Page 168 - Water and wastewater engineering

WELLS 4-23

In addition, because each well is identical, the individual drawdowns of the wells pumping
by themselves will be equal. Thus, we may compute one value of u and apply it to each well.
2
(025m ) (274 10 4 )
.
.
u 3 2 188 10 9
.
d
.
( 42 63 10 m /s )(10 d)(86 400, s/d)

9
Using Equation 4-2 with u 1.88 10 , find W ( u ) 19.51. The drawdown of each indi-
vidual well is then
.
.
s (1 34 m )(19 51 ) 26 15 m
.

Before we begin calculating interference, we should label the wells so that we can keep track
of them. Let us call the two outside wells A and C and the inside well B. Let us now calculate
interference of well A on well B, that is, the increase in drawdown at well B as a result of pump-
ing well A.
Because we have pumped only for 10 days, we must use the transient-flow equations and
calculate u at 75 m.
2
(75m ) (274 10 4 )
.
u 3 2 170 10 4
.
(
( 42 63 10 m /s )(10 d )(86 400, s/d )
.

4
Using Equation 2-8 with u 1.70 10 , find W(u) 8.10. The interference of well A on

B is then
.
.
s Aon B (1 34. )(8 10 ) 10 86 m

In a similar fashion, we calculate the interference of well A on well C.

8
2

.
.
u 150) ( 3 01 10 ) 6 78 10 4
150 (
and W ( u ) 6.72. The interference of well A on well C is then
.
Aon C (1 346 72. )( . ) 9 00 m
s
Because the well arrangement is symmetrical, the following equalities may be used:
s
A onB s BonA s ConB
and
s A onC
s ConA
The total drawdown at each well is computed as follows:
s A s B on A s C on A
s
.
.
s A 26 15. 10 86 9 00 46 01 or 46 m
.
B s s A on B s C on B
s
B s 26 15 10 86 10 86 47 86 or 48 m

.
.
.
.
C s A s 46 01 or 46 m
.

Drawdowns are measured from the undisturbed piezometric surface.
The results of these calculations have been plotted in Figure 4-10 .