116-2 Using Passive Capillary Lysimeter Water Flux Measurements to Improve Flow Predictions In Variably Saturated Soils.

Poster Number 128

See more from this Division: S01 Soil Physics
See more from this Session: Advances In Soil and Vadose Zone Hydrology: The Contributions of Glendon Gee: II
Monday, October 17, 2011
Henry Gonzalez Convention Center, Hall C
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Yakov Pachepsky1, Andrey Guber2, Diederik Jacques3, Martinus van Genuchten4, Ralph Cady5 and Thomas Nicholson5, (1)Bldg. 173 BARC-EAST, USDA-ARS, Beltsville, MD
(2)USDA-ARS, Beltsville, MD
(3)SCK-CEN, Mol, Belgium
(4)Department of Mechanical Engineering, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil
(5)U. S. NRC, Rockville, MD
Passive capillary lysimeters (PCLs) are uniquely suited for measuring water fluxes in variably-saturated soils. The objective of this work was to compare PCL flux measurements with simulated fluxes obtained with a calibrated unsaturated flow model. A Richards equation-based model was calibrated using TDR data from a loamy soil profile involving 12 replicates along transects at five depths.  The fluxes themselves were measured at depths of 15 and 55 cm, and were estimated at the depth of 105 cm using the soil storage dynamics. Annual cumulative fluxes were used to compare measurements and simulations. Large discrepancies were found between simulated and measured fluxes. In an attempt to explain these discrepancies, the fluxes were also computed using a simpler, multiple bucket-type, soil-water model (MWBUS) which was calibrated independently with the TDR soil water monitoring data. PCL measurements and the MWBUS-simulated results were in a very good agreement. Further analyses showed that improvements in the fit of the multiparametric Richards model was achieved by introducing water losses to runoff, whereas no runoff was observed in the experiment. The simulated loss of water to runoff apparently distorted simulated fluxes in the soil profile.  This study demonstrated that PCL flux measurements can be extremely useful for improving modeling of variably saturated flow in soils.
See more from this Division: S01 Soil Physics
See more from this Session: Advances In Soil and Vadose Zone Hydrology: The Contributions of Glendon Gee: II