A little early preparation and an aggressive water-release plan kept Lost Creek dam from the unprecedented position of completely losing its flood-control capabilities during the rare spring snow-on-rain storm that threatened flooding this week on the Rogue River.
Flows out of the dam and into the Rogue on Tuesday were increased from an already astronomical 10,000 cubic feet per second to nearly 12,000 cfs to ensure Lost Creek Lake did not prematurely fill in the midst of a storm event, according to the U.S. Army Corps of Engineers, which operates the dam.
Had Corps hydrologist Kevin Mcallister not ratcheted up the dam’s release to its second highest in the dam’s 42-year operating history, the lake would have filled and forced the Corps to open the spillways and pass whatever water volume enters the reservoir upstream, Mccallister said.
That’s essentially acting as if the dam were never there.
“Instead of 12,000 cfs coming down, it would have been the 15,000 cfs or so that was coming in,” Mcallister said. “That’s never happened. It’s just not a safe way of managing the project.”
The force of the storm, its spring timing and the dense mid-elevation snowpack conspired to nearly render the Rogue Basin’s largest flood-control reservoir useless during a flood event for the first time in its history.
Most big storms and massive floods on the Rogue have occurred in December or January, with the New Year’s Day flood of 1997 being the most recent. In that case, nearly 16,000 cfs was released at one time at Lost Creek dam, the only higher releases on record than that of Tuesday morning, Corps records show.
But winter storms occur when the Corps is ready for them, with reservoir elevation levels drawn down around 1,812 feet above sea level. With full pool at elevation 1,872 feet, that leaves 60 feet of reservoir space to corral water flowing off the upper Rogue Basin mountains.
But this storm began in April, more than two months into the Corps’ regular filling schedule at Lost Creek Lake. The lake’s elevation was at just under 1,863 feet when the storm moved in Sunday morning.
That left just 9 feet to play with while corralling heavy rains that melted snow below the 8,000-foot level.
With forecasts last week calling for a strong tropical storm headed to Southern Oregon’s snow country, Mcallister last Tuesday ordered the reservoir off its regular filling schedule and set outflows artificially high to create more reservoir space.
The week began with flows of about 1,400 cfs out of the reservoir, but they were increased about 800 cfs Tuesday, and by Wednesday outflows matched inflows. That meant the reservoir filling scheduled stopped and the lake’s surface level stalled instead of rising.
“I was matching inflow, but on Friday I really started to ramp it up,” Mcallister said.
Outflow on Friday jumped to 4,000 cfs and then 5,000 cfs Saturday, further keeping the reservoir level down.
By the time the storm hit Sunday, Mcallister’s aggressive pre-storm approach had created an extra foot of reservoir space.
“I think our ability to get ahead of it rather than wait and see was very crucial to this operation,” said Mcallister, the Corps’ lead regulator for Rogue projects.
“We’re not releasing a lot more now like we would have if we didn’t clear that space out beforehand.”