According to the city of Dallas, the Mill Creek Drainage Relief Tunnel will provide 100-year flood protection for nearly 2,200 commercial and residential properties in east Dallas. Once complete, the approximately 30-ft-dia structure will carry a maximum flow of 9 million gallons per minute. 

The project is the largest hard-rock tunnel project currently under construction in the Western Hemisphere, according to Halff Associates, the project’s designer. In this image, taken in July by Mark Witte, Halff’s staff photographer and graphic designer, workers look down a 100-ft-deep inlet shaft to see the breakthrough of the tunnel-boring machine—nicknamed “Big Tex”—as it completed a five-mile journey that lasted two years.

“When photographing these projects, I often look for opportunities to capture views from an uncommon perspective,” says Witte. “And getting over the heads of these construction workers helped capture the enormous scale of the project.”