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Spectral Wave Decay Due to Bottom Friction on the Inner Shelf

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Annual rept.

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The long-term goals of this research are to observe and model wave and boundary layer processes to determine wave dissipation in the coastal and nearshore ocean using novel instrumentation techniques. The primary scientific objective of this project is to measure the bottom dissipation of surface gravity waves as they shoal across the continental shelf. Detailed observations of the bottom boundary layer, resolving the thin oscillatory boundary layer, will be made at several field sites with differing wave forcing, mean currents, and sediment bed types to develop a spectral wave dissipation model for the continental shelf. At each site, continuous maps of the small-scale morphology will be made surrounding the detailed bottom boundary layer measurements to study changes in the bed in response to wave forcing, and to correctly interpret the effects of these morphology changes on the bottom boundary layer observations. The spectral dissipation model will include the potentially strong influence of a wave-forced mobile bed, and parameterizations for low frequency currents. At each of the field deployment sites, dissipation in the bottom boundary layer and wavecurrent forcing are being measured with a hierarchy of acoustic-based instrumentation including a 0.8 cm-resolution, three component Bistatic Coherent Doppler Velocimeter BCDV which measures vertical profiles of velocity and sediment concentration over a 60 cm range above the bed at a 20Hz rate. These small-scale measurements of the bottom boundary layer are extended through the water column with in situ travel-time current sensors and up to the ocean surface with a high speed Broad Band Acoustic Doppler Profiler. As the local sediment morphology can greatly influence the characteristics of the bottom boundary layer, a two axis scanning sonar altimeter has been developed to quantitatively measure fine-scale morphology over a 4 by 2m area centered on the BCDV profile measurements.

Subject Categories:

  • Physical and Dynamic Oceanography
  • Geology, Geochemistry and Mineralogy

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