The structure and development of foredunes on a locally prograding coast: insights from ground-penetrating radar surveys, Norfolk, UK

The internal structure of coastal foredunes from three sites along the nort h Norfolk coast has been investigated using ground-penetrating radar (GPR), which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non-destructive or geophysical techni que. Combining geomorphological and geophysical investigations into the str ucture and morphology of these coastal foredunes has enabled a more accurat e determination of their development and evolution. The radar profiles show the internal structures, which include foreslope accretion, trough cut and fill, rollover and beach deposits. Foredune ridges contain large sets of l ow-angle cross-stratification from dune foreslope accretion with trough-sha ped structures from cut and fill on the crest and rearslope. Foreslope accr etion indicates sand supply from the beach to the foreslope, while troughs on the dune crest and rearslope are attributed to reworking by offshore win ds. Bounding surfaces between dunes are clearly resolved and reveal the rel ative chronology of dune emplacement. Radar sequence boundaries within dune s have been traced below the water-table passing into beach erosion surface s. These are believed to result from storm activity, which erodes the upper beach and dunes. In one example, at Brancaster, a dune scarp and erosion s urface may be correlated with erosion in the 1950s, possibly the 1953 storm . Results suggest that dune ridge development is intimately linked to chang es in the shoreline, with dune development associated with coastal prograda tion while dunes are eroded during storms and, where beaches are eroding, a stable coast provides more time for dune development, resulting in higher foredune ridges. A model for coastal dune evolution is presented, which ill ustrates stages of dune development in response to beach evolution and sand supply. In contrast to many other coastal dune fields where the prevailing wind is onshore, on the north Norfolk coast, the prevailing wind is direct ed along the coast and offshore, which reduces the landward migration of sa nd dunes.