Abstract:
Coastal barriers are particularly susceptible to the predicted effects of
accelerated of sea-level rise and the potential for increased impacts of intense storms.
Over centennial scales, barriers are maintained via overtopping during storms, causing
deposition of washover fans on their landward sides. This study examines three
washover fans on the south shore of Martha’s Vineyard using a suite of data including
vibracores, ground penetrating radar, high resolution dGPS, and LiDAR data. From these
data, the volumes of the deposits were determined and range from 2.1—2.4 x 104 m3.
Two overwashes occurred during Hurricane Bob in 1991. The water levels produced by
this storm have a return interval of ~28 years, resulting in an onshore sediment flux of
2.4—3.4 m3/m/yr. The third washover was deposited by a nor’easter in January 1997,
which has a water level return interval of ~6 years, resulting in a flux of 8.5 m3/m/yr.
These fluxes are smaller than the flux of sediment needed to maintain a geometrically
stable barrier estimated from shoreline retreat rates, suggesting that the barrier is not
in long-term equilibrium, a result supported by the thinning of the barrier over this time
interval.
