparton, Wangaratta and Euroa in October 1993 when 12 ‘mountain’ rivers in
the region suddenly flooded simultaneously. A
total of 5,500 people were evacuated as floodwaters swirled into more than 4,000 homes,
shops, farms and orchards. Thousands of
livestock, fruit and vegetable crops, and dairy production were lost. These losses and
massive damage to roads and bridges all contributed to total estimated costs of
$440 million in 1997 values. (Also see Case Study 1.)
Flash Floods - Flash flooding results from relatively
short, intense bursts of rainfall, often from thunderstorms. It can occur in almost all parts of Australia and
poses the greatest threat of loss of life. People
are often swept away after entering floodwaters on foot or in vehicles. These floods can also result in significant
property damage and major social disruption. They
are a serious problem in urban areas where drainage systems are often unable to cope. Two frightening examples occurred in 1971. In Elizabeth Street, Melbourne, metre-deep
floodwaters washed cars away and in Canberra, 7 motorists died after their cars were swept
off a road into a flooded creek during intense rain.
(Also see Case Study 3.) 
Severe storms and cyclones, especially in northern Australia, can
cause vast areas to be affected by flash floods. Damage
may be limited to property and stock losses, but in some of the more severe cases, human
lives have been lost or fatal injuries sustained by people caught in flash floods, such as
those which have occurred in the normally-dry Todd River at Alice Springs, NT.
Flood Warnings
Except for flash floods, there is usually a reasonable warning
period possible. Common terms used in
warnings issued by the Bureau of Meteorology are as follows:
Minor Flooding - Causes inconvenience, closing minor
roads and low-level bridges.
Moderate Flooding - Low-lying areas inundated,
requiring removal of stock, equipment and evacuation of isolated homes. Main road and rail bridges may be covered.
Major Flooding - Higher areas inundated,
towns/properties isolated, extensive damage.
Local Flooding - Intense rainfall, some high run-off
but usually no flooding in main streams.
Significant River Rises - This warning is issued if it
is not certain that the initial flood levels will be exceeded in the main streams. It lets people know that appreciable rises are
expected.
AUSTRALIAN FLOODS - CASE STUDIES
1. Brisbane,
Queensland 1974
The Weather Systems -
The wet season in northern Australia is the result of a monsoonal air flow usually
restricted to far northern parts of the continent. In
January 1974 however, this moist mass of tropical air moved steadily southward producing
substantial rainfall over much of Queensland. The
main ‘trigger’ for the Brisbane Floods was the weakening Cyclone
‘Wanda’ which crossed the Queensland coast on 24 January about 150 kilometres
north of Brisbane. It only caused minor wind
damage but added heavy rainfall to an already saturated river catchment. Furthermore, it triggered the monsoonal air mass
over southern Queensland into periods of intensive rain over a five day period. Among the highest recordings were 1,318mm (almost
60 inches), whilst in Brisbane itself 819mm of rain fell, producing the worst city
flooding in Australian history to date.
Record Flooding - By 26 January flooding
was reported in the upper Brisbane Valley, with the nearby city of Ipswich on the Bremer
River (Brisbane River tributary) experiencing major flood levels. In Brisbane, periods of intense rainfall flooded
small creeks, drains and floodways. These
local floods, when added to the rising Brisbane River, produced the highest flood levels
to date this century, swamping one third of the city centre and 17 suburbs.
Human Toll and Damage - Tragically, 16 people died,
300 were injured and 8,000 made homeless as 56
homes were swept away and 1,600 largely submerged. In
all, 13,000 buildings were affected with insurance claims totalling about $328 million
(1997 values), but this figure reflected only ‘rain damage’ and special
commercial cover as domestic flood insurance is not generally available. The total estimated damage cost was in fact $980
million, with road and bridge repairs alone costing $112 million (1997 values). At the height of the flood, even ships, including
a large oil tanker, were torn from their moorings on the river and damaged. At the same time, throughout south-eastern
Queensland and northern NSW where every river was in major flood, the total damage bill
(including Brisbane) was a staggering $2,200 million (1997 values).
2. 1990
Great Floods - QLD/NSW/VIC 
The April/May, 1990 floods in eastern Australia were huge. They covered more than one million square
kilometres of Queensland and New South Wales and a smaller area of Victoria (in a separate
extreme flood). The map shows the extent of
the floods - an area larger than Germany!
Causes - In
central-northern NSW and central-southern QLD, continual, heavy rains partly caused by
cyclones, drenched the flat inland plains. Then
further torrential rainfalls created almost instant floods.
Many rivers had already flooded once and were in flood again at even higher levels.
Effects - In both States, road and rail links were
severed for long periods. Floodwaters invaded
towns and many communities and properties were isolated.
Graziers faced a grim submergence of entire properties from river overflows, while
livestock deaths of up to one million were estimated.
Emergency services were stretched to the limit to provide essential rescues,
evacuations and food drops.
Nyngan, NSW - The interaction of numerous flooded river systems
in northern NSW and southern Qld made flood height prediction difficult. Residents of Nyngan, on the Bogan River,
strengthened levee banks in expectation of a record flood height which was eventually
exceeded! Almost every building was flooded
and 2,500 people were evacuated, mainly by helicopters, under emergency conditions as all
town services were lost. Considerable cost
and hardship occurred because the town did not have a disaster plan to cope with levee
bank failure. Residents could not return to
their homes for three weeks, billeted by the people of Dubbo, about 160 km away.
