Hibi Yoshihiko
Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi, Tenpaku-ku, Nagoya, Aichi 468-8502, Japan.
J Contam Hydrol. 2022 Dec;251:104090. doi: 10.1016/j.jconhyd.2022.104090. Epub 2022 Sep 28.
Many studies have used numerical simulations and experiments to simulate saltwater intrusion in a nearshore aquifer. Thus, it is known that seawater recirculation occurs in a porous medium just below a sloping beach, and a saltwater wedge occurs in the medium below where the slope intersects the water level at low tide. This study investigated the salt distribution in the surface water when subterranean recirculation of seawater is occurring and there is a saltwater wedge in an underlying porous medium, along with the relationships between the seawater recirculation and the tidal amplitude and beach gradient. The salt distribution in a subterranean aquifer and in surface seawater where the shore sloped gently seaward with a constant slope of 1/10 or 1/5 under tidal amplitudes of 0.5, 1.0, or 2.0 m was numerically simulated by the ASGMF method, which couples water pressure and water flow in a porous medium with those in the overlying surface water and can simulate variable-density flows and the salt concentration distribution in both the porous medium and the surface water. The results showed that the recirculation of seawater depended on the tidal amplitude, being greater when the amplitude exceeded 1.0 m, but that it was unlikely to occur when the beach gradient was steep. Thus, the aspect ratio (width to depth) of the seawater recirculation decreased as the tidal amplitude increased above 1.0 m. Furthermore, the simulated surface water level was often lower than the tidal water level; thus, the surface water level was not consistent with the tidal water level imposed at the right boundary of the simulation domain but varied slightly under the influence of water flow in the surface water and gas flow in the atmosphere. The salt concentration in the surface water was not always the same as the seawater salt concentration because a thin freshwater layer and a brackish water layer of mixed freshwater and saltwater overlay the seawater.
许多研究采用数值模拟和实验来模拟近岸含水层中的海水入侵。因此，已知在倾斜海滩下方的多孔介质中会发生海水再循环，并且在斜坡与低潮位水位相交处下方的介质中会出现咸水楔。本研究调查了在海水发生地下再循环且下层多孔介质中存在咸水楔的情况下地表水的盐分分布，以及海水再循环与潮汐振幅和海滩坡度之间的关系。利用ASGMF方法对潮汐振幅为0.5、1.0或2.0米时，岸边以1/10或1/5的恒定坡度向海缓缓倾斜的地下含水层和地表海水中的盐分分布进行了数值模拟，该方法将多孔介质中的水压和水流与上覆地表水的水压和水流耦合起来，能够模拟变密度流以及多孔介质和地表水中的盐浓度分布。结果表明，海水再循环取决于潮汐振幅，当振幅超过1.0米时海水再循环更强烈，但当海滩坡度较陡时不太可能发生。因此，当潮汐振幅增加到1.0米以上时，海水再循环的纵横比（宽度与深度之比）减小。此外，模拟的地表水水位往往低于潮汐水位；因此，地表水水位与施加在模拟域右边界的潮汐水位不一致，而是在地表水水流和大气气流的影响下略有变化。地表水的盐浓度并不总是与海水盐浓度相同，因为在海水上方覆盖着一层薄薄的淡水层和一层淡水与咸水混合的微咸水层。
