Geomorphology and Sea-level Rise on one of Canada's Most Sensitive Coasts: Northeast Graham Island, British Columbia

• Published in: Journal of coastal research pp. 220 - 226
• Main Authors: Walker, I.J., Barrie, J.V.
• Format: Journal Article
• Language: English
• Published: Coastal Education & Research Foundation (CERF) 01.12.2006
• Subjects: Beaches; Coasts; Dunes; El Nino; Sand; Sandspits; Sea level; Sea level rise; Sediments; Storms
• ISSN: 0749-0208; 1551-5036

This paper documents the geomorphology of one of Canada's most dynamic coastlines, northeast Graham Island, Queen Charlotte Islands (Haida Gwaii). This area has undergone major sea-level changes (-150 to +16 m) over the Holocene and is currently rising at +1.6 mm a⁻¹. Relict shorelines and recent progradational ridges tell of landscape response to sea-level changes. Given a macrotidal range, energetic wave climate and ongoing erosion, the Geological Survey of Canada identifies this as one of Canada's most sensitive coasts to future sea-level rise. Retreat of 1-3 m a⁻¹ and tens of metres in extreme years (e.g., El Niño 1997-98) occurs on East Beach, while the dissipative shores of North Beach prograde at 0.3-0.6 m a⁻¹. Over 100 km of sandy beach are maintained by strong littoral transport by tidal currents and storm waves. Northward longshore transport on East Beach heads westward around Rose Spit to North Beach, particularly during SE storms. Despite a moist climate and dense vegetation, aeolian activity is high and moves sand onshore into foredunes and driftwood jams that stabilize the backshore against wave attack. Foredunes migrate on the order of metres per year while larger parabolic dunes migrate slower (metres per decade). Migrating shore-attached bars feed beach-dune systems while their leading edge is a locus for beach erosion. Dendrochronological (tree-ring) evidence is explored to provide proxy evidence of past climate changes and geomorphic responses. Instead of landward erosion of the beach and deposition in the nearshore per the Bruun model, the response of this coast to ongoing sea-level rise involves high onshore sand transfer, accretion and foredune migration that provide a buffer against wave attack. This preliminary examination sets the geomorphic stage for a larger, interdisciplinary study on sea-level rise impacts that threaten communities, ecological reserves, cultural sites and critical infrastructure in the region.