Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 10 6 2006 10.5194/hess-10-817-2006 http://www.hydrol-earth-syst-sci.net/10/817/2006/ http://www.hydrol-earth-syst-sci.net/10/817/2006/hess-10-817-2006.html http://www.hydrol-earth-syst-sci.net/10/817/2006/hess-10-817-2006.pdf 817 827 2006-11-09 Novel evaporation experiment to determine soil hydraulic properties K. Schneider klaus.schneider@iup.uni-heidelberg.de O. Ippisch K. Roth Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany Institute of Parallel and Distributed Systems, University of Stuttgart, Stuttgart, Germany formerly: Interdisciplinary Center for Scientific Computing, University of Heidelberg, Germany A novel experimental approach to determine soil hydraulic material properties for the dry and very dry range is presented. Evaporation from the surface of a soil column is controlled by a constant flux of preconditioned air and the resulting vapour flux is measured by infrared absorption spectroscopy. The data are inverted under the assumptions that (i) the simultaneous movement of water in the liquid and vapour is represented by Richards' equation with an effective hydraulic conductivity and that (ii) the coupling between the soil and the well-mixed atmosphere can be modelled by a boundary layer with a constant transfer resistance. The optimised model fits the data exceptionally well. Remaining deviations during the initial phase of an experiment are thought to be well-understood and are attributed to the onset of the heat flow through the column which compensates the latent heat of evaporation. Eching, S. O., Hopmans, J. W., and Wendroth, O.: Unsaturated hydraulic conductivity from transient multistep outflow and soil water pressure data, Soil Sci. Soc. Am. J., 58, 687–695, 1994. Gardner, W. R. and Miklich, F. J.: Unsaturated conductivity and diffusity measurements by a constant flux method, Soil Sci. Soc. Am. J., 93, 271–274, 1962. Ippisch, O., Vogel, H.-J., and Bastian, P.: Validity limits for the van Genuchten-Mualem model and implications for parameter estimation and numerical simulation, Adv. Water Resour., 29, 1780–1789, 2006. Jin, Y. and Jury, W. A.: Characterizing the dependence of gas diffusion coefficient on soil properties, Soil Sci. Soc. Am. J., 60, 66–71, 1996. Jury, W. A., Gardner, W. R., and Gardner, W. H.: Soil Physics, John Wiley &\ Sons, New York, 5th edn., 1991. Mualem, Y.: A new model for predicting the hydraulic conductivity of unsaturated porous media, Water Resour. Res., 12, 513–522, 1976. Murray, F. W.: On the computation of saturation vapor pressure, J. Appl. Meteorol., 6, 203–204, 1967. Parker, J. C., Kool, J. B., and van Genuchten, M. T.: Determinig soil hydraulic properties from one-step outflow experiments by parameter estimation: II. Experimental studies, Soil Sci. Soc. Am. J., 49, 1354–1359, 1985. Philip, J. R. and de Vries, D. A.: Moisture movement in porous materials under temperature gradients, Trans. Am. Geophys. Union (EOS), 38, 222–232, 1957. Rawlins, S. L. and Campbell, G. S.: Water potential: Thermocouple psychrometry, in: Methods of soil analysis, Part 1. Physical and mineralogical methods, edited by: Klute, A., Agronomy Series 9, 597–618, Am. Soc. Agron., Madison, WI, 2nd edn., 1986. Robinson, D. A., Jones, S. B., Wraith, J. M., Or, D., and Friedman, S. P.: A review of advances in dielectric and electrical conductivity measurement in soils using time domain reflectometry, Vadose Zone J., 2, 444–475, 2003. Romano, N. and Santini, A.: Determining soil hydraulic functions from evaporation experiments by a parameter estimation approach: Experimental verifications and numerical studies, Water Resour. Res., 35, 3343–3359, 1999. \vSimůnek, J., Wendroth, O., and van Genuchten, M. T.: Parameter estimation analysis of the evaporation method for determining soil hydraulic properties, Soil Sci. Soc. Am. J., 62, 894–905, 1998. Tamari, S., Bruckler, L., Halbertsma, J., and Chadoeuf, J.: A simple method for determining soil hydraulic properties in the laboratory, Soil Sci. Soc. Am. J., 57, 642–651, 1993. Topp, G. C. and Miller, E. E.: Hysteretic moisture characteristics and hydraulic conductivities for glass-bead media, Soil Sci. Soc. Am. Proc., 30, 156–162, 1966. van Dam, J. C., Stricker, J. N. M., and Droogers, P.: Inverse method to determine soil hydraulic functions from multistep outflow experiments, Soil Sci. Soc. Am. J., 58, 647–652, 1994. Wendroth, O., Ehlers, W., Hopmans, J. W., Kage, H., Halbertsma, J., and Wösten, J. H. M.: Reevaluation of the evaporation method for determining hydraulic functions in unsaturated soils, Soil Sci. Soc. Am. J., 57, 1436–1443, 1993.