Germann, Peter

Photograph

Dates

Peter Fritz Germann 1944 (St. Gallen, Switzerland) - 6th December 2020 (Bern, Switzerland)

Biography

Peter Germann was born in St. Gallen Switzerland in 1944. He grew up in Bischofszell. He attended school in Bischofszell and St. Gallen. In 1963-1969 he studied for a Degree in Forestry at ETH Zurich, and then stayed with Professor Richard to carry out research for a PhD at the Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft (WSL) 1969-1976. He continued his work in the Laboratories of Hydraulics, Glaciology and Hydrology (VAW) during the period 1976-1980, a period that included a year working at the Institute of Hydrology in Wallingford, UK. His PhD work was a study of the water relations on a forested slope in the Reitholzbach catchment based on maintaining a network of 35 nests of tensiometers at 10 different depths down to 3m, set out on a triangular grid amongst the trees. At this time these were still manual tensiometers coupled to mercury manometers that were read every 2-3 days for 3 years. One of the features that this remarkable data set revealed was that during infiltration wetting could occur at depth in some cases, apparently by-passing the tensiometers above. Another was the large heterogeneity in responses between sites and between wetting events.

In 1980 Peter took up a post as Assistant Professor in the Department of Environmental Sciences at the University of Virginia in Charlottesville where he stayed until 1986. He then moved as an Associate Professor to the Department of Soils and Crops at Rutgers University. In 1989 he was offered a Professorship at the Institute of Geography, University of Bern back in Switzerland where he stayed until he retired in 2009. He held an Emeritus position at Bern until 2015, during which time the University published his book on preferential flows. He continued to publish papers until shortly before his death in 2020 which followed 2 major strokes.

Hydrological Achievements

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 that is based on an assumption of the equilibration of capillary potentials in some “representative elementary volume” of soil pores. This was in part instigated by his PhD research, and in part with his period as a visiting post-doc in 1979 at the Institute of Hydrology at Wallingford UK. There he first met and worked with Keith Beven who had a field site on a cracking clay soil and had also studied the role of macropores in soil water flows. Together they published a highly cited review paper in Water Resources Research on Macropores and Water Flow in Soils in 1982 (and revisited 30 years later in 2013). They also developed an approached based on kinematic wave theory to the problem of preferential flow, and Peter later developed this further into a theory of viscosity (rather than capillarity) dominated film flows subject to Stokes’ law during infiltration. Peter was a careful experimentalist both in the laboratory and in the field and made use of a variety of time domain reflectometry, sonic and tracer experiments to study preferential flows. The culmination of this work is summarised in the book “Preferential Flow: Stokes approach to infiltration and drainage”. The book is still available for free through the University of Bern (https://boris.unibe.ch/119081/1/preferential_flow.pdf).

Anecdotes

From Keith Beven:

I was working at the Institute of Hydrology in Wallingford, UK, employed as a mathematical modeller when in 1978 Peter sent in a proposal to spend a year as a post-doc at the Institute. Essentially the proposal outlined a programme to investigate the role of macropores in soil hydrology using a combination of laboratory, field and modelling work, so it was sent first to the Soil Physics section. Interestingly, nobody in Soil Physics was interested in hosting Peter to do the work (a step too far from. Darcy-Richards “real” physics perhaps) and eventually the proposal landed on my desk. I was already well aware of the potential for macropore flows in subsurface stormflows based on my thesis working with Darrel Wyman’s East Twin catchment data (see Beven, 2001) and, since arriving at Wallingford, in running some field drainage experiments in the Grendon Underwood catchment, in that case on heavy Denchworth series cracking clays. So I expressed some enthusiasm in supporting Peter’s project and he arrived with his family early in 1979. The work we did led to a series of 3 papers in J. Soil Science in 1981, and the well-cited review paper on Macropores and Water Flow in Soils in Water Resources Research in 1982 and, much later, the Revisited paper in 2013, which includes some information and a photograph of the tracing experiment we did at Grendon Underwood in 1979. The latter, I think, was instructive in that it was done at the end of the winter on well-wetted soil when all the cracks should have been closed. In fact, it took the Rhodamine dye we added at the surface some 60 seconds to reach a mole drain at a depth of 45 cm, and destructive sampling showed that the cracks were still transmitting water (and that the grass roots were mostly on the surface of the peds.

