PUB00012

• Year: 1999
• Title: Sustainability of Ground-Water Resources: U.S. Geological Survey Circular 1186
• CWCB Section: Interstate & Federal
• Author: William M. Alley, Thomas E. Reilly, O. Lehn Franke
• Description: Illustration of the hydrologic, geologic, and ecological concepts to assure wise and sustainable use of ground-water resources
• Publications - Doc Type: Historical

EASTERN SNAKE RIVER PLAIN, IDAHO

The previous example illustrates how capture of
surface water might be distributed over a basin atter equilib-
rium of the ground-water system has occurred. Computer
simulations of the Eastern Snake River Plain aquifer by
Hubbell and others (1997) illustrate how the effects of
pumping on streamflow might be distributed through time
before the ground-water system reaches equilibrium.
Highly permeable basaltic rocks of the Eastern Snake
River Plain in Idaho provide conduits for rapid recharge of
precipitation and water from extensive irrigation. Ground-
water flow in this basaltic aquifer is primarily from northeast to
southwest, as shown in Figure C-3. The aquifer is connected
to the Snake River and discharges to the river largely through
major springs, such as Thousand Springs at the downstream
end of the flow system.

EXPLANATION

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Boundary of Eastern
Snake River Plain
Generalized ground-
water-flow path
Site location for
hypothetical
pumping well

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o 50 KILOMETERS

IDAHO

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Figure c-3. Eastern Snake River Plain aquifer
system. (Modified from Hubbell and others, 1997;
reprinted with permission of the National Ground
Water Association. Copyright 1997.)

Thousand Springs

The timing of the effects of pumping on spring
discharge to the Thousand Springs reach and to the
entire eastern Snake River were simulated for each of four
potential well sites (sites A-D in Figure C-3). For simulations
at sites A to C, pumping was simulated at a constant rate for
100 years. Figure G-4 shows the depletion of flow to the river
as a percentage of pumpage during the 1 DO-year simuiation.
The river losses from pumping at site A are 50 percent
of the pumpage after 23 years and about 90 percent after
100 years. Slightly more than half of the river depletion
caused by pumping at site A occurs along the Thousand
Springs reach.
Pumping at site B, located much closer to the
Thousand Springs reach, has almost 90 percent of the
pumpage obtained from capture of spring flow after 10 years
of pumping. Most of the losses are from the Thousand Springs
reach; river flow in the other reaches is only slightly affected by
pumping at site B.
Site C is more distant from the Snake River. Pumping
at this location has litlle effect on flows to the river for more
than 10 years; however, depletion continuousiy increases
during the long period of continuous pumping. The river deple-
tion after 100 years of pumping at site C is about 70 percent
of the pumpage.

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