Managing stormwater effectively is a crucial part of urban and commercial development in Australia. As urban areas expand, more surfaces like concrete and asphalt replace natural ground, preventing water from being absorbed. This leads to excess runoff that must be managed to prevent flooding and drainage issues.
Two primary solutions exist for handling this runoff, stormwater retention and stormwater detention. While these terms may sound similar, they serve different purposes and have distinct applications.
In this guide, we’ll explore the key differences between both stormwater management solutions and how they function, giving you the insights needed to manage runoff effectively.
Stormwater retention refers to the process of collecting and storing stormwater for future use. Unlike detention, where water is temporarily held before being slowly released, retention systems keep water on-site indefinitely. This harvested water is typically used for non-potable applications such as:
A retention system involves underground or above-ground tanks that capture and store water from roofs, pavements, and other non-absorbent surfaces. Advanced filtration and treatment systems should be installed to improve water quality, ensuring it meets reuse standards.
Stormwater detention, often referred to as On-Site Detention (OSD), is a method used to control the rate at which stormwater is discharged into public drainage systems. Rather than permanently storing the water, an On-Site Detention tank temporarily holds runoff and releases it at a controlled flow rate, preventing flash flooding and excessive load on municipal stormwater infrastructure.
An OSD system consists of an underground detention tank equipped with controlled outlet mechanisms, such as orifice plates or pumps. These regulate the discharge flow to match council-mandated levels.
| Feature | Stormwater Retention | Stormwater Detention (OSD) |
| Purpose | Store water for future use | Temporarily hold and slowly release water |
| Water Reuse | Yes, for irrigation, toilets, and non-potable uses | No, water is eventually discharged |
| Regulatory Requirement | Encouraged for sustainability | Often mandatory for new developments |
| Impact on Public Drainage | Reduces reliance on potable water | Minimises peak stormwater discharge |
| Installation Locations | Roofs, underground, above-ground tanks | Underground tanks, open spaces |
Most Australian councils require stormwater detention systems for developments that increase impervious surfaces. Regulations vary by state and local government, but it is usually required for:
It’s important to check with your local council to determine specific OSD system requirements for your site.
Many modern developments incorporate a hybrid stormwater system, using both retention and detention solutions. This approach allows:
For example, a development might feature an OSD tank that first diverts a portion of collected water into a retention tank for reuse, while the excess is slowly discharged into the drainage system.
Both stormwater retention and stormwater detention play crucial roles in urban development. Whether your project requires an OSD tank, a full retention system, or a combination of both, understanding their differences ensures compliance, efficiency, and environmental responsibility.
By integrating a well-planned stormwater system, developments can mitigate flood risks, enhance sustainability, and reduce water costs. Always consult with stormwater system contractors and local councils to determine the best approach for your site.
If you need expert advice, contact Buildaroo today at 0421 841 919 or fill out our online form to get started on your stormwater management solution.
