The framework of the present study is the development of a new approach to describe the displacement of fresh water by salt water in a layered coastal aquifer. The aquifer is composed of horizontal layers possessing different hydraulic conductivities, which are also different in the saltwater and the freshwater zones. A one‐dimensional analysis is performed, describing the displacement of the saltwater‐freshwater interface under the influence of freshwater flow toward the sea. Several analytical solutions are found revealing the effects of various parameters on the interface displacement process. On the basis of these solutions, several type curves for different freshwater saltwater hydraulic conductivity are drawn. The model is calibrated by matching a type curve with field data taken from an observation well and is further used to predict the evolution of the interface shape and position.