Watertable dynamics forced by waves

Extensive field observations of the coastal watertable along the east coasts of Australia have revealed that wave runup and tidal action produce a landward increasing superelevation of the mean watertable level. In particular, field measurements of groundwater dynamics in coastal barriers exhibit previously unidentified features showing landward downsloping watertable from the runup limit mainly due to runup infiltration on the ocean side, which are important for understanding ecosystem in coastal areas and for pollution control. 

This thesis has focused on the wave effects. In order to gain insight into the process of infiltration due to wave runup and the resulting watertable overheight, comprehensive experiments have been conducted in a wave flume with regular waves and no tide, using sands of two different sizes (d₅₀=0.18mm and 0.78mm). It has been found that the steady-state asymptotic inland watertable overheight ῆ_͚͚ depends on the beach profile, the incident wave height H_i and the wave period T, but not directly on the hydraulic conductivity K of the beach material. This steady state overheight has been compared with the field data from the Palm Beach isthmus which gives the magnitude of the wave induced watertable overheight in a situation with both waves and tides. 

In order to model the watertable landward of the shoreline, the modified Boussinesq equation which includes the infiltration effect from wave runup is used. The infiltration velocity U₁ is indirectly determined from the watertable data. The runup infiltration velocities have maximum values approximately midway between the shoreline and the runup limit for both the field data and the laboratory experiments, but the magnitudes are different. It is obvious that the tidal phase is very important. Infiltration velocities are large when the shoreline moves landwards on a partly saturated beach on a rising tide. For steady wave conditions and no tide, the resulting watertable model is presented. 

Numerical modelling of the watertable with the glassy/dry boundary as a boundary condition is also attempted.