ARS | Publication request: Modeling Preferential Flow and Transport at the Plot and Field Scales

Submitted to: International Conference on Preferential Flow and Transport Processes in Soil
Publication Type: Abstract Only
Publication Acceptance Date: October 23, 2006
Publication Date: November 9, 2006
Citation: Van Genuchten, M.T., Simunek, J., Gerke, H.H., Boivin, A., Coquet, Y., Gardenas, A., Schaap, M. 2006. Modeling Preferential Flow and Transport at the Plot and Field Scales. International Conference on Preferential Flow and Transport Processes in Soil held in Ascona, Switzerland, Nov 4-9, 2006. Pg No. 71

Technical Abstract: This presentation provides an overview of various approaches for modeling the preferential movement of water and solutes in macroporous soils or unsaturated fractured rock. A large number of models of varying degrees of complexity are currently available, each one invoking a different set of assumptions. Models include relatively simplistic formulations involving the use of composite soil hydraulic functions, more complex process-based dual-porosity and dual-permeability models, as well as more refined geometry-based models assuming discrete fracture or macropore networks. Dual-porosity models results when the Richards or advection-dispersion equations are used for flow or transport in the fractures, while immobile water is assumed to exist in the matrix. By comparison, dual-permeability models result when water flow and/or solute transport are assumed to occur also in the matrix. Application of dual-porosity and dual-permeability models requires estimates of the hydraulic properties of the fracture pore network, the matrix region, or some composite of these. Measurements of the separate or composite functions can be obtained using a combination of tension infiltrometry and more traditional methods. Field measurements suggest that the fracture hydraulic conductivity is generally about one order of magnitude larger than the matrix conductivity at saturation. A recent analysis of the UNSODA unsaturated soil hydraulic database revealed similar differences. Advantages and disadvantages of the various preferential flow formulations are discussed. We also present several examples showing application of the different models to various field situations, especially for flow and transport in tile-drained fields