MORPHOLOGICAL AND SEDIMENTOLOGICAL IMPACTS OF HURRICANE IVAN AND IMMEDIATE POST-STORM RECOVERY ALONG THE NORTHWESTERN FLORIDA BARRIER-ISLAND COASTS

Ivan, a massive category 3 hurricane, caused widespread erosion and overwash along the northwestern Florida coast. This study examines the storm-induced morphological and sedimentological impact and immediate post-storm recovery along a 300-km coast through coring, trenching, ground-penetrating radar imaging, aerial photography, and pre- and post-storm beach-profile surveys.

Regional-scale inundation and overwash occurred within 100 km from the storm center at landfall. Significant beach/dune erosion was measured as far as 300 km to the east. The highest elevation of beach/dune erosion extended considerably above the measured surge level, indicating that storm-wave setup and swash runup played significant roles in controlling the elevation of beach erosion. A simple empirical formula re-produced the wave setup and swash runup reasonably well. Beach recovery began immediately after the storm. Within 90 days, the berm crest recovered to its pre-storm elevation, although located approximately 15 m landward for non-overwashed sites and 30 to 40 m for overwashed sites. The steep pre-storm foreshore slope was restored from the gentle storm-profile with 30 days.

Along the overwashed coast, erosional and depositional characteristics of washover deposits differ substantially in different barrier-island sub-environments, such as dune field, interior wetland, and back-barrier bay, controlled by the pre-storm elevation and accommodation space. Along the coast that was not substantially overwashed, an erosional surface was observed along the impacted foredune and backbeach. This erosional surface represents an elevation loss from 0.5 to over 2.0 m. A storm layer of up to 50-cm thick was deposited above the erosional surface. Generally, the storm-layer thickness decreases away from the storm center, and landward from the high tide line. Factors such as beach width and orientation, and sediment properties and supply caused variations in the thickness of storm deposit.