Before Peter’s stay in Wallingford was finished, I moved to a position at the University of Virginia in Charlottesville but, by chance, there was also a hydrologist position there a year later. I suggested Peter apply and he was successful so we had another couple of years working together including field work in the Shenandoah National Park and later in Maine (where we had more experience of surprising macropore activity). Peter also brought his rather remarkable thesis data set with him. This was from a network of 35 tensiometers on a 1.5 triangular grid on a forested slope in Switzerland. Data had been collected at multiple depths every 2 or 3 days for each year. At that time, spatial variability in soils was a hot topic, and one of the things to do with such data was to calculate variograms. So I calculated thousands of variograms for every day of sampling and every level in the profile. The outputs were received as a thick wad of line printer plots (no graphical display terminals then). I found it was possible to have every shape of variogram conceivable, from all nugget variance to continuously increasing to continuously decreasing to triangular. Just occasionally it was possible to see the effects of a storm working its way through the system at successive sampling times and depths, but otherwise it was impossible to make strong inferences. Those results never did get published.

I came back to the UK after 3 years but Peter stayed on at UVa and later at Rutgers University before being offered the position back in Switzerland where he worked until he retired. In 1985, we both attended an International workshop in Wageningen on Water and Solute Movement in Heavy Clay Soils, where we presented a paper on flow in distributions of macropores based on the kinematic wave approach. In the bar one evening we then had a long discussion with John Philip about how it was possible that film flow in a macropore, which would have a curved meniscus and therefore a potential at less than atmospheric pressure, could possibly result in an outflow at the base of an undisturbed column which required a positive pressure. I have never been able to decide whether John was really serious, or whether he was just teasing these two earnest young(ish) academics committed to the importance of preferential flows.

From Tammo Steenhuis:

As an assistant professor in the late seventies and eighties, my friend and colleague Rich Muck and I experimented on a hillside. We found that all applied chloride was lost in the runoff water in a short time. We tried to publish it and it was twice rejected on grounds that the results and our findings were wrong. With the help of Peter and Keith Beven, it was finally published on the third try. It helped me greatly to make it to the next step of an academic career.

Throughout the years, I enjoyed meeting and talking with Peter. He was always very inspiring. He always had ideas that took me years to understand. Some of them I am still trying to understand. He is greatly missed.

Selected Publications

Books

Germann, P. F., 2013, Preferential Flow: Stokes approach to infiltration and drainage, University of Bern Press. Available at https://boris.unibe.ch/119081/1/preferential_flow.pdf

Papers

Beven, K.J., Germann, P.F. (1980), 'The Role of Macropores in the Hydrology of Field Soils'. Institute of Hydrology, Report No. 69, Wallingford, UK, 46 pp.

Germann, P.F., Beven, K.J. (1981), 'Water flow in soil macropores, I. An experimental approach'. J. of Soil Science, v.32, 1-13.

Beven, K.J., Germann, P.F. (1981), 'Water flow in soil macropores, II. A combined flow model'. J. of Soil Science, v.32, 15-29.

Germann, P.F., Beven, K.J. (1981), 'Water flow in soil macropores, III. A statistical approach'. J. of Soil Science, v.32, 29-31.

Beven, K.J., Germann, P. (1982), 'Macropores and water flow in soils", Water Resources Research, 18(5), 1311-1325.

Germann, P. F., W. M. Edwards, and L. B. Owens. 1984, Profiles of bromide and increased soil moisture after infiltration into soils with macropores. Soil Science Society of America Journal 48(2): 237-244.

