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Diffuse versus conduit flow in coastal karst aquifers; the consequences of island area and perimeter relationships

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doi: 10.3390/geosciences8070268
Authors:Larson, Erik B.; Mylroie, John E.
Author Affiliations:Primary:
Shawnee State University, Department of Natural Sciences, Portsmouth, OH, United States
Other:
Mississippi State University, United States
Volume Title:Geosciences (Basel)
Source:Geosciences (Basel), Vol.8, 25p. Publisher: MDPI, Basel, Switzerland. ISSN: 2076-3263
Publication Date:2018
Note:In English. 38 refs.; illus., incl. sketch maps, 1 table, sects.
Summary:The majority of limestone islands are made of eogenetic carbonate rock, with intrinsic high porosity and permeability. The freshwater lenses of small islands are dominated by diffuse flow regimes as the island perimeter is everywhere close to the meteoric catchment of the island interior. This flow regime produces flank margin caves at the lens margin, where dissolution is enhanced by mixing corrosion, superposition of organic decay horizons and higher flow velocities as the lens thins. The lens interior develops touching-vug flow systems that result in enhanced permeability and lens thinning over time. As islands become larger, the area (meteoric catchment) goes up by the square, but the island perimeter (discharge zone) goes up linearly; diffuse flow becomes inefficient; conduit flow develops to produce traditional epigenic cave systems that discharge the freshwater lens by specific turbulent flow routes, which in turn are fed by diffuse flow in the island interior. Locally, diffuse flow to the island perimeter continues in coastal proximal areas between major conduit flow routes to produce flank margin caves. The Bahamian Archipelago represents a case history in which tectonics is limited, the rocks are entirely eogenetic and the diffuse to conduit flow transition is demonstrated.
Subjects:Aquifers; Atmospheric precipitation; Carbonate rocks; Carbonates; Catchment hydrodynamics; Caves; Diffusion; Flows; Ground water; Hydrodynamics; Hydrology; Islands; Karst; Limestone; Permeability; Porosity; Sedimentary rocks; Bahamas; Caribbean region; West Indies
Coordinates:N204500 N280000 W0720000 W0793000
Record ID:839255-17
Copyright Information:GeoRef, Copyright 2020 American Geosciences Institute.
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100 1 |a Larson, Erik B.  |e analytic author  |u Shawnee State University, Department of Natural Sciences, Portsmouth, OH 
245 1 0 |a Diffuse versus conduit flow in coastal karst aquifers; the consequences of island area and perimeter relationships 
300 |a 25 p. 
500 |a In English. 38 refs. 
500 |a Affiliation: Shawnee State University, Department of Natural Sciences; Portsmouth, OH; USA; United States 
500 |a Affiliation: Mississippi State University; ; USA; United States 
500 |a Key title: Geosciences (Basel) 
500 |a Source note: Geosciences (Basel), Vol.8, 25p. Publisher: MDPI, Basel, Switzerland. ISSN: 2076-3263 
500 |a Publication type: journal article 
504 |b 38 refs. 
506 0 |a Open access 
510 3 |a GeoRef, Copyright 2020 American Geosciences Institute. 
520 |a The majority of limestone islands are made of eogenetic carbonate rock, with intrinsic high porosity and permeability. The freshwater lenses of small islands are dominated by diffuse flow regimes as the island perimeter is everywhere close to the meteoric catchment of the island interior. This flow regime produces flank margin caves at the lens margin, where dissolution is enhanced by mixing corrosion, superposition of organic decay horizons and higher flow velocities as the lens thins. The lens interior develops touching-vug flow systems that result in enhanced permeability and lens thinning over time. As islands become larger, the area (meteoric catchment) goes up by the square, but the island perimeter (discharge zone) goes up linearly; diffuse flow becomes inefficient; conduit flow develops to produce traditional epigenic cave systems that discharge the freshwater lens by specific turbulent flow routes, which in turn are fed by diffuse flow in the island interior. Locally, diffuse flow to the island perimeter continues in coastal proximal areas between major conduit flow routes to produce flank margin caves. The Bahamian Archipelago represents a case history in which tectonics is limited, the rocks are entirely eogenetic and the diffuse to conduit flow transition is demonstrated. 
650 7 |a Aquifers  |2 georeft 
650 7 |a Atmospheric precipitation  |2 georeft 
650 7 |a Carbonate rocks  |2 georeft 
650 7 |a Carbonates  |2 georeft 
650 7 |a Catchment hydrodynamics  |2 georeft 
650 7 |a Caves  |2 georeft 
650 7 |a Diffusion  |2 georeft 
650 7 |a Flows  |2 georeft 
650 7 |a Ground water  |2 georeft 
650 7 |a Hydrodynamics  |2 georeft 
650 7 |a Hydrology  |2 georeft 
650 7 |a Islands  |2 georeft 
650 7 |a Karst  |2 georeft 
650 7 |a Limestone  |2 georeft 
650 7 |a Permeability  |2 georeft 
650 7 |a Porosity  |2 georeft 
650 7 |a Sedimentary rocks  |2 georeft 
651 7 |a Bahamas  |2 georeft 
651 7 |a Caribbean region  |2 georeft 
651 7 |a West Indies  |2 georeft 
700 1 |a Mylroie, John E.,  |e analytic author  |u Mississippi State University 
773 0 |t Geosciences (Basel)  |d Basel : MDPI, 2018  |x 2076-3263  |y GBSEDA  |n Geosciences (Basel), Vol.8, 25p. Publisher: MDPI, Basel, Switzerland. ISSN: 2076-3263 Publication type: journal article  |g Vol. 8  |h illus., incl. sketch maps, 1 table, sects. 
856 |u urn:doi: 10.3390/geosciences8070268