ABSTRACT

Offshore wind power has been currently attracting attention as part of SDGs efforts, and the cumulative installed capacity worldwide has increased more than 10-fold in the last decade. As the world's energy sources shift from fossil to renewable energy, the increase of construction of offshore structures associated with marine development will probably generate undesirable underwater noise that is harmful to marine life living near construction sites. In order to reduce underwater noise and improve the marine acoustic environment, this study clarifies the generation mechanism and propagation behavior of underwater noise by pile driving and discusses how to reduce the noise.

INTRODUCTION

As countries embark on various initiatives to achieve the SDGs, wind power generation is attracting significant attention as a stable source of electricity (Khezri and Bevrani, 2015; Cardozo, van Ackooij and Capely, 2018; Snow and Snow, 2018). The amount of offshore wind power generation is expected to increase further in the future, as we work toward achieving carbon neutrality by 2050 (Chaudhary, Teodorescu and Rodriguez, 2008; Esteban, Diez, López and Negro, 2011; Wind Europe, 2017). Offshore wind power could be an extremely useful source of electricity for Japan, a maritime nation that is not blessed with abundant energy resources and is surrounded on all sides by the sea. However, underwater noise is an unavoidable problem when constructing offshore wind turbines. A particularly large source of noise during construction is pile driving into the seabed. In shallow water of less than 30 m depth, the construction method is to drive piles directly into the seabed (Tsouvalas and Metrikine, 2016), but multiple pile driving for offshore building construction results in an uninterrupted sound of approximately 170 dB. This underwater noise will adversely affect whales, dolphins, and sound-sensitive fish that use echolocation, and depending on the magnitude of the pressure amplitude generated, may even damage the internal organs of underwater organisms (Richardson, Greene, Malme and Thomson, 1995; Nowacek, Thorne, Johnston and Tyack, 2007). Organisms living in the vicinity of the construction site may be exposed to this noise over a long period of time (Guan and Miner,2020). If the transition to sustainable energy sources continues, and if offshore wind power construction goes into full swing accordingly, underwater noise will become an increasingly serious problem in the future.

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