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Numerical Modeling Of Atoll Island Hydrogeology

机译：环礁岛水文地质学数值模拟

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We implemented Ayers and Vachers' (1986) inclusive conceptual model for atoll island aquifers in a comprehensive numerical modeling study to evaluate the response of the fresh water lens to selected controlling climatic and geologic variables. Climatic factors include both constant and time-varying recharge rates, with particular attention paid to the effects of El Nino and the associated drought it brings to the western Pacific. Geologic factors include island width; hydraulic conductivity of the uppermost Holocene-age aquifer, which contains the fresh water lens; the depth to the contact with the underlying, and much more conductive, Pleistocene karst aquifer, which transmits tidal signals to the base of the lens; and the presence or absence of a semiconfining reef flat plate on the ocean side. Sensitivity analyses of steady-steady simulations show that lens thickness is most strongly sensitive to the depth to the Holocene-Pleistocene contact and to the hydraulic conductivity of the Holocene aquifer, respectively. Comparisons between modeling results and published observations of atoll island lens thicknesses suggest a hydraulic conductivity of approximately 50 m/d for leeward islands and approximately 400 m/d for windward islands. Results of transient simulations show that lens thickness fluctuations during average seasonal conditions and El Nino events are quite sensitive to island width, recharge rate, and hydraulic conductivity of the Holocene aquifer. In general, the depletion of the lens during drought conditions is most drastic for small, windward islands. Simulation results suggest that recovery from a 6-month drought requires about 1.5 years.
机译：在全面的数值模型研究中，我们实施了环礁岛含水层的Ayers and Vachers（1986）包容性概念模型，以评估淡水镜对选定的控制气候和地质变量的响应。气候因素包括恒定的补给率和时变的补给率，尤其要注意厄尔尼诺现象的影响及其带来的西太平洋干旱。地质因素包括岛屿宽度；全新世时代最含水层的水力传导率，其中包含淡水晶状体；与下面的，导电性更高的下新世喀斯特含水层接触的深度，该潮汐将潮汐信号传输到晶状体的底部；并且在海洋一侧是否存在半密闭的礁石平板。稳态模拟的敏感性分析表明，透镜厚度分别对全新世-更新世接触的深度和全新世含水层的水力传导率最敏感。建模结果与已发表的环礁岛透镜厚度观测值之间的比较表明，背风岛的水力传导率约为50 m / d，迎风岛的水力传导率约为400 m / d。瞬态模拟的结果表明，在平均季节条件和厄尔尼诺现象期间，镜片厚度波动对全新世含水层的岛宽，补给率和水力传导率非常敏感。通常，在干旱的小岛上，干旱条件下晶状体的枯竭最为严重。模拟结果表明，从6个月的干旱中恢复大约需要1.5年。

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