Quantitative value characterising a size measure of a drainage area 

...

r_e = \sqrt{\frac{A_e}{\pi}}

...

It makes a physical sense of a geometrical average distance from well to the drainage area

...

r_e = \sqrt{A_e}

for square-shape drainage area

 boundary.

For a circular-shape drainage area with centred well it makes a direct sense of a distance between a well and 

which can be is misnomer for other shapes of drainage area.

It usually makes a physical sense of an average distance from a well to the drainage area boundary.

See also

...