Groundwater waves in a coastal aquifer: A new governing equation includingvertical effects and capillarity

Groundwater waves, that is, water table fluctuations, are a natural phenome non in coastal aquifers. They represent an important part of the interactio n between the ocean and aquifer and affect the mass exchange between them. This paper presents a new groundwater wave equation. Because it includes th e effects of vertical flows and capillarity, the new equation is applicable to both intermediate-depth aquifers and high-frequency waves. Compared wit h the wave equation derived by Nielsen ed al. [1997], the present equation provides a closer representation of groundwater waves. In particular, it pr edicts high-frequency water table fluctuations as observed in the field. A validation of the new equation has been carried out by comparing the analyt ical solutions to it with predictions from direct simulations using the num erical model SUTRA. The effects of various physical parameters and their re lative importance are also discussed.