Brief relief, or a sign of more? The Boise River is dropping again

The U.S. Army Corps of Engineers reduced flows coming out of Lucky Peak Dam by 500 cubic feet per second between 3 p.m. on Sunday and 8 a.m. on Monday in an effort to offset additional water in the Boise River from the weekend’s rain.

Mary Mellema, a U.S. Bureau of Reclamation hydrologist, said Monday that the Corps plans to cut back another 200 cfs Tuesday morning.

The three reservoirs on the Boise River system — Lucky Peak, Anderson Ranch and Arrowrock — had a total of about 35,000 acre-feet of capacity left as of Monday morning. That’s about 10,000 more acre-feet than Mellema anticipated last week. The extra space resulted from a lower level of inflows to the three reservoirs than the Bureau anticipated, Mellema said.

The Corps and Bureau believe that, based on inflow forecasts, the three reservoirs have enough space to absorb the water coming in while reducing Lucky Peak’s discharge slightly, she said.

Reductions at Lucky Peak are showing up farther downstream, with the Boise River at the Glenwood Bridge dropping a few hundred cfs. Shortly before noon Monday, the gauge there was at 8,974 cfs. Mellema said that number should drop to somewhere between 8,450 cfs and 8,500 cfs this week. Flood stage as measured at the Glenwood Bridge is 7,000 cfs.

The Corps and Bureau, which cooperate on decisions on how much water to release from Lucky Peak, have yet to decide on whether to further reduce flows.

“We’ll see. I mean, this is a day-by-day thing,” Mellema said. “And we’ll be evaluating it hourly.”

This story was originally published June 12, 2017 at 12:29 PM with the headline "Brief relief, or a sign of more? The Boise River is dropping again."