Jan. 22--Folsom Dam sits at the edge of the foothills above the Sacramento Valley, offering California's floodable state capital region critical protection.
But several scary winter storms in the 1980s and 1990s -- as well as one two years ago that threatened to puncture nearby Oroville Dam -- have shown Sacramento and California that its flood control network isn't as muscular as thought.
At the same time, the most recent drought taught state officials equally that sometimes water goes missing when needed. The dam's reservoir holds nearly a billion acre-feet of water when full that has long been divvied up annually among cities and agricultural interests in the Sacramento Valley. Two years ago, in a drought, it essentially went dry.
Those twin troubles have prompted several billion dollars of flood control work since then, a cooperative effort among federal flood safety officials and state and local water officials. As part of that effort, the 64-year old Folsom Dam on the American River is about to undergo the second phase of a major makeover to turn it into a better multi-utility tool for both storm and drought years.
Federal officials have launched work on a five-year, $373 million project to raise the dam 3 1/2 feet by adding rock and soil to its earthen dykes and seals on the gates at the top of the concrete portion of the dam.
Combined with a safer spillway completed in 2017, federal dam officials say the flood-prone region is on its way to 300-year or more flood safety, meaning there will only be a one-in-300 chance in any given year that the combination dam and downstream levee system will fail.
Sacramento Congresswoman Doris Matsui calls it the ongoing challenge that comes with the beauty of living at the confluence of two major rivers. "You're never safe," she said. But the new spillway, the ongoing levee upgrades and current dam raise are giving Sacramento one of the most advanced flood protection systems in the country, she said.
But the recent moves have offered officials flexibility in their dual and sometimes opposing objectives of using the dam as both a flood stopper and water container.
Here is a checklist of key implications:
No repeat of 1986 near flood catastrophe?
During a historic 1986 storm, with the dam at risk of being over-topped by the fast-rising reservoir, dam operators began releasing more water into the lower American River than its levees were designed to handle. At one point, as the river ate away at the levees, the Sacramento city fire chief asked permission to evacuate one neighborhood as a precaution, former Sacramento City Manager Bill Edgar said.
City officials waited, though, and rains abated, allowing federal dam managers to reduce river flows to safe levels. But a lesson was learned: Sacramento did not have the flood protection it thought it did.
An event like that is less likely to happen now for four reasons:
-- The dam will be 3 1/2 feet taller, meaning the federal Bureau of Reclamation, which manages the dam, will have an additional 43,000 acre feet of water storage capacity in the reservoir.
-- The new spillway is 50 feet lower, allowing operators to release more water sooner, as a precaution, prior to major storms.
-- Federal officials have recently incorporated more sophisticated weather forecasting into their dam management protocols.
-- Downstream, most of Sacramento's levees on the Sacramento and American rivers have been significantly bolstered since the 1986 flood threat, allowing them to withstand bigger water flows in urgency moments.
Less Folsom Dam failure risk
Ever since the Oroville Dam nearly failed during a heavy rain year in 2017, California has been analyzing dam strength and safety. The new Folsom Dam spillway and the upcoming increased height are expected to make the dam itself stronger as well as more flexible to operate.
Folsom Dam is in fact a series of eight earthen dikes that flank a central concrete dam. The raising of the dikes will offer more protection during high wind and wave events, officials said. The concrete portion of the dam already is taller than the earthen dikes. It's height will not need increasing, but the project includes putting new seals on its top row of spill gates to allow the dam to hold more water.
More water in California drought years
Folsom Dam is primarily a flood control facility, but it also serves as a reservoir for drinking water and agricultural irrigation. The dam raise will add 4 percent capacity to the reservoir, and Bureau of Reclamation Commissioner Brenda Burman said her agency has new federal authority to hold more water in the reservoir in winter and spring than was allowed in the past.
That flexibility helps the region respond to the new challenge being posed in a climate change era of warmer winters with more heavy rain storms followed by drought years.
In 2018 a report in the scientific journal Nature Climate Change said California will be exposed to "precipitation whiplash" in which the seasons rainfall is concentrated in narrower windows of time. To make matters worse, global warming will bring more rainfall and less snow, putting more pressure on Northern California's flood-control infrastructure.
Local water districts in the Sacramento and Central Valley areas, meanwhile, are working on a mutual "water bank" system that will allow them to store more drinking water in the ground to draw on in drought years, while drawing on Folsom Lake and other surface water sources more in wet years.
Folsom Lake recreation and habitat bonus
In some years, water levels have been so low in Folsom reservoir that boating ramps are left high and dry, and recreational use of the lake is limited to non-existent. That is less likely to happen once the operator, the Bureau of Land Management, is able to maintain essentially another 3.5 feet of lake elevation.
Also, bureau chief Burman said, the new project includes more sophisticated water temperature measuring devices, which will allow dam operators to release water at temperatures (typically lower-level cooler water) that are more conducive to fish and riparian health downstream.
California dams remain at risk
The February 2017 crisis at Oroville Dam, the nation's tallest, laid bare the risks lurking in many of the state's reservoirs.
A massive crater erupted in Oroville's 3,000-foot-long flood-control spillway, prompting the state Department of Water Resources to limit flood releases even as a massive rainstorm kicked in. Lake Oroville rose high enough that water began flowing over the dam's emergency spillway -- a concrete lip sitting atop a natural hillside -- for the first time since the dam opened in 1968. A day later engineers noticed the hillside was dangerously eroding, and law enforcement officials ordered the emergency evacuation of 188,000 downstream residents.
Although the hillside didn't collapse, fixing the two spillways cost more than $1 billion. The state ordered operators of 93 dams -- facilities whose construction records and blueprints suggested the possibility of flaws -- to conduct intensive inspections of their spillways. A Sacramento Bee evaluation of years of annual inspection reports at those 93 dams showed that flaws often went unrepaired for years, including cracked concrete, rusted equipment and busted sensors, valves and gates.
As for Oroville, an independent forensic team hired at the direction of the federal government found that the dam's spillway was the victim of "long-term systemic failure" by state and federal regulators. The report found that the spillway was poorly designed and built, and its flaws were exacerbated by inadequate repairs in the years that followed.
The 584-page report added that dam officials neglected safety while focusing on "water delivery needs" of the downstream local water agencies throughout California that rely on water stored at Oroville. The authors said the 2017 near-disaster was inevitable.
Sacramento homeowner flood insurance need
The dam raise also could have some effect on property owners' pocketbooks downstream. Flood insurance rates could drop for many residents when this and several other ongoing local flood projects are finished if, as expected, federal emergency officials redraw their flood maps to show that most residents have 200-year or 300-plus-year flood protection.
That said, Sacramento's flood control manager advises home and property owners to maintain flood insurance. Because of its two major rivers and its low-lying land, the area will always be in danger of flood, said Rick Johnson, head of the Sacramento Area Flood Control Agency.
"You always want to keep flood insurance when you live in a deep flood plain," he said. "Mother Nature always has a way of doing something."
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