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A physical study of upwelling flow dynamics in long canyons Waterhouse, Amy Frances


Long canyons are topographic features that are responsible for increased upwelling along coastal margins. Located between Vancouver Island and Washington State, Juan de Fuca Canyon is a long canyon that begins at the continental slope and continues into the Strait of Juan de Fuca. This canyon is a conduit for significant nutrient flux to the Strait of Juan de Fuca and has been associated with seasonal upwelling onto the shelf. A n eddy, visible at the surface, forms at the mouth of the Juan de Fuca Strait and is an area of increased plankton growth. A physical model of this canyon has been constructed in order to understand the upwelling dynamics i n long canyons. The physical model is spun up to an initial rotation rate and the flow is forced by increasing the rotation rate over the equivalent of several days. Flow visualization is used to determine the strength and location of upwelling, the strength of the deep canyon vorticity, and the deepest depth of upwelling. Two main stages of the flow are observed. The first stage involves increased upwelling on the shelf close to the canyon mouth. Horizontal isopycnals (represented by horizontal layers of dye) show increased stretching along the upstream wall of the canyon. The second stage of the flow is indicated by reduced upwelling and the formation of an eddy at the canyon mouth. The vorticity of this eddy is related to the side wall vorticity, as well as water column stretching. Parameters from previous short canyon experiments are replicated and show that long canyons have increased upwelling under similar conditions. The Rossby scale taken from previous short canyon experiments did not properly characterize the flow as separation was observed at the canyon mouth in all experimental runs.

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