Showing papers on "Hydraulic conductivity published in 1985"

Soil physics with BASIC :transport models for soil-plant systems

Abstract: 1. Introduction. 2. Physical Properties of Soil. 3. Gas Diffusion in Soil. 4. Soil Temperature and Heat Flow. 5. Water Potential. 6. Hydraulic Conductivity and Water Transport Equations. 7. Variation in Soil Properties. 8. Infiltration and Redistribution. 9. Evaporation. 10. Solute Transport in Soils. 11. Transpiration and Plant- Water Relations. 12. Atmospheric Boundary Conditions. Appendix. Index. No responsibility is assumed by the author or publisher for any errors, mistakes, or misrepresentations that may occur from the use of these programs.

Stochastic Analysis of Unsaturated Flow in Heterogeneous Soils: 1. Statistically Isotropic Media

Abstract: Steady unsaturated flow with vertical mean infiltration through unbounded heterogeneous porous media is analyzed using a perturbation approximation of the stochastic flow equation which is solved by spectral representation techniques. The hydraulic conductivity K is related to the capillary pressure head ψ by K = Ks exp (−αψ), where Ks is the saturated conductivity, and α is a soil parameter. A general formulation is presented for the case with Ks and α represented as statistically homogeneous spatial random fields. In part 1, solutions are developed assuming α is constant and representing Ks variability by one-dimensional and three-dimensional isotropic random fields. Results are obtained for head variances and covariance functions, effective hydraulic conductivities, variances of the unsaturated hydraulic conductivity, flux variances, and variance of pressure gradient. When the parameter α is relatively large, corresponding to coarse textured soils, the head variance decreases and all of the results demonstrate a trend toward gravitationally dominated one-dimensional vertical flow. The effective conductivity is dependent on the correlation scale of ln Ks and the mean hydraulic gradient.

Prediction of soil water properties for hydrologic modeling

Abstract: Water flow in soils can be characterized for many boundary and initial conditions by solving governing differential equations. Thus, a physically consistent means of quantifying water flow in soils in terms of the soil properties governing the movement of water and air exists. One reason why this state-of-the-art technology is not yet fully utilized is the difficulty of obtaining the required inputs which are the relationships between matric potential and hydraulic conductivity as a function of soil water content. Approximate water flow models based on physical principles or empirical results may simplify the computational requirements, however, inputs are still required. This paper presents procedures to (1) estimate input parameters for the Brooks-Corey, Campbell, and Van Genuchten soil water retention and hydraulic conductivity functions based on readily available soil properties, and (2) to estimate infiltration parameters.

Stochastic Analysis of Unsaturated Flow in Heterogeneous Soils: 2. Statistically Anisotropic Media With Variable α

Abstract: Steady unsaturated flow in heterogeneous soil with an arbitrarily oriented mean hydraulic gradient is analyzed using spectral solutions of the stochastic perturbation equation which describes the capillary pressure head ψ. The unsaturated hydraulic conductivity is related to ψ by K = Ks exp (−αψ), where Ks is the saturated hydraulic conductivity and α is a soil parameter, and both Ks and α are treated as three-dimensional statistically homogeneous, anisotropic random fields. Analytical results are obtained for the capillary pressure head variance and the effective (mean) unsaturated hydraulic conductivity. The head variance depends upon the degree of anisotropy of the ln Ks covariance; when α is random, the head variance increases with mean capillary pressure head. The effective hydraulic conductivity for arbitrary orientation of the mean hydraulic gradient J is shown to have tensorial properties, but its components depend on the magnitude and direction of J and the orientation of the stratification in the soil. When α is random, the degree of anisotropy of the effective conductivity depends strongly on mean capillary pressure.

IN SITU MEASUREMENT OF FIELD-SATURATED HYDRAULIC CONDUCTIVITY, SORPTIVITY, AND THE α-PARAMETER USING THE GUELPH PERMEAMETER

Abstract: The Guelph permeameter method is used in 0.02-m- and 0.03-m-radius wells to measure in situ the field-saturated hydraulic conductivity (K10) and matric flux potential (φm) of a heterogeneous, anisotropic, structured loam soil. The K10, estimates, obtained using both Richards (GP-R) and Laplace (GP-L

Determining soil hydraulic properties from one-step outflow experiments by parameter estimation. I: Theory and numerical studies

