ABSTRACT
Groundwater flow equations are partial differential equations. When considering forward problems, i.e., problems in which the parameters—hydraulic conductivity and specific storage—are specified, such equations relate the dependent variables head and flux to the independent variables, the coordinates of the flow domain and the time. However, flow equations are only valid inside the flow domain, and not on the boundaries, because there the porous medium ends and other phenomena occur, which will influence the groundwater flow inside the domain. These interactions at the boundaries are governed by other physical laws and have to be described separately by mathematical expressions, the so-called boundary conditions.
