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The author asserts that the equation of motion for water in an unsaturated soil deserves an identity that is distinct from Darcy's Law.

Vadose Zone Journal November 01, 2004, Vol.3, 1059. doi:https://doi.org/10.2113/3.4.1059

The guest editors introduce the special section and the scope of the hydrogeophysics papers. The papers present methods for estimating hydrogeological parameters using GPR, TDR, and induced polarization for monitoring the dynamics of processes based on resistivity and EM-induction methods and for advanced characterization of the subsurface through improved instrumentation, inversion approaches, acquisition geometry, or data processing.

Vadose Zone Journal November 01, 2004, Vol.3, 1060-1062. doi:https://doi.org/10.2113/3.4.1060

Ground penetrating radar (GPR) signal analyses were applied to synthetic GPR data and to GPR data measured for a large sand tank. The purpose was to assess the possibility of identifying a continuously variable soil moisture profile from a single measurement with a highly mobile off-ground monostatic antenna.

Vadose Zone Journal November 01, 2004, Vol.3, 1063-1071. doi:https://doi.org/10.2113/3.4.1063

Effective soil hydraulic parameters are estimated by hydrodynamic inversion of soil moisture time series obtained by full-wave electromagnetic inversion of ground penetrating radar data. The method offers great promise for the laboratory- and field-scale hydraulic characterization using remote sensing.

Vadose Zone Journal November 01, 2004, Vol.3, 1072-1081. doi:https://doi.org/10.2113/3.4.1072

The water content of a soil can be estimated with relations using the relative dielectric permittivity, which can be determined by GPR measurements. The estimates in variations of the amount of water in a sand box, obtained by GPR data, are compared with the actual variations of water imposed on the sand box. The results are very similar.

Vadose Zone Journal November 01, 2004, Vol.3, 1082-1092. doi:https://doi.org/10.2113/3.4.1082

Vertical radar profiling (VRP) is a noninvasive technique for monitoring moisture content changes in the vadose zone. This paper illustrates the acquisition and use of VRP data to monitor infiltration and unsaturated flow above a quaternary alluvial aquifer, and the use of these data to calibrate a model of the flow.

Vadose Zone Journal November 01, 2004, Vol.3, 1093-1105. doi:https://doi.org/10.2113/3.4.1093

Ground penetrating radar has growing applications for investigating the vadose zone. Undisturbed flow processes can be studied because of the noninvasive nature of this method. An irrigation experiment illustrates the potential of this method for small-scale experimental setups.

Vadose Zone Journal November 01, 2004, Vol.3, 1106-1115. doi:https://doi.org/10.2113/3.4.1106

A radar transmission model was developed to evaluate field conditions for the use of GPR instruments in landmine detection. Model predictions were validated with GPR profiles measured in field soils representing various soil textures and soil water contents. Results demonstrate the potential and pitfalls of using GPR-based landmine sensors.

Vadose Zone Journal November 01, 2004, Vol.3, 1116-1127. doi:https://doi.org/10.2113/3.4.1116

A TDR waveform analysis methodology is presented that gives a quantitative estimate of the dielectric permittivity and therefore the water content profile along the length of a TDR probe. The method is based on a deterministic model of the TDR waveform, which makes the method applicable to standard TDR instrumentation and TDR probes.

Vadose Zone Journal November 01, 2004, Vol.3, 1128-1145. doi:https://doi.org/10.2113/3.4.1128

A new time-domain reflectometry probe design for use in highly saline media was developed and tested. The new design combines the advantages of uncoated probes (i.e., electrical conductivity can be measured) and coated probes (i.e., water content measurements can be made at high electrical conductivity).

Vadose Zone Journal November 01, 2004, Vol.3, 1146-1151. doi:https://doi.org/10.2113/3.4.1146

A time domain reflectometry probe based on one single metallic rod is investigated for water content measurements. The probe is analyzed both experimentally and theoretically, and the derived characteristics are compared with those of the standard two-wire probes.

Vadose Zone Journal November 01, 2004, Vol.3, 1152-1159. doi:https://doi.org/10.2113/3.4.1152

The electrical induced polarization properties of multiphase porous media are demonstrated to possess a complex dependency on the volumetric water content for sands containing air and water, and for sands containing kerosene and water. A model explaining such a behavior is proposed.