Abstract: The numerical feasibility of determining water retention and hydraulic conductivity functions simultaneously from one-step pressure outflow experiments on soil cores by a parameter estimation method is evaluated. Soil hydraulic properties are assumed to be represented by van Genuchten's closed-form expressions involving three unknown parameters: residual moisture content 6, and coefficients a and n. These parameters are evaluated by nonlinear least-squares fitting of predicted to observed cumulative outflow with time. Numerical experiments were performed for two hypothetical soils to evaluate limitations of the method imposed by constraints of uniqueness and sensitivity to error. Results indicate that an accurate solution of the parameter identification problem may be obtained when (i) input data include cumulative outflow volumes with time corresponding to at least half of the final outflow and additionally the final outflow volume; (ii) final cumulative outflow corresponds to a sufficiently large fraction (e.g., >0.5) of the total water between saturated and residual water contents; (iii) experimental error in outflow measurements is low; and (iv) initial parameter estimates are reasonably close to their true values. Additional Index Words: unsaturated hydraulic conductivity measurement, water retention measurement, transient flow, inverse prob-

Stochastic Analysis of Unsaturated Flow in Heterogeneous Soils: 3. Observations and Applications

Abstract: Results of stochastic theory for flow in heterogeneous soils are analyzed by comparisons with laboratory experiments and field observations, and through applications examples. The two key theoretical results are (1) the variability of capillary pressure or moisture content increases when mean capillary pressure increases and (2) the anisotropy ratio (horizontal/vertical) of effective (mean) unsaturated hydraulic conductivity increases when mean capillary pressure increases or mean moisture content decreases. Comparisons with the field data on moisture content and capillary pressure variability show trends similar to those predicted by the theory. Calculations of hydraulic conductivity anisotropy based on two actual soils show that the variations in soil texture produce large changes in anisotropy as the mean capillary pressure changes. Several previously reported field observations and laboratory experiments support the theoretical finding of a capillary pressure dependent hydraulic anisotropy for unsaturated flow. The importance of this anisotropy effect in applications involving groundwater recharge, irrigation, surface runoff generation, and waste isolation is discussed.

Hydraulic conductivity tests on compacted clay

Abstract: Permeability tests were performed in the laboratory on compacted clay to study the effects of type of permeameter, hydraulic anisotropy, diameter of test specimens, storage time, and desiccation cracking. Essentially identical hydraulic conductivities were measured with compaction‐mold, consolidation‐cell, and flexible‐wall permeameters. With good bonding between lifts, hydraulic conductivity was isotropic. Test specimens having a diameter of 15 cm were twice as permeable as specimens having a diameter of 4 cm, but this difference is too small to be of any consequence. There was no tendency for hydraulic conductivity to increase with increasing storage time. Desiccation cracks in compacted clay close only partially when the clay is moistened and permeated, unless substantial effective stresses are applied to aid in closing the cracks.

Hydraulic conductivity of natural clays permeated with simple liquid hydrocarbons

Abstract: The hydraulic conductivity, k, of clayey soils is strongly influenced by the physicochemical properties of permeating liquid hydrocarbons. Tests on natural Sarnia soils mixed with pure liquids at a...

Field Determination of the Three-Dimensional Hydraulic Conductivity Tensor of Anisotropic Media: 2. Methodology and Application to Fractured Rocks

Abstract: The analytical solutions developed in the first paper can be used to interpret the results of cross-hole tests conducted in anisotropic porous or fractured media. In the particular case where the injection and monitoring intervals are short relative to the distance between them, the test results can be analyzed graphically. From the transient variation of hydraulic head in a given monitoring interval, one can determine the directional hydraulic diffusivity, Kd(e)/Ss, and the quantity D/Ss, by curve matching. (Here Kd(e) is directional hydraulic conductivity parallel to the unit vector, e, pointing from the injection to the monitoring interval, Ss is specific storage, and D is the determinant of the hydraulic conductivity tensor, K.) The principal values and directions of K, together with Ss, can then be evaluated by fitting an ellipsoid to the square roots of the directional diffusivities. Ideally, six directional measurements are required. In practice, a larger number of measurements is often necessary to enable fitting an ellipsoid to the data by least squares. If the computed [Kd(e)/ss]½ values fluctuate so severely that a meaningful least squares fit is not possible, one has a direct indication that the subsurface does not behave as a uniform anisotropic medium on the scale of the test. Test results from a granitic rock near Oracle in southern Arizona are presented to illustrate how the method works for fractured rocks. At the site, the Oracle granite is shown to respond as a near-uniform, anisotropic medium, the hydraulic conductivity of which is strongly controlled by the orientations of major fracture sets. The cross-hole test results are shown to be consistent with the results of more than 100 single-hole packer tests conducted at the site.

