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

Ground-Water Hydrology 37
INFLOW, IN CUBIC FEET PER SECOND
400
350
300
250
200
150
100
50
September-November mean inflow between J.C. Boyle Power Plant and Iron Gate Dam
Cumulative departure from average precipitation at Crater Lake (1932-2005)
0
1965 1970 1975 1980 1985 1990 1995 2000
250
200
150
100
50
0
-50
CUMULATIVE DEPARTURE FROM AVERAGE PRECIPITATION, IN INCHES
Figure 17. September to November mean gains in flow (a proxy for ground-water discharge) between the John C.
Boyle power plant (USGS station number 11510700) and Iron Gate Dam (11516530), and the cumulative departure from
average precipitation at Crater Lake, Oregon.
Summary of Geographic and Temporal Variations
of Ground-Water Discharge to Streams
Analysis of streamflow data indicates that many streams
in the upper Klamath Basin have a large component of ground
water. Most streams throughout the world rely on groundwater
discharge to support flows during the dry season. The
upper Klamath Basin and other basins on the eastern flank of
the Cascade Range are unique in that ground water discharge
composes a large proportion of the total streamflow. This is
attributable to the substantial regional ground-water system
that exists in the permeable volcanic terrane. Some major
streams in the basin, such as the Wood River and Spring
Creek, are virtually entirely ground water fed. It has long
been recognized that much of the water flowing into Upper
Klamath Lake originates as ground-water discharge (Bureau of
Reclamation, 1954, p. 150). Of the 2,200–2,300 ft 3 /s average
total inflow to the lake (from Hubbard, 1970, and Reclamation
records), at least 60 percent can be attributed to ground-water
discharge in the Wood River subbasin and springs in the lower
Sprague River drainage and the Williamson River drainage
below Kirk. This quantity does not include ground-water
discharge to upper parts of the Williamson and Sprague River
systems, which would make the figure even larger. The large
component of ground water in streamflow influences the
hydrologic response of the basin to climate cycles, and has
implications for flow forecasting (Risley and others, 2005).
OR19-0048_fig17
Discharge from all major ground-water discharge areas
in the basin fluctuates over time. Ground-water discharge
fluctuations are primarily climate driven, and, therefore,
discharge from the various sources tends to vary in unison.
Owing to the effects of ground-water storage, regional-scale
discharge areas integrate climate conditions over multiple
years. Consequently, ground-water discharge fluctuations
tend to follow a pattern similar to the cumulative departure
from average precipitation. A practical implication of this
observation is that ground-water discharge from storage may
support robust streamflow during a dry year following a series
of wet years. Conversely, it may take multiple years of average
or above average conditions following a protracted drought to
replace ground-water storage and return spring discharge (and
hence, streamflow) to predrought conditions.
Ground-water discharge variations can represent
substantial volumes of water on an annual basis. The
combined ground-water discharge to the lower Williamson,
Sprague, and Wood Rivers just upstream of Upper Klamath
Lake can vary by at least 450 ft 3 /s in response to climate
cycles. This equates to an annual volume of 326,000 acreft.
The actual variation in ground-water discharge to Upper
Klamath Lake and its tributaries is larger, because the probable
variations in ground-water discharge to Fort Creek, Crooked
Creek, and springs discharging directly to the lake have not
been included. Gaging station data show that net ground-water
inflow to the Klamath River (and ground-water fed tributaries)
between Keno and Iron Gate Dam probably varies at least 150
ft 3 /s in response to climate.