Abstract
This report details the results from the marine environmental survey along the export corridor and within the development site for the Hywind Offshore Windfarm off the coast of east Scotland.
Statoil intends to install the Hywind Offshore Windfarm, with five floating wind turbines anchored to the seafloor together with an export cable to the mainland. The Turbine Site Area is situated 25 km east of Peterhead where the cable route will landfall. The water depth in the surveyed Export Cable Route area reaches between 1 and 98 m LAT and in the Turbine Site Area 97 to 188 m LAT.
MMT was contracted in 2013 to undertake marine geophysical seabed mapping and environmental surveys of the Turbine Site Area and export cable corridor as well as a nearshore survey of the landfall.
The environmental survey objective was to identify and map the extent of existing habitats and describe sensitive habitats and species or habitats and species of special conservation interest within the turbine area and cable corridor.
The survey area is divided in two main parts; the Turbine Site Area with accompanied construction and anchoring areas and the Export Cable Route.
The geophysical data acquisition was performed to determine water depths, seabed features, shallow geology, object detection and cable crossing positions. Instruments used during the geophysical survey were multibeam echo sounder, side scan sonar, sub-bottom profiler and magnetometer.
The environmental data acquisition comprises of sediment sampling, photography and video recording for ground truthing the seabed and to map the existing habitats. The instruments used were grab sampler and drop down video-camera.
The environmental survey started on the 23rd of August 2013 and was completed on the 1st of September.
An area of approximately 60 km2 was covered by the geophysical survey. Within this area 34 sampling sites and 6 video transects were assigned and performed during the environmental survey. In the cable corridor the EC Habitats Directive (The Council of the European Communities, 1992) Annex I “Bedrock reef” and “Stony reefs” were found as well as aggregations of the tube building Ross worm Sabellaria spinulosa.
Sabellaria spinulosa worms build tubes out of sand and when aggregated in large densities they form complex structures that due to their elevation and extension are considered to be biogenic reefs. These S. spinulosa aggregations were identified in approximately 1/3 of the Turbine Site Area as well in the offshore end of the Export Cable Corridor. Most aggregations found in this survey had a low coverage of the seabed, around 1 – 10 % and are not considered as biogenic reefs. Two larger areas in the centre and southeast corner of the Turbine Site Area along with some smaller scattered areas meet the criteria for the score of an “Low graded S. spinulosa reef” (Gubbay, 2007) included under areas of special conservation interest code 1170 Reefs of Annex I, EC Habitats Directive (The Council of the European Communities, 1992).
MMT has performed the Statoil Hywind Windfarm project without any fatality or injury.
Appendices:
- Appendix A: SAMPLE POSITION LIST
- Appendix B: GRAB & TRANSECT FIELD PROTOCOLS
- Appendix C: GRAB IDENTIFICATION PROTOCOL
- Appendix D: GRAB & TRANSECT PHOTO PROTOCOL
- Appendix E: PARTICLE SIZE ANALYSIS RESULTS
- Appendix F: CHEMICAL ANALYSIS RESULTS
- Appendix G: BEDLOAD ANALYSIS RESULTS
- Appendix H: CHART INDEX