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Processes controlling the retreat of the Isles Dernieres, a Louisiana barrier-island chain

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Abstract

The Isles Dernieres is a low-lying, transgressive barrier-island chain situated about 150 km west of the modern Mississippi delta. Much of the Isles Dernieres consists of highly dissected salt-marsh muds that lie at or slightly above sea level and are covered by a veneer of sand along the shoreline facing the Gulf of Mexico. Maximum berm elevations are generally less than 1.5 m above mean sea level. Since the mid-1800s, the initial island has been fragmented into four islands, and the beach face has retreated landward at a rate of more than 10 m/yr. The dominant processes controlling degradation of the chain are cold fronts that pass through the area several times each year and occasional hurricanes. Beach surveys over a 2-year period on the Isles Dernieres document irreversible beach-face retreat in conjunction with multiple cold fronts and one major hurricane (Gilbert). Although both the hurricane and the cold fronts caused the island to erode, the erosional patterns of the two storm types differed from each other. During the two years, over 60 cold fronts collectively caused about 37 m of beach-face retreat, whereas Gilbert itself produced more than 40 m of retreat. A major difference between the two storm types was in the percentage of washover sand produced by each. Commonly, the cold fronts did not create enough of a storm surge to overtop the berm, so most of the material removed from the beach face must have moved offshore or alongshore. Gilbert, in contrast, inundated the study site, and essentially all the sand removed from the beach face moved to the backshore.

Additional Publication Details

Publication type:
Conference Paper
Publication Subtype:
Conference Paper
Title:
Processes controlling the retreat of the Isles Dernieres, a Louisiana barrier-island chain
ISBN:
0872628086
Year Published:
1991
Language:
English
Publisher:
Publ by ASCE
Publisher location:
New York, NY, United States
Larger Work Title:
Coastal Sediments '91
First page:
1111
Last page:
1121
Number of Pages:
11
Conference Title:
Proceedings of a Specialty Conference on Quantitative Approaches to Coastal Sediment Processes
Conference Location:
Seattle, WA, USA
Conference Date:
25 June 1991 through 27 June 1991