Generally in Victoria major regional floods occur about every 5 to 10 years.  Larger floods are less frequent but it is not unknown for more than one major flood to occur in a catchment in successive years.

Flooding can be simply described as an overflowing or accumulation of a body of water onto normally dry land. While flooding is usually a natural event, and one which is important to retain biological diversity, it becomes an important issue for the community when water accumulates where it is not wanted.

In Victoria there are three main causes, which act either independently or in combination: prolonged heavy rainfall, storm surge and high tides. Tsunamis and dam failure are other causes, but a combination of low frequency of occurrence, small impacts (in the case of tsunamis), and good safety management (for dams) means the flood risk for these is small. 

Floods are usually caused by heavy prolonged rainfall. Excessive rainfall produces surface runoff which flows overland into rivers and streams. When there is a large amount of runoff, water overflows the river banks onto the adjacent floodplain, which is the low lying land bordering a creek, river or lake.  This is known as riverine flooding.

Flooding can also affect built up urban land by overland flows that occur during severe storms when the capacity of drainage systems is exceeded.

For coastal areas, flooding can be caused by high tides or storm surges, which result in higher water levels along the coastline, often in combination with riverine flooding.

The management of floods and floodplains brings together the resources of various agencies, authorities, municipal councils, emergency services and the flood affected community to take appropriate and timely action in relation to flood prevention, response and recovery. It often involves making trade off decisions about the economic, social and environmental costs and benefits of activities on the floodplain having regard to the flood risk.