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Inverse Dual-Permeability Modeling of Preferential Water Flow in a Soil Column and Implications for Field-Scale Solute Transport

J. Maximilian Köhne^a,c,*, Binayak P. Mohanty^a and Jirka imnek^b

^a Dep. of Biological & Agricultural Engineering, Texas A&M Univ., Scoates Hall, College Station, TX 77843-2117
^b Univ. of California, Dep. of Environmental Sciences, 900 University Av., A135 Bourns Hall, Riverside, CA 92521
^c currently, Institute for Land Use, Univ. Rostock, Justus-von-Liebig Weg 6, 18059 Rostock, Germany

View larger version (32K): [in a new window]   Fig. 1. Experimental data and inverse HYDRUS-1D simulation results for the loam column, infiltration (left) and drainage (right): (a, b) cumulative infiltration and outflow, (c, d) pressure heads at the 10-, 20-, and 30-cm depths, and (e, f) water contents at the 10- and 30-cm depths.

View larger version (33K): [in a new window]   Fig. 2. Experimental data and inverse HYDRUS-1D simulation results for the infiltration into the medium-sand (left) and coarse-sand (right) columns: (a, b) cumulative infiltration and outflow, (c, d) pressure heads at 10-, 20-, and 30-cm depths, (e, f) water contents at the 10- and 30-cm depths.

View larger version (23K): [in a new window]   Fig. 3. Infiltration into the loam column with a preferential flow path (PFP) made of medium sand. Comparison of experimental cumulative flow data and dual-permeability model simulations using independently estimated parameters (forward), or inversely identified parameters based on data of pressure heads and water contents in the matrix, and domain-specific (inverse-local) or bulk-soil related (inverse-lumped) outflow. (a) Infiltration, (b) outflow, (c) outflow from the matrix, and (d) outflow from the PFP.

View larger version (28K): [in a new window]   Fig. 4. Same as Fig. 3, but showing pressure heads in matrix and preferential flow path (PFP) at depths of (a) 5, (b) 35, and (c) 65 cm.

View larger version (15K): [in a new window]   Fig. 5. Same as Fig. 3, but showing water contents in the matrix and preferential flow path (PFP) at the 35-cm depth.

View larger version (24K): [in a new window]   Fig. 6. Infiltration into loam column with preferential flow path (PFP) made of coarse sand. Comparison of experimental cumulative flow data and dual-permeability model simulations using independently estimated parameters (forward), or inversely identified parameters based on data of pressure heads and water contents in the matrix, and domain-specific (inverse-local) or bulk-soil related (inverse-lumped) outflow. (a) Infiltration, (b) outflow, (c) outflow from the matrix, and (d) outflow from the PFP.

View larger version (24K): [in a new window]   Fig. 7. Same as Fig. 6, but showing pressure heads at depths of (a) 5 and (b) 65 cm.

View larger version (16K): [in a new window]   Fig. 8. Same as Fig. 6, but showing matrix water contents at depths of 5 and 35 cm.

View larger version (26K): [in a new window]   Fig. 9. Drainage from the loam column with the preferential flow path (PFP) made of coarse sand. Comparison of experimental cumulative outflow data and dual-permeability model simulations using independently estimated parameters (forward), or inversely identified parameters based on data of pressure heads and water contents in the matrix and domain-specific (inverse-local) or bulk-soil related (inverse-lumped) outflow. (a) Outflow, (b) outflow from the matrix, and (c) outflow from the PFP.

View larger version (26K): [in a new window]   Fig. 10. Same as Fig. 9, but showing pressure heads in the matrix and in the preferential flow path (PFP) at depths of (a) 5 and (b) 65 cm.

View larger version (21K): [in a new window]   Fig. 11. Same as Fig. 9, but showing water contents in the matrix and in the preferential flow path (PFP) at the 35-cm depth.

View larger version (40K): [in a new window]   Fig. 12. Soil hydraulic van Genuchten functions fitted to the soil water retention curve measured at equilibrium (static) and obtained by fitting the numerical solution of Richards' equation to water flow measurements performed on homogeneous soil materials (infiltration and drainage), and obtained by fitting the dual-permeability model to flow measurements conducted with heterogeneous soil systems consisting of loam (matrix) and medium or coarse sand (preferential flow path, PFP): medium sand (a) water content and (b) hydraulic conductivity, coarse sand (c) water content and (d) hydraulic conductivity, and loam (matrix) (e) water content and (f) hydraulic conductivity.

View larger version (30K): [in a new window]   Fig. 13. Rainfall, drain discharge flux, and cumulative drain outflow as observed at the Bokhorst field site for three runoff seasons between 1991 and 1995 (data: Lennartz et al., 1999), and inverse dual-permeability model (DPM) simulation results for the sequential and simultaneous approaches.

View larger version (34K): [in a new window]   Fig. 14. Bromide tracer concentrations as observed in drain outflow at the Bokhorst field site for three runoff seasons between 1992 and 1995 (data Lennartz et al., 1999) and inverse dual-permeability model (DPM) simulation results for the sequential and simultaneous approaches. The only parameter fitted in the solute transport equation was the first-order solute transfer coefficient.

View larger version (28K): [in a new window]   Fig. 15. Same as Fig. 14, but in the solute transport equation, both the first-order transfer coefficient and the fracture dispersivity (1994/1995: additionally the matrix dispersivity) were fitted.