Issues

We developed a method for soil water content simulation combining predictions using various pedotransfer functions (PTFs). The combined prediction consisted of weighting the results of water content simulation made with 19 published PTFs. The weighted prediction was more accurate than the prediction using the best single PTF.

This study presents quantitative and visual experimental evidence that the level of grain surface roughness of a porous medium may be a critical physical factor that controls colloid retention through heightened static friction, especially for colloids at the air–water–solid interface.

Experiments reproducing one-dimensional vertical tracer transport were performed under steady-state and transient flow induced by water-table fluctuation in the bottom half of a 1-m-long column. Breakthrough data were used to compare dispersion under both flow conditions and to test the capacity of existing transport models to reproduce the observed data.

Concerns regarding antimicrobials in the environment have increased in recent years. Limited research exists, however, on the fate and transport of these compounds once they have been discharged in human and animal wastes. This study investigated the fate and transport of two antimicrobials, sulfadimethoxine and ormetoprim, in two soils and a sand.

We studied the transport behavior of malathion in homogeneous soil liquid chromatographic columns. The parameters for the resulting malathion breakthrough curves were estimated with the CXTFIT2.1 and continous time random walk models. Malathion transport was influenced mainly by nonequilibrium sorption to soil solids.

A new type of combined penetrometer-moisture probe was developed for simultaneous measurements of water content and penetration resistance of soils on natural hillslopes. It has a robust configuration and can be used for gravelly and rocky soils. The maximal penetration depth is 5.5 m. Its usefulness for hydrogeomorphological studies is discussed.

We used a two-dimensional computer model to estimate design hydraulic loading rates for onsite wastewater systems using 12 soil textural classes. Our results show that, due to the importance of unsaturated flow, medium-textured soils should have higher design rates than has been assumed.

We evaluated relations between the mineralogy of lower unsaturated zone sediments and grain coatings with the concentration of selected ions (e.g., nitrate and sulfate) found in those sediments and underlying shallow ground water. The mineralogy of grain coatings was demonstrated to affect the storage of nitrate and sulfate in the unsaturated zone.

A new set of pedotransfer functions, based on a closed-form model, was developed from the Vereecken data set. The performance of these functions was as good as the existing published pedotransfer functions. Using the matrix saturated conductivity K_o instead of saturated hydraulic conductivity K_sat improved the shape of the predicted hydraulic conductivity curve.

A conceptual model for fracture-dominated subsurface flow and transport in a reclamation cover was developed and then validated via field data and numerical analysis. The system is described as an equivalent porous medium because chemical equilibration between fresh water in the macropores and salt-rich pore water in the matrix was fairly rapid.

This work outlines the details of image analysis procedures used to estimate concentration values from digital pictures of porous media transport experiments. We also provide a novel approach to quantify the errors in the concentration estimates. The proposed method was validated using a theoretical problem and a laboratory data set.

Analytic expressions for the depth and temporal variation of matrix potential and Darcy flux were derived for the linearized one-dimensional Richards equation subject to a sinusoidally varying surface flux. The solution shows that the amplitude of the potential and flux variation decays exponentially with depth.

A new solution of Richards' equation a function of the matric potential is derived to solve the problem of vertical-up, vertical-down and horizontal water infiltration into a sand. The effect of van Genuchten's shape parameters of the soil water retention curve on the application of the solution to other porous media was investigated, and the solution provides a more realistic description of the infiltration process pioneered by Green and Ampt in 1911.

Soil water repellency (WR) is involved in many important hydrologic processes but still a quantitative description of the water content dependence of WR is not available. A multiple linear empirical model was derived that permits description of the WR vs. water content curve.

A new method and apparatus for field-saturated hydraulic conductivity, though highly simplified, are useful because (i) mathematical formulation partly compensates for methodological shortcuts, and (ii) with great spatial variability, being able to measure faster at a greater number of locations is more important than maximizing accuracy at each location.

