This study aims to evaluate the influence of pile driving noise through broadband large-area simulation for the potential offshore wind farms (OWFs) in Changhua County, Taiwan. The underwater noise simulation is based on the Range-dependent Acoustic Model (RAM) and ocean environmental inputs to broadband sound transmission calculation. The sound exposure level (SEL) and the cumulative sound exposure level with auditory weighting function for mid-frequency cetaceans in 24 hours (SELMF,24hr) are included in the noise impact assessment criteria. The results show that the SEL of piling in the offshore area of Changhua can reach 146 dB ∼ 159 dB in the habitat of Sousa chinensis. Noise mitigations are recommended to reduce the impact of behavioral effects.
Taiwan's energy is highly dependent on imports, and the rise of environmental awareness has led to the development of green energy such as wind power. Since Taiwan, densely populated with nearly two-thirds mountainous, is hard to develop the wind turbines. The Taiwan Strait is the region with the largest wind energy in the global offshore wind speed rankings of 4C Offshore. This area sustains wind energy throughout the year and provides favorable conditions for the development of offshore wind farms (OWFs). According to the national energy policy, the objectives are to complete 520 MW shallow water wind farms in 2020, to install 3 GW prior to the year of 2025 and to reach the target of "Thousand Wind turbines Project". However, some of the potential OWFs are close to the habitat of the Chinese White Dolphin (Sousa chinensis) which is classified as the critically endangered group by the International Union for the Conservation of Nature (IUCN) in 2008. The range of the habitat is within 3∼5 km from shore in waters of depth less than 15 m. Increased noise levels due to impact of pile driving may cause behavioral disturbance, temporary hearing threshold shift (TTS) or permanent threshold shift (PTS) to marine mammals (Richardson el al. 1995). The criteria 186 dB re 1 μPa2s cumulative Μ-Weighted SEL for PTS and 171 dB re lμPa"j single strike M-Weighted SEL for TTS have been used in pinnipeds (Southall, 2007). Other criteria for assessing threshold shift are cumulative unweighted SEL 180 dB for PTS and single strike unweighted SEL 165 dB for TTS in harbor porpoise (Lucke, 2009). For assessing the behavioral effect in marine mammals, single strike unweighted SEL 150 dB in harbor porpoise and pinnipeds (Brandt, 2009) and 145 dB for minor behavioral effect (Lucke, 2009). U.S. National Oceanic and Atmospheric Administration, National Marine Fishery Service (NOAA NMFS) classifies marine mammals into five categories based on different hearing characteristics. Chinese White Dolphin belongs to mid-frequency (MF) cetaceans. Two criteria for assessing PTS are unweighted SEL 230 dB and cumulative sound exposure level with auditory weighting function for mid-frequency cetaceans in 24 hours(SELMF,24hr) 185 dB (NOAA Fisheries, 2016). The threshold for behavioral change remains the level B 160 dB (rms). Due to different sensitive species, countries have different distances and thresholds for underwater noise (Erbe, 2013). The German Federal Government requires an exclusion zone of 750 m from pile driving for marine mammals and to keep the received level at 750 m below SEL 160 dB and below a peak-to-peak SEL of 190 dB (Werner, 2010).
