A multi-million-dollar project to help protect Sacramento from flooding is facing a significant setback. CBS News Sacramento is learning that there are problems with the ground where the new Sacramento Weir is being built.

For more than 100 years, the Sacramento Weir has helped protect the region during strong winter storms.

"It diverts that water away from our urban areas where there's the most risk within our system and it pushes it into the bypass," said Todd Bernardy, principal engineer with the California Department of Water Resources.

Bernardy helps manage the state's network of weirs.

"These are very, very good tools to have in our toolbox to protect nearly 780,000 people who live in the floodplain," he said.

In 2023, the U.S. Army Corps of Engineers began expanding the weir by an additional 1,500 feet to nearly double the amount of water that can bypass the river.

But now, inspectors on the $350 million project have found a problem on the north abutment of the construction site. Engineers call it "differential settlement," which means the dirt underneath the weir's foundation is becoming unstable.

"You're dealing with underground, you're dealing with earth and nature forces, and so you want to make sure that you get that right," Bernardy said.

In July, a two-star general from Army headquarters in Washington, D.C., led an inspection of the site's construction problems. The Army Corps would not comment on camera but in a statement that "we're evaluating it and determining the right solution," and "our top priority remains ensuring the long-term safety and reliability of this critical flood management structure."

"The important part is to make sure that that thing is performing and works the way that it was designed to do, and if that takes adjustments in the field, then that's what it takes," Bernardy said.

Work currently continues on other parts of the weir, while engineers seek a solution. But completion of the project could now be delayed by another year due to the discovery.

"I am confident that the corps team will be able to resolve whatever construction issues they have out there," Bernardy said.

The Army Corps says so far, the complication has not changed the overall price tag of the weir. They hope to complete an analysis of the construction issue by the end of this month.