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The tidally averaged momentum balance in a partially and periodically stratified estuary

Journal of Physical Oceanography

By:
, , , and
DOI: 10.1175/2010JPO4389.1

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Abstract

Observations of turbulent stresses and mean velocities over an entire spring-neap cycle are used to evaluate the dynamics of tidally averaged flows in a partially stratified estuarine channel. In a depth-averaged sense, the net flow in this channel is up estuary due to interaction of tidal forcing with the geometry of the larger basin. The depth-variable tidally averaged flow has the form of an estuarine exchange flow (downstream at the surface, upstream at depth) and varies in response to the neap-spring transition. The weakening of the tidally averaged exchange during the spring tides appears to be a result of decreased stratification on the tidal time scale rather than changes in bed stress. The dynamics of the estuarine exchange flow are defined by a balance between the vertical divergence of the tidally averaged turbulent stress and the tidally averaged pressure gradient in the lower water column. In the upper water column, tidal stresses are important contributors, particularly during the neap tides. The usefulness of an effective eddy viscosity in the tidally averaged momentum equation is explored, and it is seen that the effective eddy viscosity on the subtidal time scale would need to be negative to close the momentum balance. This is due to the dominant contribution of tidally varying turbulent momentum fluxes, which have no specific relation to the subtidal circulation. Using a water column model, the validity of an effective eddy viscosity is explored; for periodically stratified water columns, a negative effective viscosity is required. ?? 2010 American Meteorological Society.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
The tidally averaged momentum balance in a partially and periodically stratified estuary
Series title:
Journal of Physical Oceanography
DOI:
10.1175/2010JPO4389.1
Volume
40
Issue:
11
Year Published:
2010
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Physical Oceanography
First page:
2418
Last page:
2434