So firstly, an aquifer of course, contains groundwater or subsurface water and

it can be unconfined or confined, so an unconfined aquifer,

such as shown here, has a water surface which can be drawn down like this.

It has a free surface, and the free surface will, generally speaking,

be at atmospheric pressure.

We, for a, a drawdown here, we have a cone of depression here where

the depression here is given by D and the drawdown or

depression at the well here is denoted by Dw, and that is called the drawdown.

To predict the drawdown,

we have Dupuit's Formula shown here in the extract from the reference handbook.

And in this formula reproduced here, the variables are k

is the coefficient of permeability, which is the same as the hydraulic conductivity,

and unfortunately in the handbook they use the symbol lowercase k here for

coefficient of permeability, although, in reality,

it's exactly the same as the conductivity or the hydraulic conductivity

which was previously denoted by K, uppercase K, in the previous segment.

h two here is the head at some radius r two and

h one is the head at the well which is of radius r one.

And a couple of notes about this, that this equation, strictly speaking,

only applies if the well drawn down, drawdown Dw,

is much less than the undisturbed depth, capital D, and also if the well

completely penetrates the aquifer, such as shown in this diagram here.

And furthermore, this equation is an equilibrium equation.

In other words, it only applies a very long time after pumping commences.

Another variable are parameters called the specific capacity,

which is defined as the volume flow rate divided by the well drawdown.

And the units of that would be either, for example, meters squared per day or

gallons per minute per foot would be typical units of specific capacity.

So here's an example.

We have an unconfined aquifer 200 feet deep.

In other words, this depth here well away from the well is 200 feet.