Unsaturated Hydraulic Conductivity from Transient Multistep Outflow and Soil Water Pressure Data

1994 ◽  
Vol 58 (3) ◽  
pp. 687-695 ◽  
Author(s):  
S. O. Eching ◽  
J. W. Hopmans ◽  
O. Wendroth
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Water Pressure ◽  
Pressure Data ◽  
Unsaturated Hydraulic Conductivity ◽  
Multistep Outflow

scholarly journals Examining the effect of pore size distribution and shape on flow through unsaturated peat using computed tomography

2009 ◽  
Vol 13 (10) ◽  
pp. 1993-2002 ◽  
Author(s):  
F. Rezanezhad ◽  
W. L. Quinton ◽  
J. S. Price ◽  
D. Elrick ◽  
T. R. Elliot ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size ◽  
Soil Water ◽  
Water Pressure ◽  
Peat Soil ◽  
Pressure Head ◽  
Peat Soils ◽  
Unsaturated Hydraulic Conductivity

Abstract. The hydraulic conductivity of unsaturated peat soil is controlled by the air-filled porosity, pore size and geometric distribution as well as other physical properties of peat materials. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT), at 45 μm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a sharp decline in hydraulic conductivity. This is because the large pores readily lose water, the peat rapidly becomes less conductive and the flow path among pores, more tortuous.

Historical development of soil-water physics and solute transport in porous media

2007 ◽  
Vol 7 (1) ◽  
pp. 59-66 ◽  
Author(s):  
D.E. Rolston
Keyword(s):  
Porous Media ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Soil Water ◽  
20Th Century ◽  
Water Flow ◽  
Unsaturated Soils ◽  
Transport Processes ◽  
Transport In Porous Media ◽  
Unsaturated Hydraulic Conductivity

The science of soil-water physics and contaminant transport in porous media began a little more than a century ago. The first equation to quantify the flow of water is attributed to Darcy. The next major development for unsaturated media was made by Buckingham in 1907. Buckingham quantified the energy state of soil water based on the thermodynamic potential energy. Buckingham then introduced the concept of unsaturated hydraulic conductivity, a function of water content. The water flux as the product of the unsaturated hydraulic conductivity and the total potential gradient has become the accepted Buckingham-Darcy law. Two decades later, Richards applied the continuity equation to Buckingham's equation and obtained a general partial differential equation describing water flow in unsaturated soils. For combined water and solute transport, it had been recognized since the latter half of the 19th century that salts and water do not move uniformly. It wasn't until the middle of the 20th century that scientists began to understand the complex processes of diffusion, dispersion, and convection and to develop mathematical formulations for solute transport. Knowledge on water flow and solute transport processes has expanded greatly since the early part of the 20th century to the present.

scholarly journals A numerical study on the effect of salinity on stability of an unsaturated railway embankment under rainfall

2020 ◽  
Vol 195 ◽  
pp. 01004
Author(s):  
Ali Kolahdooz ◽  
Hamed Sadeghi ◽  
Mohammad Mehdi Ahmadi
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Water Retention ◽  
Numerical Study ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Unsaturated Hydraulic Conductivity ◽  
Influence Of Water ◽  
Dispersive Soils

Dispersive soils, as one of the main categories of problematic soils, can be found in some parts of the earth, such as the eastern-south of Iran, nearby the Gulf of Oman. One of the most important factors enhancing the dispersive potential is the existence of dissolved salts in the soil water. The main objective of this study is to explore the influence of water salinity on the instability of a railway embankment due to rainfall infiltration. In order to achieve this goal, the embankment resting on a dispersive stratum is numerically modeled and subjected to transient infiltration flow. The effect of dispersion is simplified through variations in the soil-water retention curve with salinity. The measured water retention curves revealed that by omitting the natural salinity in the soil-water, the retention capability of the soil decreases; therefore, the unsaturated hydraulic conductivity of the soil stratum will significantly decline. According to the extensive decrease in the hydraulic conductivity of the desalinated materials, the rainfall cannot infiltrate in the embankment and the rainfall mostly runs off. However, in the saline embankment, the infiltration decreases the soil suction; and consequently, the factor of safety of the railway embankment decreases.

