Approximate expressions for the equilibrium position of the intruded wedge and the movement of the interface in an unconfined coastal aquifer are derived. The earlier works of R.R. Rumer and D.R.F. Harleman, and J. Bear and G. Dagan are extended giving the attention to the thickness of the fresh-water layer at sea line. Experiments are performed in the laboratory on a two-dimensional model containing isotropic, homogeneous porous media.