Geology Reference
In-Depth Information
monitoring with time), parameters needed are basically in relation with the
geometry of the well (length of casing, radius of well, water level in the
well).
The calculation is based on the Thiem equation of steady state flow to a
well. The equation of Bouwer & Rice (equation 1) gives
K
, which is calculated
from recovery/drawdown of the water level in the well after suddenly
removing/adding a slug of water from/in the well (Fig. 1).
2
c
r
ln (
Rr
/
)
1
ln
y
c
w
o
Bouwer & Rice equation:
K
=
(1)
2
L
t
y
1
K
is the hydraulic conductivity [m/s],
y
is the vertical distance between
water level in the well and equilibrium water table before the test [m]—
y
0
at
t
= 0 and
y
t
at
t
,
t
is the time [s],
R
e
is the effective radius over which the
head loss
y
is dissipated in the flow system [m],
r
w
is the well radius [m],
r
c
is the casing radius [m],
L
is the height of the portion of well through
which water enters [m].
R
e
only depends on the geometry of the well and
the flow system. Pre-established curves allow evaluation of ln (
R
e
/
r
w
) using
an abacus (Bouwer and Rice, 1976) giving parameters as function of
L
/
r
w
.
Field data should fit on a straight line when they are plotted as ln
y
t
=
f
(
t
).
So the expression (1/
t
) ln
y
0
/
y
t
is the slope of the corresponding straight line.
Injection pulse:
followed by
Pumping pulse:
followed by
drawdown of water level
recovery of water level
Figure 1.
Injection pulse and pumping pulse.
