Gross Reservoir Expansion expected to be completed in 2025

Back in 2017, the U.S. Army Corps of Engineers issued a record of decision and a 404 permit allowing Denver Water to proceed with a $380 million expansion of its Gross Dam and reservoir. The Gross Reservoir Expansion Project will raise the height of the dam, completed in 1954, by 131 feet, allowing the reservoir to nearly triple in size. The expansion of Gross Reservoir will supply an additional 77,000 acre-feet (approximately 25 billion gallons) of water storage. Denver Water says the additional storage capacity will help prevent shortages during droughts and help offset an imbalance in the utility’s collection system.

The Gross Dam was originally designed to be expanded in the future to increase water storage capacity. With the metro area’s population projected to grow by 1 million people by 2040, Denver Water says the time has come to complete the original design intent by raising the dam to create a larger reservoir. Once all permits are secured, the construction plan is set in three phases over a total of four to five years.

Denver Water is still waiting for approval of the hydro power license amendment application by the Federal Energy Regulatory Commission. In addition, the applicability of the 1041 review process is the currently subject of discussions and litigation between Boulder County and Denver Water.  Although the entire project is expected to be completed in 2025, the time frame is likely to change as a result of the outcomes of these regulatory and planning processes.

Located 12 miles southwest of Boulder in Coal Creek Canyon, the expansion project has been in the planning and permitting stage for 16 years. Many community concerns have been voiced and Denver Water has taken steps to address many of them. This will be the third summer that Denver Water has had a public information yurt where staff are available to answer questions and take feedback. The informational yurt is located near the caretaker’s offices at 3656 Gross Dam Road and is open at least four days a week between Memorial Day and Labor Day.

For all information pertaining to the Gross Reservoir Expansion project including cost, construction planning and progress, and community responsiveness, you can visit Denver Water’s webpage dedicated to this project by clicking here.