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Two-layer exchange flow through the Burlington Ship Canal

University of British Columbia

In summer, the temperature difference between Hamilton Harbour and Lake Ontario drives a two-layer exchange flow through the Burlington Ship Canal. Warmer Hamilton Harbour water forms the upper layer in the canal before floating out onto the surface of Lake Ontario, while cooler lake water forms the bottom layer in the canal prior to sinking into the harbour's hypolirnnion. During periods of exchange flow, large amounts of water are exchanged between the harbour and the lake, thus an understanding of this phenomenon is necessary to determine the water quality of either body. In the summer of 1996, an extensive field study was conducted to obtain a better understanding of exchange flow dynamics in the Burlington Ship Canal. Acoustic Doppler Current velocity Profiler (ADCP) and Conductivity-Temperature-Depth (CTD) profiles measured during 5 drifts along the canal from a boat on July 25, 1996 were analyzed in the present study. Differential Global Positioning System (DGPS) was employed to determine surface location within the canal. Density in the canal was calculated from temperature and conductivity using a lakewater equation of state. A hyperbolic tangent function was fit to each of the velocity and density profiles in the ship canal. This fit provided a convenient way of characterizing the density and velocity of each layer, the interface location, and thickness of the interface. Flows into and out of Hamilton Harbour were estimated by integrating the velocity profiles with respect to depth. By forcing control locations at the ends of the Burlington Ship Canal, a line was calculated as an initial estimate of the interface profile using the measured flow for each layer and the density difference. As a first approximation, the line provides a reasonable fit to the data. However, unsteadiness in the flow limits the validity of the concept of hydraulic control and other aspects of steady 2- layer hydraulics. Predictions of the interface fit should be extended to account for unsteady effects. In addition, barotropic and frictional effects should be considered. All of the drifts, except for one where mixing was caused by the passage of a large ship through the canal rather than exchange flow, exhibit similar mixing patterns. The bulk Richardson number associated with velocity, J8 = 0.30, and the bulk Richardson number associated with density, Jη = 0.25. These values compare very favourably with published values of J from theoretical, numerical and experimental work. In the Burlington Ship Canal, mixing may be predicted once the background flow is known. Unfortunately, steady, 2-layer hydraulics cannot provide an accurate estimate of the background flow. [Certain scientific formulae used in this abstract could not be reproducted.]

Thesis/Dissertation

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2009-05-26

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http://hdl.handle.net/2429/8220

Civil Engineering

University of British Columbia

UBCV

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