The porosity wave is an incompressible fluid flow process where a dynamic change in the porosity of a porous medium is coupled to a dynamic pressure change in the fluid, which in turn induces the fluid to flow. For this wave to occur, the solid matrix of the porous medium must be deformable, and the pressure changes must be slow enough for the fluid to behave incompressibly, i.e. the fluid is forced to move instead of just compressing. Therefore, in this process one obtains a damped travelling wave of porosity, pressure, and fluid. The theoretical description of porosity waves was first presented by Spanos (2002). In the diffusional limit, the inertial terms appearing in the theory are negligible, and the porosity wave becomes a porosity diffusion process. This diffusion process was first recognized and analysed by Geilikman et al. (1993).