Publication Details

Category Text Publication
Reference Category Journals
DOI 10.1016/j.jhydrol.2010.03.018
Title (Primary) Non-equilibrium in soil hydraulic modelling
Author Vogel, H.-J.; Weller, U.; Ippisch, O.
Journal Journal of Hydrology
Year 2010
Department BOPHY
Volume 393
Issue 1-2
Page From 20
Page To 28
Language englisch
Keywords Soil hydrology; Upscaling; Modelling; Soil hydraulic properties; Spatial heterogeneity; Preferential flow
Abstract A notorious problem in modelling water dynamics within the unsaturated zone is preferential flow and temporal non-equilibrium between water content and water potential. These phenomena originate from the ubiquitous spatial heterogeneity of soil hydraulic properties and substantially hampers the prediction of solute transport from the soil surface towards groundwater. The characteristic scale of these processes is the soil profile or 'pedon scale' where modelling of water dynamics is typically based on the well established Richards equation which has been augmented by various conceptual approaches to represent preferential flow phenomena. In this paper we investigate through numerical case studies hydraulic non-equilibrium during infiltration of water into relatively dry, heterogeneous soil profiles, which is the most prominent scenario where non-equilibrium conditions affect the overall dynamics of water and solutes. We start from well-defined local heterogeneities in a two-dimensional domain and we analyze the dynamics of water content and water potential at the models full spatial resolution. Based on our numerical results we approach the problem of how to represent the heterogeneous setting by an effective one-dimensional description. For practical purposes of large scale applications, such one-dimensional schemes are highly required. As a prerequisite, soil types need to be represented by a reduced set of effective hydraulic properties. The main challenge is to preserve preferential flow phenomena in such simplified one-dimensional models. We demonstrate that classical approaches of volume averaging do not reflect non-equilibrium effects. From the different concepts for representing hydraulic non-equilibrium we focus on an approach proposed by Ross and Smettem [Ross, P., Smettem, K.R.J., 2000. A simple treatment of physical non-equilibrium water flow in soil. Soil Sci. Soc. Am. J. 64, 1926-1930] to decouple water content and water potential. This concept is corroborated by our numerical results and we discuss the possibility to link non-equilibrium dynamics and the related model parameters to observable structural properties of the material.
Persistent UFZ Identifier
Vogel, H.-J., Weller, U., Ippisch, O. (2010):
Non-equilibrium in soil hydraulic modelling
J. Hydrol. 393 (1-2), 20 - 28