Horizontal two-dimensional groundwater-level fluctuations in response to the combined actions of tide and rainfall in an unconfined coastal aquifer

Groundwater hydrodynamics in the coastal area is significantly affected by tidal fluctuations and other driving factors such as rainfall. A series of analytical studies have been carried out in the past to investigate the water-table dynamics in coastal aquifers under different scenarios. Nevertheless, the horizontal two-dimensional analytical solution of the water-table fluctuation in an unconfined aquifer system under the combined actions of tide and rainfall has not been studied. To this end, a horizontal two-dimensional analytical solution is derived with the Dupuit-Forchheimer assumption by using the Fourier transform method in the present study. Subsequently, water-table fluctuations are estimated based on the present analytical solution. The joint effect of rainfall and tide could lead to complex water-table fluctuations, and the influences of different factors can be quantitatively investigated using the present analytical solution. In addition, the accuracy of the present analytical solution is further validated by numerical models, which indicate that the nonlinear effect could be neglected for a relatively large aquifer thickness, under which the present linearized analytical solution can give satisfying results. The present analytical solution extends the theoretical understanding of groundwater dynamics under the mutual effect of tide and rainfall.