Updated: March 6, 2000.
Copyright © 2000 by Jacob Bear, Haifa, Israel. 
All Rights Reserved.

Computer-Mediated Distance learning

Course on

INSTRUCTOR:

JACOB BEAR

GLOSSARY

 AQUICLUDE: A geological formation that may contain water, but is incapable of transmitting significant quantities under ordinary field conditions (e.g., a clay layer).

 AQUIFER: A geological formation which (1) contains water and (2) permits significant volumes of water to move through it under ordinary field conditions.

 AQUITARD: A geological formation that (1) is much less pervious than and (2) is much thinner than the aquifer that underlies or overlies it. It acts as a semi-pervious membrane through which leakage between aquifers separated by it may occur.

 ARTIFICIAL RECHARGE: The technology of augmenting groundwater resources artificially. In such technology, water available above ground surface, say in a river or lake, is injected through wells (called "artificial recharge wells") into an underlying aquifer. Water can be recharged into a phreatic aquifer also through ponds, (referred to as "infiltration ponds"). Surface water is allowed to infiltrate through the bottom of such ponds, travel through the unsaturated zone, eventually reaching an underlying phreatic aquifer.

CONCEPTUAL MODEL:.A conceptual model consists of a set of assumptions that reduce the real problem and the real domain to simplified versions that are satisfactory in view of the modeling objectives and the associated management problem. The conceptual model serves as a basis for the mathematical one

CODE: A computer program.

CODE VRIFICATION: An activity to verify that a code solves what it claims it can solve. Verification is done by comparing the solution obtained by using the code with an analytical solution of the same problem.

CONTINUUM A domain is regarded as a continuum with respect to a specified extensive quantity (e.g., a continuum of mass), if a value of the corresponding intensive quantity (e.g., mass density), can be assigned to every point of that domain.

CONTINUUM APPROACH: The description of phenomena in a domain regarding the latter as a continuum. For example, a porous medium is not a continuum at the microscopic level, but, by the process of averaging, we transform it into a continuum at the macroscopic level.

 CONTROL VOLUME A spatial domain which has a fixed (arbitrary) shape and maintains a fixed position in space. In the Eulerian approach, extensive quantities may enter and leave this volume, and be stored within it, but its shape and position in space remain unchanged.

 EXTENSIVE QUANTITY: An extensive quantity is a quantity that is additive. Mass, momentum, and energy, of a phase or of a component of a phase, are examples of extensive quantities.

 HUBBERT POTENTIAL The piezometric head, i.e., the potential and pressure energy per unit weight, for a compressible fluid.

HYDRAULIC RADIUS: The ratio between a volume and the area of the surface that surrounds it. In a plane, it is the ratio between the area of a domain and the length of its circumference. In a porous medium, it is the ratio between the volume of the void space and total area of the solid matrix surface, within a given porous medium domain.

INVERSE PROBLEM The term is used when referring to the problem of identifying or estimating the numerical values of domain coefficients (e.g., the permeability of a porous medium domain), given values of state variables (e.g., piezometric head) actually measured in the domain.

MACROSCOPIC LEVEL: The level at which a porous medium is visualized as a continuum, and phenomena of transport in it are described in terms of variables, each of which is a volumetric average over an REV.

MODEL: A model may be defined as a selected simplified version of a real system, and phenomena that take place within it, which approximately simulates the system' excitation-response relationships that are of interest.

MODEL CALIBRATION: The activity of verifying that a model of a given problem in a specified domain correctly describes the phenomena that takes place in that domain. It is a combination of model validation and parameter estimation. During model calibration, values of various relevant coefficients are adjusted in order to minimize the differences between model predictions and actual observed measurements in the field.

MODEL VALIDATION: The activity of checking whether a model correctly describes the phenomena in a given domain under a set of specified conditions. This can only be done by comparing model predictions with measurements in field and laboratory experiments.

NAVIER-STOKES EQUATION: This is the momentum balance equation, written for a Newtonian fluid.

 PIEZOMETRIC HEAD: Energy of a fluid, per unit weight. It is composed of the potential energy per unit weight, expressed by the elevation of the point, and the pressure head. Dimensions: L. Units: meters.

 POROUS MEDIUM: A porous medium domain is a portion of space that (1) is occupied by a number of phases, at least one of which is a solid phase, and (2) for which a REV can be found.

REV: Abbreviation for "representative elementary volume" of a porous medium domain. To describe phenomena in a porous medium regarded as a continuum, the same phenomena at the microscopic level have to be averaged over the REV. By taking an average of a variable, or of a domain characteristic over a REV at a point in the domain, and repeating the procedure for all points in the latter, a unique macroscopic description of the behavior within the domain is obtained. This description, in terms of the averaged values, is independent of the size of the REV.

STOCHASTIC MODEL: A model in which the various coefficients that represent material properties (e.g., porosity, permeability, dispersivity) are regarded as random phenomena. This stems from the realization of the uncertainty involved in assigning specific deterministic values to such coefficients.

TRANSMISSIVITY: A coefficient that under the assumption of essentially horizontal flow in a confined aquifer describes the ability of the aquifer to transmit water through its entire thickness. It is obtained as a product of the aquifer's hydraulic conductivity and its thickness.