Seafloor Site Characterization for a Remote Island OWC Device Near King Island, Tasmania, Australia

Abstract

We present findings from a geotechnical survey for a gravity-based Wave Energy Converter (WEC) to be installed in King Island, Tasmania. The goal of this work was to assess the deployment location for a 200 kW Oscillating Water Column (OWC) and to identify possible challenges for the foundation of the structure to make it Australia’s first operational offshore OWC for a remote offshore island. The proposed location for this OWC is the southeast coast of King Island, Tasmania, approximately in a depth of ~5.5 m LAT. The survey included sub-bottom profiling, sediment cores, surficial sediment strength by penetrometer drops, seabed imagery, as well as long-term deployment (>6 months) of pressure sondes and an acoustic wave current profiler (AWAC). Our findings demonstrate that the WEC can be installed in the proposed location with significant wave height Hs ~1–1.5 m and peak period Tp of 12–14 s, and that the site exhibits sufficient sand coverage and quasisteady bearing capacity. The period between the survey and prospective deployment is only one year, demonstrating the efficiency of the survey methods (in particular, the use of the penetrometer) and OWC design but also the suitability of the candidate site for this device design.

Geotechnical Approach to Early-Stage Site Characterisation of Shallow Wave Energy Sites

“…However, this method does not replace the usefulness of core samples, or laboratory sediment investigations as only the top layer (<20 cm) is able to be penetrated in sandy environments. Yet, this was successfully used in further King Island assessments to determine the homogeneity of non-cohesive sediments within the survey region [27]. The aggregation of data in this method (site-suitability model) is able to go beyond the scope of most standards [7], particularly with the inclusion of ground-truthed core samples within the bedrock interpola- The identification of the most sufficient deployment area is a culmination of condensed field deployments and rigorous data analysis.…”

Field Observations of Scour Behavior around an Oscillating Water Column Wave Energy Converter

“…Whilst multiple previous studies have focused on the energy conversion efficiency or internal flow patterns of gravity based OWC WECs [2,4,5], little research has been undertaken on the effects of an OWC WEC on its surrounding environment, and in turn the risks to structure stability or potential reductions in energy efficiency that could occur due to scour (localized sediment erosion) or settlement of the device. This is despite previous site characterization studies for multiple wave energy sites identifying active sediment environments [6,7].…”

“…A previous site characterization study at the site by Cossu, et al [7] undertook a sub-bottom profiling analysis to assess the sediment layer thickness at the project site in March 2019 which found that all areas in the survey area had a sediment layer thickness exceeding 1 m. The sediment layer had a thickness of approximately 2-3 m in the area corresponding to Location 1 in Figure 1b. Sand characteristics were also measured in the same study at the site location via dry sieve analysis of retrieved sediment cores.…”

“…Event14-17 March 2019Geotechnical site survey[7], including multi-beam seabed survey, sediment coring and sub-bottom profiling.8 August 2019-ongoing Deployment of Sofar Ocean Spotter buoy on-site for continuous measurements.3 December 2020 Multi-beam seabed survey.…”

Modelling Morphological Changes and Migration of Large Sand Waves in a Very Energetic Tidal Environment: Banks Strait, Australia

“…In situ measurements of surficial seafloor sediment strength was determined with the BlueDrop penetrometer described by [55,56]. The characteristics of the impact signature were analysed to obtain the kind of substrate-soft, medium, and hard substrate-based on the deceleration curves after impact.…”