Why is OnSiteDetention (OSD) required ?
Most Councils' existing drainage infrastructure was built 30-40 years ago when the population was modest and the urbanisation was slow. The rapid urban growth over the last decade or so has significantly increased impermeable surfaces such as roads, driveways, buildingroofs, carparks. More impermeable surface results in less rainwater being absorbed into the soil and more overland flow. When the existing drainage networks can not cope with the excessive amount of surface water , flooding occurs. OSD is one of the most common and effective measures adopted by many Councils to limit site discharge to capacity of the existing stormwater drainage system.
How does an OSD system work ?
How does an OSD system work ?
It captures and temporarily hold site runoff . The stored volume is gradually released to the street mostly by means of an orifice, a small round hole. In most cases the orifice is sized to reduce the development site discharge to the existing level ,i.e. pre-development level. The OSD does not reduce the site runoff volume but constricts site discharge to a rate that the existing Council's pipe system can cope with, avoiding overloading and local flooding.
Is it expensive to construct an OSD system?
The OSD building cost varies greatly depending on design approaches. A cost-effective design will utilise driveways, carparks, frontyards/backyards to function as an OSD storage area(s). This approach often involves good engineering of site topography to integrate with the landscaping features and Council's requirements. Where site constraints are prime factors (Examples narrow space, steep terrain) underground OSD tanks which are usually more expensive can be used.
Examples of OSD & Pipe Drainage System
