Cost-effective geotechnical and sedimentological early site assessment for ocean renewable energies

Soil mechanical properties of the seabed are related to a number of challenges in the development of ocean renewable energy. Early site assessment is an important part of the development of an ocean renewable energy project, and soil mechanical and sediment dynamical site characteristics should already be addressed at this stage. However, the suitability of the site for the installation of a ocean renewable energy converter (OREC) is still under evaluation and budgets are often strongly limited at this stage of the project. It follows that there is a need for cost-efficient survey strategies. Different methods have been tested in a tidal energy project in the Bay of Fundy, Canada, and a wave energy project in Yakutat, Alaska. Camera systems displayed sediment type, abundance of rocks, plants and small-scale bedforms. Portable free-fall penetrometers were deployed for testing of sediment strength and stratification at the uppermost seafloor. Areas of different sediment strength were identified, and loose, poorly compacted sediment layers quantified. Additionally, rocks and bedrock faces which were covered by a thin sediment layer and remained undetected by seafloor imaging sonars and grab samples, were found. Buried pressure sensors were used in preliminary experiments to monitor pore pressure variations with wave forcing and test the susceptibility to sediment liquefaction. First surveys using these methods attested that they deliver valuable information with regard to sediment and soil mechanical characteristics, while being deployable from local small fishery or harbor authority vessels. Availability of such vessels and devices is high, while purchasing/renting costs are rather low. This allows to perform such tests very cost-effectively, and thus provides a promising strategy for early site assessment in ocean structure engineering before larger budgets are available.