Charleville, Qld - Here, a similar situation occurred several days
earlier when over 80% of the town (of about 3,000 people) was flooded, inundating all
services. The hospital had to be evacuated by
boat and a massive air evacuation saw over 2,000 residents uplifted (mainly by
helicopters) to the higher, local airport, around which a huge ‘tent city’ was
established. This accommodated 2,300
residents and up to 1,000 emergency workers at the height of the disaster and was
responsible for providing over 15,000 meals per day at the peak period.
Damage - In Nyngan and Charleville alone, nearly 2,000
homes were inundated and in many cases were badly damaged.
Although about 40 were beyond repair, emergency workers and residents cleaned and
restored the majority to good condition after weeks of toil. Most commercial and public buildings were also
badly affected and very heavy retail stock losses occurred.
The story was repeated many times over in smaller towns and properties in NSW and
Qld and at the same time a series of brief, but violent floods wreaked havoc in the
Gippsland region of north-eastern Victoria, leaving a trail of death and damage.
Cost - Across the three affected States, the Great Floods
of 1990 claimed 7 lives, caused 60 injuries and left 5,000 temporarily homeless. The total estimated cost of these floods was $415
million (1997 values), most of which was uninsured.
3. Coffs
Harbour, NSW 1996
This coastal town in northern NSW received 168mm of rain (and up to
300mm in the region) within 2 hours on 25 November 1996.
This resulted in a devastating flash flood. One
woman died when she was swept more than one kilometre from her home to the sea and 300
people had to be evacuated. Over 500 homes
and 100 businesses were damaged as well as roads and many cars. Part of the local banana crop was also destroyed
due to erosion and landslides. Most of the
$140 million damage was not covered by the $35 million insurance payout.
FLOOD SURVIVAL AND PROPERTY PROTECTION
Many communities now have flood prevention or reduction strategies
such as: restricting or not approving floodplain development; use of dams, diversions and
levees; and building-raising or flood-proofing.
As an individual, if your area is subject to flooding, the following
advice could save your property or life. Please
ensure that you and your family understand and heed it:
Know Your Local Flood History
Ask your local council or State/Territory Emergency Service about
the following:
What the terms major, moderate and minor flooding mean to your area
and at what official river height your home becomes isolated or inundated.
Local flood plans: whether you may need to evacuate; how to find the
nearest safe location.
Emergency Kit - Check List (for use during and
after a flood)
A portable radio and torch with fresh batteries, candles and
water-proof matches.
Reasonable stocks of fresh water and tinned food, strong shoes and
rubber gloves.
A first aid kit and basic first aid knowledge and good supplies of
essential medication.
A water-proof bag for clothing and valuables and your emergency
contact numbers.
Act on Flood Warnings
Listen to your local radio for information. Check that your
neighbours know of the warning.
Stack your furniture and possessions above likely flood-level, (on
beds etc and in roof) with electrical equipment on top. Secure heavy objects that could
float and cause damage.
Move garbage, chemicals, poisons, fuel etc to a high, secure place.
Protect/relocate stock and equipment in commercial/industrial
premises.
If on a farm move livestock to high ground.
Check your car, fill it with fuel and check your emergency kit and
fresh water stocks.
If You Need to Evacuate
You may be asked to evacuate, but if you plan to leave of your own
accord tell the police or State/Territory Emergency Service and neighbours. In either case you should take these actions:
If possible empty freezers and refrigerators leaving the doors open.
Collect and secure your valuables, papers, photo albums and
mementos.
Place a sandbag in the toilet bowl to prevent ‘backflow’
of sewage.
Turn off electricity, gas and water. Don’t forget your
emergency kit.
During and After the Flood
If you remain in your home or when you return take these
precautions:
Keep your emergency kit safe and dry. Do not eat food which has been
in contact with floodwater and boil all water until supplies have been declared safe.
Don’t use gas or electrical appliances which have been
flood-affected, until safety-checked.
Beware of snakes and spiders which may move to drier areas in your
house.
Avoid wading, even in shallow water as it may be contaminated - if
you must enter shallow floodwater, wear solid shoes. Check with police for safe
routes before driving anywhere and don’t enter water without checking depth and
current.
Keep listening to your local radio or TV station and heed all
warnings and advice.
FIND FURTHER INFORMATION
As a project on floods, find out more about:
effects on people of the ‘Great Floods’ of 1990 and how
they were helped;
how levee banks are built and what makes them effective;
other types of flood control measures; and
the beneficial effects of flooding
(eg River Nile).
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EMERGENCY MANAGEMENT AUSTRALIA, PO
Box 1020 Dickson, Australian Capital Territory 2602, AUSTRALIA
Telephone: + 61 (0) 2 6266 5402 Facsimile: +61 (0) 2 6266
5029 Email: ema@ema.gov.auAUSTRALIAN EMERGENCY MANAGEMENT INSTITUTE,
Mount Macedon Road, Mount Macedon, Victoria 3441, AUSTRALIA
Telephone: + 61 (0) 3 5421 5100 Facsimile: +61 (0) 3 5421
5272 Email: aemi@ema.gov.au |
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This page was last updated May 31, 2001 |
