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Scientific Investigations Report 2007–5050

Scientific Investigations Report 2007–5050
Version 1.1, April 2010

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Summary and Discussion

The demand for water has increased in recent years in the upper Klamath Basin owing to changes in water management resulting from endangered species issues. Problems associated with the increased demand have been exacerbated by drought. As a result, interest has increased in the use of ground water and in understanding how the regional ground-water system can be utilized to prevent future water shortages. Until recently, key aspects of the regional ground-water system were not well known, and information was insufficient to make informed ground-water-management decisions. This report describes part of the results of cooperative efforts by the U.S. Geological Survey and the Oregon Water Resources Department to quantitatively characterize the regional ground-water flow system in the upper Klamath Basin to provide resource managers and basin residents the information needed to make sound resource-management decisions.

The 8,000-square-mile upper Klamath Basin is semiarid, with most of the basin interior receiving less than 20 inches per year of precipitation. Upland areas in the basin are mostly forested, and broad river valleys and lake basins in the basin interior are largely cultivated or in pasture. Irrigated agriculture covers roughly 500,000 acres in the basin. Of this area, roughly 190,000 acres are within the Bureau of Reclamation Klamath Project (this does not include refuge lands in the Project area). Most water for the Klamath Project comes from Upper Klamath Lake. A smaller amount of land in the basin is irrigated using ground water. In 2000, an estimated 59,600 acres were irrigated using ground water.

The upper Klamath Basin spans parts of the Cascade Range and Basin and Range geologic provinces, and is underlain principally by late Tertiary and Quaternary volcanic rocks. The volcanic deposits in the basin are generally permeable and host a substantial regional ground-water system recharged from precipitation in the Cascade Range and uplands within and on the eastern margin of the basin. A prominent system of north to northwest trending faults divides the interior parts of the basin into a series of sediment-filled structural subbasins. Ground-water flow is controlled by topography, distribution of recharge, the geometry of the stream system, and the geology. The regional geology has been divided into eight hydrogeologic units on the basis of their stratigraphic position and broad hydraulic characteristics. These hydrogeologic units are useful in assessing ground-water potential of specific areas.

Precipitation in the upper Klamath Basin totals about 10 million acre-feet per year. Most of this water returns to the atmosphere at or near where it falls through evapotranspiration. Roughly 2 million acre-feet per year enter the ground-water system. Most of the water that enters the ground-water system discharges elsewhere in the basin to streams, wells, or through evapotranspiration directly from the water table in wetlands.

An estimated 1.8 million acre-feet per year of ground-water discharges to streams. Discharge to streams occurs throughout the basin, but prominent areas of ground-water discharge include the flanks of the Cascade Range, the margins of the Wood River Valley, the area near the confluence of the Williamson and Sprague Rivers (including Spring Creek), the upper Williamson River near Yamsay Mountain, Bonanza Springs on the Lost River, and Klamath River Canyon below John C. Boyle Dam. Much of the ground-water discharge to streams is through major spring complexes. Ground water flows to streams throughout the year, supplying substantial water to streams in the basin. For decades, hydrologists have recognized that much of the water flowing into Upper Klamath Lake originates as ground water that discharges to tributary streams within 12 miles of the lake, or directly to the lake.

Ground-water discharge to streams is not constant, but varies seasonally and from year to year in response to climate cycles. In most large spring complexes, such as the headwaters of Spring Creek or the Wood River, discharge variations due to longer-term, decadal climate cycles are larger than seasonal variations. Discharge to major spring complexes, such as those feeding Wood River and Spring Creek may vary by a factor of 2. Basinwide, climate-driven ground-water discharge variations exceed 450 cubic feet per second, a rate that equates to an annual volume of 326,000 acre-feet.

Ground-water discharge from wells increased gradually from the late 1940s to about 2000, with small increases in the rate of growth related to droughts in the late 1970s and early 1990s. Ground-water pumpage for irrigation in 2000 was about 150,000 acre-feet per year. Ground-water use increased markedly in response to water shortages in 2001 and subsequent water-banking efforts. As a result, ground-water pumpage for irrigation in 2004 was about 226,000 acre-feet per year.

