NNMREC Estimating the Acoustic Impact of a Tidal Energy Project Chris Bassett, Jim Thomson, and Brian Polagye University of Washington Mechanical Engineering 161 st Meeting of the Acoustical Society of America Seattle, WA May 24, 2011

NNMREC Tidal Energy Basics  Power  Technology requires strong currents (> 1 m/s)  Power density ~ V 3  Siting  Estuaries with large tidal ranges  Relatively shallow (< 80 m) for operational reasons  Ideally near load center  Devices – early development  Cross-flow and horizontal-axis  Pile and gravity foundations  Generators & gear boxes MCT Strangford, UK 14x2 m, 1200 kW Clean Current Race Rocks, BC 3.5 m, ~65 kW Verdant Power New York, East River 5 m, 33 kW

NNMREC Tidal Energy Technology  OpenHydro 6m turbine:  Direct-drive permanent magnet generator  Gravity foundation  No yaw mechanism  Cut-in speed ~ 0.7 m/s OpenHydro 10 m Bay of Fundy Turbine (Source: OpenHydro)

NNMREC Site Information Tripod Deployments  Proposed pilot project Admiralty Inlet, Washington  Primary inlet to Puget Sound  Depth ~ 60 m  Urban waterway

NNMREC Stationary Hydrophone Measurements  Autonomous hydrophone (16 GB capacity)  80 kHz sampling  1% duty cycle for 3 months  Records 7 sec. every 10 min.

NNMREC Ambient Noise  Mean SPL (0.02 – 30 kHz)  119 dB re 1μPa  Significant variability associated with anthropogenic noise (Example spectra)(All data) Bedload Transport Ship Average Conditions Quiet

NNMREC Pseudosound  Pseudosound due to turbulent pressure fluctuations  Recorded above 20 Hz above 0.3 m/s  Masks low frequency ambient noise  Removed from ambient noise analysis  Ongoing work with flow shields

NNMREC Estimated Source Level  Broadband SL (0.02 – 3 kHz):  Operating at peak power output (14 rpm)  154 dB per turbine  Measurements by the Scottish Association of Marine Sciences (SAMS) (Source: OpenHydro)

NNMREC Implication for Received Levels Broadband Levels  SONAR Equation: RL = SL – 15log(r) – α r 0  Broadband SL:  Operating at peak power output (14 rpm)  2 turbines  Incoherent sources

NNMREC Implication for Received Levels Broadband Received Levels  Artificial time series with ambient SPLs and RLs from turbines added in to 70% of recordings.  Assume limited spatial variability in ambient noise levels.  Calculated for multiple distances assumed to be equidistant from sources  Turbine impact is relatively small except locally

NNMREC Comparison to Other Sources  Puget Sound  urban waterway with many anthropogenic sources

NNMREC Conclusion  Insufficient source data are currently available  Complex environments suitable for tidal energy are difficult to study  Noise impacts will likely be local  context is important

NNMREC Thank You This material is based upon work supported by the Department of Energy, Snohomish County PUD, the National Science Foundation.  Field Engineers Joe Talbert and Alex DeKlerk  Captain Andy Reay-Ellers