California's reservoirs are filling fast, like a water glass under a faucet turned up high — even as a series of new storms are poised to deliver a one-two-three punch to Central California.
Despite rainfall totals not seen since 2011, experts say the situation at Isabella Dam, located 40 miles upstream from Bakersfield, shares no meaningful parallels to the crisis at Lake Oroville that led to an evacuation order affecting some 188,000 residents in downriver communities.
“Isabella and Oroville are two separate dams, two separate types of construction,” said Sam Winder, senior project manager for the Isabella Dam Safety Modification Project, the U.S. Army Corps of Engineers’ effort to better protect the earthen dam from earthquakes, seepage and extremely rare megafloods.
For one thing, Winder said, Isabella’s service spillway is “built on solid granite.”
Oroville’s main spillway is lined with concrete, but on Feb. 7 that concrete began to come apart. An emergency spillway, essentially an earthen hillside that had never been used, also proved to be less than optimal.
Isabella’s spillway has been used three times — in 1969, 1980 and 1983 — and it has shown some erosion, but not at levels that are cause for concern.
How else is Isabella’s situation different from Oroville?
It was more than a decade ago that the Isabella Dam system was identified by the Corps of Engineers as one of the most at-risk facilities in the nation.
Not only was water found to be seeping beneath the dam but the geological foundation on which the auxiliary dam was constructed was determined to be made of an alluvial rock material that could be "potentially liquefiable" in a strong earthquake, causing the collapse of the dam and allowing a wall of water to race through the Kern River Canyon toward Bakersfield — should the lake have substantial water in it at the time.
When several exploratory trenches were dug across the Kern River Fault, which runs directly below the auxiliary dam, radiocarbon dating and other testing methods showed the fault to be active.
In 2006, a “restricted pool” was put in place, reducing the allowed capacity of the reservoir to about 65 percent of capacity, or just more than 361,000 acre-feet. As of midweek, the level of the lake stood at 57 percent — so as the new storms hit, managers of the lake level still have some room to work with.
Kern River Watermaster Dana Munn, who works closely with the Corps of Engineers as well as downstream water interests, said managing the lake level in a big water year like this one can be a dynamic enterprise — and sometimes it can seem like a moving target.
For example, on Feb. 1 projections for the April-to-July snow runoff in the Kern River watershed was a healthy 203 percent of normal. Ten days later, that estimate had been raised to 245 percent of normal.
Dana wants all water released from the lake to stay in Kern County, but with so much rain in the valley — Bakersfield has already exceeded its normal for the season — there’s no demand for irrigation and water recharge basins are filling.
One step is to begin turning away supplies from the state water project and use Kern River water.
But if more water comes downriver than there is room for, it could flow north to the Tulare Lake region, or more likely it will be sent into the California Aqueduct and head toward Southern California.
“In either case, it’s lost to local usage,” Munn said. And that’s near heresy to a Kern County water man.
One thing is sure, many during this water year are wishing they had Isabella’s full storage capacity of 568,000 acre-feet available. But until improvements to the dam are finished several years from now, water managers have to work within the restricted zone.
According to Winder, the Corps of Engineers expects to have chosen a project contractor by fall of this year. Soon afterward, Isabella residents will begin seeing heavy equipment arriving and by early 2018, the construction of the massive emergency spillway will likely have begun.
Meanwhile, in order to err on the side of caution, the Corps has begun daily inspections of the dam and its instrumentation.
Some still ask why the Corps of Engineers didn’t fix Isabella Dam during the drought years, while the water was low.
The first reason is money. Congress allocates funding annually for specific work done by the Corps. That work is on a timetable. Without funding, no dirt is going to be moved.
But the issue is also getting the right design. It’s vital engineers get the design right before construction.
Besides funding and the need to complete the design work, there's yet another big reason planners couldn’t tear up the timetable and accelerate construction.
The construction timetable is, at least in part, based on years of planning that included multiple public meetings in the Kern River Valley and in Bakersfield. The Corps of Engineers simply doesn't have the option of ignoring approved plans or disregarding timetables established following public comments.