Soil Water Retention and Relative Permeability for Full Range of Saturation

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Common conceptual models for unsaturated flow often rely on the oversimplified representation of medium pores as a bundle of cylindrical capillaries and assume that the matric potential is attributed to capillary forces only. The adsorptive surface forces are ignored. It is often assumed that aqueous flow is negligible when a soil is near or at the residual water content. These models are successful at high and medium water contents but often give poor results at low water contents. These models do not apply to conditions at which water content is less than the residual water content. We extend the lower ... continued below

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Zhang, Z. F. September 28, 2010.

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Common conceptual models for unsaturated flow often rely on the oversimplified representation of medium pores as a bundle of cylindrical capillaries and assume that the matric potential is attributed to capillary forces only. The adsorptive surface forces are ignored. It is often assumed that aqueous flow is negligible when a soil is near or at the residual water content. These models are successful at high and medium water contents but often give poor results at low water contents. These models do not apply to conditions at which water content is less than the residual water content. We extend the lower bound of existing water-retention functions and conductivity models from residual water content to the oven-dry condition (i.e., zero water content) by defining a state-dependent, residual-water content for a soil drier than a critical value. Furthermore, a hydraulic conductivity model for smooth uniform spheres was modified by introducing a correction factor to describe the film flow-induced hydraulic conductivity for natural porous media. The total unsaturated hydraulic conductivity is the sum of those due to capillary and film flow. The extended retention and conductivity models were verified with six datasets from the literature. Results show that, when the soil is at high and intermediate water content, there is no difference between the un-extended and the extended models; when the soil is at low water content, the un-extended models overestimate the water content but under-estimate the conductivity while the extended models match the retention and conductivity measurements well.

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  • Report No.: PNNL-19800
  • Grant Number: AC05-76RL01830
  • DOI: 10.2172/1001513 | External Link
  • Office of Scientific & Technical Information Report Number: 1001513
  • Archival Resource Key: ark:/67531/metadc831898

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  • September 28, 2010

Added to The UNT Digital Library

  • May 19, 2016, 3:16 p.m.

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  • Dec. 1, 2016, 10:39 p.m.

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Zhang, Z. F. Soil Water Retention and Relative Permeability for Full Range of Saturation, report, September 28, 2010; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc831898/: accessed June 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.