Date of Award

Fall 2006

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Ocean and Earth Sciences

Committee Director

Larry P. Atkinson

Committee Member

Chester E. Grosch

Committee Member

John M. Klinck

Committee Member

Arnoldo Valle-Levinson

Call Number for Print

Special Collections LD4331.O35 N27 2006

Abstract

Four oceanographic surveys and two periods of moored data were analyzed to describe the subtidal exchange hydrodynamics between a subestuary (Nansemond River) and its adjacent estuary (James River) in the lower Chesapeake Bay. The surveys were carried out during two semidiurnal periods (~25 hrs), which included two spring and two neap tides. Velocity profiles and hydrographic data were recorded over an area ~4 km long and ~1 km wide allowing a spatial resolution rarely obtained with observational data. The results obtained in the surveys were extended with instruments deployed at the entrance to the subestuary during winter and summer time (~80 days for each deployment). The combination of both data sets allowed a comprehensive characterization of the main factors driving the subtidal circulation. The circulation pattern observed in the subestuary is caused primarily by the interaction between local topography and winds. Buoyancy forcing, Earth's rotation and centripetal accelerations are secondary factors. The curved funnel shape of the lower subestuary favors a subtidal recirculation. This recirculation is enhanced by an adverse pressure gradient and by westward wind, which drives inflow over the shallow parts and outflow in the channel. The adverse pressure gradient is caused by intrusion of low-salinity waters through the shoals of the subestuary, especially during episodic increases of river discharge at the estuary. The subestuary's transverse partition of the wind-induced circulation shows good agreement with previous results obtained mainly with analytical and numerical models. Thus, the observational data presented in this research are among the few to validate such numerical results.

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DOI

10.25777/za48-3m34

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