Folsom Dam is being raised. What that means for droughts, boating and your flood insurance
Folsom Dam has long quietly served as a backstop for Sacramento, offering critical flood protection to one of the most at-risk metropolitan areas in the country. But a few scary winter storms in the 1980s and 1990s proved that the dam and the region’s extensive system of river levees weren’t as fail-safe as thought.
That’s prompted several billion dollars of flood control work since then. Now, as part of that, the dam itself is about to get a major makeover that could lead to lower flood insurance rates and more time on the lake for boaters.
Federal officials have launched work on a $373 million project to raise the dam 3.5 feet. The project will take five years to complete and will include rock and soil fill and rip-rap on the eight earthen berms that bracket Folsom Lake.
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.
Other work still needs to be done on downstream levees and in the Yolo Bypass off the Sacramento River. 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.
The project will have impact beyond flood control, regional leaders say. 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 the River Park neighborhood as a precaution, former 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 3.5 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.
Sacramento homeowner flood insurance need
Currently, only residents living in 100-year flood zones in the region are required to have flood insurance. Those areas are mainly in Natomas and south Sacramento.
Flood insurance is optional for most homeowners, and will remain that way after this project is finished. 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.”
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.
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 Reservoir 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.
This story was originally published January 22, 2020 at 5:00 AM.