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Hydrologic Monitoring and Trends in the Upper Klamath Basin over the Last Decade

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  • Over the last decade hydrologic monitoring efforts in the Upper Klamath Basin (UKB) of Oregon have increased in response to the continued strain on surface water and groundwater to meet competing biological and agricultural demands. The Oregon Water Resources Department (OWRD) increased its stream gaging network from three to ten gages, and approximately 80 long–term sites were added to the OWRD and US Geological Survey (USGS) well monitoring network to track both anthropogenic and climate related stresses to the hydrologic system. The expanded monitoring effort accompanied several hydrologic studies to better understand the basin hydrology. A major result of the hydrologic investigations was to quantify groundwater/surface water interactions in the UKB (e.g., Gannett, et. al. 2007). For example, the estimated gross groundwater discharge in UKB is roughly 2600 cubic feet per second (cfs), of which 1800 cfs occurs into or above Upper Klamath Lake—approximately 70 percent of the lakes’ gross annual inflow. Data collected over the last 10 years demonstrate that dry climate conditions persist in the UKB. Recorded precipitation at Crater Lake reveals below normal precipitation in seven of the last ten years. Although near normal precipitation has occurred in the last few years, this trend has only halted not reversed the decadal decline in summer baseflows and groundwater levels at most monitoring locations above Upper Klamath Lake (UKL). The trends in stream baseflows generally follow groundwater levels observed in nearby wells. Most monitoring locations reflect hydrologic lows similar to or slightly above the droughts of 1992 and 1994. USGS stream gages operated on the lower Sprague and Williamson Rivers reflect baseflows similar to those encountered during the drought of the late 1930s and early 1940s. Below UKL, anthropogenic stresses are more prominent than climate influences on streamflow and groundwater. Streamflow below Link River Dam is entirely regulated. Groundwater monitoring shows the added pumping stresses from expanded use since 2001 have locally produced 15 to 20 feet of decline in the Klamath Valley and Tule Lake sub basin. The increased groundwater pumping has also resulted in a greater amount of seasonal fluctuation.
  • Presented at The Oregon Water Conference, May 24-25, 2011, Corvallis, OR.
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