A version of this story was also published in the March 2022 issue of Storm Water Solutions magazine, and can be accessed here.
In December 1861, as the Civil War raged in the Eastern United States, the young city of Sacramento, California, was fighting its own battle—with raging flood waters. The American River levee failed east of 30th Street, flooding what is now River Park and sweeping into the city. To relieve the flooding, city officials cut the levee at R and 5th Streets. Some of the flooding subsided, but houses were swept away in the current.
As newly elected Governor Leland Stanford was rowed to the state capitol on January 10, 1862 through the waterlogged streets of downtown, he may have had choice words for the gold prospectors who founded Sacramento in the 1840s at the confluence of the Sacramento and American Rivers. Seemed like a good idea at the time, no doubt. But with the economic opportunities came enormous challenges in navigation and flood control.
The city’s fight to stay dry continues to the present day, spearheaded by the Sacramento Area Flood Control Agency, California Department of Water Resources, Central Valley Flood Protection Board, Bureau of Reclamation, and the U.S. Army Corps of Engineers.
“Flood fighting is always a partnership,” said Col. James Handura, commander of the USACE Sacramento District. “No agency can do this alone, no matter how large or well-funded.”
The Sacramento District is one of USACE’s largest, with a civil works budget just short of a billion dollars ($933.3 million). The district’s area of responsibility extends far beyond the city, encompassing all of California’s Central Valley and watersheds that stretch into Colorado. But much of their attention is focused on this urban area, which rivals New Orleans as the most at-risk city for flooding nationwide.
Since Hurricane Katrina in 2005 prompted a re-evaluation of levee safety standards, the district’s local projects are concentrated in two spots—Folsom Dam, near the community (and prison) Johnny Cash made famous; and the Natomas Basin, just north of downtown Sacramento.
Reducing flood risk in the Natomas Basin
Natomas is tantalizingly close to Sacramento’s urban center. It’s home to Sacramento International Airport and Sleep Train Arena. Served by both Interstates 5 and 80 and with miles of open land, it seems a prime target for investors. But development in the basin has proceeded in fits and starts, prompted by changes in levee standards.
“Natomas is home to 100,000 residents,” said Rick Johnson, executive director of the Sacramento Area Flood Control Agency. “However, it has less than a 100-year level of flood protection due to the threat of deep underseepage.”
In 1998, USACE certified that Natomas had 100-year flood protection, meaning there is a one-in-100 chance of flooding in any given year. But after Katrina, it reevaluated the levees and revoked the certification.
“We began constructing levee improvements in 2007, along with the California Department of Water Resources and the Central Valley Flood Protection Board,” said Johnson. “Meanwhile, USACE sought Congressional approval and federal appropriations for this work.”
By 2013, SAFCA and their partner agencies had completed 18.3 of the 42 miles of levee improvements required in Natomas to meet current flood control standards. In 2014, Congress authorized construction of the American River Watershed Common Features Natomas Basin Project, giving USACE the authority to complete the remaining 24 miles of levee improvements.
The levee improvements vary according to specific conditions along the banks of the Sacramento. Reach B is an adjacent levee, one that’s built next to another to widen it. On Reaches A and I, USACE is installing seepage cutoff walls because of space limitations and structure protection needs. The agency is also improving pumping plants to ensure pumps and outlet pipes meet current standards and are able to handle interior drainage needs during heavy storms.
The work left to do in Natomas is concentrated either in the northeastern part of the basin, which is more sparsely populated and agricultural, or near the intersection of I-5 and Garden Highway, which is much more highly populated.
“Once the projects currently authorized and under construction are completed, we estimate they will provide most of the Sacramento area with a 200-year level of flood protection, or more,” said Johnson.
Increasing the temporary storage capacity of Folsom Lake
To the east of Sacramento lies the community of Folsom. Home to one of the oldest prisons in California, the town has paradoxically grown into an affluent suburb. Historic Sutter Street sits on bluffs overlooking one of the most picturesque stretches of the American River. Kayakers, bikers, runners, diners, craft beer and wine enthusiasts descend on this spot year-round.
Barely two miles upstream of this Northern California gem is the infrastructure that makes it all possible—Folsom Dam. Authorized in 1944 and built in 1956, the dam was put to the test even before its completion. A series of record storms on the American River filled Folsom Lake to capacity during the winter of 1955, but the unfinished dam held, sparing the entire Sacramento area from a dismal echo of 1861-2.
Since the dam’s completion, the federal Bureau of Reclamation has administered the dam. The Sacramento District has cooperated with Reclamation to construct most of the improvements and upgrades to the dam and supporting flood control structures downstream.
The partnership between the two agencies was on full display during the Joint Federal Project, an effort to add a new emergency spillway to Folsom Dam that was completed in 2017. They also jointly signed a new Water Control Manual in 2019, updating the process of making water release decisions to account for new, more precise technology.
“The new Water Control Manual reduces flood risk by prescribing water releases during the early stages of a potential flood event, while inflows are still relatively low,” said Drew Lessard, area manager of the Bureau of Reclamation’s Central California Area Office. “This creates more flood storage to better absorb the peak inflows and stay within the capabilities of downstream levees.”
The Folsom Dam Raise project, authorized by Congress in 2018, builds on the JFP by raising the entire Folsom Dam system up to 3.5 feet. This will increase the surcharge capacity of Folsom Lake—its “reserve” capacity, only used in imminent flooding emergencies—by 42,000 acre-feet.
The 3.5-foot raise is set to commence on Dikes 1-6 later this year, along with the Left and Right Wing dams and Mormon Island Auxiliary Dam. Dike 8 was completed in late spring 2020, and the other dikes will follow in 2024.
In addition to its flood risk management aspects, the Folsom Dam Raise project will also upgrade the dam’s temperature control shutters, a plus for local fish populations.
“Environmental mitigation is an increasing factor in our projects,” said Handura. “We want to be good stewards of this planet and balance the needs of human communities with the ecosystem, plant and animal life.”
Other projects in the Sacramento area
The Sacramento District has currently allocated $1.8 billion to projects outside Natomas, including Folsom Dam Raise. But some of their other work along the Sacramento and American Rivers directly contributes to reinforcing these efforts.
The district is currently widening the Sacramento Weir and Bypass in a collaboration between USACE, SAFCA, and the California Department of Water Resources. It provides direct flood relief to Natomas by diverting excess water into the flood plain between Sacramento and Davis, but also relieves pressure on the city’s entire system as a whole.
“The net benefit to widening the Sacramento Weir and Bypass is so the flood control system can handle greater flows discharged from Folsom Dam via the American River during larger storm events,” said Johnson.
In addition, the district is conducting levee seepage and riverbank erosion protection improvements at many locations along the Sacramento and American Rivers. This work extends outside the Sacramento area to towns such as Marysville and Hamilton City.
“This area has been in a flood fight for over 150 years,” said Handura. “We’re proud to partner with other federal, state and local agencies to continue that fight as a united front, with the ultimate goal to reduce flood risk for the region.”