Vadose Zone Journal November 01, 2004, Vol.3, 1160-1168. doi:https://doi.org/10.2113/3.4.1160

Radiometry is known as a passive remote sensing technique for measuring water contents in environmental science. Models used to infer water content from radiometry data are discussed, and the comparability between remotely sensed water content predictions and ground truth water content data is investigated.

Vadose Zone Journal November 01, 2004, Vol.3, 1169-1179. doi:https://doi.org/10.2113/3.4.1169

Laboratory experiments were performed in a sand box to measure the electrical signal generated by flow of a homogeneous fluid, by diffusion of salt, and by advective transport of salt. Each of these phenomena produces a characteristic spontaneous electrical potential, analysis of which provides information about the motion of the fluid or of the salt front through the porous medium.

Vadose Zone Journal November 01, 2004, Vol.3, 1180-1192. doi:https://doi.org/10.2113/3.4.1180

An electrical field of electrokinetic nature is produced in response to groundwater flow. A sandbox experiment is presented to analyze the electrical field associated with a pumping test in a Plexiglas tank filled with a tapwater-infiltrated sand. The response is analyzed both in steady-state pumping conditions and in the relaxation phase following the shutdown of the pump.

Vadose Zone Journal November 01, 2004, Vol.3, 1193-1199. doi:https://doi.org/10.2113/3.4.1193

Electrical streaming potential monitoring is presented as a viable method for characterizing subsurface flow processes and for estimating subsurface hydraulic parameters. A modeling approach is presented that facilitates this characterization and the parameter estimation. The procedures are demonstrated using steady-state infiltration numerical simulations.

Vadose Zone Journal November 01, 2004, Vol.3, 1200-1206. doi:https://doi.org/10.2113/3.4.1200

Downhole electromagnetic induction was used to track the migration of a NaCl plume in the vadose zone under steady water flow conditions. The plume evolved in a manner consistent with site stratigraphy. The calculated mass of added NaCl was more dependent on the assumed immobile water content than on clay content or temperature.

Vadose Zone Journal November 01, 2004, Vol.3, 1207-1214. doi:https://doi.org/10.2113/3.4.1207

The impact of noise and data gaps (random or coherent) on the inversion of electrical resistivity is assessed. Results indicate that a geostatistical reconstruction of the data gaps prior to the inversion improved the interpretability of near-surface electrical resistivity profiles and the associated inference of geologic structure.

Vadose Zone Journal November 01, 2004, Vol.3, 1215-1229. doi:https://doi.org/10.2113/3.4.1215

A genetic algorithm and perturbation sensitivity analysis are combined to optimize electrical resistivity tomography surveys. This optimization method opens the way for tailored, time evolving, monitoring of vadose zone flow and transport processes.

Vadose Zone Journal November 01, 2004, Vol.3, 1230-1239. doi:https://doi.org/10.2113/3.4.1230

Different approaches have been described for the in situ measurement of the gas-phase diffusivity in the vadose zone. This review compares the experimental setups and compiles a database of measured field data, which is compared with the predictions of porosity-based empirical relationships.

Vadose Zone Journal November 01, 2004, Vol.3, 1240-1248. doi:https://doi.org/10.2113/3.4.1240

Numerical and analytical solution methods are presented for analyzing time lags of CFC gases in the unsaturated zone using data from a Danish field site. Results illustrate the effects of changes in water content, thickness of the unsaturated zone, and effective diffusion on calculated time lags.

Vadose Zone Journal November 01, 2004, Vol.3, 1249-1261. doi:https://doi.org/10.2113/3.4.1249

A field experiment was used to explore the potential for predictive modeling of multicomponent VOC mixture transport in the vadose zone. Biodegradation rate constants obtained from column experiments, coupled with site-specific hydrological data, were used to simulate field-scale attenuation. The results were compared with field measurements.

Vadose Zone Journal November 01, 2004, Vol.3, 1262-1275. doi:https://doi.org/10.2113/3.4.1262

We hypothesized that anomalies in the depth distribution of the natural soil gas radon-222 at contaminated sites may be useful to indicate the presence and quantity of nonaqueous phase liquids. The hypothesis is tested using data from laboratory and lysimeter experiments in conjunction with transport modeling.

