PNNL

Abstract

Admiralty Inlet has been selected as a potential tidal energy site. It is located near shipping lanes, is a highly variable acoustic environment, and is frequented by the endangered southern resident killer whale (SRKW). Resolving environmental impacts is the first step to receiving approval to deploy tidal turbines. Several monitoring technologies are being considered to determine the presence of SRKW near the turbines. Broadband noise level measurements are critical for determining design and operational specifications of these technologies. Acoustic environment data at the proposed site was acquired at different depths using a cabled vertical line array from three different cruises during high tidal period in February, May, and June 2011. The ambient noise level decreases approximately 25 dB re 1 µPa per octave from frequency ranges of 1 kHz to 70 kHz, and increases approximately 20 dB re 1 µPa per octave for the frequency from 70 kHz to 200 kHz. The difference of noise pressure levels in different months varies from 10 to 30 dB re 1 µPa for the frequency range below 70 kHz. Commercial shipping and ferry vessel traffic were found to be the most significant contributors to sound pressure levels for the frequency range from 100 Hz to 70 kHz, and the variation could be as high as 30 dB re 1 µPa. These noise level measurements provide the basic information for designing and evaluating both active and passive monitoring systems proposed for deploying and operating for tidal power generation alert system.