Three-dimensional groundwater flow to a lake: an explicit analytical solution

Steady, Darcian groundwater flow near a hemispherical lake contacting a confined homogeneous aquifer of semi-infinite depth is studied analytically by the method of separation of variables. The lake bottom is modeled either as an equipotential (the Dirichlet boundary) or as a surface with a thin sediment skin (the Robin boundary). The lake disturbs an incident uniform flow such that three regimes (gaining, losing and flow-through) are possible depending on the ambient velocity, aquifer conductivity, lake diameter, the bottom head, sediment thickness and conductivity in case of silted beds. Explicit expressions for the specific discharge and stream function are derived. Inflow and outflow rates are calculated. Implications for other equipotential surfaces placed in ambient fields are discussed.