Kern River flows to drop again after noise detected in Isabella Dam outlet tunnel

June 26, 2023
by Lois Henry
A full Lake Isabella and mountains packed with snow stand behind the new labyrinth weir constructed as part of the Army Corps of Engineers safety project that was completed in October 2022. Lois Henry / SJV Water
Lois Henry

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Outflows from Lake Isabella into the Kern River will be cut to zero starting at 1 a.m. Tuesday so dam operators can check the source of  “funny noises” coming from the outlet tunnel, according to Kern River Watermaster Mark Mulkay and an Army Corps of Engineers press release.

“They’ve been hearing funny noises in the tunnel. The thinking is that it’s probably debris,” Mulkay said. “So, to minimize any future damage, they want to get in there and see if they can fix it quickly and outflows will start up again.”

Though the situation isn’t exactly “routine,” Mulkay said, it’s also “not unheard of” either.

“The main thing for the public to understand is this is something that’s scheduled, it isn’t an emergency.”

He said outflows are expected to ramp back up to current levels within 24 hours.

This comes two months after the Army Corps previously halted outflows April 26 when a vibration was detected either in the dam or the power plant at the dam’s base. The power plant, operated by Isabella Partners, was shut down and water rerouted to the outlet tunnel.

No explanation for the vibration was ever given.

In email correspondence, an Army Corps spokesman wrote that the dam “did not experience issues with vibrations” and directed questions about any vibration to Isabella Partners. Phone calls to a Kernville number listed for Isabella Partners were never answered and the Army Corps said it did not have contact information for the power plant operators.

According to an Army Corps press release issued Monday, the current flow stoppage is to accommodate a “routine inspection” of the outlet tunnel.

The Army Corps will conduct, “a routine inspection of the conduit at the base of the dam following this year’s heightened reservoir inflows and subsequent releases,” the release states.

The agency estimated the inspection will take eight hours or less to complete and flows will begin ramping back up starting at 500 cubic feet per second to 5,300 cfs.

The release doesn’t mention noises or concerns about debris in the outlet tunnel.

Lake Isabella will gain about 8,000 acre feet from the outflow interruption, according to the Army Corps release.

The lake’s capacity is 568,000 acre feet. It held 485,128 acre feet as of Monday evening and runoff was coming in 5,197 cfs, according to the Army Corps hourly readings website.

Mulkay had said in previous interviews that the Army Corps had hoped to keep the lake in the 400,000-acre-foot range to run tests on improvements to the dam that were recently completed after a years-long safety project.
But this year’s runoff coming down from the massive snowpack is just too much, he added.
Holding the lake at 400,000 acre feet would require much larger outflows into the river, which could flood homes and damage infrastructure. When outflows went above 7,800 cfs in late May, pilings along Highway 178 pulled away from the road and a large gash appeared in the blacktop, as reported by SJV Water.
With temperatures heating up later this week, inflows from runoff could accelerate.

SJV Water is an independent, nonprofit news site dedicated to covering water in the San Joaquin Valley. Get inside access to SJV Water by becoming a member.


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