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Structure and composition of a strongly stratified, tidally pulsed river plume

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Title Structure and composition of a strongly stratified, tidally pulsed river plume
Names Nash, Jonathan (creator)
Kilcher, Levi F. (creator)
Moum, James N. (creator)
Date Issued 2009-08-14 (iso8601)
Note Copyrighted by American Geophysical Union.
Abstract The initial composition of a river plume depends on the cumulative turbulent
entrainment within the estuary and how this dilutes the supplied freshwater. Here we
examine the relative roles of turbulence and freshwater input using observations from the
Columbia River estuary and plume during two periods with contrasting river flow. Within
the estuary, intense turbulence observed on flood and ebb stages is controlled by the
bottom stress and scales with tidally dominated near-bottom velocity as u³tidal. Shear
associated with the estuarine circulation is found to have a much weaker influence on
turbulence dissipation rates. On the basis of these observations, we suggest that properties
of the Columbia River tidal plume should be controlled by the ratio of horizontal
advection to turbulent mixing within the estuary. This ratio depends on the magnitude of
freshwater river input (characterized by its volumetric flow rate Qf) as compared to
turbulent fluxes due to tidal mixing. This is summarized in terms of the estuary
Richardson number RiE, a nondimensional ratio between Qf and u³tidal. From 17 tidally
resolving offshore surveys during spring/neap tides and low/high river flows, we find that
the plume’s median salinity, thickness, and turbulent mixing are each predicted through
RiE. It is hoped that these simple formulations will provide guidance in assessing critical
properties of river plumes and their influence on coastal circulation.
Genre Article
Topic turbulence
Identifier Nash, J. D., L. F. Kilcher, and J. N. Moum (2009), Structure and composition of a strongly stratified, tidally pulsed river plume, J. Geophys. Res., 114, C00B12.

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