The city of Austin is almost a month into its biggest flood control project: building flood walls along the Cedar River.

If all goes well, Ulland Bros, Inc. could finish the majority of North Main Flood Control Project base work along the Cedar River from Fourth Street through East Side Lake before spring.

“They want to get the majority of the work right around Mill Pond done this winter,” Public Works Director Steven Lang said.

Many residents have seen construction workers at the Mill Pond area, as well as tearing up trees by Barley’s Restaurant and R&F Apartments. That’s part of the work needed to put in sheet piling about 30 feet below ground to anchor the city’s new flood wall, Lang said workers will then put in concrete footing on top of the sheet pile, and then the upper portion of the wall and settings for the city’s “invisible wall,” a series of aluminum stop logs that can be stacked up to three feet past the high-water mark from the record 2004 flood.

The wall will be about 7 feet higher than North Main Street’s current elevation, according to Lang.

To account for the difference, North Main Street from the Austin Municipal Pool to Eighth Avenue will be raised about two feet. The permanent wall will be constructed two feet higher than that, and the invisible wall will make up the difference.

The invisible wall’s flexibility allows the city to put in the aluminum logs whenever a major flooding event is forecast, which mans the city would be prepared for floods even worse than the one Austin experienced in 2004.

“We’ll probably end up putting them in more often than what we need,” Lang said. “We want to err on the side of being conservative.”

North Main Street from the pool to Eight Avenue will be closed from May through October so construction crews can raise the road. If all goes well, the $14.5 million project will wrap up by July 1, 2015.

Correction: A previous version of this article misidentified the contractor working on the North Main Flood Control project as Reiner Contracting.