What is Sacramento’s plan to stop flooding? Are rivers overflowing? Your questions, answered

With the storm system continuing in Northern California and flood warnings issued in the Sacramento area, some residents are concerned about what this means for rivers and waterways.

Reader Roslyn Bell asked The Bee’s service journalism team: “What is the flood plan for (Sacramento)...?”

After seeing earlier Sacramento River crest forecasts, another reader asked if there will be major levee breaks. Previous forecasts showed potentially record-high numbers, with water levels at 32 feet. It has since dialed down to less than 30 feet as of Monday afternoon.

Here’s what we know:

Sacramento’s plan for flooding

The city of Sacramento is monitoring conditions throughout the city, said Carlos Eliason, Sacramento’s department of utilities media specialist.

He said that they are patrolling certain portions of levees, which are manmade walls that help contain and control water, as well as creeks, ditches and canals.

Crews are going out and doing visual inspections 24/7, Eliason said, checking for cracks, physical failures and toppled trees.

The Yolo Bypass is another mechanism that helps prevent flooding in Sacramento.

The bypass helps divert excess floodwater away from the Sacramento metropolitan area, Ted Sommer, retired lead scientist for the California Department of Water Resources, said in an email response.

In times of heavy rain, the Sacramento Weir, a system made of gates in the river, is opened to reroute water from the Sacramento River near the I Street Bridge and the confluence with the American River to the Yolo Bypass.

The Sacramento Weir is made of 48 gates and is the only one of five in the Sacramento River that is operated manually, meaning a person has to pull a latch to release the gate. The other weirs on the river work automatically when it reaches specific elevations.

But with current conditions, there’s no plan to open the Sacramento Weir, according to the Department of Water Resources.

In order for it to open, water levels must be 29.87 feet, according to regulations set by the U.S. Army Corps of Engineers. The latest forecast from the California Nevada River Forecast Center shows that levels at the Sacramento River at I Street are expected around 27.7 as of 1:34 p.m. Monday.

The monitor stage for the American River at the H Street Bridge is 39 feet and the flood stage is 42. As of Monday, the river is at 29 feet and not projected to rise much more.

The National Weather Service issued a flood warning Sunday night for Cosumnes River at Michigan Bar in preparation for Monday’s rain. The river at McConnell was at nearly 38 feet Monday afternoon. This area’s flood stage is 46 feet.

County officials were not immediately available to comment.

The city and county opened Hart Senior Center in James Marshall Park (915 27th St.) for those needing to evacuate due to the storm. An evacuation order was issued Wilton, in south Sacramento County, and people experiencing homelessness who live along the American River were advised to move.

Should we be worried about levee breaks?

Not necessarily.

Forecasts at the crest are below the threshold of when weirs are open.

“Both these two weirs,” Sommer said, referring to the Sacramento and Fremont weirs, “are essentially ‘overflow valves’ that help keep the Sacramento River at manageable levels.”

He added that the Yolo Bypass has about five times the capacity of the Sacramento River to absorb large volumes of floodwater.

“The bottom line is that the lower valley still has lots of capacity to absorb floodwaters from the Sacramento river,” Sommer said. “However, this doesn’t mean that some levee section couldn’t start leaking because of storm damage or other problems.”

Most recently with the storm on New Year’s Eve, privately owned levees in the Cosumnes River near Wilton failed, resulting in major flooding.

This story was originally published January 9, 2023 at 3:08 PM.