- Dana Branham, Dallas Morning News

Crews are nearly set to begin digging a miles-long tunnel under Dallas that, when it’s operational in 2023, will provide flooding relief to parts of the city that have historically gone underwater during heavy downpours.

The Mill Creek Tunnel will stretch from Uptown Dallas, near Woodall Rodgers Freeway, to White Rock Creek and Barber Avenue in South Dallas.

City Council member Lee Kleinman lauded the tunnel boring machine that will carve out the tunnel as a “modern engineering marvel right in our own backyard.” It’s 38 feet in diameter and 230 feet long, and its spinning head will cut a five-mile path through rock 100 to 150 feet below the city’s surface.

And during construction, the project will become the largest hard-rock tunneling project in the world, Kleinman said. Once the tunnel is complete, it’ll be able to handle a maximum of 9 million gallons of water per minute to prevent flooding during heavy rain.

Council members and staff who worked on the project signed the machine’s head Tuesday and snapped selfies at a news conference unveiling the assembled machine at the tunnel’s outfall site, near Dixon Circle and State Highway 352.

The enormous machine is named Big Tex — with permission from the State Fair of Texas, of course, said council member Adam Bazaldua.

Bazaldua said the project means reimagining public safety for his southern Dallas district.

“This project shows the city’s commitment to protecting homes, properties and businesses, which also saves lives,” he said, adding that the tunnel will provide flood protection for about 2,200 properties over 3,200 acres.

Before the years of tunneling can begin, though, crews will spend about two months taking apart the machine and reassembling it underground.

The many pieces that make up the machine were delivered at the outfall site and assembled there. Crews tested every nut and bolt, said project manager Nick Jencopale.

Now it’ll be taken apart again into pieces that “one, can be picked up by the crane, and two, can fit down the shaft,” he explained.

The machine will run 24 hours a day, and officials promised minimal impacts to neighborhoods above the tunnel.

“There will be minimal utility relocation as well as minimal street and traffic impacts given the size and significance of this project, which is very important,” Assistant City Manager Majed Al-Ghafry said during the news conference.

As for the huge amount of rock the tunnel will displace, officials hope it can be recycled as fill material for other projects. The rest will be sent to other sites approved by the city and county, said Rachel Sackett, director of marketing for Southland Holdings, the parent company over the tunneling contractor.