A comparison of three field methods for measuring saturated hydraulic conductivity

Abstract: The saturated hydraulic conductivity, Ks, was measured on a loamy sand, a fine sandy loam, a silt loam and a clay at four 100-m2-area sites in southern Ontario. Twenty measurements of Ks were obtained by each of three different measurement techniques at each of the four sites. The techniques included: (1) the air-entry permeameter method; (2) the constant head well permeameter method using the Guelph Permeameter; and (3) the falling-head permeameter method applied to small soil cores. The Ks data were found to be better described by the log-normal frequency distribution than by the normal frequency distribution. Statistical comparison of the mean Ks values indicated significant differences between some or all of the methods within each site. This site-method interaction was interpreted in terms of the influence of macropores and air entrapment on each of the measurement techniques. The measured Ks values ranged over an order of magnitude on the sand, one to two orders of magnitude on the loams, and three ...

Approximate Analysis of the Borehole Permeameter in Unsaturated Soil

Abstract: An approximate analysis of the steady constant-head uncased borehole permeameter in homogeneous unsaturated soil is presented. A bulb-shaped region of saturated soil, the “saturated bulb,” adjoins the water-filled length of the hole. The problem is solved by matching approximate models of the “inner” saturated flow within the bulb and of the “outer” flow in the surrounding unsaturated soil. The quasilinear analysis, with sorptive number α characterizing the capillary properties of the soil, is applied to the outer, unsaturated flow. Certain approximations made are geometrical, and others simplify the physics by treating gravity and capillarity as separable. The results agree well with the limited body of relevant detailed numerical solutions, and the model is consistent also with saturated flow results and formulae. In general, the capillary properties of the soil cannot be ignored: for a borehole of radius 0.05 m, the error committed in ignoring capillarity increases from 2.8 to 280% as α decreases from 10 to 0.1 m−1. The concepts and methods (the saturated bulb, use of the quasi-linear analysis, matching inner and outer flows) apply to a range of steady mixed saturated-unsaturated flow systems with water applied under positive hydrostatic pressure to an initially unsaturated soil mass. The study leads to some doubt about the practicality of using the borehole permeameter to measure saturated hydraulic conductivity in the absence of an independent determination of α.

Hydraulic Conductivity of Two Prototype Clay Liners

Abstract: Two prototype liners were constructed at a site near Austin, Texas, using clays of low and high plasticity. The clays were compacted to 100% of standard Proctor density at a water content slightly wet of optimum using a sheepsfoot roller. The overall hydraulic conductivity (k) of each liner was determined by ponding water on the liners and measuring the rate of seepage. The field-measured k’s of the liners were surprisingly high (4x10\u-\u6 and 9x10\u-\u6 cm/s). After water in the ponds was removed, laboratory permeability tests were performed on hand-carved samples obtained from the liners, on samples obtained with a thin-walled sampling tube, and on laboratory-compacted samples. Field permeability tests were also performed with ring infiltrometers. The tests showed that: (1) Essentially all of the laboratory tests, even on undisturbed samples, produced a measured k that was approximately 1,000 times less than the field-measured k, and (2) ring infiltration tests showed considerable scatter but the average k was close to the overall field-mesasured k. The findings raise important questions about whether laboratory permeability tests on compacted clay are relevant to clay liners and reinforce previous suggestions that compacted clay liners may contain numerous hydraulic defects such as fissures, slickensides, zones of poor bonding between clods of clay, and zones of relatively poor compaction. The desirability of field permeability tests is evident from the results reported.

Peatmoss Effect on the Physical and Hydraulic Characteristics of Compacted Soils

Abstract: MEASUREMENTS of the water retention characteristics, saturated hydraulic conducivity and the penetration resistance were made on three soil types having varying organic matter contents and different amount of compaction effort. Compaction changes the ability of the soils to hold moisture, increases penetration resistance and decreases the available water capacity and saturated hydraulic conductivity of the soils. On the other hand, organic matter generally increases the ability of the soils to hold moisture, expands the available water capacity, increases the saturated conductivity and decreases the penetraiton resistance of compacted soils.

