The hydraulic conductivity of an unconfined carbonate aquifer at the uplifted atoll of Minami-Daito, Japan, was evaluated by a combination of cross-spectral analysis, analytical solution, and density-dependent groundwater modeling based on observed groundwater levels in 15 wells and at sea level. The island area was divided into 10 subregions based on island morphology and on inland propagation of ocean tides. The hydraulic conductivity was obtained for each subregion using analytical solutions based on phase lags of M₂ constituents of ocean tides at each well by assuming two aquifer thicknesses (300 and 1,800 m) and two effective porosities (0.1 and 0.3). The density-dependent groundwater model evaluated the hydraulic conductivity of the subregions by reproducing observed groundwater levels. The hydraulic conductivity in the subregions was estimated as 3.46 × 10⁻³ to 6.35 × 10⁻² m/s for aquifer thickness of 300 m and effective porosity of 0.1, and as 1.73 × 10⁻³ to 3.17 × 10⁻² m/s for aquifer thickness of 1,800 m and the effective porosity of 0.3. It was higher in southern and northern areas, and higher in interior lowland than in the western and eastern areas. Fissures and dolomite distributions on the island control differences of the omnidirectional ocean tidal propagation and cause these differences in hydraulic conductivity. The method used for this study may also be applicable to other small islands that have few or no data for hydraulic conductivity.

基于在 15 口井和海上观测到的地下水位，通过交叉光谱分析、解析解和密度相关的地下水模型相结合，评估了日本南大东隆起环礁无承压碳酸盐含水层的水力传导率等级。根据岛屿形态和海洋潮汐的内陆传播，将岛屿区域划分为10个分区。使用基于 M _{2 的}相位滞后的解析解获得每个子区域的水力传导率通过假设两个含水层厚度（300 和 1,800 m）和两个有效孔隙度（0.1 和 0.3）来计算每口井的海洋潮汐成分。密度相关地下水模型通过再现观察到的地下水位来评估子区域的水力传导率。 对于含水层厚度为 300 m 和有效孔隙度为 0.1，子区域的水力传导率估计为 3.46 × 10 ^-3至 6.35 × 10 ^-2 m/s，以及为 1.73 × 10 ^-3至 3.17 × 10 ^-2 m/s，含水层厚度为 1,800 m，有效孔隙率为 0.3。南部和北部地区较高，内陆低地高于西部和东部地区。岛屿上的裂缝和白云岩分布控制了全方位海洋潮汐传播的差异，并导致了这些水力传导率的差异。本研究使用的方法也可能适用于其他很少或没有导水率数据的小岛。