This page features photos of Gross Reservoir, Boulder Creek and the creek’s 2013 floods on Colorado’s Front Range.
Located in Boulder County, Gross Reservoir was created as a water storage and regulating facility; it was completed in 1954 after the construction of Gross Dam. Water from the western side of the Continental Divide flows through the Moffat Tunnel, where it is stored in the reservoir for use along the Front Range, primarily in and around Denver.
In 2017, Denver Water, the public utility that manages the stored water, was granted a permit under section 404 of the Clean Water Act by the U.S. Army Corps of Engineers (USACE) that allowed the organization to move forward with a proposed expansion project. The project will raise the level of the dam by 131 feet and nearly triple its storage capacity.
In response to the USACE’s permit approval, several environmental groups sued USACE, claiming that the agency was violating the Clean Water Act, Endangered Species Act and National Environmental Policy Act by granting permission to expand. Nearby residents and some local government officials also opposed the dam’s construction because of its environmental impacts, but in November 2021, Boulder County agreed to a $12.5 million settlement that allows Denver Water to proceed without further litigation.
The 31-mile-long Boulder Creek perennially flows through the center of Boulder and is a critical water source for the community. But in September 2013, a cold front met with humid monsoon air stalled over the state, causing days of heavy rain and catastrophic flooding.
In just five days, Boulder received 17 inches of rain, which is only three to four inches shy of the city’s average annual precipitation. The floods resulted in at least eight recorded deaths, over 11,000 evacuations and 19,000 damaged homes, 1,500 of which were destroyed. Since 2013, Boulder County has dedicated over $3 billion to long-term recovery efforts, such as buyout programs and recovery assistance.
Learn more:
Michael Booth, “‘Powerless’ against Denver Water, Boulder County Oks deal to triple size of Gross Reservoir,” The Colorado Sun, November 7, 2021.
| Date | Varies |
| Location | Boulder Creek, Colorado (map) |
| Credit | Ted Wood or Mitch Tobin/The Water Desk (see captions) |
| Rights | Free to reuse under Creative Commons license. |
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