CDS® Unit a reliable base for stormwater harvesting plan

The outstanding performance and design flexibility of the CDS® gross pollutant trap provided North Sydney Council with an efficient solution that cleans runoff to Sydney Harbour while furnishing a more secure water supply for irrigating the Cammeray Golf Course.

The 9-hole course at Cammeray, just north of the Harbour Bridge, has a stormwater culvert running beneath it that drains 94ha of urban land, including the Warringah Freeway (the main northern approach to the Harbour Bridge and Tunnel).

Stage one of the council’s stormwater harvesting plan was to install a gross pollutant trap capable of removing litter, sediment and hydrocarbons from all the stormwater running off the Warringah Freeway. The device was also intended to provide a reliable and pre-screened off-take for pre-screening as the first part of the stormwater harvesting system.Both objectives were met by the CDS® Unit.

Athassel Constructions won the tender to install a CDS® P3030 Unit, based on cost, performance and flow reliability.The non-blocking screen of the CDS® Unit allows it to treat more water by volume than any other screening system, while the large off-line storage in the sump virtually eliminates re-suspension of captured pollutants and permits safer maintenance practices and a lower cleaning frequency.

With a sump storage capacity of more than 10 tonnes and a total storage of more than 30 tonnes, the 5-metre diameter CDS® P3030 unit was well suited to the high flows and pollution loads coming from the catchment.

The design flexibility of the CDS® Unit also helped the council to economise on the future installation of a pump station.The unit was customised to allow two 50 L/s pumps to be located inside the unit itself, behind the screens.

Stage two of the project involves installation of pumps, storage and disinfection, but meanwhile the CDS® Unit has been working successfully to protect the environment.

North Sydney Council now has 12 CDS® Units and one Rocla CleansAll® gross pollutant trap protecting the foreshore and harbour.Based on average removal rates, these devices can be expected to prevent up to 200 tonnes of pollutants from entering the downstream waters each year.They will also help to secure future water supplies by providing reliably treated stormwater for harvesting.