Aeolian sediment transport across beach wrack

This field study identifies the short-term (hours) effect of freshly deposited wrack on aeolian transport and surface elevation changes on the backshore and foredune of a barrier island at Avalon, New Jersey, USA. Storm wave uprush reached the dune toe on 21 October 2008 and deposited a line of vegetative wrack about 2 m wide (cross-shore) and 70 mm high near the dune toe (upper wrack) and a line about 0.3-0.5 m wide and 30 mm high about 5 m from the dune toe (lower wrack). Fourteen cylindrical sediment traps were deployed 23 October 2008 when the wind blew onshore at an angle of 8 deg to the trend of the dune. Wind speed at 1 m elevation at the dune toe averaged 6.3 m s ^-'1. The lower wrack line was nearly covered with sand about an hour after initiation of transport, diminishing its effect as a barrier to cross-shore transport. The upper wrack line caused greater reduction in trapping rates, with downwind traps collecting only 3.2% and 12.7% of upwind amounts. Data from erosion pins revealed the greatest scour just landward of the lower wrack line. More sand accumulated at the upper wrack line than within other cross-shore zones. The wrack low on the beach influences sand transport rate for a limited time and is readily removed by storm waves, whereas the uppermost wrack line lasts longer, traps more sand, influences the sediment budget of the existing foredune more directly, and forms the basis of the new foredune crest.