Minimal-seepage depth of isobaric cavity under Ponded conditions

A zero-pressure isobar is reconstructed in a potential Laplacian field generated by a sink-source pair that models steady-state Darcian seepage from a ponded soil surface to a cavity draining a homogeneous isotropic half-plane. At sufficiently small flow rates (cavity depths under the soil surface) the obtained contour is almost spherical. For a given "sphere" its depth under a constant-head plane is found providing minimal inflow rate.