Mixing processes and hydraulic control in a highly stratified estuary

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 three 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 2 x 10-3 m s' . 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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• MacDonald, Daniel George, 1970-

Advisor dc:contributor.advisor

• W. Rockwell Geyer.

• Civil and Environmental Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/16902

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/16902