Stage Four

Stage Four:  Extension of East Point outfall

Stage Four of the Larrakeyah Outfall Closure Plan involves extending the East Point outfall pipeline to discharge to deeper water, to take advantage of strong currents and tidal movements. 

Power and Water commissioned a tidal study off East Point in July 2010 to improve its understanding of tides and currents in this area of the Harbour.

Tracers were released into the water over two days, at two locations and at varying depths so scientists could track their movements over a number of hours.

Power and Water worked with scientists from Charles Darwin University (CDU) and the Australian Nuclear Science and Technology Institute (ANSTO) to release a coloured dye (Rhodamine WT) and a radioisotope (Technitium-99m) into the water about 1km out from the existing East Point outfall.

Scientists in two boats then travelled back and forth across the area as the tracers dispersed, measuring their concentration at different depths.

The results from the tidal study were used to calibrate a model of the harbour, which scientists have been working on for about five years. The harbour model then helped scientists and engineers predict how effluent discharged at different sites would disperse, in order to determine the best location for the new outfall.

Power and Water is currently preparing Public Environment Reports (PERs) for the duplication of the East Point rising main (stage three) and the extension of the East Point outfall (stage four).

The PER will assess and determine how best to manage any environmental impacts associated with duplicating the rising main to East Point and extending the East Point outfall.

The timing of construction for these works will depend on the outcome of the PER.

Media release: July 2010, Scientists colour water in East Point tidal Study

Fact sheet on tidal study