Construction kicks off at Gross Reservoir
Construction began April 1 on Denver Water’s five-year project to expand Gross Reservoir by raising the height of the dam.
The reservoir and dam, located in the foothills west of Boulder, were named after former Denver Water Chief Engineer Dwight Gross. The dam was completed in 1954 to store water from the West Slope for Denver’s growing population.
Learn more about the history of Denver Water’s Gross Reservoir Expansion Project.
The dam was originally designed to be raised in the future when needed.
Now, Denver Water is raising the height of the dam by 131 feet to help ease a storage imbalance in the utilities’ water collection system. Once completed, Gross will be the tallest dam in Colorado.
“We’ve been busy bringing trucks, cranes and other heavy equipment to the site to prepare for construction,” said Doug Raitt, construction manager of the Gross Reservoir Expansion Project for Denver Water. “A lot has to be done just to prepare the site for all the work that has to happen.”
Early work involves blasting rock on the sides of the canyon to make way for the additional concrete that will be placed over the downstream face and above the existing dam.
Crews also are building a walkway on the upstream side, or reservoir side, of the dam to provide access for workers to walk from one side of the dam to the other.
Get up-to-date information about construction work on the Gross Reservoir Expansion Project at grossreservoir.org.
Upcoming work includes hydroblasting 2 to 3 inches of concrete from the face of the dam so the new concrete will adhere to it. Part of the dam’s spillway will also be removed to prepare for the addition.
To raise the dam, crews will start at the bottom and extend the base of the dam out. Then they will build a series of steps up to the dam’s new height — similar to what you see on the sides of an Egyptian pyramid.
“When it’s done, it will be the largest dam in Colorado and nearly triple the storage capacity of the existing reservoir,” said Jeff Martin, manager of the Gross Reservoir Expansion Project for Denver Water. “We’re really excited to begin construction on this important project.”
Martin said that work conducted during 2022 and 2023 will be mostly site preparation for the on-site concrete production and foundation work on the rock on the sides of the dam and around the bottom.
At the height of construction there may be as many as 400 workers on site at a time, Raitt said.
“Raising a dam is often trickier than simply building a new one,” Raitt said. “We have to continue sending water through the dam during construction while transforming the dam into a new structure.”
Throughout the project, safety will be the No. 1 priority at the site.
“Denver Water and our construction partners have an emphasis on safety for the public and our workers every day,” Raitt said. “We all go through safety training and will continue to evaluate our operations throughout the project.”
Protecting the environment and wildlife is another important part of the project. Denver Water worked with biologists to make sure there were no bird nests in the area before the start of construction and will continue to do so throughout the project.
Additional environmental mitigation efforts were put in place to protect South Boulder Creek and the reservoir from sediment and erosion washing in during the work. These efforts will continue throughout the project.
Denver Water also is spending time updating community members around the reservoir.
“It's important that we let them know what's happening with the project,” Raitt said.
“For months, we’ve been doing outreach to the community with public meetings, newsletters and emails. We’ve received a lot of feedback from our neighbors letting us know what's important to them and we’ll continue to work with them and update them throughout the project.”