Aiming High: How Raising a Denver Dam Lifts Water Security for 1.5 Million People
As the highest dam raise in the U.S., the Gross Reservoir Expansion project will triple capacity to safeguard Denver’s water future. Photos courtesy of Denver Water.
The sunshine. The Rockies. The active outdoor lifestyle. The Denver area has many draws — and one big drawback: water security.
Dry spells and variable snowfall — exacerbated by drought, climate variability and rising demand — make water a precious commodity. Ensuring a reliable water supply is a shared challenge for millions across Colorado’s urban corridor known as the Front Range.
“We are in the arid west and want to make sure that our communities stay vibrant,” said Jeff Martin, gross reservoir expansion program manager at Denver Water. “We are seeing the uncertainties of climate change right now in the form of more frequent, extreme droughts and precipitation events.”
The Gross Reservoir Dam Expansion project is rising to meet this challenge — literally. By increasing the height, length and thickness of the dam, Denver Water is significantly upping its storage capacity. When complete, this will be the tallest dam in Colorado.
To reach the project’s ambitions, Denver Water chose Kiewit-Barnard Joint Venture as the general contractor. Myriad tests later, Amrize was selected to supply the cement, based on product performance and reliable supply capabilities.
The expansion will help local Front Range communities thrive, home to roughly 80–85% of Colorado’s residents, from Fort Collins to Colorado Springs. Photo courtesy of Denver Water.
3 ways the expansion reaches new heights
1. Triples storage capacity to meet growing demand
The Gross Reservoir currently provides drinking water to about 1.5 million people. Tripling the storage capacity of the reservoir to meet future demand requires significant structural updates.
- Increasing the dam height by 131 feet (from 340 to 471 feet)
- Extending its length by 890 feet
- Increasing thickness by up to 90 feet
These changes will allow the dam to safely hold a much larger volume of water while meeting modern safety and durability standards.
“The Gross Reservoir Expansion Project will provide future water security to our customers — one quarter of the state’s population — by increasing redundancy and flexibility in our system,” said Jeff Martin, gross reservoir expansion program manager at Denver Water.
2. Adds flexibility to balance times of abundance and scarcity
Water supply is high in the springtime, thanks to snowmelt and rain. A larger reservoir will allow Denver Water to capture more of that plentiful supply — and have more to release in high-demand and drought situations.
By adding this extra buffer, the entire Front Range system, which serves 80-85% of Colorado’s residents, becomes much more resilient against the shifts in climate affecting the West.
3. Uses building materials that go the distance
The dam expansion will require the tallest roller-compacted concrete (RCC) in the U.S. — and a vast amount of it too. By the end of the project, Amrize will have supplied 75,000 tons of OneCem Portland limestone cement to Kiewit-Barnard JV to produce:
- 740,000 cubic yards of roller-compacted concrete
- 68,000+ cubic yards of foundation concrete
OneCem provides the precise performance characteristics required for RCC, including:
- Lower heat of hydration
- Reduced shrinkage potential
- Improved long-term durability
‘Made in America’: Local-to-local supply with a national standard
The cement for the Gross Reservoir Dam expansion project is produced at Amrize’s Portland, CO, facility — a site that proudly carries our ‘Made in America’ label. This label warrants that all aspects of the product, from the raw materials to processing to manufacturing, are made in the United States.
Even as a local supplier, many miles of mountain roads separate our plant from the remote dam. So we employed our network of storage terminals across Colorado to ensure an uninterrupted supply of the massive material volumes.
Rising higher for the 'Mile High City'
The dam's stepped design supports the trucks that deposit each layer of concrete onto the original structure, giving the expanded dam its new, taller profile. Photo courtesy of Denver Water.
Photo courtesy of Denver Water.
As of early 2026, the Gross Reservoir Dam expansion remains on schedule, thanks to partners ready to meet the urgency of the vision.
Once complete, this will be the tallest dam raise in the United States made with RCC — fitting for the ‘Mile High City.’ But for all its “largest,” “tallest,” “highest” credentials, what’s really important is the impact on people. Thanks to the right materials and the right expertise supporting the boldest of ambitions, the Gross Reservoir Dam should improve water security for Denver communities for many generations to come.