8.2. Construction Phase

8.2.1. Impact Piling

  1. The impact piling scenarios modelled were as follows:
  • single piling – wind turbine foundation piles (3,000 kJ);
  • single piling – OSP jacket piles (4,400 kJ);
  • two concurrent piling event – wind turbine foundation piles (3,000 kJ); and
  • two concurrent piling events – wind turbine foundation pile (3,000 kJ) and OSP jacket pile (4,400 kJ).
  1. All cases are presented both with and without the use of 30 minutes of ADD prior to installation.
  2. Impact ranges were modelled for all three locations, as shown in Figure 8.1   Open ▸ , however only the most adverse case injury ranges have been reported in this section. The 90th percentile of the transmission loss was used for the calculations, which is considered to be a worst case while taking into account outliers due to extreme changes in bathymetry and sea conditions, for example.

Figure 8.1:
Locations Modelled Within the Ossian Array (Red Line)[13]

Figure 8.1: Locations Modelled Within the Ossian Array (Red Line)[13]

  1. All impact piling injury ranges are based on a comparison to the relevant impulsive noise thresholds as set out in section 5. Disturbance effects are presented in volume 2, chapter 10 using the dose-response approach described in section 5.3.
  2. The injury ranges for peak sound pressure are based on the noise from the maximum hammer energy over the entire installation.
  3. It should be noted that peak sound pressure is a time domain parameter and does not necessarily add together to produce higher received peak sound pressure levels. Even if two piling hammers were to strike their piles synchronously (i.e. to the exact millisecond) the noise waves will arrive at different locations at different times. Consequently, the peak pressure ranges for simultaneous piling do not differ from the peak injury ranges identified for single piling spreads.
  4. During impact piling the interaction with the seabed and the water column is complex. In these cases, a combination of dispersion (i.e. where the waveform shape elongates), and multiple reflections from the sea surface and bottom and molecular absorption of high frequency energy, the noise will lose its impulsive shape after some distance (generally in order of several kilometres).
  5. An  article by Southall (2021) discusses this aspect in detail, and notes that “…when onset criteria levels were applied to relatively high-intensity impulsive sources (e.g. pile driving), TTS onset was predicted in some instances at ranges of tens of kilometres from the sources. In reality, acoustic propagation over such ranges transforms impulsive characteristics in time and frequency (see Hastie et al. 2019; Amaral et al. 2020; Martin et al., 2020). Changes to received signals include less rapid signal onset, longer total duration, reduced crest factor, reduced kurtosis, and narrower bandwidth (reduced high-frequency content). A better means of accounting for these changes can avoid overly precautionary conclusions, although how to do so is proving vexing”. The point is reinforced later in the discussion which points out that “…it should be recognised that the use of impulsive exposure criteria for receivers at greater ranges (tens of kilometres) is almost certainly an overly precautionary interpretation of existing criteria”.
  6. Consequently, great caution should be used when interpreting any results with predicted injury ranges in the order of tens of kilometres.

8.2.2. Single Piling

  1. Distances are presented at which noise levels decrease to below PTS/TTS threshold values in terms of cumulative SEL and peak sound pressure level. It should be noted that the potential PTS/TTS ranges reduce significantly with the use of ADD because it is assumed that an animal swims away from the area for 30 minutes before being exposed to noise from piling, therefore significantly reducing its cumulative SEL for any given start range.
  2. Distances are presented in Table 8.5   Open ▸ to Table 8.9   Open ▸ for wind turbine foundation pile installation at 3,000 kJ and Table 8.10   Open ▸ to Table 8.14   Open ▸ for OSP jacket pile installation at 4,400 kJ.

 

Table 8.5:
Marine Mammals: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation using 3,000 kJ Hammer, Cumulative SEL Metric (N/E – Threshold Not Exceeded)

Table 8.5: Marine Mammals: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation using 3,000 kJ Hammer, Cumulative SEL Metric (N/E – Threshold Not Exceeded)

 

Table 8.6:
Marine Mammals: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Peak SPL Metric

Table 8.6: Marine Mammals: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Peak SPL Metric


Table 8.7:
Fish: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Moving Fish

Table 8.7: Fish: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Moving Fish

 

Table 8.8:
Fish: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Static Fish

Table 8.8: Fish: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Static Fish

 

Table 8.9:
Fish: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Peak SPL Metric

Table 8.9: Fish: Potential Injury and Disturbance Ranges for Single Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Peak SPL Metric

 

Table 8.10:
Marine Mammals: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric (N/E – Threshold Not Exceeded)

Table 8.10: Marine Mammals: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric (N/E – Threshold Not Exceeded)


Table 8.11:
Marine Mammals: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Peak SPL Metric

Table 8.11: Marine Mammals: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Peak SPL Metric

 

Table 8.12:
Fish: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric for Moving Fish

Table 8.12: Fish: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric for Moving Fish


Table 8.13:
Fish: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric for Static Fish

Table 8.13: Fish: Potential Injury and Disturbance Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Cumulative SEL Metric for Static Fish

 

Table 8.14:
Fish: Potential Injury Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Peak SPL Metric

Table 8.14: Fish: Potential Injury Ranges for Single OSP Jacket Pile Installation at 4,400 kJ Based on the Peak SPL Metric

 

  1. Potential disturbance ranges for all fish species are sown in Table 8.15   Open ▸ for both the 3,000 kJ and 4,400 kJ case. Disturbance to marine mammals is discussed in volume 2, chapter 9 in terms of dose-response, as shown in Table 5.3   Open ▸ and discussed in section 5.3.

