Army Corps lowers Lost Creek Lake water level
The U.S. Army Corps of Engineers on Tuesday began drawing down the water level in Lost Creek Lake another 8 feet to gain more room for runoff under a new winter flood-control plan it will use until the dam's potentially flawed radial gates can be strengthened.
Corps hydrologists early Tuesday bumped releases by 150 cubic feet per second into the Rogue River above the flow coming into Lost Creek Lake, which will slowly dip Southern Oregon's largest reservoir under its normal winter minimum pool.
The goal is to gain another 20,000-acre-feet of storage capacity by Dec. 15, heading into the Rogue basin's traditional storm season.
"It will be a gradual reduction," said Jim Buck, the Corps' Rogue basin operations manager. "If we have a storm, we'll store a little bit of water and then get back on (increased flows). Our goal is to get where we want to be by Dec. 15."
The draw-down was the latest part of the Corps' new flood-control operation that went into effect after this summer's discovery that radial gates could fail during the worst of flood events, possibly triggering unrestricted flows through the spillway.
The gates have been used only once — during the 1997 New Year's Day flood — and they operated flawlessly.
But inspections show they could fail to operate properly should water rise into the top 12 feet of the lake and place pressure on the gates. The radial gates are separate from the main spillway and are used only if the main spillway cannot release water fast enough to keep up with inflows.
Lost Creek Lake typically is drawn down by Nov. 1 to its current surface elevation of 1,812 feet above sea level. That leaves 60 feet of reservoir space to capture runoff from winter storms, the likes of which caused major basin flooding in 1955 and 1964.
The new draw-down will mean the Stewart State Park boat ramp likely will be unusable some time early next week when the reservoir elevations drops below 1,810 feet above sea level, Buck said.
The draw-down plan was drafted with help from Oregon Department of Fish and Wildlife biologists to ensure a minimum impact to the incubation rates of wild spring chinook salmon eggs now in Rogue River gravel beds.
Releasing all that water in October and early November could alter water temperatures that play a key role in egg incubation rates, hatch-out times and, ultimately, wild chinook survival rates, said ODFW fish biologist Tom Satterthwaite.
That's why Satterthwaite requested that the Corps not start the draw-down until Tuesday and drag it out for a month, he said.
The changes will not alter the Corps' plans to fill the reservoir as scheduled next May.
Like several Willamette Valley dams built in the 1940s and '50s, Lost Creek dam was built with radial gates and a spillway designed to control water once the lake's elevation hits 1,860 feet above sea level and continues to climb. The gates then could be opened to control flows down the spillway, ensuring that water doesn't cascade over the top of the dam.
But the pressure of the gates' weight and the push of reservoir water against them could cause enough friction that there is a slight risk that the gates might not work properly when needed, according to a Corps assessment.
Repairs to the gates are expected to cost about $7.5 million. Buck has requested money for the repairs, but Lost Creek dam remains a lower priority for repairs than Willamette Valley dams where the gates are used regularly.