Rates of Landward Sand Transport over the Foredune at Skallingen, Denmark and the Role of Dune Ramps

Abstract

Landward migration of barriers occurs in response to a negative sediment budget and/or sea level rise. The ability of the foredune to migrate landward while maintaining its size is determined by the rate at which aeolian sediment transfers across the foredune take place. On the transgressive barrier spit Skallingen, sediment deposition on the crest and lee slope of the foredune was measured at two locations over the periods 1996–1999 and 2001–2002, respectively. Temporal and spatial variability of accretion rates occurred on different scales and annual accretion volumes up to 9 m3 per m beach width were obtained. In addition to the local sediment budget (i.e. beach width), the frequency and magnitude of storms and the pattern of wind speed and direction, the presence of a dune ramp is also important for the beach to dune sediment transfer. The study suggests that the critical ramp size for beach/dune sediment transfer corresponds to a ramp-to-crest distance of 1 m or a relative ramp height of 0.6. A conceptual model is presented which attempts to outline the controls on dune ramp development and the beach/dune sediment budget.