Watertable wave dispersion in sandy coastal aquifers

Abstract

In this paper, the dispersion of watertable waves in sandy coastal aquifers is investigated through both field and laboratory observations. The observations are used to assess the performance of various small-amplitude dispersion relation theories. In all cases, the simplest shallow, capillary-free aquifer theory is shown to be inadequate. Field observations of semi-diurnal tidally forced watertable waves can be reproduced reasonably `well upon consideration of the effects of vertical flows. At this oscillation frequency capillary effects are shown to be small. Laboratory experiments conducted with a much faster oscillation period [O(T)] = 100's of seconds, analogous to oceanic long waves) begin to highlight some limitations of the current theories. Much of the discrepancy between the theories and data can be overcome by consideration of capillary effects which become more influential at the higher oscillation frequencies. The dispersion of higher harmonic components generated due to a sloping ocean-aquifer interface are also investigated in the laboratory and significant discrepancies between data and predictions persist suggesting that processes not previously considered are significant. One example may be the influence of horizontal flow in the capillary fringe.