Hydraulic head data from wells and springs shows that ground water flows from principal recharge areas in the Cascade Range and uplands in the basin interior and eastern margins toward discharge areas in the lake basins and stream valleys in the basin interior. In addition, head gradients indicate the potential for flow between structural subbasins in a generally north to south direction. Ground water in the upper Klamath Basin generally flows toward two areas of low hydraulic head: the Klamath River Canyon and the Tule Lake subbasin. Ground water that flows toward the Klamath River Canyon discharges to the river between Keno and John C. Boyle Dam. Some ground water that flows into the Tule Lake subbasin discharges there and is removed by evapotranspiration or pumped to the Lower Klamath Lake subbasin. Head gradient data indicate that some ground water also flows southward out of the Tule Lake subbasin basin toward the Pit River Basin. The amount of southward flow presently is not known.

Hydraulic head in the upper Klamath Basin fluctuates primarily in response to climate, pumping, canal and irrigation operations, and lake stage. Basinwide, climate exerts the largest influence on water levels. Water levels in upland areas have declined more than 12 feet between 2000 and 2006 in response to drought conditions; however, they are expected to rise again when wet conditions return. Because climate-driven fluctuations affect the entire basin, they have the largest influence on the hydrologic system and are responsible for the large variations in ground-water discharge to streams.

Water level fluctuations in response to pumping are most commonly seasonal, with the water level declining during the irrigation season and recovering more or less fully by the following spring. Prior to 2001, year-to-year water-level declines due to pumping were rare in the upper Klamath Basin. The large localized increase in pumping that began in 2001 has resulted in year-to-year declines in the Klamath Valley and Tule Lake subbasin. The total decline between 2001 and 2004 exceeds 15 feet in parts of these areas and is larger than can be attributed to drought alone. These year-to-year declines have been accompanied by amplified seasonal declines. How long it will take water levels to recover fully after wet climate conditions return and pumping stress is reduced is not known. Data clearly show that pumping stresses can cause measurable head responses over broad parts of the ground-water system.

Irrigation and canal operation also affect water levels, particularly in shallow aquifers. Water levels in these aquifers rise at the beginning of the irrigation season and decline during the off-season. The magnitude of this fluctuation is generally 5 to 10 feet in the main part of the Klamath Project. Water levels in wells near Upper Klamath Lake fluctuate in concert with lake stage.

This study was intended to develop an understanding of the regional ground-water flow system in the upper Klamath Basin to help resource managers and basin residents develop a strategy for managing ground water. Developing a ground-water management strategy for the upper Klamath Basin will require consideration of general characteristics of ground-water flow and characteristics unique to the upper Klamath Basin. Generally, increases in the rate of pumping from a ground-water system will eventually be offset by either increased rates of recharge or (more likely) diminished rates of discharge. Mechanisms whereby ground-water recharge is increased by pumping are rare. In some circumstances, the lowering of hydraulic head caused by pumping could cause increased leakage from streams to the ground-water system. Conditions where this could occur in the upper Klamath Basin are rare. Pumping ground water near basin boundaries can cause the boundaries to shift, effectively capturing recharge from adjacent basins. However, only a fraction of the pumpage would be made up by flow from adjacent basins given likely pumping locations. Diminishment of discharge is the more likely consequence of ground-water extraction. Most of the decrease would be in ground-water discharge to streams, although reductions in discharge to phreatophytes (riparian or wetland vegetation with roots that extend to the water table) and in flows of ground water moving out of the basin in the subsurface could occur as well.

The timing and distribution of the effects of ground-water use are dictated to a large degree by the location of pumping. Pumping very near to discharge areas, such as springs, can diminish the flow of the springs relatively quickly. There have been several instances (with varying amounts of documentation) where ground-water pumping has affected spring discharge in the upper Klamath Basin. Springs affected by pumping in the past include those in Bonanza, elsewhere in the Lost River subbasin, and near Whisky Creek in the Sprague River subbasin.

Ground water is a major component of streamflow in the upper Klamath Basin, and, consequently, ground-water development has the potential to affect streamflow. Because the rate, spatial distribution, and variability of ground-water discharge in the upper Klamath Basin is now well understood, ground-water management strategies can be developed that minimize the effects of ground-water use.

Recently, a considerable effort has been made by various agencies, including the U.S. Geological Survey, the Oregon Water Resources Department, the California Department of Water Resources, and the Bureau of Reclamation, to monitor ground-water levels and ground-water discharge in the upper Klamath Basin. This information has been valuable in developing the present understanding of the regional ground-water system and its response to natural and human-caused stresses. Continued data collection will be important in the future to quantify the response of the ground-water system to stresses.

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