Two quasi-steady methods for unsteady analyses of the motion of the salt-fresh interface in unconfined coastal aquifers are investigated. Their performance is evaluated through comparisons of the results from the quasi-steady models with results from a more exact model. The comparisons show that the quasi-steady models overestimate the rate of response of the interface. It is concluded that the more exact model should be used for one-directional flow studies despite the extra effort required. Quasi-steady models do have a place in two-dimensional analyses but their limitations, demonstrated by this study, should be recognised.