Geology Reference
In-Depth Information
discharge wells. Theis (1935) has shown that transmissivity could be calculated
from the recovery water level data and this method is often used in estimating
transmissivity from single bore-wells. From the time-drawdown data of an
observation well located at a distance '
r
', the aquifer parametres can be
determined. The other data required for the computation are the drawdown
from the observed data, the time factor and the constant discharge of the
pumped well. The type curve and the data curve (plotted on double logarithmic
paper) are matched and the following data are noted from a common match
point. (No attempt is made to elaborate the theoretical aspects of the method.)
Another method has been described by Jacob, which involves plotting of
observed data on a semi-logarithmic paper and fitting the data to straight
line. Both transmissivity and storage coefficient can be determined.
Theis Method
T
=
Q
/4
s
w
(
u
);
u
=
r
2
S
/4
Tt
from match point
where
s
= 0.174 m,
t
= 5.2 × 10
-2
day,
w
(
u
) = 1.0, 1/
u
= 100,
u
= 0.01 and
r
= 130 m
Jacob's Straight-line Method
2.25
Tt
r
0
T
= 2.30
Q
/4
s
;
S
=
,
2
where
'
T
' is the transmissibility (m
2
/day), '
Q
' is the discharge in m
3
/day,
s
is log cycle difference in drawdown (m), '
S
' is the storage coefficient, '
t
0
'
time intercept on the zero-drawdown axis (
s
= 0) and '
r
' is the distance
between pumping well and observation well.
Selection of Pump Sets
The selection of proper pumping set is important to ensure yields from wells
and factors to be considered are:
(a) finished inside diameter and total depth of the well
(b) yield from the well, the desired pumping rate and hours of pumping per
day
(c) the lowest pumping water level (in dry season)
(d) the total head on the pump
(e)
the power required
CONCLUSIONS
The chapter provides practical tips for carrying out the pumping tests that
are at one hand important experiments in groundwater hydrology and on the
other hand quite cumbersome and to be handled with utmost care to obtain
