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

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.

Multi-modal Approach for Benthic Impact Assessments in Moraine Habitats: a Case Study at the Block Island Wind Farm

“…It is particularly important to understand the effects of offshore wind development on the seafloor, which contributes significantly to ecosystem services globally (Costanza et al 1997;Liquete et al 2013;Dannheim et al 2019). Accurate seafloor habitat maps are essential for developers to appropriately site and design wind farms (Barrie et al 2014), to satisfy environmental assessment requirements, and for scientists to have a baseline from which to monitor and measure change (Shields et al 2009; Barrie et al 2014;e.g., LaFrance et al 2014;Pearce et al 2014;Schlappy et al 2014;Carey et al 2019). A review of European studies primarily conducted in soft seafloor settings concluded that knowledge on changes to benthic ecological functioning due to offshore marine renewable operations is limited and will require hypothesis-driven research combined with ecological modeling (Dannheim et al 2019).…”

“…However, benthic sampling devices (grab samples) and paradigms for consistently understanding recovery (successional stage theory, Pearson and Rosenberg 1978;Rhoads and Boyer 1982;Rhoads and Germano 1982) traditionally used in soft sediment environments are of little use in hard bottom areas (Taylor and Wilson 2003;Sheehan et al 2010). Use of high-resolution multibeam echosounder (MBES) data and high-resolution ground-truth imagery has been recommended for mapping these habitats (Kenny et al 2003;Diaz et al 2004; NOAA Habitat 2020) and has been used to characterize hard bottom and mixed habitats before construction at offshore renewable energy sites in the UK (Sheehan et al 2010;Pearce et al 2014), Norway (Schlappy et al 2014;Saskov et al 2015), and the U.S. (Carey et al 2019).…”