By Denver Water for the Superior Chamber of Commerce

The expansion of Gross Reservoir in Boulder County cleared its final federal hurdle when the Federal Energy Regulatory Commission gave its approval for the project earlier this summer and ordered Denver Water to proceed with design and construction.

The $464 million (in 2025 dollars) expansion involves raising Gross Dam by 131 feet, nearly tripling the capacity of a reservoir that plays a vital role in its ability to reliably provide water to 1.5 million people in Denver and surrounding suburbs.

“This is a major milestone that comes after nearly 17 years of careful study, public involvement, planning, and state and federal permitting,” said Jim Lochhead, CEO/Manager of Denver Water. “This federal order to expand Gross Reservoir is critical to our ability to ensure a reliable supply of water to our customers in the future, while providing a net environmental benefit for the state.”

The project will significantly benefit South Boulder Creek in Boulder County. Denver Water will establish a 5,000 acre-foot environmental pool in Gross Reservoir that will be used to increase streamflow during low flow periods. This will benefit 17 miles of aquatic habitat in South Boulder Creek from Gross Dam to its confluence with Boulder Creek. Additionally, Denver Water will restore approximately two miles of South Boulder Creek with the City of Boulder

Gross Reservoir will be the tallest dam in Colorado and will contain about 1.5 million cubic yards of concrete, about half the volume of Hoover Dam. There are many steps to building a dam 471 feet high. Final dam design will continue into 2021 to meet the current completion date of 2025. The project requires preparatory work such as quarrying and preparing the existing dam and foundation for the new dam.

At its peak, the project will create more than 150 jobs at the site in Boulder County. Approximately 120 additional jobs per year will be created as a result of the construction in different industries within the Denver Metropolitan area.

Denver Water’s Board of Water Commissioners approved a two-year, $4.5 million contract with joint venture Kiewit Barnard for planning and pre-construction work during the final design phase of the project.

Once started, Denver Water anticipates being able to complete the bulk of dam raising activities within three years (spring, summer and fall) by working around the clock as weather and conditions allow.

The Gross Reservoir Expansion Project is in the process of growing its contractor team. If your company is interested in joining the team, please complete this contractor interest form. The information gathered here will be provided to the CMGC contractors.

More information at