Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
The research presented in this study is motivated by the need to improve prediction of sediment transport in estuaries. A novel application of the Acoustic Doppler Velocimeter (ADV) in the lower Chesapeake Bay is shown to estimate in-situ particle fall velocity at a single point without affecting the ambient turbulence. Acoustic backscatter from the ADV proved to be the best estimator of mass concentrations due to its apparent insensitivity to the size or density of muddy aggregates. Fall velocities are estimated analytically from a balance of settling and diffusive flux gradients using two methods, one employing Reynolds concentration flux, and the other estimating eddy diffusivity using the von-Karman Prandtl equation. Single elevation estimates of fall velocity using the ADV to estimate Reynolds concentration flux produced the best estimates of fall velocity, which are on the order of 1 mm/s. A novel method is presented to measure TKE production using a profiling ADV instrument that has been contaminated by boat motion. The relative importance of physical processes that determine particle size distributions differs in three mid-Atlantic U.S.A. estuaries (York R., Elizabeth R., Chesapeake Bay) with different hydrodynamics and benthic characteristics as well as in different depth regimes within each estuary. Surface particle size dynamics in all of the estuaries are affected by irregular advection events. Middepth regions in the energetic estuaries are controlled tidally by the combined processes of TKE production decreasing particle size and differential settling increasing particle size. Middepth regions in the low energy estuary are controlled by irregular resuspension and trapping at the pycnocline of large low density particles. Bottom regions in all estuaries are most strongly influenced by resuspension, tidally in the energetic estuaries and irregularly in the low energy estuary. The interrelationships between metal concentrations, particle size, percent fixed solids (PFS), chlorophyll a, and molar Carbon to Nitrogen (C/N) ratios of suspended sediment are investigated in a heavily industrialized and polluted estuary, the Elizabeth R., VA. The relationship between PFS, C/N and aggregate size are also investigated in a relatively energetic, high concentration, and undisturbed estuary, the York. R., VA. Standard paradigms of contaminant concentration relationships with particle size and particle constituents were not supported in the low energy, low concentration suspended sediments of the Elizabeth R. (Abstract shortened by UMI.).
© The Author
Fugate, David C., "Estuarine suspended aggregate dynamics and characteristics" (2002). Dissertations, Theses, and Masters Projects. Paper 1539616653.