珊瑚岛淡水透镜体抽水倒锥影响因素研究

为研究珊瑚岛淡水透镜体抽水倒锥的形成和影响因素,构建了西沙永兴岛淡水透镜体三维数学模型,运用Visual Modflow软件对模型进行数值求解,获得了淡水透镜体外包络面、倒锥外形和相关因素对倒锥的影响。模拟计算表明,淡水水头的计算值与实测值之差为-0.58%～-3.86%;取年均降雨量的40%为回补量,永兴岛淡水透镜体最大计算厚度为15 m;抽水倒锥上升高度随抽水强度和时间的增加而增加,随井底到淡水透镜体底部边界距离的增加而减少;倒锥对抽水强度十分敏感,工程中应予以严格控制,对于永兴岛上长期开采的水井,建议抽水速率不超过5 m3/h。研究成果可用于制订淡水透镜体的开采策略,实现珊瑚岛地下淡水资源的持续开发和利用。

Research on Influential Factors upon the Up-cone of the Freshwater Lens in a Coral Island

Three-dimensional freshwater lens mathematical model is built to research the influential factors upon the up-cone of the lens in a coral island.The model is solved numerically by Visual Modflow software.The surface of the lens is obtained and the formation as well as influential factors of the up-cone is simulated.The numerical calculation indicates that the difference of freshwater heads between calculation and measurement is from-0.58% to-3.86%.Taking 40% of the annually mean rainfall as compensation for the lens,the maximum thickness of the lens in that island is about 15.0 m.The up-cone interface ascends with the increase of the pumping time and rate,but decreases with the increase of the distance between the bottoms of the well and the lens.The up-cone is hypersensitive to the pumping rate.So the rate must be controlled strictly in engineering practice and doesn’t exceed 5 m3/h for the well in that island.The results of the research may be used for working-out exploitation strategy of the lens for the freshwater resource to be realized sustainable utilization.