5.1 Theory on OSD



What is On-Site Detention(OSD)?

In simple terms, it is a way of collecting the rainfalls on a site (known as stormwater), storing it temporarily and then releasing it slowly so that it does not worsen the downstream flooding.


Why do we need OSD ?

The aim of providing OSD for new developments or redevelopments is to delay and reduce the stormwater flows(discharge) from the pre-development levels, thus reducing flood risks caused by stormwater runoff.


What happen if there is no OSD ?

  • Frequent surcharge at local drains
  • Further bank erosion at local creeks
  • Downstream flooding would get steadily worse
  • Completed flood mitigation works would become less effective
  • Community would suffer increased flooding
  • Local council would be forced to spend more on further flood works
  • Developers would have passed on the cost of dealing with the increased runoff to the rest of the community / council.


Which developments need OSD facilities ?

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


How do OSD look like ?

There are generally 3 types of OSD which is:



Editor:- Dilah – 11 March 14


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