Tide-induced ground-water flow in deep confined aquifer

Water-elevation variation in rivers can be large due to tides even far away from the coastline. For deep confined aquifers, the possibility of leakage from rivers is small. Nevertheless, the fluctuation of river elevation can induce a stress change in soil and in turn can induce ground-water flow below. The present study focuses on the effect of the fluctuation assuming the time scale for consolidation is much larger than that of the ground water. The total stress change in the deep confined aquifer affects the water-pressure head through deformable soil medium. If the subsurface profile contains only one dominant confined aquifer, a vertically averaged one-dimensional problem with periodic total stress change and constant line pumping is examined. The governing equation is a linear diffusion equation with time-varying forcing terms. Laplace transform and Fourier transform are invoked. The response distribution in space is of the error-function type. The pumping effect can be superimposed due to linearity. Away from the loading, deeper aquifers rather than those close to the ground surface are affected by the dynamic loading. Pressure peaks appear earlier for location farther away from the loading. Field data support the model.