Science Suggests Flow Changes in Palisades Dam Discharges
Media Contact: John Redding , (208) 378-5212
Chris Ketchum , (208) 378-0461 ext. 40
For Release: November 04, 2003
To begin the winter flow operations, discharges in the Snake River immediately below Palisades Dam will gradually be reduced this week.
Flows from Palisades Dam will be reduced to 950 cubic-feet-per-second and maintained during the 2003-2004 winter season. Flows immediately below the dam were recorded at 1350 cfs on Monday. Tributary flows between the Irwin and Heise river gage are expected to total about 400 cfs, resulting in a flow of 1350 cfs in the Snake River near Heise.
In the past 20 years, the winter flow has ranged from a low of 700 cfs in 1988-1989 to more than 3000 cfs following wet years. Winter flows have been near 1050 cfs in each of the last three years. Recent research suggests that conditions for native fish may be degraded when the same winter conditions are repeated in consecutive years. It appears that this operation will mutually benefit both storage for irrigation and the cutthroat trout fishery.
A comprehensive statistical analysis was recently conducted to evaluate the relationship between seasonal flows on the South Fork and trout populations. This analysis was done primarily from a fishery perspective. The goal of the analysis was to determine the timing and magnitude of flows that favor cutthroat production over non-native rainbow trout.
"The new studies recommend winter flows that would more closely follow normal hydrologic conditions, while also keeping flows constant before spring snowmelt increases river flows," said Chris Jansen-Lute, Reclamation Natural Resource Specialist. "This may depart from prior research which focused on establishing minimum flows, but research indicates higher flows late in the spring, when natural flows are increased by melting snow, benefit native cutthroat trout habitat."
For irrigation storage, the lower winter flows will result in more water stored in the system at Palisades Reservoir and less in American Falls Reservoir, thereby increasing the flexibility to meet irrigation demands. It also increases the potential opportunity to move the water downstream when the higher flows are needed for the fishery, Jansen-Lute said.
"American Falls has the higher priority water right and moving the water downstream in the spring is consistent with water rights, system operating objectives and Reclamation's contractual obligations to reservoir space holders," said Mike Beus, Reclamation water manager. "This operation delivers water to irrigators and supports native fish by putting the water in the river when both the crops and fish need it.
Although flows are not expected to drop below the 950 cfs level, they could be increased if exceptional winter precipitation occurs. In the event of higher spring flows, normal river management practices would be engaged as to not compromise 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.
Current hydrologic conditions are severely dry and lower winter flows have been implemented in similar situations in the recent past. This proposed winter operation will be monitored closely and will be adjusted if conditions warrant, said Beus.
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 13.
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