REVIEWS & ANALYSES:

Tian-Chyi J. Yeh and Jirka Simunek

Stochastic Fusion of Information for Characterizing and Monitoring the Vadose Zone
While inverse problems are generally considered ill posed and intractable, it is argued in this paper that well-posedness and tractability can be achieved by incorporating stochastic conceptualizations into inverse modeling procedures. The principles of several geostatistically based inverse approaches are described, followed by a description of their applications to several classical inverse problems, hydraulic tomography, and electrical resistivity tomography for vadose zone characterization and monitoring. A stochastic fusion of information technique is introduced and shown to be a promising approach to effectively characterize vadose zone properties and monitor vadose zone processes.
Vadose Zone J 2002 1: 207-221. [Abstract] [Full Text] [Figures Only] [PDF]  

R. S. Mansell, Liwang Ma, L. R. Ahuja, and S. A. Bloom

Adaptive Grid Refinement in Numerical Models for Water Flow and Chemical Transport in Soil: A Review
The use of pregenerated, fixed grids in numerical simulations of water flow into dry soil or convection-dominated solute transport may provide inaccurate results. Incorporation of automated adaptive grid algorithms permits accurate solutions with local resolution similar to a very fine uniform grid, but with less computational cost. A review of the advantages of local grid adaptive refinement methods applied to numerical solutions of the equations for flow and transport in soils is presented.
Vadose Zone J 2002 1: 222-238. [Abstract] [Full Text] [Figures Only] [PDF]  

ORIGINAL RESEARCH PAPERS:

G. L. Butters and P. Duchateau

Continuous Flow Method for Rapid Measurement of Soil Hydraulic Properties: I. Experimental Considerations
A new method is presented in which continuous flow is imposed on a soil moisture pressure cell while simultaneously measuring water and air pressure. Application of Darcy's Law with inversion of Richards' equation yields the soil water characteristic and the unsaturated hydraulic conductivity function for both inbibition and desorption. The significant advantage of this new method over conventional moisture extraction procedures is that the new method requires only a fraction of the time needed by the conventional method to acquire data over the entire tensiometer range.
Vadose Zone J 2002 1: 239-251. [Abstract] [Full Text] [Figures Only] [PDF]  

Allen G. Hunt and Glendon W. Gee

Water-Retention of Fractal Soil Models Using Continuum Percolation Theory: Tests of Hanford Site Soils
Fractal scaling is used to predict water retention curves of 43 Hanford Site soils. The deviation from prediction at low moisture contents is probably due to the lack of percolation of capillary flow and suggests a lower limit for the applicability of equilibrium moisture retention theory. The volumetric moisture content at which this deviation sets on appears to be the same value at which solute diffusion vanishes.
Vadose Zone J 2002 1: 252-260. [Abstract] [Full Text] [Figures Only] [PDF]  

Jianting Zhu and Binayak P. Mohanty

Spatial Averaging of van Genuchten Hydraulic Parameters for Steady-State Flow in Heterogeneous Soils: A Numerical Study
The land surface pixels representing the Soil-Vegatation-Atmosphere Transfer (SVAT) scheme in hydroclimatic models generally are very large in size, ranging from several hundred square meters to several hundred square kilometers. Considering that due to spatial variability of soil properties many soil textures may be enclosed within each pixel, the assignment of effective soil hydraulic properties to each pixel is problematic. The effect of soil spatial variability within a pixel on the pixel-scale steady-state evaporation and infiltration is examined, and effective pixel-scale soil hydraulic parameters are determined.
Vadose Zone J 2002 1: 261-272. [Abstract] [Full Text] [Figures Only] [PDF]  

Alex Furman, A. W. Warrick, and Ty P. A. Ferré

Electrical Potential Distributions in a Heterogeneous Subsurface in Response to Applied Current: Solution for Circular Inclusions
The analytic element method is applied to derive solutions to the Laplace equation for electrical fields in subsurface environments containing heterogeneous inclusions circular in shape. The solutions are in ready form to evaluate the sensitivity of electrical resistance tomography (ERT) measurements to location and size of inclusions. With the advantage of enhanced accuracy compared with numerical solutions, the solutions are used to find the most sensitive ERT arrays for various inclusion locations.
Vadose Zone J 2002 1: 273-280. [Abstract] [Full Text] [Figures Only] [PDF]  

