Emma Besseau

B.Sc. (Honours) Thesis

LARGE GRAVEL/COBBLE SUBMARINE DUNES IN GRAND PASSAGE, NOVA SCOTIA: ARE THEY DEAD OR ALIVE?

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The Bay of Fundy is home to the world’s highest recorded tides and consists of several channels within Digby County, Nova Scotia, Canada. Each of the channels, including Digby Gut, Petit Passage, and Grand Passage, show the occurrence of dune formations in high resolution from bathymetry data collected with multi-beam sonar. Grand Passage was the location chosen for this study since sets of well-formed dunes are present in relatively shallow water. However, it is unknown whether these dune formations are mobile or static. The interpretation of dune mobility comes from knowledge of the geology of the area, available data on current speeds, and video footage collected in Grand Passage as part of this project. The surrounding geology is composed predominately of North Mountain Basalt, an early Jurassic formation. The separation of Brier and Long Island, forming Grand Passage, is thought to be a result of strike-slip faulting between the two islands, followed by fluvial and glacial erosion. Experimentation was conducted using a rectangular frame made of PVC piping and two GoPro cameras to capture video footage of the seabed at the southern entrance to Grand Passage. Still images captured from the video footage were then analyzed to determine grain size along the channel axis and mobility parameters were calculated from the observed grain sizes. Results showed that the dunes consist of mainly cobble grains (Wentworth scale, 64 – 256 mm) with abundant biological material. The critical Shields parameter and particle Reynolds number were calculated for the average grain size diameters found in each still and compared to a mobility curve. It is found that the crests of the dunes are active while the dunes become inactive with greater depth.

Keywords: Grain size, mobile, static, crest, Wentworth scale, shields parameter, Reynolds number, mobility curve
Pages: 34
Supervisor: Alex Hay