Gavin Manson

A lengthy historical record of coastal evolution was combined with measurements made at weekly to bi-weekly intervals over approximately 550 days of coastal monitoring to investigate the evolution of the McNab’s Island area, a transgressive drumlin shoreline hosting gravel beaches.

Sub-annual to annual-scale records of bluff retreat, bluff erosion, foreshore erosion, till water content, well water level, sea level, waves, winds, precipitation, and air temperature demonstrate that storms are important in causing bluff and beach failure and retreat. Increased wind speed, wave height, water level, and precipitation accompanying storms interact with barrier beaches and clay- rich till bluffs and cause geographically variable coastal change over sub-annual time scales.

Historical charts, airphotos and records of sea level, winds, and waves indicate that rates of coastal change are spatially and temporally variable and that the interactions of rising sea level, storminess and sediment supply to barrier beaches have controlled the evolution of the study area over decadal time scales.

Rapid coastal change occurs only when sediment supply limitation, rapidly rising sea level, and increased storminess coincide, as between 1955 and 1964. Storminess and sea-level rise are both related to the North Atlantic Oscillation and affect sediment supply, giving rise to nonlinear and cyclic behaviour. Episodes of rapid beach and bluff retreat are preceded by long periods of stability and beach progradation during which offshore sediment reserves are depleted and the beach is morphodynamically conditioned to future failure due to accelerated sea-level rise and increased storminess.

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Supervisor: D.J.W. Piper