GGU-PUMPTEST: Time-drawdown method

The theoretical principles are described in Langguth/Voigt on pages 165 to 167. The example file "Time-drawdown method Gauge 3b.pvs" can be found in the program's example folder.

This method entails a drawdown in a well with a constant pumping rate. At the same time, the course of the drawdown is measured in a nearby monitoring well.

The graphical representation of the test results is in a semi-logarithmic scale (drawdown against time). The following data is required:

distance between the extraction well and the monitoring well;
the constant pumping rate in the extraction well;
the aquifer thickness H;
the specification of confined or unconfined aquifer;
the drawdown h against time in the monitoring well.

After defining the input values they are entered against time and the best-fit curve determined. The permeability can then be determined.

Example:

This is the example given for Gauge 3b in Langguth/Voigt. The following values were measured in Gauge 3b:

Table 1 Gauge 3b measured data

Time [s]	h [m]	Time [s]	h [m]
12.0	0.050	861.0	1.000
18.0	0.100	1080.0	1.050
22.0	0.150	1420.0	1.110
36.0	0.250	1800.0	1.150
54.0	0.350	2160.0	1.200
81.0	0.450	2760.0	1.250
122.0	0.550	3480.0	1.300
226.0	0.700	4380.0	1.350
346.0	0.800	5280.0	1.390
434.0	0.850	8100.0	1.480
549.0	0.900	11600.0	1.550
689.0	0.950	14150.0	1.580

The pumping rate in the extraction well is 0.02667 m³/s. Gauge 3b is 23.0 m from the extraction well. The aquifer is 10.0 m thick. It is a confined aquifer.

In the menu item "File/New", press the "Distance-drawdown method" button and then go to the menu item "Edit/Edit values".

After selecting the "0 values to edit" button enter "24" as new number, because the test comprises 24 measured values.

Enter the values given in Table 1.

These values represent the times and corresponding drawdown in the monitoring well relative to the at-rest groundwater level. Navigate through the table using the "Forw." button in order to enter further values. After leaving the input box clicking on "Done" go to the "Evaluation/Time-drawdown method" menu item.

Enter the values in the dialog box and confirm with "OK". The following result box will be shown.

The "a" and "b" values describe the course of the best-fit curve through the data. The "r" value is the correlation coefficient, representing the quality of the best-fit curve. Below this, the permeability, the transmissivity and the storage coefficient are given. The t0 value describes the intersection of the best-fit curve with the time axis.

The solution given in Langguth/Voigt is:

T = 9.4 · 10^-3m²/s;
S = 4.6 · 10^-4m²/s.

The minor differences are due to the purely visual evaluation employed by Langguth/Voigt.

If you adopt the result text, it is entered into the "Result text" box in the form.