Saturated and field-saturated water flow parameters describe or quantify the ability of a porous medium to transmit water when the porous medium is saturated or nearly saturated. This chapter discusses various parameters that include saturated and field-saturated hydraulic conductivity, matric flux potential, the macroscopic capillary length parameter, the effective Green–Ampt wetting front pressure head, and sorptivity. It provides information on the air-entry and water-entry pressure heads. Agricultural soils often exhibit extensive spatial and temporal changes in pore characteristics due to changes in soil texture, structure, horizonation, root growth, faunal burrowing, freeze–thaw action, and other processes. As a result, saturated and field-saturated water flow parameters tend to be highly variable, with coefficients of variation as high as 400% or more, and statistical distributions that are often highly skewed.

In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air-filled pores control the unsaturated hydraulic conductivity of peat soils using high-resolution (45 mu m) three-dimensional (3D) X-ray computed tomography (CT) and digital image processing of four peat sub-samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross-sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air-filled pore hydraulic radius, tortuosity, air-filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air-filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright (C) 2010 John Wiley & Sons, Ltd.

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.

Efficient use of irrigation water is becoming an important issue in nursery and greenhouse production across the world. Different water conserving systems have been proposed with some relying on good substrate capillary rise properties. However, little is known about the appropriate capillary properties of various substrates. Hence, this paper summarizes the different steps that were followed in order to identify the appropriate capillary rise properties for proper plant growth in nurseries. A first step was to develop a model of capillary rise based on the unsaturated hydraulic conductivity curve, the models developed in a second step, and then the models were validated against field data in a third step. Therefore, this conceptual framework is proposed by the authors for assessing the suitability of substrates for plant growth by characterizing the substrate, using the evapotranspirative demand as input, and a model to predict the substrate performance under nursery or greenhouse conditions. Alternatively, a comparison of the unsaturated hydraulic conductivity curve with a chart is proposed as a simpler but less accurate way of assessing the behaviour of substrates prior to nursery use.

Water availability for landscape nursery irrigation is foreseen as a major impediment for this industry within the next decade. Among various solutions proposed to increase irrigation efficiency, thereby reducing the water volumes required, are closed and semi-closed subirrigation systems designed to grow plants potted in organic growing media. These systems, however, require organic substrates that have good capillary properties. However, standards for such capillary properties are not available. This study compared substrates composed of peat, bark, and sand having contrasting capillary properties, in a nursery experiment to establish guideline values for the proper and efficient operation on capillary mat devices. It also proposes a theoretical model of capillary rise using the hydraulic characteristics of growing media to predict the suitability of various substrates. Substrates with 60% (per volume) sphagnum peat were found to provide the best capillary rise and best growth, based on empirical measurements, relative to substrates with 30% sphagnum or 30% sedge peat. The proposed theoretical model concurred with these observations.

Infiltration Under Constant Head and Falling Head Conditions D.E. Elrick, D.E. Elrick Department of Land Resource Science, University of Guelph, Guelph, on, CanadaSearch for more papers by this authorR. Angulo-Jaramillo, R. Angulo-Jaramillo Laboratoire d'édute Des Transferts en Hydrologie et Environnement (UMR 5564 CNRS, UJF, INPG, IRD)Grenoble, FranceSearch for more papers by this authorD.J. Fallow, D.J. Fallow Department of Land Resource Science, University of Guelph, Guelph, on, CanadaSearch for more papers by this authorW.D. Reynolds, W.D. Reynolds Greenhouse and Processing Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, on, CanadaSearch for more papers by this authorG.W. Parkin, G.W. Parkin Department of Land Resource Science, University of Guelph, Guelph, on, CanadaSearch for more papers by this author D.E. Elrick, D.E. Elrick Department of Land Resource Science, University of Guelph, Guelph, on, CanadaSearch for more papers by this authorR. Angulo-Jaramillo, R. Angulo-Jaramillo Laboratoire d'édute Des Transferts en Hydrologie et Environnement (UMR 5564 CNRS, UJF, INPG, IRD)Grenoble, FranceSearch for more papers by this authorD.J. Fallow, D.J. Fallow Department of Land Resource Science, University of Guelph, Guelph, on, CanadaSearch for more papers by this authorW.D. Reynolds, W.D. Reynolds Greenhouse and Processing Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, on, CanadaSearch for more papers by this authorG.W. Parkin, G.W. Parkin Department of Land Resource Science, University of Guelph, Guelph, on, CanadaSearch for more papers by this author Book Editor(s):Peter A.C. Raats, Peter A.C. RaatsSearch for more papers by this authorDavid Smiles, David SmilesSearch for more papers by this authorArthur W. Warrick, Arthur W. WarrickSearch for more papers by this author First published: 01 January 2002 https://doi.org/10.1029/129GM04Citations: 14Book Series:Geophysical Monograph Series AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Summary This chapter contains sections titled: Memories of John Philip Introduction Infiltration Equations: Based Only on Sorption Infiltration Equations: Based on Sorption and Gravity Laboratory Tests Concluding Remarks Citing Literature Environmental Mechanics: Water, Mass and Energy Transfer in the Biosphere, Volume 129 RelatedInformation

