16.1.3 Decommissioning Phase

  1. Since the methods used to remove infrastructure are expected to be similar to those used for installation, this impact is expected to be similar in nature to the equivalent construction phase impact. In particular, a buoyed decommissioning area analogous to the buoyed construction area will be in place resulting in the anticipated deviations for the main commercial routes defined for the construction phase being directly applicable for the decommissioning phase. On this basis, the risk of third-party to third-party vessel collision for commercial vessels is considered the same during the decommissioning phase as during the construction phase. However, it is noted that the deviations will be well established by the decommissioning phase, and that vessels will likely be more familiar with the Array than during the construction phase.
  2. The impact will be present throughout the decommissioning phase which is expected to be of similar duration to the construction phase (i.e. maximum of 8 years). Given that third-party vessels are expected to be compliant with Flag State regulations including the COLREGs, the likes of collision avoidance action seek to ensure that the likelihood of an encounter developing into a collision incident is low. This is furthered by the promulgation of information and charting of the buoyed decommissioning area which will increase awareness of ongoing decommissioning activities, thus allowing third-party vessels to passage plan in advance.
  3. The most likely consequences associated with the MDS are as per the equivalent construction phase and operation and maintenance phase impacts.

16.1.3.1  Frequency of Occurrence

  1. The frequency of occurrence is considered to be extremely unlikely based on the available sea room, the outputs of the modelling, and consideration of historical incident data.

16.1.3.2  Severity of Consequence

  1. The severity of consequence is considered to be serious.

16.1.3.3  Significance of the Risk

  1. Overall, the severity of consequence is deemed to be serious and the frequency of occurrence is considered to be extremely unlikely. The risk will therefore be of tolerable significance.

16.1.3.4  Additional Mitigation and Residual Risk

  1. No additional shipping and navigation mitigation is considered necessary because the likely risk, in the absence of mitigation beyond the embedded mitigation measures outlined in section 18.1, is ALARP and not significant in EIA terms.

16.2 Displacement From Adverse Weather Routeing

  1. Some vessels and vessel operators may wish to transit alternative routes during periods of adverse weather. Adverse weather includes wind, wave and tidal conditions as well as reduced visibility due to fog.

16.2.1 Construction Phase

  1. No specific adverse weather routeing was observed within the baseline vessel traffic data studied, however the long‑term 12 month AIS analysis (see Appendix E) showed a minor weighting towards summer months for cargo vessels, tankers, and oil and gas vessels in terms of traffic volumes. This may indicate that such vessels prefer to pass further inshore of the shipping and navigation study area in adverse conditions (which may be more likely during winter months).
  2. Adverse weather can hinder a vessel’s standard route, its speed of navigation, and/or its ability to enter the destination port. Adverse weather routes are assessed to be significant course adjustments to mitigate vessel motion in adverse weather conditions. When transiting in adverse weather conditions, a vessel is likely to encounter various types of weather and tidal phenomena, which may lead to severe roll motions, potentially causing damage to cargo and equipment, and/or discomfort and danger to persons on board. The sensitivity of a vessel to these phenomena will depend on the actual stability parameters, hull geometry, vessel type, vessel size and speed.
  3. The following key points of relevance to adverse weather were raised during consultation (see section 4):
  • Smyril Line stated that vessels would likely not transit through offshore wind farms in adverse weather conditions.
  • It was suggested at the Hazard Workshop that vessels would likely seek to make the most direct safe transit possible during adverse weather.
  • Wilson Ship Management indicated transit choice through the area would depend on weather conditions, and stated preference for passing inshore.
  1. There is open sea area inshore of the site boundary (the closest baseline wind farm is Seagreen 1 Offshore Wind Farm, located 27 nm inshore) and therefore the buoyed construction area is not considered as hindering any preference for inshore routeing.
  2. Details would be promulgated to facilitate advanced passage planning including in adverse conditions. Under COLREGS (IMO, 1972/77), vessels are also required to take appropriate measures with regards to determining a safe speed, taking into account various factors including the state of visibility, the state of the wind, sea, and current as well as the proximity of navigational hazards. In particular, vessels would be able to account for forecast for adverse conditions within their passage planning.
  3. Most likely consequences are minor alterations to existing adverse weather routeing noting the data indicates a preference for inshore routeing in such conditions. As a worst case vessels may be required to pass further offshore than preferred leading to large deviations in adverse conditions and safety concerns.

16.2.1.1  Frequency of Occurrence

  1. The frequency of occurrence is considered to be extremely unlikely based on the available sea room, the outputs of the modelling, and consideration of historical incident data.

16.2.1.2  Severity of Consequence

  1. The severity of consequence is considered to be serious.

16.2.1.3  Significance of the Risk

  1. Overall, the frequency of occurrence is considered to be extremely unlikely and the severity of consequence is deemed to be serious. The risk will therefore be of tolerable significance.

16.2.1.4  Additional Mitigation and Residual Risk

  1. No additional shipping and navigation mitigation is considered necessary because the likely risk, in the absence of mitigation beyond the embedded mitigation measures outlined in section 18.1, is ALARP and not significant in EIA terms.

16.2.2 Operation and Maintenance Phase

  1. As noted in the equivalent construction phase discussion, no specific adverse weather routeing was observed within the baseline vessel traffic data studied, however the long‑term 12 month AIS analysis showed a minor weighting towards summer months for cargo vessels, tankers, and oil and gas vessels in terms of volume.
  2. There is open sea area inshore of the site boundary (the closest operational wind farm is Seagreen 1 Offshore Wind Farm, located 27 nm inshore) and therefore the Array is not considered as hindering any preference for inshore routeing. During the operation and maintenance phase, vessels may be more likely to pass through the Array than during the construction phase, however based on consultation input (see section 4) it is unlikely that vessels would choose to transit through the Array during adverse weather conditions.
  3. All infrastructure will be shown on appropriate Admiralty Charts ensuring vessels can passage plan to account for the Array. In particular, vessels would be able to account for forecast for adverse conditions within their passage planning. Under COLREGS (IMO, 1972/77), vessels are also required to take appropriate measures with regards to determining a safe speed, taking into account various factors including the state of visibility, the state of the wind, sea, and current as well as the proximity of navigational hazards.
  4. Most likely consequences are minor alterations to existing adverse weather routeing noting the data indicates a preference for inshore routeing in such conditions. As a worst case vessels may be required to pass further offshore than preferred leading to large deviations in adverse conditions and safety concerns.

16.2.2.1  Frequency of Occurrence

  1. The frequency of occurrence is considered to be extremely unlikely based on the available sea room, the outputs of the modelling, and consideration of historical incident data.

16.2.2.2  Severity of Consequence

  1. The severity of consequence is therefore considered to be serious.

16.2.2.3  Significance of the Risk

  1. Overall, the frequency of occurrence is considered to be extremely unlikely and the severity of consequence is deemed to be serious. The risk will therefore be of tolerable significance.

16.2.2.4  Additional Mitigation and Residual Risk

  1. No additional shipping and navigation mitigation is considered necessary because the likely risk, in the absence of mitigation beyond the embedded mitigation measures outlined in section 18.1, is ALARP and not significant in EIA terms.