Open Collections

Abstract

We investigate the occurrence of shear instability in the Fraser River estuary. Instabilities observed with an echo sounder are compared with a linear stability analysis based on observed velocity and density profiles. We find that each set of observed instabilities coincides with an unstable mode predicted by the Taylor-Goldstein equation. Each of these instabilities occurs in a region where the gradient Richardson number is less than the critical value of 1/4. Both the Taylor-Goldstein predictions and the echo soundings indicate the instabilities are concentrated either above or below the density interface. This “one sidedness” is in contrast to the archetypal Kelvin-Helmholtz instability. Although the dominant source of mixing in the estuary appears to be caused by shear instability, when the tide produces strong near-bed velocities, small-scale overturning due to boundary layer turbulence is apparent throughout the depth. An edited version of this paper was published by AGU. Copyright 2009 American Geophysical Union.