2.8. Cumulative Projects

  1. Cumulative projects for marine mammal species were considered across the regional marine mammal study area, following the cumulative effects assessment methodology described in section 10.12.1 of volume 2, chapter 10. Those projects for which piling is expected to temporally overlap (or to occur in adjacent years) with piling for the Array, and for which quantitative information was available, were included in iPCoD modelling. The Tier 1 (see section 10.12.1 of volume 2, chapter 10) Green Volt Offshore Wind Farm was screened out at this stage since no impact piling will be undertaken for this project. Tier 2 and Tier 3 projects for which quantitative information was not available were not possible to include in models as any estimate would be unlikely to reflect realised piling programmes, and these projects are summarised in Table 10.52 of volume 2, chapter 10. To capture the end of the offshore construction phase at the cumulative projects, the cumulative iPCoD models included an additional year before piling at the Array commenced. A summary of cumulative projects included in iPCoD modelling and indicative offshore piling schedules is provided in Table 2.10   Open ▸ .

 

Table 2.10:
Indicative Offshore Piling Programmes and Schedules for Cumulative Projects[2]

Table 2.10: Indicative Offshore Piling Programmes and Schedules for Cumulative Projects[2]

 

  1. The Array piling scenario carried forward to the cumulative assessment was the maximum temporal scenario as this represented the largest potential effect from piling from the model simulations for the Array alone. Although the number of animals potentially affected was greater for the maximum spatial scenario ( Table 2.6   Open ▸ and Table 2.7   Open ▸ ), the results of the iPCoD model based upon the maximum temporal scenario predicted a greater effect on the respective impacted populations.
  2. Both cumulative projects conduct piling in two phases, beginning as early as 2023 (Hornsea Three), and since the duration of robust predictions from iPCoD modelling is limited to 25 years, to maintain focus on predictions from the Array only the second phase of each project’s respective piling phase is included in the cumulative iPCoD models. Hence, the number of piling days presented in Table 2.11   Open ▸ is only a proportion of the total piling days presented in Table 2.10   Open ▸ . For Berwick Bank, the second piling phase comprises one third of the total piling phase (one year out of a total of three-piling years across both phases), so this has been modelled as one third of the total piling days (SSE Renewables, 2022a).
  3. For Hornsea Three, no specific information was available on the split between the two piling phases (Ørsted, 2018a), so an approximately equal split has been assumed (i.e. each piling phase comprises approximately half of the total piling days). Piling at Hornsea Three also comprises two elements: concurrent piling of wind turbines, OSPs and accommodation infrastructure within the array area, and single piling of booster stations within the cable corridor. All single piling for booster station has been assumed to occur in the second piling phase and has been included in the cumulative models.
  4. There is no potential for significant cumulative impacts for injury (PTS) from elevated underwater noise during piling for the cumulative projects presented in Table 2.11   Open ▸ as iPCoD simulations for these projects have modelled zero animals experiencing PTS.
  5. The iPCoD models were set up as described in sections 2.3 and 2.4 for reference populations and demographic parameters, respectively, and with the same number of days of residual disturbance and number of animals experiencing disturbance and injury specified in section 2.6.
  6. Cumulative projects were only included in species’ models if they overlap spatially with the species-specific management units described in Table 2.10   Open ▸ . For harbour porpoise and minke whale, the cumulative iPCoD models included both Berwick Bank and Hornsea Three, and for bottlenose dolphin and grey seal, models included Berwick Bank only.
  7. The number of animals affected for each of the key species and number of days on which piling occurred was taken from the MDS for each of the cumulative projects (SSE Renewables, 2022b, Ørsted, 2018b). A summary of the number of animals for each species affected and number of piling days for each cumulative project is provided in Table 2.11   Open ▸ . In cases where less than one animal was expected to experience disturbance or injury, this was rounded up to one animal for the relevant models.

 

Table 2.11:
Summary of Number of Animals Predicted to Experience Disturbance for Cumulative iPCoD Scenario

Table 2.11: Summary of Number of Animals Predicted to Experience Disturbance for Cumulative iPCoD Scenario

 

  1. Time points selected from the iPCoD model outputs coincide with key periods in the piling schedule, and with statutory reporting periods for Special Areas of Conservation (SAC), are summarised in Table 2.12   Open ▸ .

 

Table 2.12:
Selected Time Points from iPCoD Simulation Output and Corresponding Events for Cumulative Scenario

Table 2.12: Selected Time Points from iPCoD Simulation Output and Corresponding Events for Cumulative Scenario

 

2.9. Summary of iPCoD Scenarios

  1. A total of 14 iPCoD modelling scenarios were run for the Array alone and the cumulative effect assessment, and these are summarised in Table 2.13   Open ▸ for each of the four key species for which iPCoD modelling has been possible.

 

Table 2.13:
Summary of iPCoD Scenarios Modelled for Key Species Associated with the Array and Relevant Cumulative Projects

Table 2.13: Summary of iPCoD Scenarios Modelled for Key Species Associated with the Array and Relevant Cumulative Projects

 

2.10. Model Outputs

  1. The outputs of the iPCoD models are focussed on describing the potential impact to a given marine mammal population under the relevant development scenario, relative to the population in the absence of the development. An estimate is provided for every time step in the scenario (here given as 25 years after commencement of piling), for each simulation (n = 1,000) and is presented in Figure 3.1   Open ▸ to Figure 3.14   Open ▸ . The ratio of the simulated impacted population to the unimpacted population sizes can then be expressed as a ratio, termed the ‘counterfactual’ of population size. A counterfactual of 1 would therefore correspond to a prediction of no difference in size between the impacted and unimpacted populations. Counterfactuals of <1 would correspond to the impacted population being smaller than the unimpacted population.
  2. The mean estimate (plus 95% confidence interval) of impacted and unimpacted population sizes across all simulations, and the corresponding counterfactuals, are reported for each species, and each scenario ( Table 3.1   Open ▸ to Table 3.14   Open ▸ ). The median counterfactual is also presented since this measure can be less sensitive to outliers. However, it is important to note that the median counterfactual may not always be representative of overall projections, and should be interpreted with caution, since this is calculated simply as the central value in the ordered set of counterfactuals from all simulations.