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78 Chapter 3 Water Sources: Groundwater

0

2
Drawdown s, ft 4 s

6

8
0.2 1 10 100
Time t, min
Figure 3.5 Time-Drawdown Curve (Data by courtesy of the U.S. Geological
Survey). Conversion factor: 1 ft 0.3048 m

Solution 1 (U. S. Customary System):
To determine the slope of the straight-line portion, select two points one log cycle apart, namely:
t 1 1 min s 1 1.6 ft (0.49 m)
t 2 10 min s 2 4.5 ft (1.37 m)
The slope of the line per log cycle is s 4.5 1.6 2.9 ft (0.88 m). The line intersects the zero
drawdown axis at t 0 0.3 min. The transmissivity and the storage coefficient of the aquifers are
T 264 Q> s
264 350>2.9
4
3
3.2 l0 gpd/ft (397 m /d/m)
S 0.3 Tt 0 >r 2
4
0.3(3.2 10 )[0.3>(60 24)]>(225) 2
4.0 10 5
Solution 2 (SI System):
A time-drawdown curve shown in Fig. 3.5 is used, except that the drawndown s (m) versus the time
(min) should be plotted instead.
To determine the slope of the straight line portion, select two points one log cycle apart, namely:

t 1 = 1 min s 1 = 0.49 m
t 2 = 10 min s 2 = 1.37 m
The slope of the line per log cycle is s 1.37 m 0.49 m 0.88 m. The line intersects the zero
drawndown axis at t 0 = 0.3 min = 0.3/(60 24) d. The transmissivity and the storage coefficient of
the aquifiers are:
T = 0.1833 Q>¢s
= 0.1833 * 1907.5>0.88
3
= 397.3 m >d>m
S = 2.24 Tt 0 >r 2
= 2.24 (397.3)[0.3>(60 * 24)]>68.6 2
= 4 * 10 -4