Analysis and Interpretation of Single-Well Tracer Tests in Stratified Aquifers

Abstract: This study deals with the definition and measurement of the dispersive properties of a stratified aquifer based on the single-well tracer test Knowledge of such dispersive properties are of fundamental importance to the evaluation, analysis, and simulation of contaminant migration in groundwater, a subject of great interest in recent years In the single-well test, tracer is pumped into the formation for a period of time and then pumped out Concentration data are obtained from the injection-withdrawal well and from one or more sampling-observation wells which may be multilevel Our analysis of such a test is based on a Lagrangian-Eulerian numerical model which considers the depth-dependent advection in the radial direction and local hydrodynamic dispersion in the vertical and radial directions Results show that the movement of an injected tracer in a stratified aquifer may be accurately simulated without resorting to the use of a scale-dependent, full aquifer dispersivity if the flow field is known in sufficient detail When the advection process is simulated accurately, the values of local dispersivity will be small, constant, and on the order of those measured in the field or laboratory at individual levels in the aquifer The full-aquifer breakthrough curves measured in observation wells in a single-well test in a stratified aquifer are determined by the hydraulic conductivity profile in the region between the injection-withdrawal well and the observation well if the travel distance between these wells is typical of most test geometries However, the relative concentration versus time data recorded at the injection-withdrawal well during the withdrawal phase is primarily a measure of mixing in the aquifer due to local dispersion which has taken place during the experiment The amount of mixing will depend on both the hydraulic conductivity distribution in the aquifer and the size of the experiment As the experiment scale increases, the effects of local vertical dispersion will become larger compared to the effects of local radial dispersion Local vertical dispersion will cause a solute traveling in a high-conductivity layer in an aquifer to migrate into adjacent low-conductivity layers where its movement will be relatively slow in comparison In the initial design of a tracer test it is important to have some idea of the type of nonhomogeneity with which one is dealing More information of a broad nature concerning the types or classifications of nonhomogeneities that exist in natural aquifers would be very useful Future research in this area is needed

Compaction of sandy forest soils by forwarder operations

Abstract: Soil compaction by repeated passes of a loaded forwarder (a log-carrying vehicle with a gross weight of 26 tonnes) was measured on 2 coarse-textured soils in pine plantations under wet conditions. On soil that was previously undisturbed, the depth of wheel ruts increased linearly with the logarithm of the number of passes, up to 19 cm for 27 passes. On old tracks, which had been used previously only for thinning operations, new ruts were formed to a depth of 5 cm. Penetrometer resistance increased 2–3 fold in the previously undisturbed soil, but decreases in resistance were measured on the old tracks, where the initial values exceeded 5 MPa. Changes in the physical properties of the soil occurred to a depth of at least 70 cm. Soil bulk density increased under all tracks and reached about the same final value on the old tracks and on the initially undisturbed soil. A moderate decrease in saturated hydraulic conductivity and an increase in water retention at 10 kPa was measured. The compacted soil is likely to be restrictive to root growth. The possibility of reducing soil compaction by reducing ground pressure from the machine was assessed on the basis of laboratory measurements of soil strength and compressibility. It is argued from the results that the use of wider, low-pressure tyres would be beneficial on these unusual compactible sands, but this would have to be evaluated in further field trials.

Spatial and temporal variability of soil physical properties of norfolk loamy sand as affected by tillage

Abstract: Physical properties of field soil vary both spatially and temporally. Because so little information is available concerning the changes in magnitude of soil physical properties as functions of soil depth, distance normal to a crop row, and time, they have largely been ignored in model development. The purpose of this study was to evaluate quantitatively the spatial and temporal variability imposed by several tillage operations on several soil physical properties. Three tillage treatments, replicated 4 times in a randomized complete block design, were (1) conventionally-disked 3 times before planting, (2) full width strip chisel plowed to a 27-cm depth, and (3) in-row-subsoiled plus bedding. Soil physical properties measured were cone index (CI), weight percentage water (Pw), bulk density (Db), soil water characteristic curve, saturated hydraulic conductivity (Ksat) and soil settling. These properties were measured 3 times: immediately after planting soybeans (Glycine max (L.) Merr.) on 16 May; on 3 June; on 8 July 1977. Soil properties were measured at the 0–14, 14–28, and 28–41-cm soil depths at 3 positions relative to the row i.e., in the row, in the trafficked interrow, and in the non-trafficked interrow. Significant differences due to tillage treatment were found for Db, CI, and the soil water characteristic. The greatest spatial variation occurred in the 0–14-cm depth and decreased with depth. Significant differences for most variables were also found for the tillage by depth and tillage by position interactions. All properties exhibited significant temporal variation.

