Coastal to offshore submarine channel sediment transport system: Savary Island, British Columbia, Canada
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Multibeam bathymetry, coupled with seismic reflection profiles and sediment cores, was collected to understand the sediment process mechanisms for active onshore-offshore sediment transfer system from coastal erosion to nearshore transfer of sediment into a submarine channel and fan system. Savary Island in the northern Salish Sea of British Columbia, Canada, emerged immediately after deglaciation and became exposed to winter storms that began a continual modification of the island. Subsequent to coastal erosion, sediments are moved from the south side of the island, by strong tidal currents and longshore drift, to the island’s north side. The mobilized sands are then entrained into and swept down submarine channels during gravity flows, likely a response to enhanced hydrodynamic tidal flow. Downslope progradation within the channels is primarily a result of downslope migrating submarine dunes that transfer sand to small submarine fans. Further transport beyond the channels into the deeper basin occurs via turbidity flows that have been active throughout the late Holocene. The prospect for Savary Island is grim, as this sediment transfer system will likely continue until the island disappears altogether.
The Canadian Hydrographic Service (Department of Fisheries and Oceans) is thanked for the diligent collection of multibeam bathymetry. The officers and crew of the CCGS Vector are acknowledged for able seamanship in collection of the geophysical and sediment sample data. Peter Neelands, Robert Kung, and Greg Middleton are thanked for invaluable assistance at sea and in the laboratory. We thank Royal Roads University for the use of the Geotek split core multisensor core logger. H. Gary Greene provided valuable suggestions that improved this paper. This research was initiated by Dr. Brian D. Bornhold, a former editor of Geo-Marine Letters, and it is to his memory that we dedicate this paper.
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