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Stormwater Detention - What Does It Mean?

Stormwater Detention

Urban development increases the number of surfaces covered by water-resistant materials such as asphalt, concrete, brick, stone, and rooftops.  

These surfaces do not allow water to pass through them and result in an increased volume of stormwater runoff. This increased runoff may overwhelm the existing drainage system and increase the potential for flooding that can present a hazard to people or cause significant damage to property. 

Many councils now mandate that new developments do not adversely impact on the performance of the local stormwater drainage system and require that onsite stormwater detention systems are incorporated into new developments to reduce the peak flow of stormwater from the site. 

Onsite detention systems reduce the peak flow by temporarily storing stormwater runoff and discharge into the council drainage system at a controlled rate. 

The Onsite Stormwater Detention Policy of the City of Casey in metropolitan Melbourne is typical of many.

In Casey, the need for an onsite stormwater detention system will be assessed as part of a planning application, and the installation of an onsite stormwater detention system will be enforced as a planning permit condition. In terms of design, the stormwater detention system must: 

  • Restrict the rate of stormwater discharge to the permissible rate of discharge during the storm event specified by Council 
  • Provide sufficient storage to ensure peak flow rates at any point within the downstream drainage system do not increase as a result of the development during the design storm event specified by Council  
  • Drain within 72 hours to ensure the storage volume is available for a subsequent storm event 

In addition, Casey state that the property owner is responsible for the operation, maintenance and replacement of the onsite stormwater detention system. It is recommended that onsite stormwater detention systems are cleared of debris and sediment at least once per year to ensure correct operation. 


Stormwater Detention Tanks 

A stormwater detention system will consist of a storage tank to collect stormwater and a valve system to slowly release water over time. This might be a separate detention tank or a standard rainwater tank with an upper and lower drain. The upper drain allows stormwater to accumulate and drain away while leaving a reservoir of water below, and accessed through the lower drain, for normal domestic use. 

Talk to our expert team to find out how Rapid Plas tanks can be used to comply with water detention requirements on your new-build property. Call our team on 1800 816 299 or email sales@rapidplas.com.au with your enquiry.