Germann, P.F., Beven, K.J. (1985), 'Kinematic wave approximation to infiltration into soils with sorbing macropores'. Water Resources Research, 21(7), 990-996.

Germann, P.F., 1985. Kinematic wave approach to infiltration and drainage into and from soil macropores. Transactions of the ASAE, 28(3), pp.745-0749.

Beven, K.J., Germann, P.F. (1985), 'A distribution function model of channelling flow in soils based on kinematic wave theory'. Proceedings of the International Symposium on Water and Solute Movement in Heavy Clay Soils, Wageningen, Neth. ILR Pubn. 37, 89-100.

Harvey, J.W., Germann, P.F. and Odum, W.E., 1987. Geomorphological control of subsurface hydrology in the creekbank zone of tidal marshes. Estuarine, Coastal and Shelf Science, 25(6), pp.677-691.

Germann, P.F., Beven, K.J. (1986), A distribution function approach to water flow in soil macropores based on kinematic wave theory, J. Hydrology, 83, 173-183.

Germann, P.F., Pierce, R.S., Beven, K.J. (1986), Kinematic wave approximation to the initiation of subsurface storm flow in a sloping forest soil, Advances in Water Resources, 9(2), 70-76.

Germann, P.F., 1986. Rapid drainage response to precipitation. Hydrological Processes, 1(1), pp.3-13.

Germann, P.F., 1987. The three modes of water flow through a vertical pipe. Soil Science, 144(2), pp.153-154.

Germann, P.F., Smith, M.S. and Thomas, G.W., 1987. Kinematic wave approximation to the transport of Escherichia coli in the vadose zone. Water Resources Research, 23(7), pp.1281-1287.

Germann, P.F., 1988. Approaches to rapid and far-reaching hydrologic processes in the vadose zone. Journal of Contaminant Hydrology, 3(2-4), pp.115-127.

Beven, K.J., Hornberger, G.M., Germann, P., (1989), Hillslope hydrology, A multiple interacting pathways model, Proc. Brit. Hydrol. Soc. Second National Hydrology Symposium, 1.1 to 1.8.

Germann, P.F., 1990. Macropores and hydrologic hillslope processes. In M G Anderson and T P Burt (Eds), Process Studies in Hillslope Hydrology., pp.327-363. Wiley:Chichester

Hornberger, G.M., K.J. Beven and P.F. Germann, (1990), Inferences about solute transport in macroporous forest soils from time series models, Geoderma, 46, 249-262.

Hornberger, G.M., P.F. Germann and K.J. Beven (1991), Throughflow and solute transport in an isolated sloping soil block in a forested catchment, J. Hydrology, 124, 81-100.

Germann, P.F., 1991. Length scales of convection-dispersion approaches to flow and tranport in porous media. Journal of Contaminant Hydrology, 7(1-2), pp.39-49.

Germann, P.F. and Di Pietro, L., 1996. When is porous-media flow preferential? A hydromechanical perspective. Geoderma, 74(1-2), pp.1-21.

Garcia‐Sanchez, L., Di Pietro, L. and Germann, P.F., 1996. Lattice–gas approach to surface runoff after rain. European Journal of Soil Science, 47(4), pp.453-462.

Germann, P.F., Di Pietro, L. and Singh, V.P., 1997. Momentum of flow in soils assessed with TDR-moisture readings. Geoderma, 80(1-2), pp.153-168.

Mdaghri-Alaoui, A. and Germann, P.F., 1998. Kinematic wave approach to drainage flow and moisture distribution in a structured soil. Hydrological sciences journal, 43(4), pp.561-578.

Germann, P.F. and Niggli, T., 1998. Dissipation of momentum during flow in soils. Hydrological sciences journal, 43(4), pp.537-548.

Germann, P.F. and Di Pietro, L., 1999. Scales and dimensions of momentum dissipation during preferential flow in soils. Water Resources Research, 35(5), pp.1443-1454.

