Dune and shoreline evolution of western Santa Rosa Island, Florida, 1973-2013.

摘要

The foredunes at twenty locations on Santa Rosa Island, Florida have been eroded to varying degree in response to Hurricanes Opal (1995), Ivan (2004) and Dennis (2005). At locations where pre-storm foredunes were high and the island was relatively wide, less coastal erosion occurred as a result of storm surge and high winds. For the western portions of Santa Rosa Island Hurricane Ivan had a greater effect on the volume of foredunes and backshore sand than did Hurricane Opal. More erosion is believed to have occurred during Hurricane Ivan because precursor erosion associated with Hurricane Opal, creating a more vulnerable setting for intense erosion during Hurricane Ivan. During calm conditions, foredunes accrete and migrate inland or prograde depending on shoreline position. In locations where a dune was not completely destroyed by storm surge from a hurricane event, the recovery rate was initially rapid, on the order of 1 ft of dune aggradation per year. In locations where the dunes were completely destroyed due to storm-surge, the recovery rate was much slower, on the order of 0.33 ft of dune aggradation per year. During the time period covered by this study (1973-2013), the foredunes migrated inland seemingly in step with the retreating shoreline. Santa Rosa Island experienced net volume loss of foredune and backshore sediment as well as a net shoreline retreat. Net volume loss of the foredunes and backshore was calculated at seventeen of the twenty locations where profiles were quantified. The greatest volume loss was approximately 58 ft3/ yr per lateral meter. The western portion of the island was the exception where net volume gain occurred at a rate of approximately 104 ft3/ yr per lateral meter. The shoreline retreated at varying degrees at all twenty locations. The most rapid shoreline retreat was approximately 8 ft/yr and the slowest rate was approximately 0.75ft/yr. During the 40-year time period covered in this study, central and western Santa Rosa Island experienced net shoreline retreat and a moderate net volume loss of sand on the backshore and foredunes, similar to results found in previous studies in the Northeast Gulf of Mexico. The retreat is associated with hurricane events that are followed by a limited recovery of the shoreline.