Morphology, formation and migration of longshore sandwaves; Long Point, Lake Erie, Canada

Abstract

This paper describes the morphology and dynamics of features termed here “longshore sandwaves”, which are developed on a large barrier spit in the Great Lakes. The sandwaves are local beach protuberances with alongshore lengths of 500–2500 m and maximum widths at the downdrift end of 50–90 m, which migrate alongshore in the direction of net drift at 150–300 m yr−1. They have a lifespan of 10 yrs or more, and their spatial and temporal scales are an order of magnitude greater than the rhythmic topography associated with the nearshore bars and rip cells which are also characteristic of the littoral zone. The sandwaves are initiated by the onshore movement and welding of inner nearshore bars during nonstorm periods in areas of local sediment abundance. The alongshore movement of the sandwaves occurs through downdrift extension which is initiated by attachment of a landward-migrating nearshore bar to the downdrift end of the sandwave and subsequent infilling of the trough landward of the bar. The presence and movement of the sandwaves results in a complex spatial-temporal pattern of beach and dune erosion and accretion, with accretion occurring opposite the sandwave and erosion focused in the embayments between sandwaves.