North America |
Building Chimney Hollow reservoir
A new reservoir in the foothills west of Loveland, Colorado, will help communities manage their water resources for decades to come. At the heart of the project was construction of an unusual type of dam which hadn’t been built in the US before.
Chimney Hollow overlook
CHIMNEY HOLLOW RESERVOIR, THE MAIN storage reservoir for the Windy Gap Project in Colorado, US, was completed in 2026 to store and bring water to nine municipal utilities, two water districts and one electric utility. At a project price of about US$750m, the reservoir will meet the needs of hundreds of thousands of municipal water users while providing recreation opportunities to those who live throughout the region. While substantial construction was finished in 2026, the project is one that took decades to reach its conclusion.
Early days The first discussion of using water from the Fraser River
for northeastern Colorado came via the Colorado-Big Thompson (C-BT) Project, which was authorised in 1937 and built over the course of two decades. This scheme harnesses water from several tributaries of the Colorado River, stores it in Lake Granby and transports it via the Alva B. Adams Tunnel to more than 1.1 million users on the east side of the Continental Divide. As that project was being built, however, design changes occurred that removed some of the water-supplying creeks from the final project. When community leaders recognised the success the Colorado-Big Thompson Project was having on their communities, they realised the success could have an unintended effect of removing water from agricultural production in project delivery boundaries. Thus, they looked again
16 | September 2026 |
www.waterpowermagazine.com
at the original C-BT Project designs and filed for a water right below the confluence of the Colorado and Fraser rivers to capture water that was not being used by any entities on the Western Slope nor was included in the original project. This water right, in a place called Windy Gap, would be used by those communities in a project separate from the C-BT Project and not managed by the federal government. Through the 1970s, those communities created a governance structure called the Municipal Subdistrict, and received the permits and contracts needed to build the Windy Gap Project, consisting of a small reservoir on the Colorado River, a pump plant and delivery pipelines from Windy Gap Reservoir to Lake Granby. Windy Gap Reservoir opened in 1985, and it delivers water to Lake Granby for those years when its junior priority has access to water and there is space in Lake Granby to store it. In some years, the junior water rights are never in priority, and more concerning, in other years Lake Granby is full of C-BT Project water and cannot store the external water from Windy Gap. By contract, the non-federal water is the first to be released from Lake Granby when water levels reach the spillway.
Drought
In 2002, a major drought in Colorado put these issues on the front burner. Not only was there no water to divert that year, but water from previous years was not available
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