The large-scale deployment of offshore wind farms is critical to achieving global renewable energy targets. However, the installation of monopile foundations through impact pile driving generates significant underwater noise, posing risks to marine ecosystems. While noise mitigation measures, such as air-bubble curtains and pulse elongation systems, have been developed to reduce peak sound levels (Lpeak) and sound exposure levels (SEL), less is understood about their effects on cumulative noise exposure (cumSEL) a key metric in regulatory frameworks like that of the United States.
This study investigates the influence of operational parameters, including the target blow count and impulse elongation, on cumulative underwater noise levels during offshore pile driving. Using the SILENCE model, a semi-analytical approach is applied to simulate noise propagation in realistic offshore conditions. The research evaluates the combined effectiveness of mitigation strategies such as pulse elongation and air-bubble curtains, as well as the effect of frequency weighting on sound levels for specific species. The results show that varying the target blow count has negligible influence on cumulative underwater noise, while impulse elongation (PULSE) achieves modest broadband reductions and more substantial reductions when species-specific1 frequency weighting is applied. The combination of PULSE with a Double Big Bubble Curtain (DBBC) offers the most effective mitigation across all marine mammal hearing groups.
This study provides insights into the complex interactions between operational parameters and noise mitigation strategies, supporting the development of effective solutions to comply with cumulative noise regulations. The findings aim to contribute to more sustainable offshore wind farm construction while minimizing impacts on marine ecosystems.