Mathematical Model And Analytical Solution Of The Tidal Fluctuation In A Coastal Confined Aquifer Extending Under The Sea

In this paper, a mathematical model was built to describe the groundwater head fluctuation in a coastal confined aquifer induced by the joint actions of the tidal loading effect and the hydraulic connection through the thin silt-layer at the suboutcrop of the aquifer. The analytical solution for the offshore and inland portions of the aquifer was derived. Each solution contains four independent parameters, i.e., the dimensionless leakance of the silt layer, the offshore extending length, the confined aquifer's tidal propagation parameter, and the loading efficiency. If the dimensionless leakance and the offshore extending length are set to be certain special values, the solution becomes the same as the existing solutions derived by several previous researchers. The impacts of the offshore extending length and the silt-layer's dimensionless leakance on the tide-induced groundwater head fluctuation in the aquifer were analyzed and discussed. Particularly, the solution for impermeable silt-layer can be used to describe the tidal fluctuation in a confined aquifer under a tidal river separated by an impermeable layer. Hypothetical example shows that neglecting the silt-layer may results in significant parameter errors and parameter estimation discrepancy between the amplitude attenuation and the time lag methods.