Hot, sunny weather and then rain on a bulging snowpack will trigger unseasonably high water releases from Lost Creek Lake and possibly lead to record flows in the upper Rogue River through the weekend as hydrologists grapple with capturing very high inflows with an almost-full reservoir.
The U.S. Army Corps of Engineers expects to see releases into the upper Rogue ramp up significantly Friday and likely peak Saturday around 5,500 cubic feet per second, causing swift-water conditions for boaters and threatening to submerge some riverside irrigation pumps, according to the Corps.
High temperatures Wednesday and Thursday, followed by rain that's expected Friday, will trigger inflows estimated to be as high as 5,600 cfs into the reservoir, according to the Corps.
"By Friday we're going to be seeing some significant increases to the releases," Buck said. "We potentially might have to go above 5,500 (cfs)."
A release of 5,500 cfs would likely see flows peak Saturday at about 6,600 cfs at Dodge Bridge, where Highway 234 bisects the Rogue near Eagle Point, Buck said. That is almost exactly twice the flow at the Dodge Bridge gauge last year at this time and above the all-time May 6 record of 6,200 cfs, he said.
The reservoir Wednesday was about 1 foot below the 1,872-foot elevation level, and inflows are not expected to push the lake past that elevation, Buck said. If it does, however, the Corps can temporarily bump the lake elevation as much as 2 more feet, he said.
"We're going to have to really watch that inflow and see how the reservoir responds," Buck said.
The 327-foot, rock-filled embankment dam has spillgates to shave water off the top to keep inflows from sweeping over the 40-year-old structure, according to the Corps.
Buck said Rogue irrigators who have their irrigation pumps set for current water levels should temporarily move them.
Sgt. Shawn Richards from the Jackson County Marine Patrol Program warns boaters and other river users to use caution and make sure they check water conditions before launching along the Rogue during high flows.
"It just may not be the appropriate time to go," Richards said. "It's certainly not going to be a gingerly float at this point. You'll be whipping through there."
Next week's weather forecast calls for a cooling period, but hydrologists will use that time to drop the reservoir levels should they need storage space for another such event. Buck said he expects outflows to remain above 4,200 cfs — or about twice the early May average — through Wednesday.
Lost Creek Lake typically fills May 1, but hydrologists have kept some wiggle room there as they head into May with a basin snowpack that was listed Wednesday at 143 percent of average.