scholarly journals Simultaneous Determination of Water Retention Curve and Unsaturated Hydraulic Conductivity of Substrates Using a Steady-state Laboratory Method

HortScience ◽  
2010 ◽  
Vol 45 (7) ◽  
pp. 1106-1112 ◽  
Author(s):  
Paraskevi A. Londra
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Hydraulic Conductivity ◽  
Water Retention ◽  
Water Pressure ◽  
Pressure Head ◽  
Laboratory Method ◽  
Water Retention Curve ◽  
Retention Curve ◽  
Unsaturated Hydraulic Conductivity

For effective irrigation and fertilization management, the knowledge of substrate hydraulic properties is essential. In this study, a steady-state laboratory method was used to determine simultaneously the water retention curve, θ(h), and unsaturated hydraulic conductivity as a function of volumetric water content, K(θ), and water pressure head, K(h), of five substrates used widely in horticulture. The substrates examined were pure peat, 75/25 peat/perlite, 50/50 peat/perlite, 50/50 coir/perlite, and pure perlite. The experimental retention curve results showed that in the case of peat and its mixtures with perlite, there is a hysteresis between drying and wetting branches of the retention curve. Whereas in the case of coir/perlite and perlite, the phenomenon of hysteresis was less pronounced. The increase of perlite proportion in the peat/perlite mixtures led to a decrease of total porosity and water-holding capacity and an increase of air space. Study of the K(θ) and K(h) experimental data showed that the hysteresis phenomenon of K(θ) was negligible compared with the K(h) data for all substrates examined. Within a narrow range of water pressure head (0 to –70 cm H2O) that occurs between two successive irrigations, a sharp decrease of the unsaturated hydraulic conductivity was observed. The comparison of the K(θ) experimental data between the peat-based substrate mixtures and the coir-based substrate mixture showed that for water contents lower than 0.40 m3·m−3, the hydraulic conductivity of the 50/50 coir/perlite mixture was greater. The comparison between experimental water retention curves and predictions using Brooks-Corey and van Genuchten models showed a high correlation (0.992 ≤ R2 ≤ 1) for both models for all substrates examined. On the other hand, in the case of unsaturated hydraulic conductivity, the comparison showed a relatively good correlation (0.951 ≤ R2 ≤ 0.981) for the van Genuchten-Mualem model for all substrates used except perlite and a significant deviation (0.436 ≤ R2 ≤ 0.872) for the Brooks-Corey model for all substrates used.

scholarly journals Soil-Water Characteristic Curves And Hydraulic Conductivity of Gaomiaozi Bentonite Pellet-Contained Materials

2021 ◽  
Author(s):  
Jianghong Zhu ◽  
Zhenyan Su ◽  
Huyuan Zhang
Keyword(s):  
Particle Size ◽  
Hydraulic Conductivity ◽  
Soil Water ◽  
Dry Density ◽  
Characteristic Curves ◽  
Factors Affecting ◽  
Unsaturated Hydraulic Conductivity ◽  
Long Time ◽  
Soil Water Characteristic Curves ◽  
High Level

Abstract The bentonite pellet-contained material (PCM) is a feasible material for the joint sealing of high-level radioactive waste repository. During the operation of the repository, the PCM will be unsaturated for a long time, and its water retention and permeability directly affect the buffer barrier seepage, nuclide migration, and joint healing. Moreover, the particle size of bentonite pellets and dry density are important factors affecting the performance of PCM. In this work, the pressure plate method and vapour equilibrium technique were utilized to test the soil-water characteristic curves (SWCCs) of the PCMs with different particle sizes and dry densities. The unsaturated hydraulic conductivity of the PCMs was predicted by combining the SWCC model and saturated hydraulic conductivity. The results showed that in the low suction range (20–1150 kPa), the dry density and particle size had a negative correlation with the water content at the same suction. In the high suction range (4200–309000 kPa), the dry density and particle size had little effect on the SWCC. The Gardner model was appropriate for describing the SWCC of PCM. In addition, the hydraulic conductivity of the PCM decreased with the increase in dry density, while increased with the increase in particle size. The influence mechanism of the SWCC and hydraulic conductivity was further discussed based on the scanning electron microscopy images and pore size distribution curves.

