Seabed Investigations & Engineering for Gulf of Maine Offshore Wind

Melissa Landon Maynard, Ph.D.Civil & Environmental Engineering, University of Maine

Seabed Investigation Requirements

Identify bathymetric featuresSeafloor topography

Identify sub-seafloor geology and materialsPresence and type of sediment or rockNatural hazards (gas, slope failures)

Identify cultural resources for avoidance/protectionHistorical relics water depth dependentHistorical relics – water depth dependentShipwrecks, lighthouses.

Identify seabed engineering propertiesIdentify seabed engineering properties

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Bathymetry

NOAA’s Office of Coast Survey Charts

Example: Chart 13288: Monhegan Island to Cape ElizabethExample: Chart 13288: Monhegan Island to Cape Elizabeth

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Bathymetry

USGS Coastal Marine Geology Program GIS data

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Geologic setting – sea level variation

Sea level was 60 m (180’) deeper 11,000 years ago than it is now.

Kelley et al., 2005

• Offshore geologic variability from land-based sedimentary features shallower than 60 m water depthp

• Evidence of historic societies have been found shallower than 60 m water depth

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Seafloor Geology & Materials

Kelley et al., 1998

Nearshore Basin: shallow marine depressionNearshore Ramp: region sloping gently seaward

Rocky Zone: exposed or shallow bedrock and gravelShelf Valley: seaward sloping troughs extending from Nearshore Basins.

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Outer Basin: deeper than 40 m with fine sedimentsHard-Bottom Plain: extensive low slope areas covered by gravel, sand and rock

Seafloor Geology & MaterialsExample: Boothbay Harbor to North Haven, Maine Analysis of Surveys

& Sampling Activity

Bathymetry Sediment samplingSub-bottom profilingSeafloor sonar Seafloor sonar (material boundary)

Blue = fine sedimentsRed = rockYellow = sand

Maine Geological Survey

Surfical Geology of the Maine Inner Continental Shelf Map Seriesgy prepresents nearshore sediments for water depths < 100 m only

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Cultural, Historical & Buried Resources

Resource EvaluationRolleri (2006)

• Sub-sea cables & pipelines

• Shipwrecks• Shipwrecks

• Evidence of historical societies (< 60-70 m water depth)Lighthouse

Ship wreck

water depth)

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Engineering – seabed propertiesAssess variability

Image: variability of sub-seafloor features exists far offshore (> 12 nm).

Engineering properties of sediments

Collect cores for processing

Perform testing in place on the seabed

Identify potential geohazards

landslides, seafloor gas, earthquake hazards

800 m long profile

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Wind Turbine FoundationsTurbine platform, seabed fixity, sediment and cost factor into foundation selection and design

GravityBase

Piles: (driven or augered)System augered)

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Fixed bottom offshore energy devices – Landon Maynard & Schneider (2010)

Foundations & AnchoringTurbine platform, seabed fixity, sediment and cost factor into foundation selection and design

Suction caissons

Piles

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Floating offshore energy devices – Landon Maynard & Schneider (2010)Drag anchors

ReferencesBarnhardt, W. A., Belknap, D. F., Kelley, A. R., Kelley, J. T., and Dickson, S. M. (1996a). Surficial Geology of the Maine inner continental shelf. Maine Geological Survey, Geologic Map 96-6 to 96-12, scale 1:100,000. http://www.maine.gov/doc/nrimc/mgs/pubs/online/ics/ics.htm.

Kelley, J.T., Barnardt, W.A., Belknap, D.F., Dickson, S.M., Kelley, A.R., (1998). The Seafloor Revealed: The geology of Maine’s inner continental shelf. A Report on the Regional Marine Research Program, Maine Geological Survey Open-File Report 98-6, 55p. http://www.state.me.us/doc/nrimc/mgs/explore/marine/seafloor/contents.htm

Kelley, J.T. , Dickson, S.M., and Belknap, D.F. (2005). Maine's History of Sea-Level Changes. http://www.maine.gov/doc/nrimc/mgs/explore/marine/facts/sealevel.htm (accessed Jan. 20, 2011).http://www.maine.gov/doc/nrimc/mgs/explore/marine/facts/sealevel.htm (accessed Jan. 20, 2011).

Landon Maynard, M. and Schneider, J. (2010). "Geotechnics for developing offshore renewable energy infrastructure industries in the US." 2nd Int. Symp. on Frontiers in Offshore Geotechnics (ISFOG), University of Western Australia, Perth, Western Australia, 8-10 November.

NOAA coastal chart 13288: http://www.charts.noaa.gov/OnLineViewer/13288.shtml (accessed Jan. 20, 2011)

Rolleri, J. (2006) “Lighthouses and Shipwrecks of Maine,” Atlas of Maine Series. http://arcims.colby.edu/website/aom06_lighthouse/viewer.htm (accessed Jan. 20, 2011)

Foundation images:

Suction caisson: Andersen, K.H., Murff, J.D., Randolph, M.F., Clukey, E., Erbrich, C., Jostad, H.P., Hansen, B., Aubeny, C., Sharma, P. and Supachawarote, C. (2005): Suction anchors for deepwater applications. Proc., ISFOG, Int. Symp. on Frontiers in Offshore Geotech., 13-30. Perth, Australia.

Drag anchor: http://www.vryhof.com/products/anchors/stevpris_mk5.html

Pil h // f l / ff h iPile: http://www.fnapl.com/offshore_equipment.asp

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