Coastal Barriers - Nomenclature, Processes, and Classification Issues

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Coastal Sciences, Gulf Coast Research Laboratory


Ocean Science and Engineering


The designation "coastal barrier", related terms and their varied interpretations, and critical concepts in coastal plain and nearshore geology, underwent numerous reincarnations over the years. This designation was first applied to shore-parallel sand and gravel-built ocean-front islands and spits that separate open marine environments from paralic inshore environments that they shelter. A more recently recognized third category includes mainland strandplain, chenier, and dunefield barriers, either as original components of mainland coasts or subsequently welded to the coastal plain. A parallel but closely related terminology, developed mostly in Australia and Brazil, identifies several specific process categories recognizable in the three basic barrier groups. In the absence of lagoons and tidal wetlands, shore ridges that front and are contiguous with the mainland coastal plain have been mistakenly assigned to the barrier island category. Greatly diminished wave energy and consequently minor littoral drift volumes account for the relative rarity and much smaller dimensions of prograded landforms in estuarine islands and bay shore beaches in paralicinshore basins. Due to wave and related littoral drift processes, however diminished in comparison with open marine shores, morphological similarities between aggraded landforms of open marine through estuarine settings are to be expected. However, the multitude of proposed "fetch-limited", diminished wave energy estuarine islands, characterized by diminutive narrow beaches, sand spits, even occasional small dunes, and miniature strandplains, lack the essential functional attributes intrinsic to true barrier islands. While barrier islands may form even on relatively low wave energy and/or sediment-deficient marine shores, the term is inappropriate for islands located in low-energy paralic basins, including estuaries, or in coastal plains where frontal shore ridges are not backed by lagoons. Landforms erroneously ascribed in a variety of facies settings as barrier islands or islands frequently are mainland-attached beach ridge plains or beach-fringed marshlands instead. Narrow marshland beaches and mainland strandplain barriers are segmented into short islands by intervening narrow tidal creeks, fluvial distributary channels, or storm cuts that separate them. Improved fundamental and functional definitions of barrier islands, their comparison with the many genetic categories of islands and mainland shore beaches found in estuarine basins and wetlands should lead to a better understanding of paralic island evolution processes on the global scale. (C) 2011 Elsevier B.V. All rights reserved.

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