The shape of the interface in steady flow in a stratified aquifer

The present work deals with the shape of the interface in a coastal aquifer in which a thin horizontal semipervious layer is present. Field observations and laboratory experiments have shown that under these conditions a discontinuity in the shape of the interface occurs such that a freshwater region exists under the semipervious layer while immediately above it, saline (or mixed) water is present in the aquifer. The paper presents an approximate solution for the shape of the interface below the semipervious layer and for the extent of the freshwater region above it under steady state conditions. The solution is based on the Dupuit assumption and on a linearization of part of the flow equations. Laboratory experiments on a Hele‐Shaw model have shown a good agreement between the forecasted interface profiles and those actually observed in the model. From the results of the experiments it follows that the separation of the interface into two parts, below and above the semipervious layer, decreases as the length of landward seawater intrusion increases. The proposed solution can readily be applied to the case of a phreatic surface under an artificial recharge basin, when the aquifer is separated into subaquifers by a sequence of semipervious layers.