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An effective field measurement of the air-entry and water-entry soil water pressure heads gives an improved description of the hydraulic properties of soils. One study obtained measurements of air-entry soil water pressure heads using a modified falling head infiltrometer. This study then estimated the value of the water-entry soils water pressure head from this value. Now direct field measurements of both the air-entry and water-entry soils water pressure heads can be easily obtained using an external tension bottle attached to the Guelph Pressure Infiltrometer at the conclusion of quasi-steady state infiltration readings.

The field-saturated hydraulic conductivity Kfs can be obtained from measurements of the long-time steady flow rates from ring infiltrometers by assuming either that the soil is a “Green and Ampt” soil that has a relationship between hydraulic conductivity K and soil water pressure ψ, such that K = Kfs, 0 > ψ > ψf; K → 0, ψƒ < ψf, or that the soil is a “Gardner” soil with an exponential relationship K = Kfs exp(αψ), where α is a constant. It is shown that infiltration into a Green and Ampt soil from a surface source with zero head is the same as that for a Gardner soil with α → ∞ (gravity dominant) and with a surface source at a head |ψfs|. The shape factor G calculated for Gardner soils using a numerical solution of Richards's equation is used to calculate Kfs and α from ring infiltrometer tests based on Q = [aH/G + a/(αG) + πa2]Kfs, where Q is the steady state flow rate, H is the constant ponded head, and a is the ring radius. The equivalent G factor for Green and Ampt soils calculated using electric analogue solutions of Laplace's equation is shown to agree very well with the numerical solution. The slope of the linear relationship between the shape factor and the depth of insertion of the ring divided by the radius of the ring is shown to have a slope approximately equal to 1/π.

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

A series of miscible displacement experiments was conducted in an unsaturated glass bead medium maintained at a constant average water content during each displacement. The variation in the form of the breakthrough curve with decreasing water content was not large and was not related in a simple way to the water content; however, there was consistent shift of the breakthrough curve to the left of the relative concentration value of 0.5 and 1 pore volume and a lone tail or slow approach to the final relative concentration of 1.0. Some of these effects may be attributed to the presence of stagnant liquid in the pores. (11 refs.)

A series of experiments have been conducted at a constant temperature on the intrusion of salt from a reservoir containing a fixed volume of solution into an underlying long vertical column of porous material, initially saturated with pure water and sealed at the bottom. The variation with time of the salt concentration in the reservoir was measured for different types of porous materials, different initial concentrations, and different mechanical treatments of the solution. The experimental results, substantiated by the theoretical analyses, indicate that the main contributor to the influx of salt into the porous material is the convective dispersion arising from the onset of horizontal variations of the salt concentration and of the vertical velocity component. The rate of this process is governed by a characteristic time where ρU and ρL are the initial densities in the reservoir and in the porous material, respectively; K is the hydraulic conductivity of the porous material with respect to the liquid initially saturating it; and H is a characteristic head of the solution. Approximate expressions have been derived for the rate of decrease of the salt concentration in the reservoir, for the influx of salt into the porous material, and for the advances of the salt front within it.

We describe improvements in the theory and practical application of the constant head well permeameter method for field measurement of saturated hydraulic conductivity above the water table.The theoretical improvements result in a new analytical solution and a numerical solution that produce