FACTORS CONTROLLING THE SURVIVAL OF COASTAL DUNES DURING MULTIPLE HURRICANE IMPACTS IN 2004 AND 2005: NORTHWESTERN FLORIDA COAST

Coastal dunes along Florida's northern Gulf coast were impacted dramatically in September 2004 by Hurricane Ivan, and again in July 2005 during the passage of Hurricane Dennis. Both category 3 storms made landfall in the northeastern Gulf of Mexico, inducing inundation and overwash resulting in extensive erosion of the dune systems. This study examines the interactive factors controlling the survival of dunes along a 300-km stretch of impacted coastline. Florida's northern Gulf coast is low energy, wave dominated, and punctuated by: 1) a series of mainland beaches backed by Pleistocene-age and younger dunes and bluffs, and 2) a discontinuous series of Holocene-age barrier islands extensively populated with incipient and established dune systems. Dune distribution on the barriers is characterized by nearshore incipient foredune ridge systems, interior hummocky dune-fields, and populations of established dunes which dominate the bay-side regions. Spatial variations in dune response to the erosional events can be linked to storm impact regimes including from most to least severe, inundation, overwash, and collision. Within this range of impact regimes, dune preservation is largely governed by: 1) antecedent morphologic parameters including width of the barrier island, height and width of the dune-fields, vegetation type, distance between dunes and shoreline, and continuity of the dune-fields, and 2) temporally variable parameters including storm intensity, duration, and frequency. Overall, established dunes which dominate the bay-side shoreline exhibited the greatest preservation, while nearshore incipient dune systems, in many cases were completely destroyed.