1996 Journal Articles
Parameter equivalence for the Brooks-Corey and van Genuchten soil characteristics: Preserving the effective capillary drive
H.J. Morel-Seytoux
Colorado State University, Fort Collins, Colorado
P.D. Meyer, R.J. Lenhard
Pacific Northwest National Laboratory, Richland, Washington
M. Nachabe
University of Colorado, Boulder, Colorado
J. Touma
Institut Français de Recherche Scientifique pour le Développement en Coopeération, Montpellier, France
M.T. van Genuchten
U.S. Salinity Laboratory, Riverside, California
Water Resources Research 32(5):1251-1258, (1996).
Abstract
This paper provides a simple way to convert Brooks-Corey (BC) parameters to van Genuchten (vG) parameters and vice versa, for use primarily in situations where saturated conditions are likely to be encountered. Essential in this conversion is the preservation of the maximum value of physical charactersitic, the "effective capillary drive" HcM [Morel-Seytoux and Khanjii, 1974], defined with a good approximation for a soil, water, and air system as HcM = Integral from 0 to infinity of krw dhc, where krw is relative permeability (or conductivity) to water and hc is capillary pressure (head), a positive quantity. With this conversion, infiltration calculations are essentially insensitive to the model used to represent the soil hydraulic properties. It is strictly a matter of convenience for the user which expression is used. On the other hand, the paper shows the other equivalences may lead to great variations in predictions of infiltration capacity. Consequently, the choice of the proper equivalence to use in calculations for rainfall-runoff modeling or for low-level radioactive waste disposal design is a serious matter.
Application of similar media scaling and conditional simulation for modeling water flow and tritium transport at the Las Cruces Trench Site
M.L. Rockhold, R.E. Rossi
Pacific Northwest National Laboratory, Richland, Washington
R.G. Hills
New Mexico State University, Las Cruces, New Mexico
Water Resources Research 32(3):595-609, (1996).
Abstract
Similar media scaling and geostatistical analyses are used to characterize the spatial variability of soil hydraulic properties at the Las Cruces Trench Site in New Mexico. A simple method is described for conditioning the hydraulic properties used for unsaturated water flow and solute transport modeling, based on the spatial distributions of initial field-measured water contents and a set of scale-mean hydraulic parameters determined from the scaling analysis. This method is used to estimate hydraulic properties for numerical simulations of the latest field-scale flow and transport experiment conducted at the Las Cruces Trench Site. Relatively good matches between the observed and simulated flow and transport behavior are obtained without model calibration. The results of this study suggest that using similar media scaling in conjunction with the described conditioning procedure can significantly reduce the uncertainty in predictions of water flow and solute transport in spatially variable soils.
Method to estimate water permeability functions of moderately wet soils with help of heat pipe technique
A.M. Globus1, G.W. Gee2, M. Fayer2, M. White2
1Agrophysical Res. Inst. of Russian Academy of Agricultural Sciences, St. Petersburg, Russia
2Pacific Northwest National Laboratory, Richland, WA
Zeszyty Problemowe Postepow Nauk Rolnichzych 436: 49-55, (1996).
Abstract
Water permeability of moderately wet soils, i.e., their unsaturated hydraulic conductivity and water diffusivity are seldom measured directly, yet are often needed by numerical models to simulate transport processes. These functions can be evaluated from steady state water content and temperature profiles in heat pipes - closed columns of uniformly moistened soil subjected to temperature gradient. For such systems Sw=DT/D(θ)=-dθ/dT where Sw is the thermogradient coefficient, DT is the thermal water diffusivity, D(θ) is isothermal water diffusivity and -dθ/dT is the rate of change of water content with temperature deduced from steady state profiles of θ(x) and T(x), x - is the distance from one of the column ends. DT varies in a relatively narrow range and can be assumed as a constant. Then D(θ) can be estimated as DTSw, where Sw is measured in various locations along soil columns. Using water retention data, the steady water content profile can be procedure for estimating D(θ) can then be applied to estimate hydraulic conductivity, K(θ). Soil columns ranging in length from 5 to 10 cm, exposed to thermal gradients of 1°C/cm for periods as short as 7 d, at initial suction values ranging from 1 to 1.5 MPa, can be used to estimate D and K with uncertainties of factor of five or less in the suction range .02 to 3 MPa.