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1 in 100 AEP Floodplain Development Control Area
Responsible agency
Department of Water and Environmental Regulation

1 in 100 Annual Exceedance Probability (AEP) Floodplain Development Control Area delineates land that may be affected by the 1 in 100 AEP flooding and therefore subject to development control.


Floodplains continue to be under pressure for more intensive uses despite the significant flood risk. This pressure is increasing as desirable undeveloped land becomes scarce. Severe floods do not occur frequently in this State so the extent of flooding and its consequences are usually soon forgotten. However, when flooding does occur, the resulting damage to property can be quite considerable. In recognising the need to contain and lessen potential flood damage, the former Public Works Department in 1975 commenced floodplain mapping of major rivers throughout the State that would provide planning bodies and Local Government with strategies for ensuring sound development on floodplains. This advisory service has continued and is now being provided by the Department of Water and Environmental Regulation.

The Department of Water and Environmental Regulation is the State Government’s lead agency in floodplain management. In accordance with the Water Agencies (Powers) Act 1984 the Department’s function is to 'develop plans for and provide advice on flood management'. In particular, its role is to:

  • prepare floodplain mapping of existing and future urban areas which are floodprone; and
  • provide advice to the Department of Planning, Lands and Heritage for land use planning and Local Government for building controls to ensure sound development on floodplains.

The Department of Water and Environmental Regulation in carrying out its role in floodplain management provides advice and recommends guidelines for development on floodplains with the object of minimising flood risk and damage. The 1 in 100 AEP flood has been generally adopted in Australia and overseas as the basis for floodplain development planning. The following guiding principles are used to ensure proposed development in floodprone areas is acceptable with regard to major flooding:

  • proposed development has adequate flood protection from a 1 in 100 AEP flood; and 
  • proposed development does not detrimentally impact on the existing 1 in 100 AEP flooding regime of the general area.

As some flood risk can be mitigated through appropriate building conditions imposed by Local Government, the relevant Local Government can be contacted to ascertain if the flood risk to this property has been mitigated.

For more information on a specific site contact our office on (08) 6364 7600 or, or see

Date updated
04/10/2020 12:27:59