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Coastal & Marine Geology Program > Coastal Classification Mapping Project > Open File Report 2005-1151

Coastal Classification Atlas

Alabama-Mississippi Coastal Classification Maps - Perdido Pass to Cat Island

USGS Open File Report 2005-1151

Robert A. Morton, Russell L. Peterson

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Classification Summary

The coastal classification maps provide a basis for establishing the lengths of shore that have a particular morphological characteristic or cultural attribute. Such information is relevant for local and state governments for planning that involves the amount of shore that is developed versus undeveloped, or the amount of parkland held in the public trust. Also there is interest regarding the amount of shore that is affected by engineering structures, referred to as armoring or hardening of the shore. Environmental protection and resource management issues such as these require quantitative data that can be derived from the classification maps.

The shore lengths and equivalent percents of the 131 km segment of coast between Perdido Pass and Cat Island are presented for each classification unit in Table 2. Sixty seven percent of this coastal segment is undeveloped, and where it is developed, the development is mostly moderate to high density (Table 2). Single family homes are more common than multi-family units such as high-rise condominiums and hotels, and 46% of the shore is classified as parks, including the Gulf Islands National Seashore in Mississippi (Table 2). Dunes are absent along 28% of the shore and only about 16% of the shore has either continuous or discontinuous dunes. An overwash terrace is present along 55% of the shore (Table 2). Sixty three percent of the shore is characterized by natural beaches more than 30 m wide or there is a protective exposed bar for approximately 3% of the shore (Table 2). Because the beaches are wide and mostly undeveloped, there is little need to maintain the beaches (14%, Table 2). Areas of complete storm overwash represent about 23% of the shore (Table 2). The overwash zones are concentrated along Bon Secour Bay and west Dauphin Island in Alabama and east Petit Bois Island, east Horn Island, and Ship Island in Mississippi. Less than 6% of the shore is influenced by hard structures (Table 2); most of the structures are walls built in the backbeach area.

Table 2. Lengths of shore and percentages for the classification units mapped between Perdido and Cat Island. Total length of this coastal segment is about 131 km.
Category Classification Length (km) Percent Pie Chart
Washover Overwash 30.0 23 Overwash pie chart - overwash 23%, no overwash 77%
Closed inlet 0.0 0
New Inlet 0.0 0
No overwash 100.8 77
Dunes Absent 37.0 28 Dune Presence pie chart - absent 28%, overwash terrace w/ ridge 3%, continuous 6%, discontinuous 10%, overwash terrace 53%
Continuous 8.4 6
Discontinuous 13.4 10
Overwash terrace 68.6 53
Overwash terrace/ridge 3.3 3
Beach width > 30 m natural 65.4 50 Beach width pie chart - exposed bar 3%, greater than 30 m maintained 13%; greater than 30 m natural 50%, less than 30 m aintained 1%, less than 30 m natural 33%
> 30 m maintained 16.5 13
< 30 m natural 42.9 33
< 30 m maintained 1.5 1
exposed bar 4.5 3
Structures No structure 123.4 94 Structures pie chart - multiple structures less than 1%, groin less than 1%, riprap less than 1%, wall 5%, no structure 94%
Wall 6.5 5
Riprap 0.1 <1
Groins 0.3 <1
Multiple structures 0.6 <1
Development Density Undeveloped 87.7 67 Density of development pie chart - high density 13%, moderate density 14%, low density 6%, undeveloped 67%
Low density 8.0 6
Moderate density 18.6 14
High density 16.5 13
Dwelling Type No dwelling 29.7 23 Dwelling type pie chart - mixed 3%, single family 21%, no dwelling 23%, park 46%, multiple units 7%
Single family 27.6 21
Mixed 3.3 3
Multi-unit 9.3 7
Park 60.9 46

Coastal & Marine Geology Program > Coastal Classification Mapping Project > Open File Report 2005-1151

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