Sources of flood water
The Flood Awareness Maps include flooding from all sources: creek, river, overland flow and storm tide.
All floods are different and may occur from one or a combination of these four sources.
Creek flooding happens when intense rain falls over a creek catchment. Run-off from houses and streets also contributes to creek flooding. The combination of heavy rainfall, run-off and the existing water in the creek causes creek levels to rise.
Brisbane has 38 creek catchments. This means creek flooding is the most common type of flooding that affects Brisbane’s suburbs.
Overland flow is run-off that travels over the land during heavy rainfall events. Overland flow can be unpredictable because it is affected by localised rainfall and urban features such as stormwater pipes, roads, fences, walls and other structures. The actual depth and impact of overland flow varies depending on local conditions but it generally occurs quickly.
River flooding happens when widespread, prolonged rain falls over the catchment of a river. As the river reaches capacity, excess water flows over its banks causing flooding. River flooding downstream can occur hours after the rain has finished.
Floodwater may rise very slowly and be slow moving. This is normally associated with Brisbane River flooding, which occurs after prolonged periods of heavy rain across the whole catchment. Floodwater can also rise quickly and be very fast moving, and then recede quickly. This is normally associated with creek flooding.
Storm tide flooding
Storm tide flooding happens when a storm surge creates higher than normal sea levels. A storm surge is caused when a low-pressure system or strong onshore winds force sea levels to rise above normal levels. The impact of storm tide or storm surge is increased during high tides and king tides and can affect low-lying areas close to tidal waterways and foreshores.