Tidal propagation in single-layer and multi-layer systems bounded by tidal rivers, seas, and oceans

The measurements of tidal signals in observation wells can be used to estimate aquifers parameters or groups of aquifer parameters; this procedure is also referred to as the tidal method. Measured heads are analyzed to determine the amplitude and phase shift of the major tidal components. A variety of analytic solutions exist to match the measured amplitude and phase shift in single aquifers, including aquifers that are confined or unconfined, aquifers covered with semi-confining layers that have zero storage or finite storage, and aquifers where the loading efficiency is included or neglected. Boundary conditions can vary from tidal rivers of finite width to seas and oceans of semi-infinite extent. Recently, new analytic solution were developed for systems consisting of an arbitrary number of layers. Aquifer layers may be separated by leaky layers (including storage in the leaky layers), or may be stratified where vertical flow between aquifer layers is approximated with a finite difference scheme. A number of examples will be presented for tidal propagation in unconfined homogeneous aquifers, unconfined aquifers with horizontal clay lenses, and multi-aquifer systems. A number of surprising results will be presented, including strange variations of the amplitude in the groundwater, and tidal signals of the groundwater that run ahead of the tide in the surface water.