Environmental Impact Assessment: Wave Swell Energy Test Site, Grassy Harbour, King Island, Tasmania

Marine Solutions conducted an environmental survey in Grassy Harbour, King Island on the 19th of December 2022, to facilitate an Environmental Impact Assessment (EIA) of the UniWave installation. The objective of the EIA is to determine if the 2-year deployment and operation of the UniWave had any detectable impact on the ocean, seafloor and ecology of the immediately surrounding area.

A suite of environmental data was collected in surveys at the UniWave site, and at two control sites at a nearby reef and inside the Grassy Harbor marina. The environmental data collection at all three locations included underwater habitat surveys, water quality profiling and sediment analysis (contaminant and particle size). An additional bathymetric mapping of the seabed around the UniWave installation was conducted.

The bathymetric mapping revealed a gently sloping uniform seabed with no notable depressions or crests around the UniWave installation. A dive survey found that the hull of the unit had been colonized by green and brown algae. These were representative of the species in the surrounding area and expected for a benign submerged installation of this duration.

Measurements of temperature, salinity, dissolved oxygen and turbidity in the receiving environment showed a shallow, fully mixed water column with little fluctuation across sites and depths and did not appear to be influenced by the UniWave. Similarly, concentrations of heavy metals and total petroleum hydrocarbons were low in the vicinity of the installation. By comparison, there were slightly elevated levels of arsenic and nickel observed in the control site in the marina.

Sediment particle size varied across the three sites and was largely related to local habitat structure. The substrate near the UniWave installation and the marina largely consisted of fine and coarse sand whereas the substrate near the reef consisted of a mixture of very fine sand and silt along with large pieces of coarse sediment and shell grit. Particle size analysis did not show any evidence of deposition or erosion caused by the presence of the UniWave structure.