Mapping and Classifying Surficial Sediment Types within the Maryland Wind Energy Area

Cribb, Coty
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University of Delaware
In this thesis, a procedure for analyzing large-scale side-scan sonar projects was developed. Side-scan sonar is a geophysical acoustic tool that can be used to image morphological features, grain-size distributions, obstructions, and human-derived hazards on the seafloor. Using a dataset provided by the State of Maryland Energy Administration, side-scan sonar images within the Maryland Wind Energy Area (WEA), encompassing over 320 km2, were analyzed to better constrain the WEA’s seafloor characteristics. The Maryland WEA is a proposed offshore region where wind energy projects could be developed. Offshore wind projects require a large capital investment. Up to 25% of total costs can be associated with wind turbine foundations that are directly influenced by seafloor conditions. Better understanding of the surficial and subsurface geology can aid in lowering costs by reducing uncertainty and allowing for optimal foundation design and siting in pre-construction planning. The procedure developed involves data processing techniques such as: data import, tracking the bottom, identifying hazards, digitizing reflection boundaries, and creating a mosaic base map. As well as comparing automated (SonarWiz and ENVI) and manual reflection classification methods. The reflection classification methods were compared based on a measure of their accuracy, ease of use, and the relative time involved in analysis. Based on accuracy, the two automated classification methods produce more consistent results than the user defined method. Additionally, the user defined method was determined to be the easiest to use, followed by ENVI, and finally SonarWiz. While the ENVI method required the shortest time investment to completion, followed by the user defined method, and again SonarWiz. Furthermore, a geologic analysis was performed on the Maryland WEA. Although no sediment samples have been collected within the boundaries of Maryland WEA, various qualitative analyses have been performed in the vicinity of the study area. These studies verify the assumption that side-scan sonar reflection intensities captured within the Maryland WEA can be correlated to a general fine, medium, or coarse grain size scheme. The results of this thesis provide a straight-forward procedure that can be used to analyze large-scale side-scan sonar datasets, like those that are/will be collected in geophysical surveys of offshore WEA’s. When combined with sub-bottom investigations (e.g., chirp sub-bottom profiling), sediment sampling, and geotechnical measurements, the side-scan sonar data can be used to place constraints on the types and distributions of sediments that will be encountered in offshore WEA’s. This information can be used by design engineers and planners to develop the most cost-effective foundations and thus aid in reducing the overall costs associated with offshore wind energy projects.