For aggregated soils, the contacts between aggregates control the unsaturated water flow. Due to their roughness, the contacts are easily drained and become bottlenecks for the movement of water. The controlling role of the contacts was verified by means of neutron radiography and numerical simulation of water infiltration through an aggregate packing.

Identifying the probability density functions of water retention parameters is a challenge when using a small number of samples. We present an unconventional maximum likelihood approach that approximates the functions as Gaussian, and apply it for uncertainty assessment of flow and tracer transport to the unsaturated zone of Yucca Mountain.

An innovative design of a button heat pulse probe (BHPP) for accurate soil water content measurements is presented. The BHHP does not suffer from measurement errors by needle deflection and is highly sensitive to soil moisture because of the central placement of the thermistor.

In this preface to the Fractals special section, the history of fractal and multifractal models applied to porous media is briefly reviewed. The 11 original research papers comprising the special section are introduced, and some areas in need of further research are identified.

This study summarizes some basic characters of fractal porous media andderives a model for fractal dimensions of solid and pore phases of stochastically apparent two-phase fractal porous media. Some other geometric properties such as the specific surface areas, porosities, and fluid velocities in fractal porous media were also derived.

Two new models were derived from probabilistic and fractal approaches for the intrinsic permeability of fractal porous media. Predictions of the models were compared favorably with estimates derived from lattice Boltzmann method simulations of saturated flow in virtual representations of deterministic and random Menger sponges.

We developed a deterministic temporal model for soil fragmentation suitable for describing progressive comminution. Through numerical experimentation, we demonstrated the creation and evolution of lognormal, local power-law, and skewed unimodal fragment size distributions, dependent on how fragmentation is modeled as a function of spatial scale.

We show that Kolmogorov fragmentation algorithms generate multifractal mass-size distributions agreeing with multifractal features formerly observed in real soil particle size distributions.

Multifractal analysis was useful for characterizing N₂ adsorption idotherms measured in a Vertisol and a Mollisol, which also were used for soil-specific surface area determination. Singularity spectra showed strongly asymmetric concave parabolic shapes that were wider on the left-hand side.

The varying range of pixel sizes with potentially fractal scaling makes it impossible to calculate true multifractal spectra for binary soil image data. Application of multifractal formalism can generate only “pseudo-multifractal spectra” that might still be useful for summarizing pore distribution information and for comparing pore data among different agricultural management regimes and soil types.

The pore size distribution (PSD) is widely used to assess the physical quality of soil. Imaging approaches are limited in terms of the range of pore sizes that can be identified. As soil processes occur across various scales, there is a need to merge scales of observation and describe soil in a multiscale manner. An approach for combining PSDs acquired at different scales was proposed and implemented on soil samples demonstrating how this can be achieved.

The lacunarity and fractal dimensions were used to characterize soil macropores and real-time tracer distributions reconstructed using x-ray computed tomography. Lacunarity reflects the size distribution of macropores and the spatial pattern of flow and transport. Lacunarity is helpful in determining whether self-similarity exists and whether a representative elementary volume can be defined.

The fractional advective-dispersive equation (FADE), which assumes that solute particles in soil undergo Levy flights, was tested. Our findings suggest that the FADE, which includes the classical advective-dispersive equation, should be used as a general framework to study solute transport in soil when the tails of the breakthrough curve are of interest.

A transient model of borehole ballooning, a common problem encountered during drilling in fractured zones, is introduced. The emphasis is on the effects of fracture surface roughness and fracture volume change. The degree of roughness was defined by fractal dimension and it was shown that it has a critical effect on the magnitude of mud gain or loss.

A Monte Carlo analysis of aquifer tests in two-dimensional fractured media was conducted to understand the relationship among fracture network parameters, the fluid flow geometry, and diffusion of pressure transients. Results suggest that flow dimension, a parameter that can be inferred from aquifer tests, may be a useful indicator for aquifer characterization.