Distance-Drawdown Automatic

Distance Drawdown (Automatic) Method

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This method is used for tests where drawdown is measured at the same time intervals in two or more observation wells different distances from the well. For each time measurement, the program calculates the slope of the best fit line of an imaginary graph of arithmetic drawdown and logarithm of the distance to the observation well (or well radius for the pumping well). This slope is used to estimate aquifer transmissivity, storativity, and radius of influence.

Transmissivity

Transmissivity is determined from the equation:

$image\TRANS.gif$

where:

Q is pumping rate

b is the slope of the graph of drawdown vs. log of radius (or drawdown per log cycle radius)

Radius of Influence

Radius of Influence is determined by the equation:

$image\RADIUS.gif$

where:

a is the drawdown at log of radius = 0

b is the slope of the distance drawdown graph

Storativity

Storativity is determined by the equation:

$image\STOR.gif$

where:

t is the time since pumping started

R is the radius of influence of the test as determined above

T is the estimated transmissivity of the aquifer.