Soil Water Retention and Relative Permeability for Conditions from Oven‐Dry to Full Saturation

Zhang, Fred

doi:10.2136/vzj2011.0019

Cited by 83 publications

(123 citation statements)

References 23 publications

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“…While this relationship, and other similar expressions, represent wet and moderately wet soil moisture conditions well, they are of limited use under dry soil conditions. Several studies have developed extensions to these functions to represent dry conditions more accurately (Webb, 2000; Khlosi et al, 2008; Zhang, 2011). The QBZ approach to modeling the flow from the irrigation system is therefore limited for two reasons: first, vapor flows are not accounted for explicitly, and second, the empirical relationship used to relate the water content to the matric potential breaks down under dry conditions.…”

Section: Methodsmentioning

confidence: 99%

Modeling Vapor Flow from a Pervaporative Irrigation System

Todman

Ireson

Butler

et al. 2013

Vadose Zone Journal

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Experimental and modeling results were used to develop a conceptual understanding of the process of pervaporative irrigation in dry soils. When irrigating in this way, a pervaporative membrane is formed into a tube, buried in the soil, and filled with water. If the surrounding soil is dry, a chemical potential gradient across the membrane draws water into the soil. Water can only desorb from the membrane as a vapor, however, so it enters the soil in the vapor phase. This study corroborates previous evidence that vapor flow can significantly affect the flux from the irrigation membrane under arid conditions. A new model of water transport from a pervaporative irrigation membrane in unvegetated soils was developed, taking into account transport in both liquid and vapor phases, and successfully simulated experimental observations of the total water flux, relative humidity, and water content distribution in three soil types. Modeling results showed that the capacity for moisture sorption within different soil types affects both condensation in the soil and the subsequent flux from the pervaporative membrane. A mathematical relationship for the moisture sorption isotherm for a soil can therefore be used to predict the flux across the membrane in that soil. If condensation is significant, liquid flows through the soil also affect the flux from the membrane. Model simulations suggest that the flux from the pervaporative membrane is primarily limited by humid conditions within the soil rather than the transport of water across the membrane, thus plant interactions with the soil conditions should increase the irrigation flux.

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Section: Methodsmentioning

confidence: 99%

Modeling Vapor Flow from a Pervaporative Irrigation System

Todman

Ireson

Butler

et al. 2013

Vadose Zone Journal

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“…2.2.1) σ w (T K ) is the surface tension of water and w (T K ) is the static dielectric constant or relative permittivity of water; 0 = 8.85 × 10 −12 C 2 J −1 m −1 is the permittivity of free space; k B = 1.308568 × 10 −23 J K −1 is the Boltzmann constant; a = 1.6021773×10 −19 C is the electron charge; z [dimensionless] is the ion charge, for which z = 1 can be assumed; and F w [dimensionless] is a soil-specific parameter, for which Zhang (2011) found that (roughly) 10 < F w < 10 4 . The term ρ w V θ,surf in Eq.…”

Section: Functions Related To Liquid Water Transportmentioning

confidence: 99%

A non-equilibrium model for soil heating and moisture transport during extreme surface heating: the soil (heat–moisture–vapor) HMV-Model Version 1

Massman

2015

Geosci. Model Dev.

