Types of flooding

A flood is an overflow of water beyond the normal limits of a watercourse. Flooding occurs when water extends over what is usually dry land. This can happen when it escapes from a natural watercourse, such as a lake, river or creek. It can also happen when water is released from a reservoir, canal or dam.

No two floods are the same and can vary depending on the quantity, duration and location of rain falling on our catchments.

Find out more about the types of flooding including:

• riverine flooding
• flash flooding
• storm tide and storm surge.

Riverine flooding

Riverine flooding is a result of heavy and sustained rainfall over a region that is generated by tropical cyclones, lows or monsoon troughs. Riverine flooding happens when there is too much water, and the flow capacity of creeks or rivers (known as waterways) become overwhelmed and burst their banks, and flood areas which are not normally under water. Riverine floods can be significant disaster events that impact individuals and communities and have long term social, economic, and environmental consequences. In inland parts of Queensland, riverine flooding can affect thousands of square kilometres for weeks or even months at a time. Find out more about riverine flooding by watching the video.

Flash flooding

Floods can occur in different ways. Flash flooding can be caused by severe storms with high volumes of rainfall over a short period of time. Flash floods can affect local creeks which can overflow and inundate parks, roads and water crossings. Flash floods can overwhelm local storm water pipes, and combined with overland flow can cause short term inundation to property and business. The pace or velocity of the water can be fast which also has damaging effects to property. Flash floods can be a serious problem in urban areas if drainage systems can't cope and tend to affect a localised area. Shallow fast moving water can wash a car off a river crossing, so if it’s flooded forget it! Find out more about flash flooding by watching the video.

Storm surge and storm tide

Storm surge is an abnormal rise in sea level over and above the normal (astronomical) tide levels. It can be thought of as the change in the water level due to the presence of a storm. These powerful ocean movements are caused by strong winds piling water up against the coast as a cyclone approaches. While significant surges usually accompany tropical cyclones, storm surges caused by large low-pressure systems can also bring dangerous storm tides and damage to coastal communities

Storm tide is the water level that results from the combination of the storm surge and the normal (astronomical) tide. A 3 metre storm surge on top of a high tide that is 2 metres above the mean sea level will produce a storm tide that is 5 metres above mean sea level.

Storm tides can swamp low-lying areas, sometimes for kilometres inland. Strong winds at the coast can also create large waves, worsening the impact.

Find out more about understanding storm surge by watching the video from the Bureau of Meteorology.

More information

Visit the Bureau of Meteorology to learn more about types of floods and what causes floods and storm surge.