Numerical simulation of groundwater level fluctuation in a coastal confined aquifer with sloping initial groundwater level induced by the tide

The tide may induce fluctuations in groundwater levels in coastal aquifers. In this paper; a numerical model describing 1D groundwater flow in a coastal confined aquifer was established based on the finite element method. Fluctuation in the tide was simplified as a sinusoidal wave. Groundwater level oscillations in a coastal confined aquifer with sloping initial groundwater level were simulated. A comparison of the results with those of the aquifer with horizontal groundwater level shows that the groundwater level oscillations induced by the tide in the coastal confined aquifer are similar to those of the tide but the fluctuation ranges of groundwater levels are smaller than those of the tide. The degree of the effect by the tide is related to the distance from the coast. The fluctuation range of groundwater levels and the tidal efficiency decrease negatively exponentially with the distance from the coast and are smaller than those of the aquifer with horizontal groundwater level. The time lag of the groundwater levels to the tide increases linearly with the distance from the coast.