地貌变化对永兴岛淡水透镜体影响的数值模拟

Numerical simulation of the effect of geomorphologic changes on freshwater lens in the Yongxing Island

淡水透镜体是岛上重要的地下淡水资源,在满足日常生活需求和维护岛礁生态系统等方面都起了关键作用。目前永兴岛的沙丘面积增加了约50%,为了研究地貌变化对岛礁淡水透镜体的影响,利用GMS软件中的SEAWAT模块构建了西沙永兴岛淡水透镜体的三维数学模型,并对与淡水透镜体形成有关的部分参数进行了敏感性分析。结果表明,降雨入渗补给系数对淡水透镜体厚度的影响最大,其次是渗透系数和给水度;在保持现有地貌条件不变的情况下,永兴岛的淡水透镜体大约在25年后再次达到稳定状态,此时淡水透镜体的最大厚度由之前的14 m增加到了17. 5 m,计算所得的淡水资源储量增加了近一倍,约为328×104m3。建立了地貌变化对岛礁淡水透镜体影响的数值模型。这对永兴岛及其他相似岛屿淡水资源的开采和管理具有重要的理论意义和实用价值。

Freshwater lens is an important groundwater resorce in an island, and plays a key role in meeting the needs of people＇ s daily life and maintaining the ecosystem of the island. At present, the dune area of the Yongxing Island increases by 50%. In order to examine the impact of geomorphologic changes on freshwater lens in the island, a 3 D mathematical model of the freshwater lens is constructed using the SEAWAT module in the GMS software. Sensitivity analysis of some parameters is also carried out. The results show that the infiltration coefficient of precipitation has the greatest influence on the thickness of freshwater lens, followed by the hydraulic conductivity- and specific yield. With the existing topography unchanged, the freshwater lens of the Yongxing Island will reach a stable state in about 25 years. At that time, the maximum thickness of the freshwater lens will increase from the previous 14 m to 17.5 m, and the calculated freshwater reserves is about 328×10^4 m^3. This paper presents a numerical model for examing the effect of geomolphologic changes on the freshwater lens, which has important theoretical significance and practical value for the further exploitation and management of freshwater resomves in the Yongxing Island and other similar islands.