What is a levee and how does it work? What to know after flooding in Sacramento County

The start of the year kicked off with an intense storm causing flooding on Highway 99 and across Sacramento County, leaving cars stranded, forcing people to evacuate out of their homes and resulting in multiple deaths.

Levees are an important part of flood-prevention infrastructure. When they fail, the results can be disastrous.

Here’s what happened with Sacramento levees during a recent storm, and how they’re supposed to work:

What happened with Sacramento area levees during the New Year’s storm?

The intense downpour on New Year’s Eve created overflowing on levees in the region.

Cosumnes River flows under Highway 99 and through south Sacramento County. The river is sustained by levees, and this time, they failed.

“The high-water levels of the river caused over-topping of the levee which later caused levee failure and significant flooding around the town of Wilton in south Sacramento County,” according to a Monday news release from the California Governor’s Office of Emergency Services.

According to Reclamation district officials in Wilton, the Cosumnes River levee has a hole the size of a football field, and will cost $1.5 million to fix damages.

“With climate change and more intense flash flooding, then there is a chance that the way things were designed simply doesn’t apply anymore and we have to rethink those designs,” said Gregory Pasternack, UC Davis Geomorphology Professor.

What is a levee?

According to the National Flood Insurance Program, a levee is a “a man-made structure” used “to contain, control, or divert the flow of water so as to reduce risk from temporary flooding.”

The key difference between a levee and dam is the way in which they are positioned. A levee goes along a river and a dam crosses a river.

“Levees are along the river, like if you’re in a bowling lane you know they’re the railings one the side,” Pasternack said. “So they keep the water in its lane.”

Levees play an important role in protecting infrastructure throughout our communities. In California there are roughly 13,800 miles of public and private levees, according to the Water Education Foundation, a water resource page.

Levees throughout the Sacramento Delta “date back to the end of the Gold Rush” and many were built by immigrant workers, Pasternack said.

Along the west bank of the Feather River at Yuba City, is the oldest operating levee in California, according to the State of California Central Valley Protection Board.

According to the Water Education Foundation, there are roughly 1,115 miles of levees in and around the Sacramento-San Joaquin Delta.

Levees across the United States are both publicly and privately owned — the Army Corps of Engineers maintains some, according to FEMA. However, 85% of levees in the USACE Levee Safety Program are locally owned and maintained.

In the case of the levees along the Cosumnes River, they are privately owned making property owners in charge of upkeep.

Levees must be continuously maintained, Pasternack said.

“Like with America’s bridges and dams, all the kinds of infrastructure, you can’t ever stop you know, because a tree grows on the levee, or animals burrow into the levee, or different landowner activities, or there could be deposition or over a long time levees can start to sink,” Pasternack said. “They have to be constantly maintained and taken care of just like your own body, you just can’t let it go.”

If you’re curious about levees in your city and who owns them, you can look them up on the National Levee Database website.

This story was originally published January 6, 2023 at 5:00 AM.