Jeng, D.-S.Seymour, B. R.Barry, D. A.Parlange, J.-Y.Lockington, D. A.Li, L.2005-12-092005-12-09200510.1016/j.jhydrol.2004.11.013https://infoscience.epfl.ch/handle/20.500.14299/221199Free surface flow of groundwater in aquifers has been studied since the early 1960s. Previous investigations have been based on the Boussinesq equation, derived from the non- linear kinematic boundary condition. In fact, the Boussinesq equation is the zeroth-order equation in the shallow-water expansion. A key assumption in this expansion is that the mean thickness of the aquifer is small compared with a reference length, normally taken to be the linear decay length. In this study, we re-examine the expansion scheme for free surface groundwater flows, and propose a new expansion wherein the shallow-water assumption is replaced by a steepness assumption. A comparison with experimental data shows that the new model provides a better prediction of water table levels than the conventional shallow-water expansion. The applicable ranges of the two expansions are exhibited.Shallow water expansionSteepness expansionCoastal aquifersGroundwater flowWatertable fluctuationsUnconfined aquiferBeachesBoundaryWavestext::journal::journal article::research article