Table 8.15:
Fish: Potential Disturbance Ranges for Single Pile Installation Based on the 150 dB re 1μPa (rms) Contour

Table 8.15: Fish: Potential Disturbance Ranges for Single Pile Installation Based on the 150 dB re 1μPa (rms) Contour

 

8.2.3. Concurrent Piling

  1. Construction may occur utilising two pile installation vessels operating concurrently. The potential cumulative SEL injury ranges for marine mammals and fish due to impact pile driving of piles are modelled as following the same piling plans with all phases starting at the same time. For injury the MDS is considered to be that of two adjacent piles, separated by a distance of 950 m due to the maximal overlap of noise propagation contours leading to the maximum generated noise levels. Conversely, for disturbance the maximum separation between two piling locations would lead to the larger area ensonified at any one time and therefore the greatest disturbance.
  2. For the modelling of disturbance, modelling has been undertaken for piling at the northern location concurrently with the central location, and the southern location concurrently with the central location. This is representative of the largest separation of the piling vessels, as detailed within volume 1, chapter 4, and a maximum separation of 30 km. Although there is a possibility of a separation between vessels of up to 41 km, variation in seabed bathymetries and water depths make the separation modelled the scenario resulting in maximum disturbance,
  3. In this section, modelling of injury ranges has been undertaken for two adjacent piles at the northern and southern locations. As for the single piling case, the maximum design scenario has been reported here.
  4. Injury ranges are presented in terms of cumulative SEL metric in Table 8.16   Open ▸ to Table 8.18   Open ▸ for foundation pile installation at 3,000 kJ at both sites, and in Table 8.19   Open ▸ to Table 8.21   Open ▸ for concurrent piling of OSP jacket pile installation at 4,400 kJ and foundation piles at 3,000 kJ at each site. The peak metric will remain the same as the single installation case. As noted previously, disturbance effects are covered in volume 2, chapter 10 using the dose-response approach described in section 5.3.2.

 

Table 8.16:
Marine Mammal: Potential Injury and Disturbance Ranges for Concurrent Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric (N/E – Threshold Not Exceeded)

Table 8.16: Marine Mammal: Potential Injury and Disturbance Ranges for Concurrent Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric (N/E – Threshold Not Exceeded)

 

Table 8.17:
Fish: Potential Injury and Disturbance Ranges for Concurrent Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Fish Moving Away)

Table 8.17: Fish: Potential Injury and Disturbance Ranges for Concurrent Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Fish Moving Away)

 

Table 8.18:
Fish: Potential Injury and Disturbance Ranges for Concurrent Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Static Fish

Table 8.18: Fish: Potential Injury and Disturbance Ranges for Concurrent Wind Turbine Foundation Pile Installation at 3,000 kJ Based on the Cumulative SEL Metric for Static Fish

 

Table 8.19:
Marine Mammal: Potential Injury and Disturbance Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric (N/E – Threshold Not Exceeded)

Table 8.19: Marine Mammal: Potential Injury and Disturbance Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric (N/E – Threshold Not Exceeded)

 

Table 8.20:
Fish Injury Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric for Fish Moving Away

Table 8.20: Fish Injury Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric for Fish Moving Away

 

Table 8.21:
Fish: Potential Injury and Disturbance Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric for Static Fish

Table 8.21: Fish: Potential Injury and Disturbance Ranges for Concurrent OSP Jacket Pile Installation at 4,400 kJ and Wind Turbine Foundation Pile at 3,000 kJ Based on the Cumulative SEL Metric for Static Fish

 

8.2.4. Drilled Pile Installation

  1. The potential impact ranges for drilled pile installation are small (or not exceeded) for all marine mammal species groups, due to the low broadband SEL levels expected from these operations, at 160 dB re 1 µPa2s (see Table 8.22   Open ▸ ). The behavioural threshold range for all marine mammal groups is also reported.
Table 8.22:
Potential Impact and Disturbance Ranges (m) for Marine Mammal Exposed to Drilled Pile Installation

Table 8.22: Potential Impact and Disturbance Ranges (m) for Marine Mammal Exposed to Drilled Pile Installation

 

  1. The ranges for recoverable injury and TTS for Group 3 and 4 Fish are presented in Table 8.23   Open ▸ based on the thresholds contained in Popper et al. (2014). Note that the guidance only states numerical thresholds for Group 3 and 4 Fish. It should be noted that fish would need to be exposed within these potential impact ranges for a period of 48 hours continuously in the case of recoverable injury and 12 hours continuously in the case of TTS for the effect to occur. It is therefore considered that these ranges are highly precautionary, and injury is unlikely to occur.

 

Table 8.23:
Median Potential Impact and Disturbance Ranges (m) for Group 3 and 4 Fish Exposed to Drilled Pile Installation

Table 8.23: Median Potential Impact and Disturbance Ranges (m) for Group 3 and 4 Fish Exposed to Drilled Pile Installation

 

8.2.5. Other Construction Operations

  1. The potential impact ranges from other construction related activities (such as cable trenching, cable laying and supporting jack-up rigs) on different marine mammal groups are presented in Table 8.24   Open ▸ . The potential impact ranges for fish are presented in Table 8.25   Open ▸ .

 

Table 8.24:
Potential Impact Ranges (m) for Marine Mammals During Other Construction Related Operations

Table 8.24: Potential Impact Ranges (m) for Marine Mammals During Other Construction Related Operations

 

Table 8.25:
Median Potential Impact and Disturbance Ranges (m) for Group 3 and 4 Fish Exposed to Other Construction Related Operations

Table 8.25: Median Potential Impact and Disturbance Ranges (m) for Group 3 and 4 Fish Exposed to Other Construction Related Operations

 

8.2.6. Construction Vessels

  1. The potential impact ranges for vessels are included in section 8.4, which summarises the vessel modelling results for all phases of the Array.