Field and Laboratory Study of Storm Swash and Overwash Dynamics

摘要

Field studies at Assateague Island quantified the flux and frequency of overwash. Repeated surveys at several washovers revealed that storm generated overwash transports sand landward up to 100 m past the beach crest for storms characterized by 1 year return periods. Post-storm winds transport this material seaward, past the frontal dune line. Thus, overwash of this magnitude does not supply permanent sediment to the island interior or bay. Very large storms could transport sediment to the bay, but this is the exception at the study site. Laboratory and field studies show that backshore structures, e.g., dunes or seawalls, inhance the backwash, and thus beach erosion. In the case of dunes however, the dune erosion feeds the storm beach and thus offsets the erosion potential. A separate laboratory study demonstrated that heavy mineral washover laminations can be related to the depth and velocity of individual overwash surges. (Author)