Many locations can be affected by both flash floods and the more general river flooding. Sometimes, a flash flood in the upper reaches of a river system can evolve into a more general river flood as it joins with other inflows and spreads out as it travels downstream. With more time to react, flood warning is more effective for these types of floods, as described in Question 4 and Question 5. The runoff from this rainfall flows across land and then down gutters, drains, gullies, creeks and rivers and may create significant floods that inundate large areas of land for days, weeks or months.

In larger catchment areas, rainfall can build up over hours, days or weeks. As there is little time to react, flash floods are particularly difficult to predict and manage in real time, and this is discussed further in Question 4 and Question 5. Flash floods are typically associated with relatively small catchment areas where there may be little or no permanent flow of water. Heavy, intense rainfall can occur suddenly, and the quickly rising floods caused by this in the minutes or hours after the rainfall are known as flash floods. Inland earthquakes, volcanoes or land slips can also cause flooding, as can breaches/releases in natural or man-made barriers to flooding such as dams and levees. Large tides and storm surges can also flood coastal areas. Recent international events have highlighted the risk of flooding from tsunamis. The floods that are produced by this rainfall are therefore equally variable, that is, every flood is different.įloods can also be caused by other mechanisms. The amount of rainfall, the intensity of the rainfall over time (the temporal pattern) and the distribution of the rainfall over an area of land (the spatial pattern) can all vary widely. The area of land that contributes runoff to a particular point is called the catchment. When rain falls over an area of land, some is absorbed by the soil, while the rest becomes runoff and flows downhill. Floods in Australia are usually caused by rainfallįloods can be caused in a number of different ways however the dominant cause of flooding in Australia is rainfall. Cities and other settlements have been constructed on floodplains to take advantage of access to water and good quality farmland. In Australia, many people live on land that is subject to occasional flooding, known as floodplains. On the other hand, there are many examples of several large floods occurring within short periods of time. They occur at irregular intervals, and many decades can pass between significant floods. They can occur suddenly and recede quickly, or may take days or even months to build and then discharge. When water inundates land that is normally dry this is called a floodĮvery flood is different. The lower sixth represents a sub-surface cross-section. Conceptual diagram developed using the Integration and Application Network (IAN) tool.

Areal flood