Video

Major milestone for Gross Dam construction

Workers ‘top out’ raising the dam in Boulder County.

In the early morning hours of Wednesday, June 3, 2026, construction crews reached a major milestone on Denver Water’s Gross Reservoir Expansion Project: completion of the dam-raising phase.

Workers placed the final layer of roller-compacted concrete at 3 a.m., raising the dam’s height to 470 feet above the valley floor.

In the coming months, crews will place one last foot of concrete on top of the roller-compacted concrete to raise the dam to its fully completed new height of 471 feet tall.

But the major work to raise the dam — a project designed to nearly triple the water storage capacity of Gross Reservoir and add balance and resiliency to Denver Water’s system that supports 1.5 million people — is done.

A giant crane pours concrete into a dump truck on top of a dam. — Workers on Gross Dam fill a dump truck with concrete on June 2, 2026. Photo credit: Denver Water.

In all, it took nearly 800,000 cubic yards of both roller-compacted and conventional concrete to raise the dam. To put that in perspective, it only took 29,000 cubic yards of concrete to build Empower Field at Mile High in Denver.

A wide view of a concrete dam with mountains and water in the background and a hill of trees in the foreground. — A look at the new Gross Dam on June 2, 2026, hours before crews topped it off with the final layer of roller-compacted concrete. Photo credit: Denver Water.

The final 21 feet of roller-compacted concrete was built in two sections with a 160-foot gap in the middle of the dam for the new spillway. You can learn about that process in this video.

Dam raising construction began in the spring of 2024.

An aerial view of a concrete dam under construction. — A look down Gross Dam in the final stage of the roller-compacted concrete process. Crews will add another foot of conventional concrete to the top of the dam over the next year, which will bring the dam to its final height of 471 feet. Photo credit: Denver Water.

Remaining work on the dam is expected to take another year and includes adding a final foot of conventional concrete on the crest that will serve as a protective layer designed to withstand the elements better than the roller-compacted concrete.

Other work on the dam over the next year includes building safety walls on the top, building the spillway crest, constructing a bridge over the spillway gap, and completing the stilling basin on the bottom of the dam.

“We’re incredibly excited and proud to have reached this milestone,” said Jeff Martin, Denver Water’s program manager for the Gross Reservoir Expansion Project. “Our crews have done an exceptional job building a high-quality dam that was designed to help provide water security for our customers for years to come.”

A man in a yellow safety vest stands near a cliff edge with a concrete dam under construction in the background. — Denver Water’s Jeff Martin, program manager for the Gross Reservoir Expansion Project, stands in front of Gross Dam on June 2, 2026, hours before crews topped off the dam with roller-compacted concrete. Photo credit: Denver Water.