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Aquifer and well test analysis and simulation: Summary

The CG programs: a summary of what they do

Note that these programs were originally written in about 1988, they run under DOS, not Windows, and have become antiquated.

Contact details:
A simulation fitted to drawdown and recovery in an aquifer test. (Well C was being pumped, the aquifer test data were recorded in piezometer D.) The CG programs can handle many stages in well or aquifer tests; variations in pumping rates including a zero rate (recovery).
David Clarke
20 Musgrave St., Crystal Brook 5523, S. Australia
Email daveclarkecb@yahoo.com

Introduction

These programs will give hydrogeologists powerful, quick and flexible help in all discharge test analysis work. They can be applied to:
Simulated data from a steady-rate well discharge test.
The blue (Isotropic) curve is the simple case with no boundaries.
The purple (Discharge) curve is for a simple discharge (water-tight) boundary.
The yellow (Recharge) curve is for a simple recharge (constant-head) boundary.
Note that these programs run under DOS using keyboard input. A mouse cannot be used within the programs.

The data for all the graphs (charts) on this page were:

All data sets were output from the CG programs as '.csv' files for convenient importation into a spreadsheet.

The graphs on this page are examples of uses to which the programs can be put; they are not neccessarily conected with the adjacent text.
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Publication

The precersors of the CG programs were first published in the BASIC language in "Microcomputer Programs for Groundwater Studies" (1987), then upgraded and converted to Pascal in "Groundwater Discharge Tests: Simulation and Analysis" (1988). Both of these books were in the Elsevier Developments in Water Science series. The programs have undergone more-or-less continuous development, as I felt the need, since then.



A data fit produced by CG. Here the well discharge test included a stepped rate test, followed by a period of recovery, followed by a one-day steady-rate test, followed by recovery.
The CG programs can analyze a data set like this as easily as for a simple, single-rate test.
The displacement between the final recovery and simulated recovery is most likely due to entrapped air in the fractured rock aquifer.
Here the data of the preceding graph are plotted against the logarithm of time.
There are many ways in which the programs might be used. Some examples are:

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In all cases output of various combinations of measured data and/or simulated data is an additional option. This can be on a plotter or it can go to disk files for further handling by third party software.



This distance drawdown graph has been produced by the stand-alone program CGSim.exe. It is based on a semi-bounded strip aquifer with T=38 inside the strip and T outside the strip (T2) equal to 260. S=0.005 and the strip width is 30m. All units here are based on metres and days.
The CG programs can, and have, been used for educational purposes. For example, as part of a short course in hydrogeology for graduates.

CGSim

Unlike most of the CG programs this one is a stand-alone. Its use would be the best way to get a feal for the capabilities of the CG programs.

Notes on CGSim

Purpose
To produce type curves:


A comparison between no boundary (isotropic), a simple discharge boundary and a semi-boundary. In all cases the boundary is 600m from both discharging well and piezometer. In the 'semibound' case transmissivity on the near side of the boundary is twice that beyond the boundary.
The type curves from CGSim can be compared to a data file produced by the main CG programs, for analysis.

Instructions for use
You should have the files CGSim.EXE, CGSimIn.TXT, CGSim.ICO, CGSim.DOC and EGAVGA.BGI, all in the same subdirectory.

You can modify the configuration file CGSimIn.txt with any text editor (eg. Notepad, Dos Edit.com) or word processor to set up initial conditions. Take care to retain the format of the file (retain a copy of the original in-case of mistakes). Read the notes in this file. Note that the configuration file can arrange for reading a .CTD data file, as in the demonstration.

To run the program from Windows Double click on CGSim.exe in Windows Explorer. (CGSim can be run from DOS or Windows.)

Once the program is running use the left and right arrow keys to highlight the parameter that you want to adjust. Use the up and down arrow keys to adjust the highlighted parameter.

A group of aquifer test simulations for changing values of distance between pumped well and piezometer. This is for the very simple case of a Theis (confined, isotropic) aquifer, it would be just as easy to produce a nest of type curves for many combinations of aquifer type and boundary configuration.
The number keys:

  1. Redraw the graph if your adjustments have caused a poor match between the data and the graph limits;
  2. Swap between time/drawdown and distance/drawdown;
  3. Change between the various solutions;
  4. Change between the graph types;
  5. Change the number of points plotted, this effects the maximum time (or distance) on the graph;
  6. Adjust the factor used to increase and decrease the parameter values;
  7. Dump the data of the current simulation to disk file. (It will go to two files, a comma delimited text file {CGSimOut.TXT} for use by spreadsheets etc., and a data file compatible with the CG well/aquifer test analysis programs {CGSim.CTD}.
To temporarily leave the program without closing it (from Windows) you can press [Alt] and [Tab] together.
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A couple of terms I have used...
* Semi-bounded aquifer - an aquifer with a straight line boundary between a section having transmissivity=T and transmissivity=T2. The pumped well and piezometer are taken to be in the T section, and both are taken to be equidistant from the boundary. Storage is the same everywhere.

An aquifer test simulation showing the slight differences to be expected depending on the location of pumped well and piezometer within a strip aquifer.
** Semi-strip aquifer - an aquifer bounded by two parallel boundaries, transmissivity=T inside the strip, T2 outside the strip. The pumped well and piezometer are both taken to be in the middle of the strip. Storage is the same everywhere.

The example data file, CLRPU1DD.CTD, fits well with a strip aquifer with T=1160, S=0.0039, and strip width=365m. As it's set up, the .CFG file starts the program using the Theis solution, change to the strip solution to get a good fit. Then experiment.

One of the minor functions of the CG programs. This sort of graph can be produced from what I've called a 'well characteristics file'. It compares well losses to total drawdown for a series of increasing discharge rates in a particular well.
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Another example of a graph produced from a 'well characteristics file': discharge rate (Q) plotted against specific capacity (Q/s).


Another example of a graph produced from a 'well characteristics file': discharge rate plotted against drawdown (s).


An example of a semibounded strip simulation fitted to data from an actual well test. (As the data were from a pumped well a bit of data manipulation was required.)
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An aquifer test analysis based on water levels recorded in a piezometer during a stepped rate discharge test.


A simulation and field data after evaluation of the well equation.


A simulation demonstrating how a time-drawdown data falls on a straight line on a log-log graph after boundary effects have come fully into play.


The same drawdown data as in the above graph, but here plotted against the square root of time.
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The CG programs can simulate well storage effects while evaluating the well equation in a well test. This graph shows a simulation based on the evaluated well equation with and without well storage effects, compared to the recorded data.


Best fit DeGlee analysis for well Waik6. T=27m2/day, L=334m.


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