Thermohaline Flow in Seawater Intrusion in Shallow Coastal Aquifers

Temperature and salinity, with largely different diffusivities, make a perfect couple that drives thermohaline flow (double diffusive convection where heat and salt are the two main concerned properties) in porous media wherever their gradients co-exist. Studies of double diffusion convection have revealed various flow regimes generated by instable and even stable vertical stratification of heat and salt including diffusive, finger, and mixed flow regimes. In the context of seawater intrusion in shallow coastal aquifers, however, temperature and salinity gradients present more likely horizontal than vertical. Moreover, while salinity gradient is apparently seaward, the direction of temperature gradient may vary over the seasons. In such cases, understanding on how thermohaline flow exhibit and influence the overall state of seawater intrusion in near-shore aquifers remains largely deficient. In this study, we examine the occurrence and characteristics of thermohaline flow in seawater intrusion in coastal aquifers under various scenarios of salinity and temperature distribution by laboratory experiments and numerical simulation. Its effects on solute transport and saltwater circulation are also investigated.