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City of Wollongong

An on-site stormwater detention (OSD) temporarily stores stormwater runoff, and reduces the rate of runoff flowing onto other properties or into Council's drainage system. This is important to help control the movement of water and reduce the chance of flooding downstream, especially in short, intense storms.

OSDs may be created above or below ground. In many cases they can be incorporated into car parks, driveways, landscaped areas, underground tanks and pits, or a combination of these. However, you can't usually use a rainwater tank as an OSD.

OSDs will usually be required for:

  • Subdivisions
  • Single dwellings, extensions, additions and improvements
  • Townhouses, villas, home units, duplexes
  • Dual occupancies
  • All commercial, industrial and special use developments and buildings
  • Tennis courts
  • Roads, car parks and other sealed areas
  • Public buildings.

OSDs are usually not required for:

  • Development that increases the impervious surface area of a site by less than 100 square metres. Note that only one exception under this rule is allowed per site.
  • Development within the 20% AEP flood extents.
  • Subdivisions of existing dual occupancies where there is no increase in impervious surface area
  • Boundary adjustments and consolidations of allotments where no additional lots are created
  • Change of use where there is no increase in impervious surface area
  • Building additions or internal alterations within the current footprint of an existing dwelling
  • New developments in subdivisions where OSD has already been provided for the entire subdivision
  • Buildings in rural or non-urban areas
  • Developments within OSD Concession Zones, shown on plans in the relevant chapter of the Wollongong Development Control Plan where runoff from the development can drain to a watercourse without affecting other properties.

If your'e not proposing to use an OSD, you must provide a written justification for this decision with your development application.

For more information on OSDs, including alternative systems, read Chapter E14 of the Wollongong Development Control Plan PDF, 7823.31 KB.