The Bureau of Reclamation began increasing water flows out of Palisades Reservoir early today as part of a three-day effort to disrupt non-native rainbow trout spawning in the Snake River and benefit native cutthroat trout populations.
“The extra water simulates the natural hydrograph or runoff of the water system,” Idaho Fish and Game fisheries manager Dan Garren said. “This really seems to facilitate (habitat) regeneration and stimulate the bottom of the food chain … it also helps trigger the instinct in cutthroat trout to start spawning.”
Flows increased from 14,000-cubic-feet per second to 15,400 cfs at 1 a.m. today. Flows will be incrementally increased through Sunday, when they peak at 18,500 cfs. After Sunday, flows will incrementally drop to an average flow of 13,000 cfs, reclamation officials said.
The operation provides the highest flows of the season at about the same time natural snow melt is peaking. The river will be fast and cold during the high-flow period. The bureau urged caution when near the river.
Most of the water sent down the system will be held in American Falls Reservoir.
“We are re-balancing the system and will be able to deliver the water from American Falls later in the season to users downstream,” said Mike Beus, water operations manager with the Bureau of Reclamation Upper Snake Field office.
Peak runoff season likely began last week, water officials said, which means water managers do not have to allocate as much storage space for flood control.
Palisades has been steadily increasing and is 61 percent full.
American Falls is decreasing due to irrigation consumption, but is still at 81 percent capacity.
The flow increase is not expected to cause any major problems for irrigators, aside from some inconvenience, said Lyle Swank, watermaster of Idaho Water District 1.
“This will bring additional debris that will have to be scooped from head gates … and irrigators will have to closely monitor and adjust head gates for the new flows beyond changes caused by crop demand,” Swank said. “But the Bureau is tasked with (providing) water for users with very different needs … and this time of year it is helpful to fisheries without causing too big a problem with other user groups.”