Released On: May 12, 2004
The change in operation follows a comprehensive statistical analysis, completed last fall, which evaluated the relationship between seasonal flows on the South Fork and trout populations.
Flows from Palisades Dam will increase to a peak of approximately 18,000 cubic-feet-per-second, causing the river to rise from an initial discharge of about 11,000 cfs starting on May 17. A flow of 18,000 cfs will be sustained from May 20 through May 22 if hydrologic conditions permit.
Following the peak, flows will gradually be reduced to summer irrigation levels. Tributary flows between the Irwin and Heise river gage are expected to total between 1000 and 2000 cfs, resulting in a flow between 19,000 and 20,000 cfs in the Snake River near Heise at the South Fork of the Snake River.
This operation follows a relatively low winter flow of 950 cfs from Palisades Dam. Lower flow resulted in more water stored in Palisades Reservoir and less in American Falls Reservoir. The resulting distribution of storage in the upper Snake River system allows an opportunity to move water downstream when the higher flows are needed for native Yellowstone cutthroat trout management without compromising the ability to deliver irrigation water to contract spaceholders.
A comprehensive statistical analysis completed last fall evaluated the relationship between seasonal flows on the South Fork and trout populations. This analysis was done primarily from a fishery perspective. The goal was to determine the timing and magnitude of flows that favor cutthroat production over non-native rainbow trout. The research suggests that conditions for native fish may be improved with steady winter flows followed by a relatively much larger spring peak flow. Working within the normal range of operations, the 2003-2004 winter/spring operations are expected to benefit native trout.
The fishery analysis coincided with a study commissioned by Reclamation to review operational flexibility in meeting ecological needs while meeting contractual obligations. The two studies reached very similar conclusions in support of flexible operations to restore healthy river dynamics and meet contractual obligations.
This fish-friendly operation would not have been possible without the cooperation and flexibility of the irrigation community.
"Working together with the many interests on the South Fork has allowed us to make the most out of a severely dry water year for irrigation, fishery, and ecological interests" said Chris Jansen Lute, Reclamation Water Resources Program Manager.
American Falls has a higher priority water right and holding water in Palisades Reservoir during the winter allows Reclamation to move water downstream to stay consistent with water rights, system operating objectives, and contractual obligations to reservoir space holders.
"This operation delivers water from Palisades Reservoir when the fish need it and then allows that water to be held where it would have otherwise been until downstream irrigators and their crops need it," said Mike Beus, Reclamation water manager.
Although peak flows are not expected to vary from the 18,000 cfs level, they could be changed if exceptional spring precipitation occurs. In the event of unexpected flows or events, flows may be changed to avoid compromise of flood control procedures, irrigation or power benefits. But current reservoir levels and long range forecasts suggest this year is an opportune time to provide a more natural spring hydrograph.
"This spring operation will be closely monitored and will be adjusted if conditions warrant," said Beus. It also will be monitored for ecological and fishery benefits.
The river level is expected to rise almost 2 feet between May 18 and May 23. River recreationists should be prepared for changeable conditions more consistent with an unregulated river.
For current river and reservoir conditions please visit www.usbr.gov/pn/hydromet. For more information on the operation of Palisades and other upper Snake River Reservoirs contact Chris Ketchum, Deputy Area Manager, Snake River Area Office, in Burley, Idaho, at (208)678-0461, extension 34.
DOI | Recreation.gov | USA.gov
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