離岸風機打樁與營運之水下噪音模擬及量測分析

Abstract

臺灣海峽具有豐沛之風能條件，有利於開發離岸風場(Offshore Wind Farm)。近年來，政府積極提高再生能源電量比例，以減少碳之排放，期望能兼顧環境永續及綠色經濟發展，以邁向非核家園願景。但目前所規劃之離岸風力發電潛力場址有部分區塊比鄰中華白海豚重要棲息地，而海事工程巨大之水下噪音和離岸風機之長期運轉噪音可能會造成鯨豚行為改變甚至聽力損傷。因此本研究分成兩個部分：第一是針對潛在風場之彰化外海進行大範圍寬頻打樁噪音模擬，評估範圍主要以打樁外 750 公尺處和中華白海豚保護區內之影響範圍，同時探討多架離岸風機同時打樁之疊加效應影響，而將聲曝值（Sound Exposure Level, SEL）和中頻調變24小時累加聲曝值（MF weighted 24-hour sound exposure level, SELMF，24h）作為噪音影響評估標準。第二部分為苗栗竹南離岸示範風場之長時間水下營運噪音量測分析，並將實際量測資料作為聲源強度，來模擬臺灣西部彰化外海多架離岸風機同時運轉之噪音影響分布。 本模擬利用RAM（Range dependent Acoustic Model）聲學傳播模式模擬風機之打樁噪音，由模擬結果預測水下噪音可能影響中華白海豚之範圍。模擬結果顯示，彰化外海南區有較大之打樁噪音影響範圍，且疊加效應可能對中華白海豚造成行為改變，影響範圍跟海床底質有關，次要為地形因素。因此於沙質底質上應加強減噪措施或是遠離白海豚棲息地，故日後可以此作為擬定風機噪音區域規範之參考。 長時間營運噪音主要在20 Hz和27 Hz出現高能量基頻，而在162 Hz有相當吻合之共振頻率，因此在中心頻率160 Hz為風機主要運轉頻段。本研究將提供未來施工作業和營運階段之評估參考，以減輕對鯨豚之影響程度，期許在生態保育與再生能源開發中創造雙贏局面。

According to 4C Offshore, Taiwan Strait has the largest wind energy in the global offshore wind speed rankings. This area sustains wind energy throughout the year and provides favorable conditions for the development of offshore wind farms (OWFs). However, parts of the planned locations for the potential OWF are close to the habitat of the Chinese White Dolphin (Sousa chinensis). The huge underwater noise of marine engineering and long-term operation noise may cause behavioral effect and hearing impairment on marine mammals. Therefore, the research has two parts. Firstly, the large-area simulation of pile driving noise in Changhua County, Taiwan. The noise assessment is carried-off mainly 750 meters from the piling locations, where the cumulative noise level effect is evaluated in the assessment area which is also a habitat of the Chinese White Dolphin. 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. Secondly, the long-term underwater operation noise monitoring and data analysis of the offshore wind farm in Zhunan Township, Miaoli County. The actual measured data is used as the source level and simulation for the impact zone of multiple offshore wind turbines operating in the offshore of Changhua. The underwater noise simulation includes using the Range-dependent Acoustic Model (RAM) to predict the influence of pile driving noise on conservation zone. The simulation results show that the overall noise impact range of southern Changhua offshore is larger than that of the northern and the cumulative effect may cause the behavioral effect. Mainly due to the different sediments, second because of the terrain; hence should be considered in noise reduction or away from the Chinese white dolphin habitat. The long-term operating noise mainly has two fundamental frequency at 20 Hz and 27 Hz. The main operational frequency band is at the center frequency of 160 Hz and the maximum energy reaches up to 142 dB in the frequency range 10 Hz to 1000 Hz. This study will provide an assessment during the construction and operational period to mitigate the impact on marine mammals, and expected that it will strike a balance between eco-conservation and renewable energy development.