U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5115—ONLINE ONLY
Prepared in cooperation with the
Idaho Department of Water Resources and
Idaho Power Company
By Jon E. Hortness, U.S. Geological Survey, and Peter Vidmar, Idaho Power Company
Declining water levels in the eastern Snake River Plain aquifer and decreases in spring discharges from the aquifer to the Snake River have spurred studies to improve understanding of the surface-water/ground-water interaction on the plain. This study was done to estimate streamflow gains and losses along specific reaches of the Snake River and Henrys Fork and to compare changes in gain and loss estimates to changes in ground-water levels over time. Data collected during this study will be used to enhance the conceptual model of the hydrologic system and to refine computer models of ground-water flow and surface-water/ground-water interactions.
Estimates of streamflow gains and losses along specific subreaches of the Snake River and Henrys Fork, based on the results of five seepage studies completed during 2001–02, varied greatly across the study area, ranging from a loss estimate of 606 ft3/s in a subreach of the upper Snake River near Heise to a gain estimate of 3,450 ft3/s in a subreach of the Snake River that includes Thousand Springs. Some variations over time also were apparent in specific subreaches. Surface spring flow accounted for much of the inflow to subreaches having large gain estimates. Several subreaches alternately gained and lost streamflow during the study.
Changes in estimates of streamflow gains and losses along some of the subreaches were compared with changes in water levels, measured at three different times during 2001–02, in adjacent wells. In some instances, a strong relation between changes in estimates of gains or losses and changes in ground-water levels was apparent.
Abstract
Introduction
Purpose and scope
Description of study area
Previous investigations
Methods for estimating gains and losses
Data accuracy and limitations
Long-term gaging stations
Acoustic doppler measurements
Unmeasured areas
Error
Current-meter measurements
Irrigation-district records
Visual inspections
Streamflow gains and losses
Lower Reach (Snake River near Minidoka to Snake River at King Hill)
Middle Reach (Snake River near Shelley to Snake River near Minidoka
Upper Reach (Henrys Fork near Ashton to Henrys Fork at mouth, near Lorenzo/Snake River near Heise to Snake River near Shelley)
Comparisons of ground-water levels with streamflow gains and losses
Lower Reach (Snake River near Minidoka to Snake River at King Hill)
Middle Reach (Snake River near Shelley to Snake River near Minidoka)
Upper Reach (Henrys Fork near Ashton to Henrys Fork at mouth, near Lorenzo/Snake River near Heise to Snake River near Shelley)
Summary
References cited
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