The question of whether Lake Isabella might “spill” has now turned to whether it will fill.
The lake is achingly close to being full. It stood at 528,663 acre feet as of Wednesday afternoon – just 39,337 acre feet shy of its full capacity.
But it needs to hit that max fill mark for the Army Corps of Engineers to test all the dam’s new hardware so the safety operations phase of the repaired dam can be completed and the dam can be returned to regular operations, according to Kern River Watermaster Mark Mulkay.
“We’re doing everything we can to get it to fill,” Mulkay said. “The Kern River interests (water districts with river rights) are asking the Corps to allow us to reduce the outflow so the lake can get to full.”
Just a few months ago, Mulkay, the Corps and others worried the massive snow pack this year could melt in a rush and put water over the dam’s spillway. But an unusually cool spring and early summer slowed the melt.
Right now, outflows are hovering around 4,600 cubic feet per second. That’s about even with inflows.
Kern River interests have asked that outflows be brought down to 3,800 cfs.
At that level, they think the reservoir would fill in 10 days, potentially less if the coming heat wave significantly boosts inflows.
“It doesn’t have to be at the very crest, but we want it to get up to, or near, the spillway to allow the Corps to do all their testing so they can give the dam a certificate of compliance,” Mulkay said. “Once we get that, it takes a whole separate organization out of the mix of managing this reservoir.”
In an email response to several questions, the Army Corps of Engineers wrote that it would work with the Watermaster on releases based on current conditions.
In response to questions about the next steps for Isabella Dam operations, the Corps spokesman wrote that the dam’s safety rating had been change allowing operators to fill the lake on a regular basis – assuming there’s enough snowmelt.
Isabella Dam was deemed unsafe back in 2006 because of seepage, an active earthquake fault that had been thought dormant and a danger of overtopping. The Corps mandated that the lake be kept at 360,000 acre feet until fixes could be made. Those were completed in October 2022.
Once the Corps issues a certificate of compliance, it will begin writing a new operations manual and Mulkay said the Kern River interests want to be heavily involved in that process.
One of their first requests, in fact it’s already been made, is to increase the maximum “carry over” amount. That’s the amount of water that can be left in the lake as of November 1st, in preparation for winter storms. Right now that maximum is 170,000 acre feet.
Kern River interests would like that to be increased. In years past, Mulkay said, the Corps has allowed irrigators to carry over as much as 245,000 acre feet as long as “we guarantee we will evacuate it back down to 170,000 acre feet as quickly as possible, if needed.”
Mulkay said the last operations manual was written back in the 1950s and a lot has changed since then.
“With all the new recharge basins and conveyance sysetms, we’ve shown we can manage outflows 7,500 cfs,” Mulkay said. Yes, there was some flooding in areas east of Bakersfield, but those are in known flood plains, he said. “And even at 7,500 cfs the damage was pretty minimal.”
And though water did go into the intertie, which connects the river to the California Aqueduct, Mulkay noted, it did not go into Tulare Lake and exacerbate flooding up there.
In all, nearly 25,000 acre feet of Kern River water sloshed through the intertie from May 20 through June 12, the first time it had been used since 2006 when the Corps ordered Lake Isabella lowered for safety concerns.