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Dauphin Island’s Contribution to Mississippi Barrier Islands

Often overlooked is the important and essential contribution that Dauphin Island makes to the four downdrift barrier islands in Mississippi (Petit Bois Island, Horn Island, Ship Island and Cat Island). Dauphin Island serves as the pathway for the westward sand movement to which all of the Mississippi barrier islands owe their existence and continued health.

The remnant higher elevation dunes and cores that decreasingly characterize the individual barrier islands provide evidence that sand supply was abundant in the geologic past1. However, conditions of surplus sands no longer exist and the present sand deficit is causing the barrier islands to erode.

The loss rates of island land over the last 150 years are substantially greater than for the previous several thousand years. This information indicates the land loss rates have become accelerated in recent times. The major mechanism contributing to the loss of land is attributed to unequal updrift erosion and downdrift deposition. In other words, more sand is being eroded updrift than is being deposited downdrift.

A second mechanism affecting the loss rates is island narrowing. The diminished state of the narrow portions of the islands like Dauphin Island’s West End make these areas especially vulnerable to overwash and breaching during storms and the resulting loss of sand from the island system.

The Mississippi barrier islands are uninhabited, owned by the federal government, and included in the Gulf Islands National Seashore that is managed by the U.S. National Park Service (NPS).  Dauphin Island is the only island in this barrier island chain which is excluded from the National Seashore designation because it is inhabited and privately owned.  Yet, from a functional standpoint, Dauphin Island provides the same contributions to the environment as does its sister islands in Mississippi.

The Mississippi barrier islands were extensively altered by Hurricane Katrina in 2005, in a manner similar to Dauphin Island.  However, since these lands are federally owned, they were recommended for restoration in the Mississippi Coastal Improvements Program (MsCIP) completed by the U.S. Army Corps of Engineers in 2009.  An attempt was unsuccessfully made to have Dauphin Island added to the MsCIP, due to a lack of support within Alabama’s Congressional delegation.  (Click here to see letters submitted by various agencies, governmental officials, and environmental organizations requesting that Dauphin Island be added to the MsCIP.)

These letters demonstrate the wide support that was received to correct the severe erosion issues affecting Dauphin Island. These letters are relevant to and are supportive of the basic concept to restore and stabilize Dauphin Island as a barrier island.

The Corps’ MsCIP report contained the following Vision Statement prepared by the National Park Service. This statement speaks to the historic role that Dauphin Island has played in the formation and development of the Mississippi Sound barrier islands in saying that:

“…by ‘capturing’ the sand that arrived from the Alabama mainland shore [i.e., the Fort Morgan Peninsula] through current and drift processes via the Mobile Bay ebb-tidal delta and steering it westward along its south shore, eastern Dauphin Island probably played an important role in originally determining the offshore position of the whole barrier island chain which extended well into southeastern Louisiana”.

Examination of historic maps shows that Petit Bois Island was actually created from Dauphin Island as a result of a major hurricane around 1900 that severed the connection between these two islands.  If mapping were available for pre-European history dating back to the last 7,000 to 10,000 years, the geologic relationship between Dauphin Island and the other barrier islands would be clear since the positions of all of the islands and their intervening passes have constantly migrated to the west, with new islands being periodically created by the effects of catastrophic hurricanes and other islands being eroded away.  The one constant variable has been the contribution of sand to the Mississippi islands from Dauphin Island through littoral drift processes.  The delivery of sand from Dauphin Island has always been critical to, and continues to be essential to, determining the physical configuration and geomorphological health of the downdrift Mississippi barrier islands.

Evidence of the significant effects that Dauphin Island’s coastal erosion problems are having on the downdrift Mississippi barrier islands is reflected in the MsCIP report’s recommendation to place 4,000,000 cubic yards of sand on the east end of Petit Bois Island – less than five miles to the west of Dauphin Island. The necessity of placing sand on the eastern end of Petit Bois Island is a direct result of the shortage of sand that is failing to be transported to the west from an ever-diminishing Dauphin Island.

Evidence of the importance that the U.S. Government places on restoring the Mississippi barrier islands is the Congress’s action in 2009 to appropriate $489 million (recent reports on National Public Radio put the figure at over 1 billion, perhaps due to some matching funds) in order to pump sand in the littoral zones as an extensive effort to nourish the islands. This will take place on Mississippi’s barrier islands while no similar action will be pursued on Dauphin Island even though it is suffering from the same coastal erosion issues.
 

1 Morton (2008)


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