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A stormwater detention system, also called an onsite detention system (OSD system), temporarily stores rain-water runoff (stormwater) from your property. It then releases it into our drainage system at a controlled rate.

You must apply for an OSD system if your property:

  • has many hard surfaces (such as roofs, driveways or buildings) that stop stormwater absorbing into the ground
  • is a multi-unit development.

Before you apply

We recommend you send a general enquiry to our drainage team before you complete your designs This helps to make sure there are no delays when you submit your application.

Send your enquiry to [email protected] and include:

  • site coverage
  • total site area
  • roof area
  • paved areas
  • landscaped area.

We will respond within 10 working days and confirm your:

  • detention volume storage requirement
  • permissible site discharge.

You must include these in your designs when you submit an application.

Apply for approval

Once we have confirmed your requirements, you can apply for approval for an OSD system.

You must provide a design that meets our requirements and pay a fee to have it evaluated. The fee is calculated according to the number of units in your development, as follows:

  • $300 for 1 to 4 units
  • $700 for 5 to 9 units
  • $900 for 10 or more units

Fees don’t incur GST.

Apply for approval for an OSD system

Include in your application:

  • the drainage design plans
  • how you will achieve the required volume of storage
  • how you will limit the flow rate of permissible site discharge
  • approved landscape plans
  • your Certificate of Title, which you can get through the Landata website.

After you apply

  • We'll send you confirmation that we've received your application.
  • We'll process your application in 4 to 6 weeks.

You can start building your OSD system after you receive an approval certificate from us.

Design requirements

Follow these requirements to make sure your OSD system meets our regulations.

  • Your design must:
    • show existing and proposed trees and tree protection zones (learn more on our Protect trees during construction page)
    • show easements on the property
    • include the volume of storage needed, confirmed by our drainage team
    • include the permissible site discharge, confirmed by our drainage team
    • include a site survey that confirms levels of existing services within or near the site
    • comply with AS/NZS 3500.3.
  • Your building envelope site must match the plans approved in your permit. Learn more on the Department of Transport and Planning website.
  • You must comply with the legal point of discharge requirements. Learn more on our Connect to the stormwater page.
  • Your proposed control pit must comply with the Standard Drawing SD999 – onsite detention control pit details on our Standard drawings page.
  • Above-ground water tanks must not be used for stormwater detention.
  • Groundwater from a basement, or excavation works more than 1.2 m in height, must not be drained into laneways, kerbs and channels.

Request an inspection

After you build your OSD system, or if your drainage approval requires an interim inspection, you must request an inspection and pay a $158.60 inspection fee (doesn’t incur GST).

We will inspect the system to check that it complies with the approved designs. You’ll need evidence of this inspection for your Certificate of Occupancy.

Request an inspection

Include in your request:

  • a copy of your signed, endorsed and approved rain water drainage plans
  • the reference number for your approved designs (found on your approval letter)
  • photos of:
    • the inside of the control pit showing the trash grate and orifice plate
    • the diameter of the orifice plate (the metal plate attachment with a hole that controls the flow of rain water) – use a ruler or other measuring device and take a closeup photo of this
    • the sump and weepholes – take a closeup photo.

These photos are mandatory. Non-compliant photos will lead to delays in assessing your application.

See the photos below for examples of what to show in your photos. 

a photo of the inside of the control pit that shows the trash grate and orifice plate
A photo of the inside of the control pit that shows the trash grate and orifice plate
A close-up photo of the orifice plate (the metal plate attachment with a hole that controls the flow of stormwater)
A close-up photo of the orifice plate (the metal plate attachment with a hole that controls the flow of stormwater)
a measurement of the diameter of the orifice plate
A measurement of the diameter of the orifice plate
A close up photo of the sump and weepholes
A close up photo of the sump and weepholes

After you submit your request

We’ll contact you within 10 business days to confirm an inspection time. It may take longer if we need more information to assess your application or have to refer it to another department at council.

If we find issues during the inspection, you’ll need to:

  • make changes
  • submit a request for an additional inspection
  • pay another inspection fee.

If you can’t make the changes to meet the requirements of the approved stormwater drainage plans, you’ll need to submit a new application for approval of the new plans with our Drainage Team.

This is considered a reassessment and attracts additional fees. You'll also need to request a new inspection.

More information

Call us on (03) 9278 4444 or email [email protected].

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