Germann, P.F., Alaoui, A. and Riesen, D., 2002. Drag force approach to the transport of colloids in unsaturated soils. Water Resources Research, 38(10), pp.18-1.

Germann, P.F. and Zimmermann, M., 2005. Directions of preferential flow in a hillslope soil, 1. Quasi‐steady flow. Hydrological Processes, 19(4), pp.887-899.

Badoux, A., Witzig, J., Germann, P.F., Kienholz, H., Lüscher, P., Weingartner, R. and Hegg, C., 2006. Investigations on the runoff generation at the profile and plot scales, Swiss Emmental. Hydrological Processes: An International Journal, 20(2), pp.377-394.

Germann, P. F. and Hensel, D., 2006, Poiseuille flow geometry inferred from velocities of wetting fronts in soils, VADOSE ZONE JOURNAL, 5(3), 867-876, DOI: 10.2136/vzj2005.0080

Vadilonga, T., Ubeda, X., Germann, P.F. and Lorca, M., 2008. Effects of prescribed burnings on soil hydrological parameters. Hydrological Processes, 22(21), pp.4249-4256.

Germann, P.F. and al Hagrey, S.A., 2008. Gravity‐driven and viscosity‐dominated infiltration into a full‐scale sand model. Vadose zone journal, 7(4), pp.1160-1169.

Hincapié, I.A. and Germann, P.F., 2009. Abstraction from infiltrating water content waves during weak viscous flows. Vadose Zone Journal, 8(4), pp.996-1003.

Hincapié, I. and Germann, P.F., 2009. Impact of initial and boundary conditions on preferential flow. Journal of Contaminant Hydrology, 104(1-4), pp.67-73.

Kutilek, M. and Germann, P.F., 2009. Converging hydrostatic and hydromechanic concepts of preferential flow definitions. Journal of Contaminant Hydrology, 104(1-4), pp.61-66.

Germann, P.F., Benjamin, L., Luscher, P. and Lin, H., 2012. Preferential flow dynamics and plant rooting systems. Hydropedology: Synergistic integration of soil science and hydrology. Acad. Press, Amsterdam, pp.121-142.

Beven, K. J. and Germann, P. F., 2013, Macropores and water flow in soils revisited, Water Resour. Res., 49(6): 3071-3092 DOI: 10.1002/wrcr.20156

Lange, B., Germann, P.F. and Lüscher, P., 2013. Greater abundance of Fagus sylvatica in coniferous flood protection forests due to climate change: impact of modified root densities on infiltration. European Journal of Forest Research, 132(1), pp.151-163.

Germann, P F, 2017, Shape of Time Domain Reflectometry Signals during the Passing of Wetting Front, Vadose Zone Journal, 16(2), doi: 10.2136/vzj2016.08.0070

Germann, P.F. and Karlen, M., 2016. Viscous‐flow approach to in situ infiltration and in vitro saturated hydraulic conductivity determination. Vadose zone journal, 15(2), pp.1-15.

Germann, P.F. and Prasuhn, V., 2018. Viscous flow approach to rapid infiltration and drainage in a weighing lysimeter. Vadose zone journal, 17(1), pp.1-12.

Germann, P.F., 2018. Viscosity—The weak link between Darcy's law and Richards' capillary flow. Hydrological processes, 32(9), pp.1166-1172.

Germann, P.F., 2018. Hydromechanics and kinematics in preferential flow. Soil Science, 183(1), pp.1-10.

Germann, P.F., 2020, Preferential flow at the darcy scale: Parameters from water content time series, SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 84 (5):1485-1494, DOI: 10.1002/saj2.20157

Germann, P.F., 2020, Viscosity Controls Rapid Infiltration and Drainage, Not the Macropores, WATER, 12(2), art. 337, DOI: 10.3390/w12020337

Links

History of the Reitholzbach catchment

Preferential Flow by Peter Germann