Forward Scouting: Use of Sediment Profile Imagery in Conjunction with Multibeam Echosounder Mapping for Offshore Wind Cable Routes and Site Characterization

Abstract

Abstract Selection of cable routes and wind turbine site assessments for offshore energy projects in the often-complex geology of the North American Atlantic coast entails very high risks for developers as well as state agencies: limited desktop data, patchy distribution of critical or sensitive habitats, and use conflicts, are a sampling of the risks encountered. The costs required to conduct multi-disciplined geophysical spreads including weather delays during marine mammal transit windows does not support exploring multiple or alternative routes. A novel approach was developed by Fugro and INSPIRE Environmental to reduce the risks and costs of required geophysical and benthic assessment surveys for offshore wind projects. Collection of field data is required by the Bureau of Ocean Energy Management (BOEM) as part of the Site Assessment Plan (SAP) for geophysical and biological characterization in offshore wind development. Collection of Sediment Profile Imagery (SPI) and Plan View (PV) imagery was integrated with multibeam echosounder (MBES) acoustic data collection to optimize route selection, provide ground-truth of acoustic data, and characterize benthic habitats in survey campaigns at three offshore wind projects. The SPI/PV data were downloaded daily and combined with on-board processed MBES data to provide near real-time guidance for optimizing survey operations. BOEM requires the mapping of sensitive habitats such as deepwater corals, eelgrass beds, and hard bottom environments including bedrock, boulder and cobble habitats as well as habitat characterization for a full benthic assessment. The data presented from these three projects using the Forward Scouting approach illustrates the utility of rapid data acquisition and interpretation to support project-critical acoustic surveys. The SPI/PV data will be presented in an innovative visualization that integrates the profile and plan view imagery and processed MBES data. The visualization of the ground-truthed and benthic assessment data with landscape-scale seabed features has provided valuable decision-making support for archeological, benthic, fisheries, and engineering assessments. These combined technologies demonstrated the success of a collaborative approach to cable route and site characterization and led to development of the Forward Scouting approach to further reduce risk to schedules and assets, reduce site investigation costs, and incorporate multi-discipline (engineering and environmental) site data during early stages of project planning that is beneficial to stake-holder engagement activities. Cable routing and site assessment is optimized when engineering and restricted-habitat constraints are minimized prior to full geophysical and geotechnical (G&G) survey operations with large assets. The SPI/PV Forward Scouting survey team can be deployed with high-frequency (>200 kHz) acoustic reconnaissance tools on small vessels that do not require permits or protected species observers (PSOs). The acoustic data collection for reconnaissance can utilize wider swath data retention without the requirement to meet International Hydrographic Organization standards and ‘sweep’ the proposed cable routes prior to defining the accepted centerline for full spread surveys. The SPI/PV photographic data provides ground-truth for the acoustic reconnaissance and if collected along the accepted centerline prior to demobilization will also provide baseline data acceptable for benthic assessment. The Forward Scouting approach offers the offshore wind industry critical advantages in cost and time by utilizing seasonal survey windows often inaccessible to the full-complement of geophysical equipment or vessels and reducing the scope of survey plans based on desktop data review. The potential for Forward Scouting is optimized with close collaboration between geophysical and SPI/PV providers.