EFFECTS OF DUNE RAMPS ON SEDIMENT SUPPLY TO COASTAL FOREDUNES:SKALLINGEN, SW DENMARK

摘要

This study was carried out to monitor the development of dune ramps on the windward side ofrnscarped coastal foredunes on a monthly time scale between two individual storm surges.rnAdditionally, aeolian sediment accretion was measured leeward the dune crest to compare accretionrnrates to the size of dune ramps and to establish a dune sediment budget. The field experiments werernconducted on Skallingen, a barrier spit in the Danish Wadden Sea, where prevailing and dominantrnwind directions are onshore. Wind tunnel experiments allowed various dune models shaped after thernerosional dunes found on Skallingen to be studied under constant flow conditions. Through thernstudy, it was found that the development of dune ramps on the windward side of vertical escarpmentsrnis characterized by a steady increase of ramp height and volume combined with a decrease of profilernconcavity due to infilling by aeolian processes. With onshore winds, a speed-up effect is present overrndune ramps as they almost extend up to the escarpment crest; otherwise the wind flow is slowedrndown. Speed-up of the airflow favors sediment transport, whereas a slow-down favors deposition. Arnnet annual sediment accretion of ~ 9 m3 m-1 was obtained leeward the dune crest, which is notrnsufficient to keep pace with dune erosion. As a result, the sediment budget of the Skallingen dunes isrnnegative and the sediment deficit is expected to become more pronounced in the near future due tornan accelerating rise of sea level combined with more frequent storm surges.