On-site stormwater detention (OSD) systems, required on all new developments in the Baulkham Hills, Blacktown, Holroyd and Parramatta local government areas since 1991, are soon to change significantly.

A new and improved OSD policy comes into effect on Tuesday 9 August 2005 when the Upper Parramatta River Catchment Trust launches the 4th edition of its On-Site stormwater Detention (OSD) Handbook at the Holroyd Centre in Merrylands. Over 200 designers, engineers, architects and developers have booked to attend the workshop being held to explain the new OSD policy.

OSD ensures that new developments do not increase downstream flooding. OSD systems restrict the rate at which stormwater leaves a site, temporarily storing the excess stormwater on the site for a short while. The four local councils apply the common OSD policy as a consent condition on all new developments.

The new OSD policy is the result of extensive studies over several years. OSD will still provide flood protection in major storms. But it will now also detain runoff in smaller storms in order to reduce bank erosion and habitat disturbance in our urban creeks. OSD systems will now also have a small sand and vegetated filter at their outlet to trap pollutants.

The Executive Officer of the Trust, Dr Stephen Lees, said that the new OSD policy "will significantly improve stormwater management in this catchment by helping make stormwater runoff more like what would have occurred prior to development. "

He also warned against complacency, "Recent record rainfalls on the Gold Coast and serious flooding at Lismore shows that severe storms can occur at any time. By having their OSD system designed and built in accordance with the new OSD Handbook, and properly maintaining it, local residents are helping to protect themselves and their neighbours in the event of a major storm."

An On-site Stormwater Detention System