The flow of soil water is characterized by water transmission parameters, field-saturated hydraulic conductivity, matric flux potential and sorptivity. Soil water flow is, in turn, the primary mechanism by which soil contaminants, such as excess plant nutrient, bacteria, viruses, salts, and industrial chemicals are transported. Consequently, knowledge of soil water transmission parameters is essential for understanding, preventing and remediating the contamination of soil water and ground water. This paper describes steady-state and transient methods for obtaining soil water transmission parameters from ponded infiltration under constant head and falling head conditions in surface rings and shallow auger holes. Also discussed are the conditions under which the various methods are most appropriate.

Tension disk infiltrometer experiments are generally conducted until apparent steady state is reached because most of the methods of analysis are based on Wooding's solution for steady state flux. However, the time necessary to reach steady state may be a penalizing aspect for soils with low permeability and the information contained in the transient stages is not utilized. Moreover, these methods assume homogeneous soil and a uniform initial water content, which may be unrealistic when a large volume of soil is sampled. In this series, we propose and compare several new methods of analysis that are based on the transient stage of axisymmetric infiltration. In the first part, we show that a two‐parameter equation—one term linear in square root of time and one term linear in time—adequately describes the transient flow from the disk infiltrometer for both simulated and laboratory tests. The technique used for the determination of the two coefficients must meet two criteria; it must verify the validity of the two‐term equation throughout the duration of the experiment, and it must account for the early‐time perturbation that is induced by the sand‐contact layer placed between the disk and the soil. We show that the best technique consists in linearizing the data by differentiating cumulative infiltration with respect to the square root of time. Direct nonlinear fitting on cumulative infiltration or infiltration flux is likely to lead to unacceptable errors, either because of the undetected invalidity of the two‐parameter equation or arising from the influence of the contact layer.

In Vandervaere et al. (2000) it was shown that the transient regime of axisymmetric infiltration can be described by a two‐term equation with one term proportional to the square root of time and the other term proportional to time. The two corresponding coefficients, C1 and C2, are functions of the hydraulic conductivity, K, and the sorptivity, S In this paper we propose four different methods to achieve the determination of S and K The four methods differ by the number of disk radii and the number of supply pressure head values which are utilized. We show that the accuracy of a given method is highly dependent on the combination of S and K values obtained. Three situations can be distinguished, depending on the disk radius: (i) the flow is dominated by the lateral capillary term; (ii) the flow is dominated by the gravity term; (iii) lateral capillary and gravity terms have equivalent weights. The seven model soils tested here all correspond to the first situation with usual disk radius values. This tends to show that a precise estimation of K is unlikely from disk infiltrometer data. We introduce a new time scale, tstab, which generalizes the concepts corresponding to the two well known time scales tgrav and tgeom We propose a guideline for the investigator to choose between all existing methods of analysis that use steady or transient flow. Finally, the four new methods are tested against numerically simulated tests with Grenoble sand and Yolo light clay.

Transport models have often been tested in laboratory studies using soil columns, usually of the order of 1 dm(3) in size. Even if the columns are undisturbed, their small size does not allow water flow and solute transport to occur as they would in the field. We therefore used a 1.7 m(3) column and applied steady-state flow rates of the order of 1 mm h(-1), and then applied pluses of tracers Br-, Cl- and (H2O)-H-2 and of atrazine (2-chloro-4-ethylamino-6-isopropylamino-S-triazine) to the surface.Classical models for tracers with these boundary conditions are the Convection-Dispersion model (CD), the two-region (mobile-immobile water) model with first-order exchange of solutes (MIM), and the transfer function models, among which the most widely used is the Convective Lognormal Transfer Function model (CLT). Thanks to simple boundary and initial conditions, analytical solutions are available for all these models.The CD model (1 parameter) was not able to fit the tracer elution curves. but use of the MIM model was satisfactory. The CLT model and the CD model (2 parameters) also gave satisfactory fits. To choose the best model we used the parameters fitted to the elution curves to predict vertical concentration profiles in the lysimeter. These predictions are compared to the profile obtained after thorough sampling of the soil when tracers reached about half way down the lysimeter. The MIM model yielded a better prediction. However, accurate predictions would require taking into account the highly stratified characteristics of this soil.Atrazine simulation was done with the CD-based one-site kinetic sorption and first-order decay equation. Again analytical solutions are provided for our experimental conditions. Values of decay and absorption parameters are in agreement with previous studies. (C) 1999 Elsevier Science B.V. All rights reserved.

