Linear Scour Depressions or Bedforms? Using Interferometric Sonar to Investigate Nearshore Sediment Transport
Abstract
A series of ambiguous features on the seafloor off the coast of Provincetown, Massachusetts USA has been identified in two bathymetric lidar surveys (2007, 2010) conducted by the US Army Corps of Engineers. Similar features in the area have been described as linear scour depressions by other investigators, but at deeper water depths. These features exhibit some of the characteristics of bedforms, they have migrated tens of meters and maintained similar 3 dimensional morphologies. However, what would be described as the slipface more closely resembles the updrift face of a linear scour depression. The features are in relatively shallow water (9 - 15 m), are 150 - 200 m long, have spacings of 100 - 150 m and are 5-6 m in height. Further investigations are being undertaken to better understand these features and nearshore sediment transport in the area. The features appear along a high energy, accreting coast with both strong wave-driven sediment flux and tidal currents. Mapping of the study area with an interferometric sonar system, which collects coincident swath bathymetry and acoustic backscatter imagery, is ongoing. Interferometric sonar increases bathymetric swath width to depth ratios, in comparison to multibeam systems, and expedites data collection by reducing costs, vessel-time and hazards associated with navigating shallow waters. In addition, sediment grab samples and a series of seismic reflection profiles will also be collected in the area to ground-truth acoustic imagery and provide a subsurface framework for the features, respectively. These datasets will allow investigators to better document bottom conditions, estimate flow velocities needed to create these features and improve our understanding of sediment transport processes and pathways in the area.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMOS13B1536B
- Keywords:
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- 3022 MARINE GEOLOGY AND GEOPHYSICS / Marine sediments: processes and transport;
- 3045 MARINE GEOLOGY AND GEOPHYSICS / Seafloor morphology;
- geology;
- and geophysics;
- 4217 OCEANOGRAPHY: GENERAL / Coastal processes;
- 4558 OCEANOGRAPHY: PHYSICAL / Sediment transport