Approximate solution of the problem of the shape of the interface in a semi-confined aquifer

Abstract The interface between steady-flowing fresh groundwater and stagnant saline groundwater in a semi-confined aquifer is described by a nonlinear ordinary differential equation of the second order, based on the Dupuit approach of horizontal flowlines in the aquifer and on the assumption that the interface is sharp. Reduced dimensionless variables have been introduced instead of the depth of the interface and the distance, respectively. An approximate solution is developed. Its accuracy is investigated. Examples of calculation results are presented for profiles with several polders in succession, with abstractions of fresh groundwater and with discontinuities in the distribution of the geohydrological constants.