Mechanical Coupling Effect on Tide-Induced Fluctuations in a Multilayer Aquifer System

We present a new analytical solution to study the mechanical coupling on tidal-induced head fluctuations in a coastal aquifer system. The conceptual model consists of two overlying confined units that extend infinitely under the sea. The proposed model assumes that the tidal fluctuations in the overlying aquifer are described by the classical equation derived by van der Kamp. For the underlying aquifer, a closed form analytical expression is derived by solving a boundary value problem that considers the loading effect produced by the overlying unit. The amplitude and phase lag of the underlying aquifer depend on both the specific storage and the thickness of the overlying unit. A parametric study shows that the mechanical coupling effect can be important for both large values of specific storage and thickness of the overlying aquifer.