Ty P. A. Ferré, Henrik H. Nissen, and Jirka Simunek

The Effect of the Spatial Sensitivity of TDR on Inferring Soil Hydraulic Properties from Water Content Measurements Made during the Advance of a Wetting Front
The effects of the spatially distributed sensitivity of time domain reflectometry (TDR) on the inversion of hydraulic properties from water content measurements is examined. The optimal TDR probe configuration for inversion of hydraulic parameters from measurements recorded during the advance of a vertical wetting front has three closely spaced rods that lie in a common horizontal plane. We recommend that a similar analysis be performed for each specific monitoring application.
Vadose Zone J 2002 1: 281-288. [Abstract] [Full Text] [Figures Only] [PDF]  

Kyle W. Blasch, Ty P. A. Ferré, Allen H. Christensen, and John P. Hoffmann

New Field Method to Determine Streamflow Timing Using Electrical Resistance Sensors
Electrical resistance sensors were employed to monitor streambed saturation to infer the onset and cessation of streamflow in ephemeral channels. The accuracy of sensor measurements was comparable to that using stream gauge and soil water content measurements. Results demonstrate that electrical resistance sensors may be used to infer the presence of surface water in diversion canals, storm-water sewers, and overland flow.
Vadose Zone J 2002 1: 289-299. [Abstract] [Full Text] [Figures Only] [PDF]  

F. X. M. Casey, N. Derby, R. E. Knighton, D. D. Steele, and E. C. Stegman

Initiation of Irrigation Effects on Temporal Nitrate Leaching
In this decade-long study, we monitored subsurface nitrate concentrations from the root zone, shallow groundwater, and subsurface drainage in a field where pivot irrigation was initiated. At all monitoring points, we measured an increase in nitrate concentration for some time, after which the concentrations decreased until a steady-state level was reached. We attributed much of the increased nitrate levels to the increased solubility and mobility of residual N due to increased soil water contents with the introduction of irrigation.
Vadose Zone J 2002 1: 300-309. [Abstract] [Full Text] [Figures Only] [PDF]  

NOTES:

J. B. Sisson, G. W. Gee, J. M. Hubbell, W. L. Bratton, J. C. Ritter, A. L. Ward, and T. G. Caldwell

Advances in Tensiometry for Long-term Monitoring of Soil Water Pressures
Performance of tensiometers, placed to depths of 7 m using auger drilling vs. placement by drive cone, was monitored for 2 yr. Both methods proved reliable, but equilibration was fastest with the drive-cone tensiometers.
Vadose Zone J 2002 1: 310-315. [Abstract] [Full Text] [Figures Only] [PDF]  

Magnus Persson and Jon M. Wraith

Shaft-Mounted Time Domain Reflectometry Probe for Water Content and Electrical Conductivity Measurements
A new type of shaft-mounted time domain reflectometry probe capable of measuring both dielectric constant and bulk electrical conductivity is described and evaluated. Short probe lengths, as short as 0.03 m, were found to be able to yield dielectric constant measurements of equal accuracy to those obtained with conventional 0.20-m three-rod TDR probes.
Vadose Zone J 2002 1: 316-319. [Abstract] [Full Text] [Figures Only] [PDF]  

BOOK REVIEWS:

Yan Jin

Highlights in Environmental Research.
Vadose Zone J 2002 1: 320. [Full Text] [PDF]  

Günter Blöschl

Geostatistics for Environmental Scientists.
Vadose Zone J 2002 1: 321. [Full Text] [PDF]  

D. G. Strawn

Heavy Metals Release in Soils.
Vadose Zone J 2002 1: 322. [Full Text] [PDF]  

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