The aim of this study is to describe technical noise mitigation measures to be applied during pile driving of offshore wind turbines as well as alternative low-noise foundation concepts and to analyse their applicability. A first version of this study was publish ed in German in July 2011. In order to also cover ongoing research and further technological development, an update was requested in December 2012. On account of the importance of noise mitigation not only in a national, but also in an international context, an English version was produced in addition. However, all research was focused on German projects.
From the perspective of nature conservation, anthropogenic noise emissions into the marine environment must be limited to environmentally friendly levels. In Germany, a dual threshold value has been defined by the approving authority BSH. The observance of this threshold value of 160 dB (single event sound pressure level, SEL) / 190 dB (peak-to-peak) at 750 m from the source is mandatory for the installation of offshore wind turbines in the German exclusive economic zone (EEZ) . For commonly used piled foundations it can only be met by applying noise mitigation measures. In Germany at least the industry has stepped up efforts to improve available noise mitigation techniques for pile driving of offshore wind turbines or to invent new systems only in the last few years.
Depending on parameters which influence the source level such as pile diameter, soil structure and blow energy, many noise mitigation systems have the potential to reduce emissions to a level that corresponds to or even falls below the noise limit mandatory in the German EEZ. However, they all have an impact on the operations layout and work schedule as the systems have to be applied prior to pile driving or require special technical features of the installation barge. Minimising the duration of the installation of the noise mitigation system is one of the major challenges when striving to achieve an application of a noise mitigation system which is economically feasible. This holds true for bubble curtains (chapter 4.2), isolation casings (chapter 4.3), and cofferdams (chapter 4.4) as well as for Hydro Sound Dampers (chapter 4.5). So far, not all of the available systems have been routinely applied, and thus the time required for the installation process cannot be predicted with certainty. Further development is aimed at the best possible integration of the installation of the mitigation system into the operations layout.