What is an OSD?
Stormwater management is a crucial aspect of urban planning and development to prevent flooding, erosion, and water pollution. On-site stormwater detention (OSD) is one of the methods used to manage stormwater runoff. It involves temporarily storing rainwater and runoff on the property where it originates, rather than allowing it to immediately flow into the local drainage system or neighbouring properties.
The benefits of OSD
The benefits of OSDs include reducing the peak flow rate of stormwater runoff, which helps to control the movement of water and minimises the risk of flooding downstream, particularly during intense storms.
OSDs can take different forms, either above ground or below ground, and they can often be integrated into various structures such as car parks, driveways, landscaped areas, underground tanks, and pits, depending on the site’s design and requirements.
It’s important to note that rainwater tanks typically cannot be considered as OSDs, as they are primarily used for collecting and storing rainwater for non-potable uses like irrigation or flushing toilets
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Types of developments requiring an OSD
OSDs are usually required for various types of developments, including:
- Subdivisions
- Single dwellings and their extensions, additions, and improvements
- Townhouses, villas, home units, and duplexes
- Dual occupancies
- All commercial, industrial, and special use developments and buildings
- Tennis courts
- Roads, car parks, and other sealed areas
- Public buildings.
Situations where OSDs may not be required
There are situations where OSDs may not be required, including:
- Development that increases the impervious surface area of a site by less than 100 square metres, with only one exception allowed per site.
- Development within the 20% Annual Exceedance Probability (AEP) flood extents.
- Subdivisions of existing dual occupancies without increasing the impervious surface area.
- Boundary adjustments and consolidations of allotments where no additional lots are created.
- Change of use that does not increase the 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 where the runoff from the development can drain to a watercourse without affecting other properties.
If a development application does not propose the use of an OSD, the applicant must provide a written justification for this decision, explaining why an OSD is not feasible or necessary for the specific project.
These requirements and guidelines may vary based on local regulations and development control plans, so it’s essential for developers and applicants to consult with the relevant authorities and planning departments to ensure compliance with stormwater management regulations.
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