Ground-Water Hydrology of the Upper Klamath Basin, Oregon and ...

Ground-Water Hydrology 57
Water levels in two observation wells near the town
of Sprague River, 36S/10E-14ACC and 36S/11E-20DCA
(fig. 33), have declined over 30 ft since monitoring began
in the early 1960s. Leonard and Harris (1974) hypothesized
that the relatively steady, and somewhat localized, longterm
decline represented a loss of hydraulic head caused
by discharge from free-flowing wells. The OWRD later
attributed the decline, at least in part, to some wells in the
area constructed in a manner that allowed ground water
from a the confined basalt aquifer in the lower parts of the
wells to flow uphole and into sedimentary units (with lower
head) in shallower parts of the well bores (Oregon Water
Resources Department, 1987). Borehole geophysical logging
has confirmed the interaquifer leakage; however the geologic
units receiving the leakage appear to be rhyolitic lavas mapped
in the area by Sherrod and Pickthorn (1992) (Mark Norton,
Oregon Water Resources Department, unpub. data). For
example, geophysical logs for one nearby well show uphole
interaquifer flow of about 200 gal/min into a unit with a
relatively high natural gamma signature indicative of silicic
material. The driller described the material as “broken lava
rock.” Water levels in both wells have been more stable since
the mid-1990s (fig. 33), likely owing to the ground-water-flow
system beginning to reach a new equilibrium.
Water levels in long-term observation well 46N/01E-
06N01 in Butte Valley were stable from the 1950s to the mid-
1970s (fig. 34). Since 1975, the water level has declined about
20 ft. The trend likely reflects increased pumping stresses
during times when precipitation is low, with intermittent times
of partial recovery during wet years in the mid-1980s and mid-
1990s.
An observation well in southern Poe Valley (40S/11E-
11BAD) shows a series of responses to development from
which it has never fully recovered (fig. 35). Most notable is
the water-level decline of about 20 ft between 1985 and 1995,
a recovery of less than 5 ft between 1995 and 1998, and a
decline of about 12 ft since 1998. Another observation well
(40S/12E-30DCB) about 3 mi south-southeast of the Poe
Valley well, in the area of the Shasta View Irrigation District,
has a similar water-level trend where the records overlap from
1994 to present (fig. 35). The total decline in well 40S/12E-
30DCB since 1998, however, is slightly greater at about 19 ft.
The similarity of the head fluctuations suggests that the effects
of pumping stresses in both areas may migrate across the
subbasin boundary.
0
10
36S/10E-14ACC
20
30
40
50
DEPTH TO WATER, IN FEET
60
70
80
90
40
50
60
70
80
90
100
1960
36S/11E-20DCA
1965
1970
1975
1980
1985
1990
1995
2000
2005
Figure 33.
Water-level fluctuations in wells 36S/10E-14ACC and 36S/11E-20DCA in the Sprague River Valley, Oregon.