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

60 Ground-Water Hydrology of the Upper Klamath Basin, Oregon and California
DEPTH TO WATER, IN FEET
130
140
150
160
170
180
41S/09E-12AAB
190
1960 1965 1970 1975 1980 1985 1990 1995 2000
2005
Figure 37.
Water-level fluctuations in well 41S/09E-12AAB at the southern end of the Klamath Hills, Oregon.
Seasonal effects reflect the general lowering of the
water table over a broad area (several square miles to tens of
square miles) in response to the combined seasonal pumping
of multiple wells and, in some places, seasonal variations in
recharge. These effects typically build up over the irrigation
season and largely recover over the following winter.
Figure 38 shows seasonal water-level declines between spring
and fall 2004 caused by increased pumping in the basin. Water
levels declined more than 10 ft over more than 130 mi 2 and
more than 20 ft over about 20 mi 2 during the 2004 irrigation
season. Declines of 10–20 ft are apparent in an area extending
from north of the Klamath Hills, through the Klamath Valley,
into the northern and eastern parts of the Tulelake subbasin.
Smaller areas in the Klamath Valley and the southeastern part
of the Tulelake subbasin show seasonal water-level declines
exceeding 20 ft in some wells. Seasonal water-level declines
of 1–3 ft were measured in most wells distant from pumping
centers. These widespread declines are due to natural seasonal
fluctuation, possibly amplified by dispersed pumping and
ongoing drought. Although a general decline in water levels
was measured during this period, levels in some wells that
are hydraulically connected to the shallow aquifer system in
the basin-fill sediments rose between spring and fall, ranging
from a fraction of a foot to as much as 3 ft. This is an annual
occurrence entirely due to artificial recharge to the shallow
system by canal leakage and deep percolation of irrigation
water.
Long-term pumping effects refer to the lowering of the
water table for more than a season, often years. Long-term
effects can be caused by both climate and pumping stresses.
Long-term water level declines typically occur over broad
regions, such as an entire subbasin. Long-term decline
generally is measured by comparing the spring high water
levels each year. Such lowering of the water table has been
observed over most of the upper Klamath Basin since about
2000 because of ongoing drought. The only exception is in
shallow aquifers in the Klamath Project area, where water
levels are maintained by recharge from canal leakage and
deep percolation of irrigation water. Long-term declines due
to pumping have occurred locally in addition to this droughtrelated
decline. Distinguishing pumping related declines from
drought related declines in the basin is difficult because of the
scarcity of data from previous drought cycles. However, near
the town of Tulelake, where long-term water-level data exist,
the rate of the year-to-year decline observed in the present
drought cycle in well 48N/04E-35L02 appears to be about
twice that observed in the most recent previous drought, from
the late 1980s through mid-1990s (fig. 39).
OR19-0048_fig37