Waves, turbulence and circulation in the Altamaha River Estuary, Georgia
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Physical processes such as sea surface waves, turbulence, and residual circulation were studied in an estuarine environment using several observational data sets and modeling experiments in the Altamaha River Estuary, GA. The wave energy within the estuary becomes periodic in time showing wave energy during ood to high water phase of the tide and very little wave energy during ebb to low water. This periodic modulation is a direct result of enhanced depth and current-induced wave breaking that occurs at the ebb-shoaling region surrounding the Altamaha River mouth. Modeling results showed that depth-induced wave breaking is more important during the low water phase of the tide than current-induced wave breaking during the ebb phase of the tide. In this shallow environment these wave-current interactions lead to an increased bottom roughness, resulting in an enhanced bottom friction coe cient. An increase of river discharge changed the estuarine turbulence ow and density charac- teristics into a more ebb-dominated and strati ed system. The Reynolds stress and turbulent kinetic energy (TKE) were increased due to increased river discharge. The spectral energy density of turbulent ow was deformed by surface waves and better satis ed the -5/3 slope for isotropic trublence when the wave-induced motions were removed. Buoyancy ux increased in magnitude with increased longitudinal density gradient and showed a weak energy source during ood tide and a relatively strong energy sink during ebb. A balance between production and dissipation of energy was not obtained, implying that turbulent transport of TKE is a consideration. Numerical modeling results revealed a complex depth dependence on turbulence intensity that varied with the tidal cycle and with the level of strati cation. The mean ow is dominated by the semidiurnal lunar tidal component (M2) and the tidal phase showed fairly constant values in the center of the channel with strong variations in the shoaling regions. When the M2 component was removed, weak landward residual ows appeared on both slack waters, which may be a result of weak turbulent mixing and greater strati cation, and strong seaward residual ow occurred during ood and ebb tides that may be attributed to strong turbulence levels.