Click the link to read the article on the Denver Water website (Jay Adams):
December 12, 2025
Workers raise dam 109 feet in 2025. Next year’s goal: Reaching the top.
The Denver Water team working on Gross Dam in Boulder County is celebrating a successful year after the dam raise is 95% complete.
“In 2025, we raised the height of the dam by 109 feet above the original structure,” said Jeff Martin, Denver Water’s program manager for the Gross Reservoir Expansion Project. “We have 22 feet left to go to reach the new height and we’re on track to reach that in 2026.”
The dam-raising aspect of the Gross Reservoir Expansion Project wrapped up for the season on Nov. 14, due to the drop in temperatures. The project is designed to nearly triple the water storage capacity of Gross Reservoir.
“We have to stop placing roller-compacted concrete when the temperatures drop below freezing,” said Casey Dick, deputy program manager for the Gross Reservoir Expansion Project.
“To prepare for winter, we put blankets on top of the new concrete to keep it from getting too cold. That’s because if the concrete freezes while it is still curing, it can lead to a weakened final product.”
Work associated with the dam raise will resume in spring 2026, when the weather warms up enough to complete the final 22 feet.
Once that work is complete, the dam will be 471 feet tall, which is 131 feet higher than the original. The completed dam also will be longer across its crest, or top. The original crest was 1,050 feet long; the higher dam will have a crest that stretches 2,040 feet from one side of the canyon to the other.
Learn more about the Gross Reservoir Expansion Project.
This year marked the second year of dam raising construction work at Gross.
As of December 2025, workers had placed more than 730,000 cubic yards of concrete. To put that in perspective, Empower Stadium at Mile High, where the Denver Broncos play their home football games, required just 29,000 cubic yards of concrete to build, about 4% of the concrete placed so far on Gross Dam.
Roller-compacted concrete is a special mix of concrete that allows crews to place it on the dam and then spread it out. The concrete is firm enough to be able to drive machinery on top of it. The process is a fast and efficient method of raising the dam. During the construction work, crews raised the height of the dam by about 1 foot per day.
Construction crews use GPS technology and survey equipment to keep track of how high they’ve raised the dam.
“The way we keep track of the elevation gain is that the bulldozers are equipped with GPS-grade control technology, which ensures that each layer of concrete is spread to the correct thickness,” Dick said.
“Once the concrete is rolled and vibrated into place, each layer ends up being 1 foot thick. It’s then checked by surveyors with their equipment to verify the exact elevation.”
Work won’t completely stop over the winter.
Mechanical and pipe work will be done inside the dam, and crews will build a stilling basin at the base of the dam. The basin’s function is to slow the speed of water coming down the dam’s spillway and safely redirect the water into South Boulder Creek.
“This season was a huge success, and our team met a ton of challenges in raising Gross Dam,” Martin said. “We had legal challenges and adverse weather challenges. We also had wildfire safety operation challenges that shut down our power supply up here. Despite all those setbacks, the dedicated team of 500 men and women rose to the challenge. I’d just like to thank everybody who committed themselves to this project and helped us make 2025 a success.”
