CEME engineers are using the expertise gained in the offshore oil and gas industry to help test the effectiveness of offshore artificial reefs (OARs) being deployed around Australia, including one earmarked for the waters off Rottnest Island.
The aim of the artificial reefs is to establish a sustainable marine environment to support productive fish communities for recreational fishing, says CEME senior lecturer Dr Scott Draper.
Dr Draper and colleagues Dr Henning Mohr and Dr Hongwei An undertook research on behalf of Subcon, a company specialising in subsea structures, to test the effectiveness of its innovative artificial reef designs.
The researchers’ initial work focused on reefs designed for Moreton Bay (Qld), Port Macquarie and Shoalhaven (NSW).
Using a model of a Subcon ReefTempleTM module they looked at how currents and waves would interact with the structure and confirm that the artificial reef modules would result in water being pushed upwards.
“The induced upwelling delivers nutrients and food up into the water column, and that’s a critical feature for attracting fish,” says Dr Draper.
“We performed some dye visualisation here in the labs, and we confirmed that their structure was designed in a way that would be good at doing that. We also measured the hydrodynamic performance of the module to determine its stability parameters.”
Subcon have since installed the concrete ReefTempleTM modules at four sites and Dr Draper says underwater images indicate the structures are covered in marine growth surrounded by fish. They have recently survived 100 year storm events at Shoalhaven and Port Macquarie intact and in position.
“So it looks like they are performing exactly how they were designed both hydrodynamically and as a productive habitat,” he says.
The CEME team is also testing the design of Subcon’s newest FishTowerTM modules to be deployed off Rottnest Island, but in conditions far harsher than the reefs deployed off the east coast of Australia.
“We need to make sure the artificial reefs aren’t going to move around under large waves off Rottnest,” Dr Draper says.
“We looked at a radically different design and performed experiments to estimate the hydrodynamic loads on the structure. This allowed Subcon to determine the optimal ballast for structures.”
The research involved tank testing at UWA’s internationally renowned O-Tube flume facility.
“With the O-Tube, you can predict, based on measurements, what the extreme weight and currents will be at the seabed in a storm, and we can replicate them in our flume because it was designed to be able to reproduce storm-like conditions,” Dr Draper says.
The Rottnest artificial reef is due to be installed in November 2016.
Tony Malkovic @TonyMalkovic