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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 64 (1980)

Issue: 9. (September)

First Page: 1558

Last Page: 1558

Title: Effects of Hurricane Frederic on Morphology of Dauphin Island, Alabama: ABSTRACT

Author(s): Bob Gerdes

Article Type: Meeting abstract


Hurricane Frederic made landfall at Dauphin Island, Alabama, on September 12, 1979. With property damage estimates as high as $2 billion, Frederic represents the costliest natural disaster in United States history.

Most of the destruction caused by Frederic was due to winds up to 65 m/s (126 knots), storm-surge (3.1 m above mean sea-level) flooding, beach erosion, and overwash. The latter of these three factors was the most significant in terms of property damage.

Photographic overflights, ground surveys, and inspection of structures after the hurricane all led to the conclusion that damage was controlled by the following features: (1) nearshore bathymetry, (2) relative elevation of different parts of the island, (3) location and orientation of pre-storm canals and driveways, and (4) placement of house-support pilings.

The ebb-tidal delta of Mobile Pass dominates the nearshore bathymetry of eastern Dauphin Island. Extending several kilometers offshore, this delta platform produced shoaling and breaking of storm waves offshore, and thus spared the eastern part of the island from more intense wave attack. However, immediately west of the delta, wave refraction and focusing produced the highest beach retreat (40 m) of any place on the island.

Dauphin Island exhibits two distinct physiographic divisions. The eastern fifth of the island is composed of a Pleistocene core topped by high dunes, with elevations over 10 m. This area escaped much of the destruction of the storm, receiving only relatively minor wind damage. The western four-fifths of Dauphin Island consists of a low-lying Holocene spit, which was completely inundated by the passage of Frederic. The overwash of this part of the island resulted in damage to virtually every building and complete destruction of many.

Streets and canals which ran perpendicular to the beach on the Holocene spit served as initial passageways for storm-driven water. These areas developed into the major overwash channels and were responsible for the most intense property damage.

Numerous small overwash channels were found to have developed in the lee of house-support pilings. Presumably scour was enhanced by the turbulence of water flowing around such pilings. In areas of high building concentration, this effect was most pronounced and caused significant damage.

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