Reducing non-uniqueness of inverting bimodal soil Kosugi hydraulic parameters

2021 ◽  
Author(s):  
Jesús Fernández-Gálvez ◽  
Joseph Pollacco ◽  
Stephen McNeill ◽  
Sam Carrick ◽  
Linda Lilburne ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Water Pressure ◽  
Full Range ◽  
Inverse Modelling ◽  
Residual Soil ◽  
Hydraulic Parameters ◽  
The Matrix

<p>Hydrological models use soil hydraulic parameters to describe the storage and transmission of water in soils. Hydraulic parameters define the water retention, <em>θ(ψ)</em>, and the hydraulic conductivity, <em>K(θ)</em>, functions. These functions are usually obtained by fitting experimental data to the corresponding θ(ψ) and K(θ) functions. The drawback of deriving the hydraulic parameters by inverse modelling is that they suffer from equifinality or non-uniqueness, and the optimal hydraulic parameters are non-physical (Pollacco <em>et al.</em>, 2008). To reduce the non-uniqueness, it is necessary to invert the hydraulic parameters simultaneously from observations of both<em> θ(ψ)</em> and <em>K(θ</em>), and ensure the measurements cover the full range of <em>θ</em> from fully saturated to oven dry, which requires expensive, labour-intensive measurements.  </p><p>We present a novel procedure to derive a unique, physical set of bimodal or dual permeabilityKosugi hydraulic functions,<em> θ(ψ)</em> and <em>K(θ)</em>, from inverse modelling. The Kosugi model was chosen given its parameters have direct physical meaning to the soil pore-size distribution. The challenge of using bimodal functions is they require double the number of parameters (Pollacco <em>et al.</em>, 2017), exacerbating the problem of non-uniqueness. To address this shortcoming, we<strong> (1) </strong>derive residual soil water content from the matrix Kosugi standard deviation, <strong>(2) </strong>derive macropore hydraulic parameters from the soil water pressure boundary between macropore and matrix, and <strong>(3)</strong> dynamically constraint the matrix Kosugi hydraulic parameters. We successfully reduce the number of hydraulic parameters to optimize and constrain the hydraulic parameters without compromising the fit of the <em>θ(ψ)</em> and <em>K(θ)</em> functions.</p><p>The robustness of the methodology is demonstrated by deriving the hydraulic parameters exclusively from<em> θ(ψ)</em> and <em>K<sub>s</sub></em>data, enabling satisfactory prediction of <em>K(θ)</em> without having measured K(θ) data. Moreover, having a reduced number of hydraulic parameters that are physical allows an improved characterization of hydraulic properties of soils prone to preferential flow, which is a fundamental issue regarding the understanding of hydrological processes.</p><p> </p><p><strong>References</strong></p><p>Pollacco, J.A.P., Ugalde, J.M.S., Angulo-Jaramillo, R., Braud, I., Saugier, B., 2008. A linking test to reduce the number of hydraulic parameters necessary to simulate groundwater recharge in unsaturated soils. Adv Water Resour 31, 355–369. https://doi.org/10.1016/j.advwatres.2007.09.002</p><p>Pollacco, J.A.P., Webb, T., McNeill, S., Hu, W., Carrick, S., Hewitt, A., Lilburne, L., 2017. Saturated hydraulic conductivity model computed from bimodal water retention curves for a range of New Zealand soils. Hydrol. Earth Syst. Sci. 21, 2725–2737. https://doi.org/10.5194/hess-21-2725-2017</p>

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