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Numerical Analysis of Solute Transport from Trickle Sources in a Combined Desert Soil–Imported Soil Flow System

^a Dep. of Environmental Physics and Irrigation, Institute of Soils, Water and Environmental Sciences, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel
^b Present address: AMEC Earth & Environmental Ltd., 160 Traders Blvd. East, Suite 110, Mississauga, ON, Canada, L4Z 3K7

View larger version (17K): [in this window] [in a new window]   FIG. 1. A conceptual scheme of the vertical two-dimensional modeling domain. Open circles indicate positions of the drip line laterals (and the crop rows) at the soil surface, while the short thick lines below them schematically represent the ponded strips. Thick solid curves indicate the boundaries between the local soil and the imported soil (Eq. [1]), while the vertical dashed lines represent the averaging domain (Eq. [10] and [11]) in the vicinity of the two inner beds. Vertical exaggeration 2x.

View larger version (14K): [in this window] [in a new window]   FIG. 2. Average constitutive relations for the local and the two imported soil materials: (a) logarithmic conductivity and (b) water content as functions of pressure head.

View larger version (76K): [in this window] [in a new window]   FIG. 3. Contours of the simulated pressure head, (top, in meters) and the Cl– concentration, c (bottom, in molc m–3) distributions in the vertical x1x2 plane of the local soil in the vicinity of the two inner beds. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength, Q = 1500 cm2 h–1. Vertical exaggeration 0.7x and 0.3x for and c, respectively.

View larger version (55K): [in this window] [in a new window]   FIG. 4. Contours of the simulated pressure head (in meters) distribution in the vertical x1x2 plane of the soil in the vicinity of the two inner beds, for the imported sandy soil material applied into narrow and deep (top) and wide and shallow (bottom) trenches. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength, Q = 1500 cm2 h–1. Vertical exaggeration 0.7x.

View larger version (92K): [in this window] [in a new window]   FIG. 5. Contours of the simulated pressure head (in meters) distribution in the vertical x1x2 plane of the soil in the vicinity of the two inner beds for the imported tuff soil material applied into narrow and deep (top) and wide and shallow (bottom) trenches. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength, Q = 1500 cm2 h–1. Vertical exaggeration 0.7x.

View larger version (64K): [in this window] [in a new window]   FIG. 6. Contours of the Cl– concentration (in molc m–3) distribution in the vertical x1x2 plane of the soil in the vicinity of the inner beds for the imported sandy soil material applied into narrow and deep (top) and wide and shallow (bottom) trenches. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength Q = 1500 cm2 h–1. Vertical exaggeration 0.3x.

View larger version (66K): [in this window] [in a new window]   FIG. 7. Contours of the Cl– concentration (in molc m–3) distribution in the vertical x1x2 plane of the soil in the vicinity of the two inner beds for the imported tuff soil material applied into narrow and deep (top) and wide and shallow (bottom) trenches. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength Q = 1500 cm2 h–1. Vertical exaggeration 0.3x.

View larger version (19K): [in this window] [in a new window]   FIG. 8. Mean profiles of the (a) vertical and the (b) horizontal components of the velocity vector, horizontally averaged across a single drip line lateral in the left-hand-side inner bed for the local soil and the two imported soil materials applied into narrow and deep (N) and wide and shallow (W) trenches. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength Q = 1500 cm2 h–1.

View larger version (16K): [in this window] [in a new window]   FIG. 9. Mean concentration profiles, obtained by averaging the Cl– concentration c(x,t) horizontally across the two inner beds for the local soil and the two imported soil materials applied into (a) narrow and deep and (b) wide and shallow trenches. Results are depicted for t = 30 d, just after the cessation of an irrigation event, for a source strength Q = 1500 cm2 h–1; zm and xm are the trench depth and width, respectively.

View larger version (21K): [in this window] [in a new window]   FIG. 10. Longitudinal and transverse (insets) components of the displacement covariance function (Eq. [10b]) associated with the two inner drip line laterals, as functions of time, for the local soil and the two imported soil materials applied into (a) narrow and deep and (b) wide and shallow trenches for a source strength Q = 1500 cm2 h–1.

View larger version (26K): [in this window] [in a new window]   FIG. 11. The solute breakthrough curve monitored at a given horizontal control plane (CP) at L = 0.75 m and (insets) the normalized accumulated mass of the solute that crossed the CP, as functions of time, for the local soil and the two imported soil materials applied into (a) narrow and deep and (b) wide and shallow trenches for a source strength Q = 1500 cm2 h–1.

View larger version (43K): [in this window] [in a new window]   FIG. 12. Contours of the amount of applied water (in meters) required to leach half of the total mass of solute applied into the flow system, as functions of the soil parameters saturated hydraulic conductivity (Ks) and the van Genuchten shape parameter characterizing different hypothetical imported soil materials applied into (a) narrow and deep and (b) wide and shallow trenches. Results are depicted for n = 3.6 for a source strength Q = 1500 cm2 h–1.

View larger version (14K): [in this window] [in a new window]   FIG. 13. Combinations of threshold values of saturated hydraulic conductivity (Ks) and the van Genuchten shape parameter above which a narrow and deep trench is more efficient in solute leaching than a wide and shallow trench for selected values of the van Genuchten shape parameter n, for a source strength Q = 1500 cm2 h–1.

View larger version (27K): [in this window] [in a new window]   FIG. 14. Contours of the amount of applied water (in meters) required to leach half of the total mass of solute applied into the flow system as functions of the trench depth (zm) and width (xm). Results are depicted for the tuff soil material for a source strength Q = 1500 cm2 h–1.