They may result from prolonged or very heavy rainfall or severe thunderstorms that can occur far away in the upper reaches of a catchment.

Less common causes include snowmelt, dam failure, storm surge and tsunami (seismic sea waves) which both involve rapid seawater flooding.

Who is threatened by floods?

People who reside or work on flood plains or on other relatively  low-lying areas near rivers,  live with the greatest threat of floods.

Periods of intense heavy rain, not necessarily in the immediate area can lead to rises in the water level of rivers/creeks, or indeed drains, to a point where channels can no longer hold the volume of water.

Alternatively, for some coastal dwellers, there is the threat from storm surge events. These are associated with low pressure systems coupled with tide and wind conditions.

It's important that residents know when their property could be at threat. The Bureau of Meteorology website provides year round weather and river height/flood information at predetermined locations for the Barwon and Moorabool Rivers.

Common types of flooding in Australia and Geelong

Slow-onset floods

Under the right weather and catchment conditions in the upper Barwon Catchment, flooding can occur along the Barwon River. 

Flooding along the Barwon River as it passes through Geelong can lead to losses of livestock, damage to crops, as well as damage to sporting / recreational facilities, road networks and businesses. 

Rapid-onset floods 

Flooding can occur more quickly in the mountain headwater areas of large rivers, as well as in the rivers draining to the coast. In these areas, the rivers 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.

A good example of a rapid flood event is flooding that occurs on Hovells Creek. The Hovells Creek catchment is 230 square kilometres and under the right conditions can cause flooding within Lara in under nine hours.

Flash floods

Flash flooding results from relatively short, intense bursts of rainfall, often from severe thunderstorms. These events occur almost in all parts of Australia and poses the greatest threat of loss of life.

People can be swept away after entering floodwaters on foot or in vehicles. Remember the important message from emergency services, 'do not drive or walk through floodwaters'.

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.

Catchment areas