The Abridged version:
- The Sacramento Weir is a crucial part of the region’s flood management system.
- The U.S. Army Corps of Engineers began an expansion of the weir in 2023 to increase the capacity of the century-old piece of infrastructure.
- A construction delay pushed the project back by a year, but officials said the new timeline will not increase regional flood risk heading into an El Niño winter.
More than a century and a half ago, in Sacramento’s nascent years as a city, torrential winter rains exposed one of its major vulnerabilities.
Through December 1861 and January 1862, storm after storm passed over the region, swelling its rivers and breaching newly constructed levees. Water inundated the state capital, reaching the second floor of some buildings in town.
The destruction wrought by the Great Flood laid bare the risks of Sacramento’s location at the confluence of two mighty and unpredictable rivers.
“The Sacramento region has one of the highest flood risks of any metropolitan region in the country,” said Lt. Col. Kara Greene of the U.S. Army Corps of Engineers. “We follow right behind New Orleans.”
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In 2017, the rains came again.
This time, as the Sacramento and American rivers rose, leaders had a solution.
The Sacramento Weir, which sits along the eastern edge of Yolo County just north of West Sacramento, serves as a “release valve” for potential floodwaters. When the rivers get high, gates open and water spills into the bypass, circumventing the region’s most populated areas.
“The Sac Weir is a critical part of the region’s entire flood management system,” Greene said.
But after more than a century of use, the Sacramento Weir is getting an upgrade in the form of a nearly 1,500-foot expansion of its current capacity. After a snag in construction delayed the project by a year, the Army Corps of Engineers now plans to complete the project by December 2027.
Greene said the new timeline does not increase flood risk for the region, as the old weir remains fully operational and the flood management system as a whole is capable of handling the amount of precipitation that could come with this year’s El Niño weather pattern.
One part of regional flood system
The Sacramento Weir is one of six weirs on the Sacramento River. It is both the oldest and the only one that is manually operated, meaning its 48 gates are opened when managers deem it necessary.
“A human being has to go out and pull the rope to open every single one of those little gates,” she said.
The Sacramento Weir is only opened during the most extreme high-water events. Over the last few decades, it has been opened twice, with the last time being 2017.
“It’s not opened often,” Greene said.
That’s because the rest of the region’s flood infrastructure, including levees, dams and the other weirs, quells the risk of catastrophic flooding.
Some of these are included in a larger effort to shore up the region’s flood infrastructure called the American River Watershed Common Features 2016 Project. When completed, the project will have done $1.8 billion worth of work in the Sacramento Valley.
“The Sac Weir is just one of many projects as part of American River Common Features that is designed to reduce risk for the people who live and work in Sacramento,” Greene said.
When it is done, the expanded section of weir will be passive, meaning that the gates do not need to be opened manually. During a flood event, the water will start spilling through the passive weir into the bypass and the manually operated section will only be used in more extreme situations.
Delayed a year
Construction on the weir expansion began in 2023, with the goal of finishing by December 2026.
But last spring, engineers on the project team identified some unexpected settling beneath one of the concrete supports they had already put in on the northern end of the site. The support is one of 26 that will eventually hold up a bridge designed to carry cars over the weir, replacing Old River Road.
The shifting land forced the team to tear out the structure, redesign it and rebuild it.
That work is ongoing, with new concrete wall placements starting to go in over the last month. Greene said that no other settling was identified, so the project should be completed by December 2027.
Despite the delay, Greene said funding for the project is secure and that the money needed to complete construction was provided up front by the federal government.
