*TM 5-813-1/AFM-88-10, Vol. 1
(The correction to 60F is usually neglected.) Usually
measured in gallons per day per square foot.
b.
Well discharge formulas.
The following
Where:
formulas assume certain simplifying conditions.
Q = well yield in gpm
However, these assumptions do not severely limit the
P = permeability in gpd per square foot
use of the formulas.
The aquifer is of constant
H = thickness of aquifer in feet
thickness, is not stratified and is of uniform permeability.
h = depth of water in well while pumping
The piezometric surface is level, laminar flow exists and
in feet
the cone of depression has reached equilibrium. The
R = radius of influence in feet
pumping well reaches the bottom of the aquifer and is
r = radius of well in feet
100 percent efficient. There are two basic formulas
(Ground Water & Wells) one for water table wells and
the following formula for available yield from an artesian
one for artesian wells. Figure 5-4 shows the relationship
well:
of the terms used in the following formula for available
yield from a water table well:
where:
m = thickness of aquifer in feet
H = static head at bottom of aquifer in feet
all other terms are the same as for Equation 5-1.
Figure 5-4. Diagram of water table well.
5-7
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