Research Institute at Idaho Falls
A Numerical Model for Analysis of Pumping Test Data
Developed by
Gary S. Johnson, and Donna M. Cosgrove
University of Idaho Idaho Water Resources Research Institute
Idaho Falls, ID
Numerical modeling of pumping tests offers a practical alternative to type-curve matching for analysis of pumping test data. Numerical modeling can be accomplished with little more effort than curve matching and provides greater flexibility in describing the real system than is offered by the entire collection of curve matching techniques, including computer based methods.
Analytical curve-matching techniques represent some idealized set of aquifer and well construction conditions. Reality never matches these idealized sets of conditions, though in many cases these techniques may be adequate. For example, the Theis type curve may be applied in some situations even though the prescribed conditions of a completely confined and infinite aquifer are never fully met.
RADFLOW is an easy to use numerical model
that is designed specifically for pumping test analysis. The program and
spreadsheet create default model characteristics that minimize the need
for modeling expertise. The trial and error calibration process may take
somewhat more time than application of a computer-based curve matching
method, however, the relatively small increase in project costs (a few
hours of data analysis may not be significant relative to cost of field
efforts) is likely to be more than offset by improved understanding of
the system being tested and more realistic representation of the system.
A more realistic representation of the system will result in parameter
estimates that are more meaningful.
RADFLOW Description
RADFLOW is a two-dimensional, axial-flow (vertical and radial dimensions) finite-difference model. The model is equipped with an EXCEL spreadsheet interface that 1) provides an input template, 2) contains formulas and macros for calculating default model constants such as grid spacing, 3) runs the Fortran executable, and 4) provides graphical output of model results and comparison to measured time-drawdown data. The user only interacts with the spreadsheet and sees little evidence that a Fortran program is operating in the background.
The axial-flow nature of RADFLOW means that it is capable of representing a multi-layer system, composed of aquifers and aquitards, but that each layer must be treated as internally homogeneous. No lateral heterogeneities or boundaries can be represented. This also implies the system must be represented as isotropic in the horizontal plane.
Users are required to describe the thickness and properties of each significant hydrogeologic layer at the test location. Time-drawdown data from as many as five observation wells are used in a trial-and-error process to calibrate the users; initial estimates of aquifer and aquitard characteristics. RADFLOW provides a graphical and statistical comparison of the simulated and measured values.
RADFLOW is composed of three files that must be loaded in a directory C:\RADFLOW . The macros within the RADFLOW.XLS file read and write to other files that must be in this directory.
More information on RADFLOW can be found
in the Ground Water Journal article by Johnson et al, vol. 39 no. 4, and
in the attached Users Manual. The Users Manual also contains a tutorial.
For assistance in troubleshooting RADFLOW
problems please contact Gary Johnson at johnson@if.uidaho.edu
The RADFLOW package is composed of three files that can be downloaded from this site. All RADFLOW files must be loaded on a directory C:\RADFLOW. Notice that this directory is on C: drive, immediately off the root directory. In summary, the procedure is as follows:
1) Download the zipped RADFLOW files.
2) Use Winzip or compatible program to open the zipped files (See bottom of page for Winzip download.) and place in a folder C:\RADFLOW.
3) Open C:\RADFLOW.XLS in EXCEL
4) Follow directions of the Users Manual
and Tutorial (in the Users Manual)
IWRRI