Underwater noise is an important consenting consideration for offshore wind, particularly during impact pile driving, which has the potential to cause auditory injury or disturbance to protected marine mammals. As part of this work, RaDIN2 assessed potential impacts on harbour porpoise and minke whale, representing very high-frequency and low-frequency cetacean hearing groups respectively.

Real world piling logs were collated from nine UK offshore wind farms, providing hammer logs for 1,448 piles. These were investigated to understand the active piling duration per pile, total installation duration per pile, gaps in piling, as well as hammer energy and blow rates for soft-start and throughout all piling. Across the wind farms analysed, only 12.5% of the piles reached or exceeded the maximum hammer energy defined in the EIA. The vast majority of piles were installed in under 2 hours, and there was considerable variation in blow rates and soft-starts across the wind farms. These findings highlight considerable variation in real world piling schedules and show that the worst -case EIA profile was generally highly precautionary in terms of hammer energy, piling duration and blow rates.

The RaDIN Movement Tool, which allows estimation of cumulative Permanent Threshold Shift (PTS) impact ranges, was updated and improved. The tool was used 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 showed that for the vast majority of the piles installed, the real piling logs predicted cumulative PTS impact ranges that were substantially less than 50% of the range predicted using the EIA piling profile.

A workshop with engineers, regulatory advisors, consenting experts, acousticians, and marine mammal specialists explored practical solutions to streamline the EIA processes. Key points included the need for: 

• better guidance and definition of soft-start;
• a framework that tolerates uncertainty while still reflecting actual offshore practice;
• better pile-specific drivability, expected piling profiles, geotechnical insight, and measured installation data to inform marine mammal impact assessment;
• PTS impact mitigation to be tailored to the residual risk rather than applied as a blanket requirement. 

Further engagement is needed to refine practical and agreed best practice guidance for soft-starts and piling profiles that balances both technical and consenting risks. 

It is recommended that the results of the RaDIN2 study are incorporated into new guidance for soft-starts and piling profiles, and EIA methodologies.