A Mathematical Model Study of Fresh‐Water Lenses

Chidley, T.R.E.; Lloyd, John William

doi:10.1111/j.1745-6584.1977.tb03166.x

Cited by 22 publications

(8 citation statements)

References 2 publications

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“…With the rising sea level, all the fissures would at some time be present on the edge of a freshwater lens where the rate of solution is relatively great. This solution rate is caused by enhanced water velocity (Chidley & Lloyd, 1977) and undersaturation of aragonite and calcite in the mixing zone of fresh and saline waters resulting from bacterially derived H 2 SO 4 that lowers the pH (Smart, Dawans & Whitaker, 1988).…”

Section: Formation Of the Tytherington Fissuresmentioning

confidence: 99%

The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK

Whiteside

Marshall

2007

Geol. Mag.

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Important vertebrate faunas occur in fissure deposits of Late Triassic-Jurassic age in SW Britain. Although the faunas are well described, their age and palaeoenvironment remain poorly understood. One such fissure system was documented in detail during quarrying operations at Tytherington and has yielded in situ palynomorphs that add much information concerning its age and palaeoenvironment. Significantly, the Tytherington fauna is of the sauropsid type that has generally been dated as Norian or pre-Penarth Group transgression and was also regarded as representing a distinct upland fauna. The palynomorphs, which include a significant marine component, demonstrate that the Tytherington Triassic fissures are infilled with Late Triassic (Rhaetian) sediments that match specific levels in the Westbury Formation. In addition, many of the Tytherington solutional fissures probably formed during the Rhaetian and are consistent with a fluctuating saline to freshwater environment. There is no prima facie evidence of solutional formation and infilling of the reptilebearing deposits before the Rhaetian trangression. The fissure reptile fauna, which includes the early dinosaur Thecodontosaurus, inhabited a small fire-swept limestone island in the Rhaetian sea. The features of the herpetofauna are entirely consistent with this island model which has Quaternary analogues.

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Section: Formation Of the Tytherington Fissuresmentioning

confidence: 99%

The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK

Whiteside

Marshall

2007

Geol. Mag.

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“…Few modeling investigations, however, have dealt realistically with atoll and small oceanic island groundwater systems, which commonly are comprised of a thin freshwater lens overlying a much thicker zone of mixed water. Instead, most numerical modeling studies of insular systems [Fetter, 1972;Lam, 1974;Anderson, 1976;Chidley and Lloyd, 1977;Falkland, 1983;Ayers and Vacher, 1983; Herman and Wheatcraft, 1984] assume a sharp freshwatersaltwater interface and/or do not take into account densitydependent flow. Pertinent features of previous modeling studies of atolls and small islands are summarized in Table 1. Of these, only the investigations by Hogan, 1988;Oberdorfer et al, 1990;Griggs, 1989;Griggs and Peterson, 1989 consider density-dependent flow, which Griggs [1989] and Griggs and Peterson [1989] have conclusively demonstrated must be considered when studying many aspects of the flow dynamics of atolls and small islands.…”

Section: In Addition They Allow Simulation Of Transient Solutions Fmentioning

confidence: 99%

Groundwater lens dynamics of Atoll Islands

Underwood¹,

Peterson²,

Voss³

1992

Water Resources Research

150

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A variable‐density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens, the structure of the transition zone, and the propagation of tidal fluctuations in a two‐layer atoll island groundwater system. Modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge‐discharge path of flow. The controls on the amount of mixing are: (1) the accumulated vertical distance, which increases with tidal range and is restricted by vertical permeabilities, and (2) vertical longitudinal dispersion. Comparison of cross‐sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven, vertical mixing processes. Although the tidal model has high computational requirements, it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations, hydrologic events, and hydrologic processes. The limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low.

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“…The above equation uses constant transmissivities, however, using the Ghyben-Herzberg approximation the transmissivities vary with the height of the water table so that the method adopted by Chidley and Lloyd (1977) for lens simulation was used in that…”

Section: Ground Water Modeling Approachmentioning

confidence: 99%

A GROUND WATER RESOURCES STUDY OF A PACIFIC OCEAN ATOLL ‐ TARAWA, GILBERT ISLANDS¹

Lloyd

Miles

Chessman

et al. 1980

J American Water Resour Assoc

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The geology and fresh ground water lens development in a typical Pacific atoll are described together with a method for hydrogeological investigation. The fresh water resources of such lenses are investigated using Tarawa as an example. It is shown that simple steady state solutions cannot be realistically applied, and that despite the paucity of hydrogeological data, which is considered typical of such islands, practical nonsteady state solutions allow resource assessments. The susceptability of lens resources to drought conditions is demonstrated.

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A Mathematical Model Study of Fresh‐Water Lenses

Cited by 22 publications

References 2 publications

The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK

The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK

Groundwater lens dynamics of Atoll Islands

A GROUND WATER RESOURCES STUDY OF A PACIFIC OCEAN ATOLL ‐ TARAWA, GILBERT ISLANDS¹

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A Mathematical Model Study of Fresh‐Water Lenses

Cited by 22 publications

References 2 publications

The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK

The age, fauna and palaeoenvironment of the Late Triassic fissure deposits of Tytherington, South Gloucestershire, UK

Groundwater lens dynamics of Atoll Islands

A GROUND WATER RESOURCES STUDY OF A PACIFIC OCEAN ATOLL ‐ TARAWA, GILBERT ISLANDS1

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A GROUND WATER RESOURCES STUDY OF A PACIFIC OCEAN ATOLL ‐ TARAWA, GILBERT ISLANDS¹