Publication Date:
2022-05-25
Description:
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 February 2003
Description:
This thesis utilizes field data from the Fraser River Estuary, a highly stratified system
located in southwestern British Columbia, Canada, to investigate the nature of mixing
processes in a highly stratified environment, and to extend two-dimensional hydraulic
theory to a three dimensional environment.
During the late ebb, a stationary front exists at the Fraser mouth. Although densimetric
Froude numbers in the vicinity of the front are supercritical in a frame of reference
parallel to the local streamlines, the front itself is oriented such that the value of the
Froude number is equal to the critical value of unity when taken in a frame of reference
perpendicular to the front. This observation presents a robust extension of established
two-dimensional, two-layer hydraulic theory to thee dimensions, and implies similarity
with trans-sonic flows, in that a Froude angle can be used to identify critical conditions in
a manner similar to the Mach angle.
Mixing processes were evaluated at the mouth during the late ebb using a control volume
approach to isolate mean vertical entrainment processes from turbulent processes, and
quantify the vertical turbulent salt and momentum fluxes. Observed turbulent dissipation
rates are high, on the order of 10-3 m2s.3, with vertical entrainment velocities on the order
of 2x10-3 m's'l. Mixing efficiencies, expressed as flux Richardson numbers, are
confined within a range from 0.15 to 0.2, at gradient Richardson number values between
0.2 and 0.25. These results are consistent with previous laboratory studies, but represent
energetic conditions that are several orders of magnitude higher.
In the estuarine channel, the variability of mixing processes was investigated through the
tidal cycle using control volume and overturn scale methods. Spatially, mixing was
observed to be more intense near a width constriction on the order of25%. Temporally,
more dominant mixing was observed during ebbs, due to increases in both vertical shear
and stratification. Mixing is active and important throughout the tidal cycle, and was
found to be the dominant process responsible for removing salt from the estuarine
channel during the ebb.
Description:
This research was funded by Office of Naval Research grants N000-14-97-10134 and
N000-14-97-10566, National Science Foundation grant OCE-9906787, a National
Science Foundation graduate fellowship, and the WHOI Academic Programs Office.
Keywords:
Tidal currents
;
Salinity
;
Hydrodynamics
;
Clifford A. Barnes (Ship) Cruise
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf
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