Rosedale Wastewater Treatment Outfall, New Zealand

To protect and improve the quality of Auckland’s beaches, a new tunnel and outfall was constructed which allows treated water to be discharged 2.7 kilometres offshore, compared to the previous distance of 600 metres.

Aurecon delivered all of the detailed design for the tunnel, the marine outfall pipe and the 38 metre deep cascade drop shaft, which was the first use of a cascade in New Zealand.

The hydraulic design required an analysis of air entrainment, initial dilution, headloss and saltwater expulsion issues for the treated effluent discharge, and shear stress and flow characteristics. The transition riser was a critical asset and was designed to improve flushing and to facilitate maintenance operations using a 3D computational fluid dynamic model.

In 2011 the project won Gold at the ACENZ Innovate NZ Awards of Excellence.

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