The Army Corps of Engineers will temporarily drop outflows from Isabella Dam to zero starting at midnight Wednesday so the power plant at the dam can shut down, according to Kern River Watermaster Mark Mulkay.
Once the power plant, run by Isabella Partners, is down, water will be routed through the dam’s gates and outflows into the Kern River will ramp back up through Thursday to 6,100-6,200 cubic feet per second.
“This is not an emergency situation,” Mulkay stressed. “This is not a failure or a catastrophic anything. This is an operational hiccup that will be taken care of in a day.”
The power plant is being shut down so operators can determine the source of a “vibration,” which began Sunday evening, as reported by SJV Water.
“They’re not sure why it’s vibrating,” Mulkay said. “It could be a bearing problem inside the plant or it could be trash or debris collected on the intake screen. They won’t know until they shut it down and take a look at it.”
In a press release issued Tuesday afternoon, the Army Corps states that switching releases from the power plant to the dam’s gates will allow the Corps “…to fully control the rate at which controlled water releases enter the Kern River ahead of increased temperatures and reservoir inflows due to snowmelt runoff. Currently, the hydropower plant controls that rate.”
The Corps doesn’t mention the vibration issue in its release.
The temporary halt to outflows from the dam will likely be noticeable but not dramatic, Mulkay said.
“It won’t dry up,” he said of the Kern River. “It’ll probably go down to a couple thousand cfs (cubic feet per second).”
Still, the fluctuating river levels could create dangerous conditions so he urged people to stay out of the water.
Mulkay stressed that this is not a structural issue within the dam, which recently marked completion of a years-long safety modification project. The Army Corps of Engineers, which owns and operates Isabella Dam, had reduced the lake’s capacity in 2006 after a study revealed the dam was vulnerable to overtopping, seepage and seismic damage.
Repairs to those issues, including construction of a striking “labyrinth weir,” were completed in October 2022.
Restarting outflows is critical as dam operators need to move water out of the reservoir to make room for the melting snowpack.
Department of Water Resources hydrologists estimate there is 1.8 million acre feet of water sitting in the snowpack above Isabella, with runoff expected to peak next month at 625,000 acre feet. There is only room, currently, for about 270,000 acre feet water in the lake.
That means outflows need to be ramped up quickly. The Army Corps had briefly increased outflows to about 6,200 cubic feet per second before the power plant vibration caused a temporary outflow halt.
A message left on a Kernville phone number listed for Isabella Partners was not returned. Power from the 12-megawatt project at the dam is sold to Clean Power Alliance in southern California, according to CPA’s website.
Isabella Partners also recently applied to add a fourth, 5-megawatt generating unit to its project that would generate electricity at lower flow rates. Its environmental report is pending approval at the State Water Resources Control Board.