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Amsterdam: Elsevier. Non-traditional settlement patterns and typhoon hazard on contemporary Majuro Atoll, Republic of the Marshall Islands. Transforming Cultures eJournal , 1 2 , 44 — Groundwater Investigations Report for N. Comte et al. Modelling the response of fresh groundwater to climate and vegetation changes in coral islands. Hydrogeology Journal , 22, — Wallace and Bailey Wallace, C. Geohydrologic factors governing atoll island groundwater resources.
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Journal Hydrol Engineering , 22, Studies employing numerical models, however, can be exceedingly time consuming, and often can only be understood and run by those involved directly in the project. There is a need for a simple method to estimate lens volume that can, first, provide estimates of lens volume rapidly yet accurately; and second, be employed more broadly by island water resources managers.
The methodology is presented, followed by application and testing for nine atoll islands in both the western Indian Ocean Republic of Maldives and the western Pacific Ocean Federated States of Micronesia. An uncertainty analysis of model input parameters also is presented and discussed. This paper also seeks to establish the generality of the method by application to islands in two separate geographical regions.
For the second objective, the model is used to establish relationships between lens thickness and lens volume, with the resulting volume curve to be used to determine available volume of fresh groundwater if the lens thickness is measured, analogous to a stage—discharge rating curve for surface water hydrology. Lens thickness can be measured using drilling methods or geophysical methods such as electromagnetic profiling.
Estimating the ground water resources of atoll islands. Water , 2, 1 — Model assumptions and limitations will also be discussed. The method has been used previously Bailey et al. Estimating current and future groundwater resources of the maldives. Journal of the American Water Resources Association. Atoll island hydrology.
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Ground Water , 19 3 , — Impacts of eustasy and hydro-eustasy on the evolution and landforms of Pacific atolls. Palaeogeography, Palaeoclimatology, Palaeoecology , , — Hydrogeology of an atoll island: A conceptual model from detailed study of a Micronesian example. Ground Water , 24, 2 — The limestone aquifer is 1—2 times more conductive than the sand aquifer, leading to rapid mixing of any freshwater within the limestone aquifer with seawater Hunt Hunt, C. Hydrogeology of Diego Garcia. Developments in sedimentology Introduction: varieties of carbonate islands and a historical perspective.
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Geology and Hydrogeology of Carbonate Islands. Method for estimating available groundwater volume of small coral islands All authors Ryan T. The distances w i between points along the cross-section to calculate the freshwater lens area are shown. The village on Mogmog is located along the southern coastal area.
Figure 1. The algebraic model for atoll island groundwater resources was first presented by Bailey et al. The algebraic model is based on results from a suite of two-dimensional 2D vertical cross-section modelling simulations Bailey et al. Numerical modeling of atoll island hydrogeology. Ground Water , 47, — The modelling simulations varied recharge rates 1. The presence of the semi-confining reef plate was also included Bailey et al.
The exponential trend line defining the relationship between recharge rate and Z MAX is used as the basis of the algebraic model, with factors included for K Hol and the influence of the reef flat plate: 1. Values of b and C as a function of island width and of S as a function of both island width and K Hol are presented in Bailey et al.
Geology and hydrogeology of carbonate islands -- Vacher, Leonard H.L. -ѕ©¶«ФД¶Б-ФЪПЯФД¶Б
The algebraic model captures the relationship between Z MAX and island parameters, i. The model has been tested successfully against observed lens thicknesses for islands in the Federated States of Micronesia FSM Bailey et al. Estimating the freshwater lens thickness of atoll islands in the Federated States of Micronesia. Hydrogeology Journal , 21 2 , — Estimating the impact of drought on groundwater resources of the Marshall Islands.
Water , 9 These values were found from comparison of numerical modelling results with observed lens thickness Bailey et al. The same procedure was used for the Marshall Islands, since their geographical location is similar to that of the FSM. The volume of extractable groundwater for an atoll island freshwater lens V lens m 3 is calculated by estimating the area of the freshwater lens for a set of cross-sections along the length of the island, and then summing the volume of the lens between cross-sections using trapezoidal geometry: 3.
Geology and hydrogeology of carbonate islands, Volume 54
The lens thickness z at each point is estimated using the freshwater lens algebraic model of Equation 1 multiplied by a factor that accounts for the shape of the lens along the cross-section. A total of 20 points are used to delineate the shape of the lens for each cross-section.
The terms in Equations 3 and 4 are shown within the island geological setting in Figure 1 for Mogmog Island, an atoll island on Ulithi Atoll Fig. The cross-sections used to delineate the island surface geometry are shown on Figure 1 d , with each cross-section separated by a distance L i see Equation 3.
The delineation of the freshwater lens area A for each cross-section is shown in Figure 1 a , with each point separated by a distance w i see Equation 4. The cross-sections in Figure 1 d are numbered, with a total of nine cross-sections used to delineate the island surface. The complete set of calculations to estimate V lens is contained in Table 1. The surface area m 2 between each cross-section is calculated, followed by the lens area A and V lens between each cross-section.
The total surface area is 0. There is no observed V lens for Mogmog for comparison. Testing of the method is described in Sections 3. The algebraic model assumes a homogeneous, isotropic aquifer along an island cross-section. If spatial variation of K Hol along the length of an island is known, a different value can be assigned to each cross-section.