Stratification on the Skagit Bay tidal flats

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Date
2012-09
Authors
Pavel, Vera L.
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Location
Skagit Bay
DOI
10.1575/1912/5353
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Keywords
Tidal flats
Tidal currents
Abstract
Estuarine density stratification may be controlled primarily by cross-shore processes (analogous to longitudinal control in narrow estuaries), or by both cross- and alongshore processes (typical of coastal plumes). Here field observations and numerical modeling are used to investigate stratification on the low-sloped, periodically inundated Skagit Bay tidal flats. Advection of stratification by the depth-averaged velocity, straining of the horizontal density gradient by velocity shear, and turbulent mixing are shown to be the dominant processes. On the south-central flats (near the south fork river mouth) velocities are roughly rectilinear, and the largest terms are in the major velocity direction (roughly cross-shore). However, on the north flats (near the north fork river mouth), velocity ellipses are nearly circular owing to strong alongshore tidal flows and alongshore stratification processes are important. Stratification was largest in areas where velocities and density gradients were aligned. The maximum stratification occurred during the prolonged high water of nearly diurnal tides when advection and straining with relatively weak flows increased stratification with little mixing. Simulations suggest that the dominance of straining (increasing stratification) or mixing (decreasing stratification) on ebb tides depends on the instantaneous Simpson number being above or below unity.
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Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2012
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Citation
Pavel, V. L. (2012). Stratification on the Skagit Bay tidal flats [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/5353
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