Vadose Zone Journal November 01, 2004, Vol.3, 1276-1285. doi:https://doi.org/10.2113/3.4.1276

Field-scale flow and transport in a three-dimensional, heterogeneous, variably saturated soil are analyzed for the case where the hydraulic conductivity and water retention depend on solute concentrations. Results of the analyses have practical implications regarding the use of sewage water for irrigation.

Vadose Zone Journal November 01, 2004, Vol.3, 1286-1299. doi:https://doi.org/10.2113/3.4.1286

A soil with a depth-decreasing macropore fraction is represented using a simple pore-network model and a dual-porosity domain. Numerical simulations are conducted for different saturation levels to demonstrate how the decreasing macropore fraction influences non-equilibrium transport.

Vadose Zone Journal November 01, 2004, Vol.3, 1300-1308. doi:https://doi.org/10.2113/3.4.1300

The hydraulic and transport parameters for two distinct mobile-immobile models were estimated through an inverse simulation procedure using water flow and bromide transport variables measured on columns of aggregated loamy soil. The effect of initial moisture content on reliability of parameter estimates was evaluated.

Vadose Zone Journal November 01, 2004, Vol.3, 1309-1321. doi:https://doi.org/10.2113/3.4.1309

Data on chloride concentration in an artificial lake and at seven depths in the underlying vadose zone were used to estimate the transport parameters and their uncertainty for the unsaturated zone. The parameter uncertainty is partially related to the lack of temporal resolution in lake water chloride concentration measurements.

Vadose Zone Journal November 01, 2004, Vol.3, 1322-1330. doi:https://doi.org/10.2113/3.4.1322

Soil stratification, by inducing two- or three-dimensional transport processes, may considerably affect solute dispersion. The analysis of the chloride time series in the layered vadose zone between a lake and an underlying aquifer illustrates that flow variability is extremely high, probably due to an unstable front below clay-sand interfaces.

Vadose Zone Journal November 01, 2004, Vol.3, 1331-1339. doi:https://doi.org/10.2113/3.4.1331

A procedure is presented for parameter estimation using inverse modeling. The SUFI-2 approach calculates parameter as well as prediction uncertainty for models with a large number of parameters. The procedure employs a global search; it is efficient and easy to implement.

Vadose Zone Journal November 01, 2004, Vol.3, 1340-1352. doi:https://doi.org/10.2113/3.4.1340

Split-application of nitrate fertilizer during a cropping period is generally known to reduce the leaching potential for nitrate-nitrogen. Combining experimental and simulation approaches we performed a long-term assessment of these practices for reducing nitrate-nitrogen leaching in cultivated Japanese upland soils.

Vadose Zone Journal November 01, 2004, Vol.3, 1353-1366. doi:https://doi.org/10.2113/3.4.1353

Combining field measurements and modeling, we show the importance of correctly specifying macroscopic water stress parameters for simulating water fluxes of a vegetated surface. A methodology is proposed to adjust water stress parameters according to variable within-field soil properties using reference unsaturated hydraulic conductivity values.

Vadose Zone Journal November 01, 2004, Vol.3, 1367-1379. doi:https://doi.org/10.2113/3.4.1367

Results of testing two capacitance-based instruments that measure volumetric soil water under field conditions are described. Estimates of the accuracy of these instruments as well as relationships that can be used to improve their accuracy for Coastal Plain soils are presented.

Vadose Zone Journal November 01, 2004, Vol.3, 1380-1389. doi:https://doi.org/10.2113/3.4.1380

Soil moisture content was measured with a capacitance and a neutron probe for a duplex fine-textured soil, and the response of the soil dry bulk density to moisture content was quantified. Measurements from the two probes were compared and the need for site-specific calibration was evaluated.

Vadose Zone Journal November 01, 2004, Vol.3, 1390-1399. doi:https://doi.org/10.2113/3.4.1390

Using field data it is shown that if neutron probes are used for determining water contents in deep vadose zones, layer-specific calibration equations are needed. A procedure to develop such calibration equations is presented.

Vadose Zone Journal November 01, 2004, Vol.3, 1400-1406. doi:https://doi.org/10.2113/3.4.1400

Subsurface drip irrigation within gravel-filled cavities is proposed to eliminate problems of backpressure and water surfacing. A theoretical solution relates the size of the cavity as a function of irrigation rate and soil properties. The method is tested with HYDRUS-2D and field data.

