| Gravity currents occur in the atmosphere, in the ocean and under man-made environments. Locally in Seattle, gravity currents occur at the Hiram M. Chittenden Locks which separate the fresh water of Lake Washington from the saltwater of Puget Sound. The denser saltwater will enter the lake as a gravity current every time there is lake-bound operation of the locks. These lock-exchanges at the Chittenden Locks were used for "semi-controlled" field experiments, and a series of laboratory experiments to model the lock-exchange at the Chittenden Locks were also a part of this research. The mixing, which occurs between the intruding current and the ambient fluid, was the focus of this research. The mixing processes were quantified using two techniques, which are used in physical oceanography to study oceanic turbulence. The Thorpe scale, {dollar}deltasb{lcub}T{rcub},{dollar} gives a length scale for an overturning motion and the Available Potential Energy of the Fluctuation (APEF) estimates the amount of potential energy in an overturn available for kinetic energy. The APEF values in the laboratory were found to be larger than the values in the field because the density fluctuations were greater in the laboratory than in the field. The gradient Richardson number, {dollar}Risb{lcub}gr{rcub},{dollar} of the mixed layer was typically lower in the laboratory than in the field either due to the fact that there was background turbulence in the field or that the mixing transition was not reached in the laboratory.; Another study looked at the exchange flow through a constriction by opening the gate partially. An accelerated shear layer near the gate produced distinct Kelvin-Helmholtz roll-ups in the laboratory. The effect of bottom topography was seen when comparing the field and laboratory data. |
