Studies on Environment in Small Islans

测定了爱护县戈果岛浅井地下水的各种水质，特别是稳定同位素比值，并与地下水位进行了比较。在尤拉区某滨海地区，氯离子浓度常远大于200 mg/L(城市水标准值)，其D-18图表明该地区地下水为海水和上游地下水的混合体。尤拉地区沿海地区井底附近地下水的无量纲值DeltaD、Delta^&lt；18、O和Cl^-的值几乎相同，估计地下水中含有大约20%的海水。无量纲氯离子的垂向分布不同于三角洲D或三角洲18&gt；O，前者在井上部具有较高的浓度。较高的浓度可能是由除海水外的氯源引起的，例如化肥。用沙池研究了沿海和岛屿地下水的行为。在海水侵入沿海承压含水层的情况下，采用Dupuit假设的解析解和边界元方法(BEM)模拟的淡水/咸水界面与实验结果吻合较好，但内陆咸水情况较低。在流体动力弥散模型中，当弥散系数随速度变化时，浓度等值线与实验值吻合较好，柯西边界条件更接近实际情况。在淡水透镜的情况下，用解析解和流体动力学弥散模型模拟的淡水/盐水界面都存在于实验视觉界面的略上方。

Various water qualities, especially stable isotope ratios, of groundwater in shallow wells were measured, together with groundwater levels, in Gogo Island, Ehime Prefecture. In a coastal region of the Yura district, chloride ion concentration far greater than 200mg/l(the stadard value of city water) was always found and the delta D versus delta^<18>O diagram suggests that the groundwater in this region is a mixture of seawater and upstream groundwater. Non-dimensional values of deltaD, delta^<18>O and Cl^- of groundwater near the bottom of a well in a coastal region of the Yura district indicate almost the same value, and it was estimated that groundwater contained approximately 20% seawater. The vertical distribution of non-dimensional Cl^- is different from those of deltaD or delta^<18>O.The former indicates higher concentration in the upper part of the well. The higher concentration may be caused by the Cl source except seawater, e.g.fertilizer.The behavior of coastal and insular groundwaters was investigated by use of a sand tank. In the case of seawater intrusion into confined coastal aquifers, both the fresh-water/salt-water interfaces simulated by using an analytical solution adopting Dupuit's assumptions and by a boudary element method (BEM) have a relatively good agreement with the experimental ones, though further inland saltwater situation in lower hydraulic gradients. In the hydrodynamic dispersion model, isopleths of concentration in the case of velocity-dependent dispersion coefficient agree well with experimental ones than in the case of constant dispersion coefficient, and the Cauchy's boundary condition is rather realistic. In the case of freshwater lenses, both the fresh-water/salt-water interfaces simulated by using the analytical solution and by the hydrodynamic dispersion model exist slightly above the experimental visual interfaces.