The sedimentology, morphology and evolution of Two Gravel Barachoix, Placentia Bay, Newfoundland

Boger, Rebecca A. (1997) The sedimentology, morphology and evolution of Two Gravel Barachoix, Placentia Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

A detailed study of gravel barrier beaches at Ship Cove and Big Barasway has shown significant differences in morphology, sediment texture and structures, as well as lateral variability within each system. The individual shoreline assemblages reflect differences in the amount and seasonal variability of sediment supply, in the hydrodynamic settings of the barachoix and, in the orientation with respect to the prevailing southwesterly waves. At Ship Cove, the bayhead barrier has a high elevation, steep beachface, and extensive cusp development; the morphology is a result of its swash alignment, its fixed sediment supply and high wave energy reaching the barrier. The sediment shows a strong cross-shore sorting by shape and size, and cusps largely influence the orientation of clast fabrics. -- The presence of a gently-sloping subtidal and intertidal platform in the central 800 m and a 200 m-long vegetated island within the bayhead barrier system at Big Barasway, result in the development of separate and distinctive flow cells, each with differing dynamics and sedimentation. The swash alignment, the high wave energy, and the fixed sediment supply of the southern section result in a similar morphology and sediment texture to that at Ship Cove. -- The moderate wave energy reaching the northern section results in a gentler beachfront slope and lower elevation. In addition, the drift alignment and sediment removal along the northern section is causing a thinning of the barrier in areas and progradation in other places. Cross-shore sorting of sediment by shape and size is weaker than that at the southern end of Big Barasway and at Ship Cove. Clast fabrics are generally weaker, although strong orientations can occur. -- Overwashing and ice foot development act to modify both shorelines. Landward movement of the barriers is estimated at 0.3 - 0.9 m/year. The outlet at Big Barasway is stable, whereas that at Ship Cove opens and closes on a daily basis in mid- to late summer. Anthropogenic modification at Ship Cove has caused instability, as a result of aggregate removal and a forced northerly relocation of the outlet. Radiocarbon dates, sedimentological and archaeological data indicate that transgression is currently occurring along the southeast Placentia Bay shore, and further modification of the coastline is anticipated in the subsequent century.

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