海水入侵的行為主要受含水層參數的異質性、含水層形貌、潮汐、含水層飽和度以及雨量等因素的控制，為了量化上述參數於沿岸地區對海淡水交界面之影響，本研究使用FEMWATER模式，利用蒙地卡羅法配合Geostatistical Software Library (GSLIB)中的Sequential Gaussian Simulation (SGSIM)隨機場生成器，模擬垂直二維沿岸含水層之海水入侵情形。本研究之模擬區域為一長度400公尺，深度100公尺之沿岸含水層。模式中含水層的水力傳導係數空間分布係由GSLIB中的SGSIM所產生。本研究先討論在不同含水層異質性情況下(包括σ_ln⁡K^2 =0.1、0.5、1.0及1.5，其中σ_ln⁡K^2為對數水力傳導係數變異數)之海水濃度不確定性分布，藉著對海淡水交介面的定義，以0.1g/L海水濃度之分布決定海淡水交界面之不確定性寬度；除了分析含水層異質性對於海淡水交界面之不確定性寬度外，本研究亦考慮五種含水層水文地質條件(含水層飽和及非飽和條件、潮汐變化條件、降雨補注及含地形坡度之含水層)對海淡水交界面不確定性寬度之影響。模擬結果指出含水層中水力傳導係數的分布會對含水層中的水流造成變異，並進而影響海水濃度的分布，範圍可達數十公尺；模擬結果亦表明含水層地形及含水層飽和度會對海淡水交界面的型態有很大的影響，而潮汐水位變化及降雨雨量對於海淡水交界面的影響並不明顯。

The behavior of Seawater intrusion in coastal aquifers is controlled mainly by the aquifer heterogeneity and the natural complexity of aquifer systems such as aquifer geometries, tidal fluctuation, aquifer saturation, and recharges of the aquifer. To systemically quantify such effects on the seawater-freshwater interface in coastal aquifers, this study employs the FEMWATER numerical model, combining Monte Carlo Simulation and Sequential Gaussian Simulation (SGSIM) random field generator, which built in Geostatistical Software Library (GSLIB), to simulate the two-dimensional seawater intrusion procedures in estuary aquifers. A profile estuary aquifer with 400m in length and 100m in depth is considered in the illustrated examples. The hydraulic conductivity fields of the aquifer are generated by SGSIM. Monte Carlo simulations with different degrees of aquifer heterogeneity, including lnK variance= 0.1, 0.5, 1.0, and 1.5, are used to obtain the concentration variation of the seawater-freshwater interfaces. The uncertainty bandwidths of seawater-freshwater interfaces can be obtained based on the defined seawater-freshwater interface of 0.1g/L. Besides the effects of different degrees of aquifer heterogeneity, this study also discusses the influence of five coastal aquifer scenarios (saturated aquifer, unsaturated aquifer, tidal aquifer, recharged aquifer and sloping aquifer) on the uncertainty bandwidths. Simulation results show that the spatial variation of hydraulic conductivity can propagate to flow uncertainties and then change the distributions of saltwater concentration significantly in saturated estuary aquifers. With different degrees of aquifer heterogeneity, the distances of the seawater/ freshwater interfaces vary from meters to tens of meters. Simulation results also show that aquifer geometries and aquifer saturation have significant impact on the patterns of seawater-freshwater interfaces. However, the recharge, and the fluctuation of tidal boundaries have relatively small influence on the variation of seawater-freshwater interfaces.

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