Abstract
The RaDIN project (Matei et al., 2024) developed a simulation tool to estimate relative auditory injury (Permanent Threshold Shift, PTS) impact ranges from impact pile driving under different scenarios, and demonstrated that the factors that most influenced the cumulative PTS ranges were animal swim speed and piling blow rate. It was shown that a high inter-blow-interval (slow blow rates) in the first 45 minutes of a piling event resulted in much smaller cumulative PTS ranges and concluded that the piling parameters assessed in EIAs may result in substantial overestimation of PTS ranges. The RaDIN project concluded with a set of recommendations which led to the RaDIN2 project. The purpose of this RaDIN2 study was to build upon the findings of the RaDIN study to further investigate how piling profiles and other physical or biological evidence can improve the realism of cumulative PTS impact ranges.
Task 1 RaDIN Movement Tool improvements: The RaDIN2 Movement Tool now implements more realistic movements of the animats as well as introducing a range of possible behavioural responses, with the possibility for animats to move with a variable speed with three avoidance triggers: distance, duration, or received sound level. The tool was also improved to include a relationship between hammer energy and source level to allow for a ramp up of the sound source, and frequency dependent sound attenuation was incorporated for specific distance bins, available for both monopiles and pin piles to allow for improved sound propagation.
Task 2 Census of real-world piling profiles: The purpose of this task was to collate real piling logs from a wide range of representative wind farm construction activities (all using impact piling). With this information, the intent was to calculate summary statistics that capture real-world piling installation operations. Piling log data was collated for 1,448 piles from nine OWF in the UK (764 monopiles, 684 pin piles). These were investigated to understand the active piling duration per pile, the total installation duration per pile, gaps in piling, hammer energy in the soft-start, hammer energy throughout all piling, blow-rates in the soft-start and blow rates throughout all piling. There was considerable variability in the real piling profiles, in terms of the blow rate, hammer energy and overall duration of piling. Across the OWFs analysed, only 12.5% of the piles reached or exceeded the maximum hammer energy defined in the EIA and only 0.55% of the piles reached or exceeded the maximum hammer energy defined in the MMMP. Blow rates varied substantially among projects and foundation types, demonstrating considerable variation in soft-start and piling practices across OWFs. The vast majority of piles were installed in under 2 hours, though piling profiles also varied considerably within and between OWFs, with no consistent installation pattern observed across projects. Collectively, these findings highlight the considerable variability in real-world piling schedules and indicate that a conservative single worst-case piling profile is unlikely to capture the full range of installation conditions encountered across offshore wind farm projects.
Task 3 Comparison of real vs EIA piling profiles: The aim of this task was to compare the cumulative PTS impact ranges produced using the EIA piling profiles, with the cumulative PTS impact ranges produced using the real piling logs. This study showed that for harbour porpoise:
- 50% of the real pin pile logs had cumulative PTS impact ranges that were <50% of the range predicted using the EIA piling profile
- 96% of the real monopile logs had cumulative PTS impact ranges that were <50% of the range predicted using the EIA piling profile 9
And for minke whales:
- 89% of the real pin pile logs had cumulative PTS- impact ranges that were <50% of the range using the EIA piling profile
- 100% of the real monopile logs had PTS-impact ranges that were <30% of the range using the EIA piling profile
This was also investigated for the MMMP phase, where it was expected that predicted ranges would align more with real piling logs due to the availability of detailed geophysical data and refined piling parameters. However, this made very little difference, and the MMMP piling profiles still substantially over-predicted cumulative PTS ranges compared to real piling logs.
Task 4 Piling schedule workshop: we delivered a 3 hour workshop to update stakeholders on the RaDIN2 project outcomes and to provide facilitated engagement between engineers, regulatory advisors, EIA and Consenting experts, acousticians, and marine mammal specialists to develop practical solutions to streamline EIA processes. The goal was that we would also gather feedback and stimulate discussion on how to collaboratively improve consenting processes, highlight limitations of the project’s proposed approach and suggest next steps for follow-up analyses. There was much discussion on the technical feasibility of implementing different soft start procedure, and that it is often difficult to perfectly control hammer energy and blow rate in high precision. A key theme raised at the workshop was the importance of continued dialogue between developers, engineers, regulators, advisors, and contractors throughout EIA and MMMP process. Participants identified a need for improved communication and collaboration before formal approval of mitigation plans, particularly regarding soft-starts, pile refusals, and realistic installation scenarios. There were concerns that current modelling approaches can compound multiple worst-case assumptions, potentially resulting in unrealistic PTS ranges that may overstate environmental risk. EIA and MMMP piling profiles often differ from actual installation practices because they are based on conservative, worst-case assumptions designed to support consenting and regulatory compliance, and there was agreement that it would be better to move beyond strictly worst-case impact assessments towards incorporating a more proportionate approach to mitigation.
Following the piling schedule workshop, it was clear that a longer dedicated workshop is required to help refine practical and agree Best Practice Guidance for soft-starts and piling profiles that balances both technical and consenting risks. Recommendations for this future workshop have been provided, and both engineers and regulators/SNCBs have agreed the importance of this.