Abstract
Physical and biological characterization of the seafloor is critically important for future offshore wind development in the New York Offshore Study Area (OSA) and, while full site characterization of any particular areas proposed for development will be performed at the project development stage, improved understanding of the OSA’s characteristics will facilitate New York State’s Offshore Wind master planning process.
The overall objective of this Analysis of Multibeam Echo Sounder (MBES) and Benthic Survey Data (Study) was to provide planning-level characterization of the geological (sediment size and type), geotechnical (density of bottom), and benthic (animal habitat) characteristics of potential offshore wind energy areas within previously identified water depth zones off the shore of New York State. This objective was accomplished with the collection and analysis of broad area reconnaissance MBES data products (primarily high resolution bathymetry and backscatter) and Sediment Profile Image (SPI) and Plan View (PV) photographic data used to ground truth the acoustic data and provide an initial assessment of benthic habitat types within the Area of Analysis. The SPI/PV imagery provided ground truth data of surface sediment characteristics (grain size, shear strength, and biological activity) that were used to identify areas with potential sensitive habitats.
The survey conducted for this Study was performed from June 21 to August 11, 2017, and collected data within four survey areas. The MBES survey collected a total of 2,498 linear nautical miles of high resolution acoustic imagery of seafloor topography and relative seafloor hardness/softness data (backscatter). All MBES data collected within the survey areas covered 229 square nautical miles (787 square kilometers) or 9% of the seafloor within the survey areas, which covered a total of 2,598 square nautical miles (8,910 square kilometers) of seafloor.
The SPI/PV survey occupied 300 stations throughout the four survey areas and collected up to four replicate image-pairs at each station. A total of 1,181 SPI images and 1,177 PV images were collected. Stations were distributed among cohesive regions of backscatter values and clustered in areas where steep gradients in backscatter values were observed. Further placement of SPI/PV stations occurred in areas where an existing regional model indicated higher degrees of uncertainty regarding the composition of seafloor surface sediments. On-board processing of acoustic data and review of SPI/PV images allowed ground truth station planning and field interpretation of the data in near real-time.
All data collected for this study indicated soft-bottom substrata that were determined to be suitable for offshore wind farm planning with respect to seafloor surface geology and benthic habitats. Data revealed a range of bedforms and surface sediment features, as well as associated benthic biotic communities, all of which can be characterized as soft substrata subject to episodic sediment transport events. No sensitive habitats (e.g., hard bottom with attached epifauna and flora) were observed in the acoustic and optical data collected. Additionally, surface sediment grain size data from this Study will help fill data gaps and improve an existing regional grain size model. The interpretations of surface sediments and benthic biological communities presented in this report are believed to be representative of the surveyed areas, given the survey design and collection of images across a range of seafloor features and textures.