The force of Forchheimer – the contributions of Philipp Forchheimer to groundwater hydrology

Philipp Forchheimer must be considered one of the most important founding fathers of modern geohydrology. Connected to his name are the Forchheimer law, which describes non-Darcian flow in porous media, and the Dupuit-Forchheimer groundwater flow assumption. Probably unbeknownst to most current hydrologists, he introduced many more important concepts, which still are cornerstones of our field of study today. The most important is the Laplace equation, which forms the basis of all quantitative modelling of groundwater flow. Flow nets, the method of images and the refraction of flowpaths at layer boundaries are further concepts useful today. Through his work in several countries, many papers and textbooks on hydraulics, the latter translated into several languages, and, finally, his connection with the famous Vienna school of soil mechanics, he left a scientific legacy that is very much alive, although many are unaware that it goes back to Philipp Forchheimer.