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

Ground-Water Hydrology of the Upper Klamath Basin,
Oregon and California
By Marshall W. Gannett, Kenneth E. Lite Jr., Jonathan L. La Marche, Bruce J. Fisher, and Danial J.
Polette
Abstract
The upper Klamath Basin spans the California-Oregon
border from the flank of the Cascade Range eastward to the
Basin and Range Province, and encompasses the Klamath
River drainage basin above Iron Gate Dam. Most of the basin
is semiarid, but the Cascade Range and uplands in the interior
and eastern parts of the basin receive on average more than
30 inches of precipitation per year. The basin has several
perennial streams with mean annual discharges of hundreds
of cubic feet per second, and the Klamath River at Iron Gate
Dam, which represents drainage from the entire upper basin,
has a mean annual discharge of about 2,100 cubic feet per
second. The basin once contained three large lakes: Upper and
Lower Klamath Lakes and Tule Lake, each of which covered
areas of 100 to 150 square miles, including extensive marginal
wetlands. Lower Klamath Lake and Tule Lake have been
mostly drained, and the former lake beds are now cultivated.
Upper Klamath Lake remains, and is an important source
of irrigation water. Much of the wetland surrounding Upper
Klamath Lake has been diked and drained, although efforts
are underway to restore large areas. Upper Klamath Lake and
the remaining parts of Lower Klamath and Tule Lakes provide
important wildlife habitat, and parts of each are included in the
Klamath Basin National Wildlife Refuges Complex.
The upper Klamath Basin has a substantial regional
ground-water flow system. The late Tertiary to Quaternary
volcanic rocks that underlie the region are generally
permeable, with transmissivity estimates ranging from 1,000
to 100,000 feet squared per day, and compose a system of
variously interconnected aquifers. Interbedded with the
volcanic rocks are late Tertiary sedimentary rocks composed
primarily of fine-grained lake sediments and basin-filling
deposits. These sedimentary deposits have generally low
permeability, are not good aquifers, and probably restrict
ground-water movement in some areas. The regional groundwater
system is underlain and bounded on the east and west
by older Tertiary volcanic and sedimentary rocks that have
generally low permeability. Eight regional-scale hydrogeologic
units are defined in the upper Klamath Basin on the basis of
surficial geology and subsurface data.
Ground water flows from recharge areas in the Cascade
Range and upland areas in the basin interior and eastern
margins toward stream valleys and interior subbasins. Ground
water discharges to streams throughout the basin, and most
streams have some component of ground water (baseflow).
Some streams, however, are predominantly ground-water
fed and have relatively constant flows throughout the year.
Large amounts of ground water discharge in the Wood River
subbasin, the lower Williamson River area, and along the
margin of the Cascade Range. Much of the inflow to Upper
Klamath Lake can be attributed to ground-water discharge
to streams and major spring complexes within a dozen or so
miles from the lake. This large component of ground water
buffers the lake somewhat from climate cycles. There are
also ground-water discharge areas in the eastern parts of the
basin, for example in the upper Williamson and Sprague River
subbasins and in the Lost River subbasin at Bonanza Springs.
Irrigated agriculture is an integral part of the economy of
the upper Klamath Basin. Although estimates vary somewhat,
roughly 500,000 acres are irrigated in the upper Klamath
Basin, about 190,000 acres of which are part of the Bureau of
Reclamation Klamath Project. Most of this land is irrigated
with surface water. Ground water has been used for many
decades to irrigate areas where surface water is not available,
for example outside of irrigation districts and stream valleys.
Ground water has also been used as a supplemental source
of water in areas where surface water supplies are limited
and during droughts. Ground water use for irrigation has
increased in recent years due to drought and shifts in surfacewater
allocation from irrigation to instream uses. The shifts in
surface-water allocation have resulted from efforts to improve
habitat for fish listed under the Federal Endangered Species
Act.
The ground-water system in the upper Klamath Basin
responds to external stresses such as climate cycles, pumping,
lake stage variations, and canal operation. This response is
manifest as fluctuations in hydraulic head (as represented
by fluctuations in the water-table surface) and variations in
ground-water discharge to springs. Basinwide, decadal-scale
climate cycles are the largest factor controlling head and
discharge fluctuations. Climate-driven water-table fluctuations
of more than 12 feet have been observed near the Cascade