珊瑚岛礁淡水透镜体三维数值模拟研究

Three-dimensional numerical simulation of freshwater len in coral islands

淡水透镜体是珊瑚岛礁上宝贵的淡水资源。为准确模拟淡水透镜体的动力学特性及其受降雨的影响,构建了西沙永兴岛淡水透镜体三维数学模型。根据试验和现场勘测获得的水文地质参数,运用有限差分法和VisualModflow对模型进行数值求解,获得了透镜体内淡水流向、水头分布、过渡带厚度与淡水贮量的季节变化。计算结果表明,以氯离子浓度600mg/L等值面为透镜体的包络面,永兴岛淡水透镜体最大厚度为16.9m,最大厚度处过渡带厚度为8.3m。透镜体淡水贮量4月最小、9月最大,9月淡水贮量较4月多8.5%。与降雨量变化相比,淡水贮量变化滞后1～2个月。本项成果可用于制定淡水透镜体的开采策略,为实现珊瑚岛地下淡水资源的持续开发利用提供参考。

Freshwater lens is the precious freshwater resources in coral islands.A three-dimensional freshwater lens model was developed to simulate the dynamic characteristics and effects of rainfall on the freshwater lens in the Yongxing Island.With finite difference method and the Visual Modflow package,the model was solved numerically,based on the hydrogeological parameters obtained from experiment and in-situ survey.The water flow direction,water head distribution,transition area thickness and the freshwater storage in the lens at different time were obtained.Taking the isoconcentration surface of Cl-1 with 600mg /L as the interface of the lens,the maximum thickness of the lens in the island is 16.9m with the transition area thickness of about 8.3m.The lens reaches its minimum storage in April and maximum in September,and the storage in September more than that in April.Comparing with the change of rainfall in a year,the change of freshwater storage is lagged 1 to 2 months.By means of the proposed methods,the exploitation strategy of safely and sustainably developing the freshwater lens can be worked out.