PROCESS AND MORPHOLOGY CHARACTERISTICS OF TWO BARRIER BEACHES IN THE MAGDALEN ISLANDS, GULF OF ST. LAWRENCE, CANADA

Abstract

Detailed field investigations of barrier beach morphology and processes at adjacent sites in the Magdalen Islands, Gulf of St. Lawrence, show that the two beaches are in distinctly different morphodynamic environments. The differences are expressed in terms of wave energy levels, sediment dispersal patterns, and nearshore, littoral, and dune geomorphology. The exposed west-facing coast has a steeper offshore gradient, is a zone of sediment bypassing, and has a complex sequence of three nearshore bars. Wave energy levels are lower on the sheltered east coast, and this is a zone of sediment redistribution and deposition with a single, linear nearshore bar. The different morphological characteristics of the two barriers are attributed to the spatial variation in energy levels and to the differences in offshore gradients on the two coasts. Computed wave energy values, derived from data monitored during two study periods (August and November, 1974), indicate that the mean wave energy levels were greater on the west coast as compared to the east coast by factors of 2.25 in summer and 2.95 in winter. This is due primarily to the dominance of winds out of the westerly quadrant throughout the year. 1975