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Abstract. Increased use of prescribed fire by land managers and the increasing likelihood of wildfires due to climate change require an improved modeling capability of extreme heating of soils during fires. This issue is addressed here by developing and testing the soil (heat-moisture-vapor) HMVmodel, a 1-D (one-dimensional) non-equilibrium (liquidvapor phase change) model of soil evaporation that simulates the coupled simultaneous transport of heat, soil moisture, and water vapor. This model is intended for use with surface forcing ranging from daily solar cycles to extreme conditions encountered during fires. It employs a linearized Crank-Nicolson scheme for the conservation equations of energy and mass and its performance is evaluated against dynamic soil temperature and moisture observations, which were obtained during laboratory experiments on soil samples exposed to surface heat fluxes ranging between 10 000 and 50 000 W m −2 . The Hertz-Knudsen equation is the basis for constructing the model's non-equilibrium evaporative source term. Some unusual aspects of the model that were found to be extremely important to the model's performance include (1) a dynamic (temperature and moisture potential dependent) condensation coefficient associated with the evaporative source term, (2) an infrared radiation component to the soil's thermal conductivity, and (3) a dynamic residual soil moisture. This last term, which is parameterized as a function of temperature and soil water potential, is incorporated into the water retention curve and hydraulic conductivity functions in order to improve the model's ability to capture the evaporative dynamics of the strongly bound soil moisture, which requires temperatures well beyond 150 • C to fully evaporate. The model also includes film flow, although this phenomenon did not contribute much to the model's overall performance. In general, the model simulates the laboratoryobserved temperature dynamics quite well, but is less precise (but still good) at capturing the moisture dynamics. The model emulates the observed increase in soil moisture ahead of the drying front and the hiatus in the soil temperature rise during the strongly evaporative stage of drying. It also captures the observed rapid evaporation of soil moisture that occurs at relatively low temperatures (50-90 • C), and can provide quite accurate predictions of the total amount of soil moisture evaporated during the laboratory experiments. The model's solution for water vapor density (and vapor pressure), which can exceed 1 standard atmosphere, cannot be experimentally verified, but they are supported by results from (earlier and very different) models developed for somewhat different purposes and for different porous media. Overall, this non-equilibrium model provides a much more physically realistic simulation over a previous equilibrium model developed for the same purpose. Current model performance strongly suggests that it is now ready for testing under field conditions.

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“…Besides the data to fit the WR of the base model and the oven‐dry pressure head, no additional data are required to fit the critical pressure value. The Rehovot sand did not respond well to the Zhang () approach, because the adsorptive component in the HC function becomes relevant at a lower absolute pressure | h | than the adsorptive component of the WR function. In similar situations, parameter h a should be fitted together with parameters ω and a to yield more reliable values.…”

Section: Resultsmentioning

confidence: 97%

“…Using the critical pressure head proposed by Zhang () as h a , its value changed to 27.55 m for the Adelanto loam and to 31.00 m for the Pachappa loam. Calculating RMSE considering all h (θ) data yielded values of 8.67·10 ‑3 and 7.44·10 ‑3 respectively.…”

Section: Resultsmentioning

confidence: 99%

An extension of water retention and conductivity functions to dryness

Inforsato

Lier

Pinheiro

2020

Soil Science Soc of Amer J

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Water retention (WR) and hydraulic conductivity (HC) are essential properties to predict water flow in soils. Commonly, these soil physical properties are represented by equations relating pressure head, soil water content, and hydraulic conductivity. The commonly used empirical equations used for this purpose have a limited range of reliability, not functioning properly in the very dry range. An approach to extend the reliability and applicability of these models has been p hed piecewise equations added to the base model and implying in changes in the base model paramete. We propose a modification of the model commonly known as Peters‐Durner‐Iden (PDI), extending the reliability of most common base models without the need to change the original parameters. The transformation is analytically equivalent, interchangeable and allows to anchor the retention function at any point instead of the residual water content. The Van Genuchten, Kosugi, Brooks‐Corey and Groenevelt equations can easily be combined to the proposed model, which may be used to predict water flow in the dry range where the commonly used equations are not reliable.

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Soil Water Retention and Relative Permeability for Conditions from Oven‐Dry to Full Saturation

Cited by 83 publications

References 23 publications

Modeling Vapor Flow from a Pervaporative Irrigation System

Modeling Vapor Flow from a Pervaporative Irrigation System

A non-equilibrium model for soil heating and moisture transport during extreme surface heating: the soil (heat–moisture–vapor) HMV-Model Version 1

An extension of water retention and conductivity functions to dryness

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