Interface refraction at the boundary between two porous media

In steady flow, refraction of the interface between fluids takes place at the boundary between porous layers of different hydraulic conductivities. An analytical and graphical solution of this problem is presented. The steady interface, which is a streamline, is refracted in such a way that the ratio between the tangents of the angles that the interface makes with the normal to the surface separating the two layers equals the ratio between the corresponding hydraulic conductivities. However, in addition to the above condition of refraction of a streamline, in the present case the angles of refraction of the interface can take only definite values depending on the slope of the boundary between the layers and the ratio of their permeabilities. Laboratory experiments, carried out on a Hele‐Shaw analog, verified the analytical solution.