Accurate measurement of in situ soil hydraulic properties is important for developing, testing, and applying water and solute transport theory. A method of measuring hydraulic conductivity (K), soil matric pressure head (ψ), and water content (θ) relationships is presented. The procedure uses a series of multipurpose time domain reflectometry (TDR) probes that measure both θ and ψ. The TDR probes are installed vertically and measure the rate of change of local soil water storage (q) along the probe during constant rate water application. The values of q are equal to local soil water flux, and assuming unit gradient, are set equal to K at the steady state θ and ψ measured at long times. The measured values of K, θ, and ψ from different water application rates are combined to obtain average K(θ) and θ(ψ) functions. To test the procedure, multipurpose TDR probes were installed vertically in a sandy soil every 0.15 m in a 7.5‐m‐long transect for a total of 50 probes per depth. This was repeated in parallel transects 0.1 m apart for four depths (0.2 m, 0.4 m, 0.6 m, 0.8 m) and a total of 200 probes. Six different water application rates were applied with subsequent drainage. Average K(θ) and θ(ψ) functions were obtained and used in an analytical solution for constant rate infiltration. Transient water storage changes were accurately predicted for all application rates.

To predict the effects of water or leachate infiltration into unsaturated field soils requires measurements of both the field-saturated hydraulic conductivity (K-fs) and the matric flux potential (phi(m)). Measurement of these soil parameters commonly requires steady-state infiltration rates, which, in the slowly permeable clay liners that are found underlying municipal landfills, can require several weeks or months to be attained. The transient, capillary-dominated, early-time method of determining K-fs and phi(m) has been found to provide a much faster, yet still reliable estimate of these now parameters. Here, an analytical solution was utilized for early-time one-dimensional infiltration under the conditions of an initial constant head followed by a falling-head phase. Six laboratory trials were conducted using precisely compacted clay cores to determine K-fs and phi(m) during both early-time and steady-state pow domains. The results of these trials showed a favorable comparison between these two techniques, with the early-time constant-head and falling-head methods producing K-fs estimates that were 60 and 75% of their respective steady-state values. This suggests that the early-time determination of K-fs and phi(m) on slowly permeable media has a definite practical advantage over lengthy steady-state analyses. A new, expeditious procedure for determining steady-state K-fs values of highly compacted soil cores, involving use of a Mariotte-equipped pressure plate chamber, was also developed and validated.

The in situ determination of the field‐saturated hydraulic conductivity of low‐permeability porous materials is a major concern for both geotechnics and soil physics with regards to environmental protection or water resources management. Recent early‐time single‐ring infiltration experiments, involving sequential constant head and falling head conditions, allow its efficient estimation. Nevertheless, the theory on which the interpretation was based was still strictly valid to nondeformable soils and implicity relied on a particular form of the hydraulic conductivity‐soil water pressure head relationship. This theory is now extended to deformable materials, without any restrictive hypothesis. A new concept, bulk sorptivity, which characterizes the solid phase movement, is introduced. Field experiments, conducted on two liners of swelling and slowly permeable materials, revealed that neglecting the soil deformation induces an underestimation of the actual coefficient of permeability of the soil.

The data from transient-flow air permeameters often exhibit curvature in the theoretically linear plots of the natual log of pressure vs, time, This was originally attributed to errors in water manometer data caused by the inertia of the water in the manometer. The resulting recommendation was to ignore the early time data when calculating the air permeability of a soil by these methods, We have demonstrated and quantified that the exhibited curvature is a direct consequence of small changes in temperature in the source air tank as a result of the cooling of the expanding air during the permeability determination. This was accomplished by interfacing the air permeameter with a computer to collect pressure and temperature data at a relatively high frequency, The data acquisition procedure facilitated the calculation of the change in pressure and temperature with respect to time, which allowed the direct solution of the differential form of the equations describing the mass flux of air from the tank through the core. The data is compared with the theoretical relationship expected for the core based on air permeability determined using a steady-state method.