GGU-PUMPTEST: Distance-drawdown method

The theoretical principles are described in Langguth/Voigt on pages 167 to 169. The example file "Distance-drawdown method.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 drawdown at a given time is measured in at least two nearby monitoring wells.

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

• the distances between the extraction well and the monitoring wells (>= 2);

• the drawdown h in the monitoring wells at a given time;

• the constant pumping rate in the extraction well;

• the aquifer thickness H;

• the specification of confined or unconfined aquifer.

After defining the input values they are entered against the distances to the extraction wells and the best-fit curve determined. The permeability can then be ascertained.

Example:

This is the example for Gauges 3b, 11b and 6b in Langguth/Voigt.

The pumping rate in the extraction well is 0.02667 m³/s. In table 2 the distances of the three gauges to the extraction well and the drawdown at time t = 5400 seconds are given.

Table 2 Gauges 3b, 6b and 11b measured data

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".

Select the "0 values to edit" button and enter "3", because the test comprises measured values from 3 wells. Enter the values given in Table 2.

These values represent the distances of the monitoring wells to the extraction well and the corresponding drawdown relative to the at-rest groundwater level.

Go to the "Evaluation/Distance-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 r₀ value describes the intersection of the best-fit curve with the distance axis.

The solution given in Langguth/Voigt is:

• T = 9.0 · 10^-3 m²/s

• S = 4.8 · 10^-4 m²/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 .