Graduation Year

2004

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Howd, Peter A.

Keywords

segmentation, acoustic backscatter, wave current interaction

Abstract

Observations of the bottom boundary layer on the inner West Florida Shelf were made with a downward looking pulse coherent acoustic Doppler profiler throughout the passage of Tropical Storm Isadore during September 2002. The storm passed through the Gulf of Mexico roughly 780 km offshore of the Florida study site. Significant wave heights ranged from 0 m to 2.5 m within a span of eight days. The excellent, non-invasive, 5 cm resolution of the near bed (bottom meter) mean flows were used to estimate bed shear velocity and bottom roughness using the standard log-layer approach. A unique opportunity to examine boundary layer structure was provided by the high-resolution data. Calculated friction velocity due to currents (u*c) and apparent bottom roughness (z0) reduced considerably when velocity measurements closer to the bed were emphasized.

This observation may be indicative of segmentation within the bottom boundary layer and has implications for common practices of estimating bed shear stress measurements from distances greater than a few tens of centimeters above the bed. Acoustic backscatter strength was used as a proxy for sediment suspension in the water column revealing no relationship between current parameters and sediment resuspension during the ten-day data set. Wave effects were included following the work of Grant and Madsen and others with strong relationships between wave and wave-current parameters and the ABS as a proxy for sediment resuspension evident.

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