Thiem Steady State Calculator

For Confined and Unconfined Aquifers

 

This estimates aquifer transmissivity using the Thiem method. Units are set Options | Units.

 

Transmissivity is determined for each possible combination of two wells. These values are then averaged for a final answer. If a file of calculations is created, the file will show each well combination and the resulting transmissivity value.

 

Procedure:

 

1. Enter the pumping rate, distance to observation wells, and steady state drawdown for each well. The default steady-state drawdown is assumed to be the last drawdown value before recovery data is collected. This value is not necessarily correct.

 

2. Select unconfined or confined aquifer type.

 

3. Press Calculate. Transmissivity will be displayed in the window.

 

3. A file of calculations can be created by pressing Save Results. The user will be prompted for a file name.

 

 

Implementation

 

The Thiem solution is applicable for situations where the aquifer has been pumped to steady-state. In the equations below, Q is the well discharge rate, K is aquifer hydraulic conductivity, D is aquifer thickness (saturated aquifer thickness for unconfined aquifers), r is the radial distance from the pumping well to the observation well, s is the drawdown in the well, h is the steady-state elevation of water in the well, referenced to the base of the aquifer, the subscripts 1 and 2 refer to the observation well closest to the pumping well, and the observation well farthest from the pumping well respectively. All values are in consistent units in the equations.

 

 

Confined Aquifers:

 

The Thiem equation describing steady-state drawdown in two observations wells is commonly written (Kruseman and de Ridder, 1991):

image\THIEMC1.gif

 

To solve for aquifer transmissivity, this equation can be re-written as:

 

image\THIEMC2.gif

 

This equation is used by Infinite Extent to estimate aquifer transmissivity using the Thiem method.

 

 

Unconfined Aquifers:

 

As the pumped aquifer reaches steady-state, drawdown in two observation wells can be described by the equation below (Kruseman and de Ridder, 1991):

image\THIEMU1.gif

Infinite Extent accepts data for the drawdown in the observation wells, rather than the water level elevation of the well. Solving for transmissivity and substituting the drawdown in the well for the elevation as applicable, gives the following equation:

image\THIEMU2.gif

 

This equation is used by Infinite Extent to estimate transmissivity for unconfined aquifers at steady-state.