Vadose Zone Journal November 01, 2004, Vol.3, 1407-1413. doi:https://doi.org/10.2113/3.4.1407

Permeability models are developed that describe mineral growth and reduction as a continuous film within the pore space. Changes in permeability and unsaturated hydraulic properties are determined based on changes in a discrete pore-size distribution and are described for a long-term low-level glassified waste facility.

Vadose Zone Journal November 01, 2004, Vol.3, 1414-1424. doi:https://doi.org/10.2113/3.4.1414

Chemical diffusion through unsaturated tuff gravels was measured using two approaches: electrical conductivity of bulk samples evaluated with the Nernst-Einstein equation, and microscale mapping of single grains using laser ablation. The results illustrate the very low diffusion potential in these gravels at low water content.

Vadose Zone Journal November 01, 2004, Vol.3, 1425-1438. doi:https://doi.org/10.2113/3.4.1425

An analytical solution is developed to calculate the wetted contact area of a rivulet under capillarity tension in inclined unsaturated fractures as a function of contact angle and flow rate. Conditions under which matrix contact area can be approximated using a simpler rectangular rivulet cross section are also derived.

Vadose Zone Journal November 01, 2004, Vol.3, 1439-1442. doi:https://doi.org/10.2113/3.4.1439

New soil water retention models for coarse-textured soils are derived based on measured particle-size distribution and the theory of polydisperse sphere systems. Two distinct models are tested, the fully penetrable sphere model and the totally impenetrable sphere model, by comparing predicted retention curves to measured ones.

Vadose Zone Journal November 01, 2004, Vol.3, 1443-1454. doi:https://doi.org/10.2113/3.4.1443

We used 47435 records from the NRCS soils database to evaluate 12 pedotransfer functions for estimating water retention parameters. Average root mean square errors ranged from 0.0687 cubic centimeters per cubic centimeter for a PTF that provided textural class average parameters to 0.0315 cubic centimeters per cubic centimeter for a model that also used two water retention points as predictors.

Vadose Zone Journal November 01, 2004, Vol.3, 1455-1463. doi:https://doi.org/10.2113/3.4.1455

The effective soil hydraulic parameters for steady-state flow across a heterogeneous landscape are derived by requiring that the effective medium discharge the ensemble mean flux across the soil surface. The effect of root water uptake on the effective medium parameters is assessed.

Vadose Zone Journal November 01, 2004, Vol.3, 1464-1470. doi:https://doi.org/10.2113/3.4.1464

The hydraulic conductivity of an anisotropic unsaturated soil is described as the product of a water content–dependent scalar variable, a water content–dependent symmetric relative connectivity–tortuosity tensor, and a symmetric hydraulic conductivity tensor at saturation. The saturation dependence of the conductivity tensor is demonstrated.

Vadose Zone Journal November 01, 2004, Vol.3, 1471-1478. doi:https://doi.org/10.2113/3.4.1471

Techniques for sampling in situ water from unsaturated fractures in low-moisture environments are lacking. Laboratory experiments demonstrate that cryogenic coring is a promising technique for freezing and collecting water in unsaturated fractures.

Vadose Zone Journal November 01, 2004, Vol.3, 1479-1482. doi:https://doi.org/10.2113/3.4.1479

The van Genuchten functions for hydraulic properties of unsaturated porous media are structurally similar to results obtained using percolation theory. The similarities allow an analysis of the van Genuchten phenomenology. Conditions under which the arguments of the functions are accurate are identified.

Vadose Zone Journal November 01, 2004, Vol.3, 1483-1488. doi:https://doi.org/10.2113/3.4.1483
Vadose Zone Journal November 01, 2004, Vol.3, 1491. doi:https://doi.org/10.2113/3.4.1491
Vadose Zone Journal November 01, 2004, Vol.3, 1492. doi:https://doi.org/10.2113/3.4.1492

Book review

Vadose Zone Journal November 01, 2004, Vol.3, 1489. doi:https://doi.org/10.2113/3.4.1489
Vadose Zone Journal November 01, 2004, Vol.3, 1490. doi:https://doi.org/10.2113/3.4.1490
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