Preferential flows and the legacy of Peter F. Germann (1944-2020)

Peter Germann died on December 6^th 2020 in Bern, Switzerland. Known for a wide range of contributions to the physics of soil-water interactions and flow, his name (along with Keith Beven, his career-long collaborator and fiend) is recognized by an entire generation of soil physicists and hydrologists who studies macropore and preferential flows. They both co-authored the classic, and highly cited 1982 review paper in Water Resources Research on Macropores and Water Flow in Soils. Peter’s PhD work between 1976-1980 was a study of soil-water relations based on maintaining a network of 35 nests of tensiometers at 10 different depths down to 3m. At that time, these were still manual tensiometers coupled to mercury manometers that were read every 2 to 3 days for 3 years. One of the features that this remarkable data set revealed was that during infiltration, wetting in some cases occurred at depths, apparently by-passing the tensiometers above. This is what we all now know as preferential flow. Another was the large heterogeneity in responses between sites and between wetting events. For the major part of his research career, Peter was a strong advocate for a reconsideration of the physics of water flow through soils and, in particular, for the limitations of the Darcy-Buckingham-Richards flow theory. Peter later developed the kinematic wave approach into a theory of viscosity (rather than capillarity) dominated film flows subject to Stokes’ law during infiltration. He summarised his research work in his 2013 book on the subject published by the University of Bern. Peter held academic positions at the University of Virginia in Charlottesville, at Rutgers University, and at the University of Bern back in Switzerland where he stayed until he retired in 2009, and held an Emeritus position until 2015.   He continued to publish papers until shortly before his death which followed 2 major strokes. In this talk, we will go over Peter’s main contribution and research highlights in the area of macropores and preferential flows. Peter was no stranger to EGU, and many know him and have met him in this session or others. For those who knew Peter, they will miss his enthusiasm, his critical mind, his genuine care for the state of soil physics, his thoughtful responses, and his humour. He was a great source of inspiration to us and many others. Peter will be missed by many in soil science.