--> ABSTRACT: Storm-Related Rejuvenation of a Northern Gulf of Mexico Estuary, by Wayne C. Isphording, F. Dewayne Imsand, and George C. Flowers; #91042 (2010)

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Storm-Related Rejuvenation of a Northern Gulf of Mexico Estuary

Wayne C. Isphording, F. Dewayne Imsand, George C. Flowers

One of several generalizations regarding the longevity of a typical estuary is that it will, ultimately, be destroyed by infilling. Although many estuaries may have had this fate, natural events commonly intervene to prolong the existence of the site. For example, any rise of sea level will extend its existence, as will a decrease in the quantity of sediment being supplied to the estuary by rivers emptying into the basin. These phenomena operate over centuries, at the minimum. One natural event that can duplicate the action of these long-term phenomena in a matter of hours, however, is the tropical cyclone. Although it has long been known that hurricanes have the power for markedly altering areas exposed above sea level, information is now available to demonstrate that th y are similarly effective in causing submarine erosion, and can scour and remove enormous quantities of sediment, even from well-protected estuaries.

Apalachicola Bay, Florida, is one of the larger estuaries in the northern Gulf of Mexico, and has one of the highest sedimentation rates of any estuary in the eastern United States. The massive influx of sediment from the Apalachicola River system has built an extensive delta system at the river's mouth and, in the vicinity of the delta, sedimentation rates of 10 mm/year have been measured. Analysis of bathymetric data dating back to the mid-1800s disclosed that the bay has been undergoing exceptionally rapid infilling that is still persisting.

The passage of two hurricanes near the bay in 1985, however, generated high-velocity currents that scoured about 3.6 billion ft3 of sediment from the bottom of the bay, completely changing the character of the texture of the bottom sediments and their mineralogy and heavy metal chemistry. Even more remarkable, perhaps, is the fact that over 83 million tons of sediment was carried by the currents out through one of the passes into the Gulf of Mexico. The removal of this quantity of sediment has thus returned the bay to bathymetric conditions existing in the early 1800s and has significantly extended the life of the bay.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.