Hydrokinetic turbines will be a source of noise in the marine environment – both during operation and during installation/removal. High intensity sound can cause injury or behavioral changes in marine mammals and may also affect fish and invertebrates. These noise effects are, however, highly dependent on the individual marine animals; the intensity, frequency, and duration of the sound; and context in which the sound is received. In other words, production of sound is a necessary, but not sufficient, condition for an environmental impact. At a workshop on the environmental effects of tidal energy development, experts identified sound produced by turbines as an area of potentially significant impact, but also high uncertainty.
The overall objectives of this project are to improve our understanding of the potential acoustic effects of tidal turbines by:
- Characterizing sources of existing underwater noise;
- Assessing the effectiveness of monitoring technologies to characterize underwater noise and marine mammal responsiveness to noise;
- Evaluating the sound profile of an operating tidal turbine; and
- Studying the effect of turbine sound on surrogate species in a laboratory environment.
This study focuses on a specific case study for tidal energy development in Admiralty Inlet, Puget Sound, Washington (USA), but the methodologies and results are applicable to other turbine technologies and geographic locations. The project succeeded in achieving the above objectives and, in doing so, substantially contributed to the body of knowledge around the acoustic effects of tidal energy development in several ways:
- Through collection of data from Admiralty Inlet, established the sources of sound generated by strong currents (mobilizations of sediment and gravel) and determined that low‐frequency sound recorded during periods of strong currents is non‐propagating pseudo‐sound. This helped to advance the debate within the marine and hydrokinetics acoustic community as to whether strong currents produce propagating sound.
- Analyzed data collected from a tidal turbine operating at the European Marine Energy Center to develop a profile of turbine sound and developed a framework to evaluate the acoustic effects of deploying similar devices in other locations. This framework has been applied to Public Utility District No. 1 of Snohomish Country’s demonstration project in Admiralty Inlet to inform postinstallation acoustic and marine mammal monitoring plans.
- Demonstrated passive acoustic techniques to characterize the ambient noise environment at tidal energy sites (fixed, long‐term observations recommended) and characterize the sound from anthropogenic sources (drifting, short‐term observations recommended).
- Demonstrated the utility and limitations of instrumentation, including bottom mounted instrumentation packages, infrared cameras, and vessel monitoring systems. In doing so, also demonstrated how this type of comprehensive information is needed to interpret observations from each instrument (e.g., hydrophone data can be combined with vessel tracking data to evaluate the contribution of vessel sound to ambient noise).
- Conducted a study that suggests harbor porpoise in Admiralty Inlet may be habituated to high levels of ambient noise due to omnipresent vessel traffic. The inability to detect behavioral changes associated with a high intensity source of opportunity (passenger ferry) has informed the approach for post‐installation marine mammal monitoring.
- Conducted laboratory exposure experiments of juvenile Chinook salmon and showed that exposure to a worse than worst case acoustic dose of turbine sound does not result in changes to hearing thresholds or biologically significant tissue damage. Collectively, this means that Chinook salmon may be at a relatively low risk of injury from sound produced by tidal turbines located in or near their migration path.
In achieving these accomplishments, the project has significantly advanced the District’s goals of developing a demonstration‐scale tidal energy project in Admiralty Inlet. Pilot demonstrations of this type are an essential step in the development of commercial‐scale tidal energy in the United States. This is a renewable resource capable of producing electricity in a highly predictable manner.