The Development of Multiple Seepage Faces on Layered Slopes

Abstract: This study provides an analysis of the water table configuration and hydraulic-head distribution in layered hillsides. A finite-element model was used to simulate two-dimensional, saturated-unsaturated, steady state flow through layered slopes. A laboratory sand tank experiment was used to verify the physical foundation of the mathematical model. It is shown that layered slopes feature multiple seepage faces, perched water tables, and wedge-shaped unsaturated zones. The hydraulic-head distribution and water table configuration are strongly dependent on the position of the impending layers and the ratio of the hydraulic conductivity between adjacent layers. This work has geotechnical implications with regard to slope stability and the control of groundwater inflows into excavations. It has hydrogeological implications with regard to flow path analysis in contamination studies. It has geomorphological implications with respect to landform development by mass movements and surface water erosions, and to drainage network development through piping.

Effect of clay mineralogy and aluminum and iron oxides on the hydraulic conductivity of clay-sand mixtures

Abstract: Changes in hydraulic conductivity and clay dispersivity of clay-sand mixtures (four reference smectites and Fithian illite) as a function of concentration (0.01 M Cl− and distilled water) and sodium adsorption ratio (SAR ≤ 30) of the percolating solution were measured. In addition, the effect of sand percentage, sand particle size, and addition of AlCl3 and FeCl3 on the hydraulic conductivity of the mixtures were measured. Clay dispersion and migration out of the 3% clay columns was substantial. The clay dispersed only in the distilled water system; dispersion increased with an increase in the percentage of exchangeable Na and was about the same for the Wyoming montmorillonite and Fithian illite. Conversely, the clay swelled in the 0.01 M Cl− solution. The swelling of the montmorillonites increased in the order: Upton, Wyoming = Belle Fourche, South Dakota > Polkville, Mississippi > Otay, California, and was higher than that of the Fithian illite. The swelling and dispersion of the clay accounted for the changes in hydraulic conductivity. Mixtures treated with FeCl3 and AlCl3 were leached with NaCl-CaCl2 solutions until the pH of the effluent exceeded 6.5. The composition of the exchangeable phase was then determined by the SAR of the leach solutions. At pH > 6.5, the polycations hydrolyzed and were present as the hydroxy-polymer species. The hydraulic conductivity of the mixtures decreased as exchangeable Na increased, but the decrease was less than in untreated mixtures, AlCl3 was more effective in maintaining hydraulic conductivity than FeCl3. In montmorillonite clay with an ESP of 20, less than 5% of a complete Al-interlayer was enough to prevent a reduction in hydraulic conductivity. Packets in the day systems tested explain the high efficiency of the Fe and Al polycations.

Relations Between Aquifer Electrical and Hydraulic Properties

Abstract: The primary factor controlling material-level relations between aquifer electrical and hydraulic properties in the clay-free aquifer materials of southern Rhode Island is an inverse relation between in-situ porosity and grain size. In-situ density, grain size and laboratory hydraulic conductivity data support this conclusion. Relations between either layer resistivities and hydraulic conductivity, or a Dar Zarrouk parameter and transmissivity, are influenced by aquifer layering and the position of the aquifer layer relative to nonproducing layers. In the study area, the best relations between electrical and hydraulic properties are obtained where the transverse resistance of the aquifer is measured.

The displacement of connate water from aquifers

Abstract: A mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers. The theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids. Depending on constraints in the recharge area, the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system. The former condition is attained when the recharge area incorporates the total depth and breadth of the formation. Where this condition is not satisfied, the concentrations that evolve are controlled by the original concentration of the formation water, the composition of recharging meteoric water, the dispersion parameters, and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike. For heterogeneous formations, the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity. This is demonstrated in the Milk River sandstone, which is characterized by several extensive zones of dilute water within narrow, high-conductivity pathways and marked increases in concentration in adjacent, lower-permeability rock. In parts of the aquifer where higher-permeability pathways appear to be absent, the isochlores form a broad linear band with a marked increase in concentration in the flow direction.