Photos: Fraser River, Moffat Tunnel and Gross Reservoir

This page features photos of the Moffat Tunnel at the Winter Park Ski Resort, the Fraser River outside of Granby, Colorado, and Gross Reservoir in Boulder County.

The Moffat Tunnel is a 6.2-mile tunnel bored through the Continental Divide. It was originally created to build a railroad line that would provide train service through the previously impassable mountains. After the tunnel’s completion, members of Denver’s Water Board saw an opportunity to create a transbasin diversion that would bring water from the Fraser Valley, on the wetter, western side of the Continental Divide to the much drier Front Range, where communities were growing. Now, the water diversion system runs parallel to the railroad tracks within the Moffat Tunnel.

The tunnel has a diameter of 10.5 feet, which allows for the passage of 1,280 cubic feet per second of water. Before reaching the tunnel, the 32-mile Fraser River begins near Berthoud Pass. Water traveling through the Continental Divide ends up in Gross Reservoir. By supplying Front Range residents, the Fraser River has been drawn so low at times that it struggles to support aquatic life.

Gross Reservoir, owned and operated by Denver Water, provides 41,000 acre-feet of storage for water coming through the Moffat Tunnel. However, a proposed expansion project intends to raise the dam by 131 feet. This would make it the tallest dam in Colorado and increase Gross Reservoir’s storage capacity by 77,000 acre-feet.

The expansion project has been controversial, with some environmental groups claiming the project would violate the Clean Water Act, Endangered Species Act and National Environmental Policy Act. Boulder County also attempted to step in the way when it required Denver Water to obtain land use permits to begin the project, although the county will likely settle for a mitigation payment from the major water utility soon.  

Learn more:

Michael Booth, “Boulder County nears $10 million deal to step out of Denver’s way on Gross reservoir Expansion,” The Colorado Sun, November 1, 2021.

Stephanie Butzer, “Shutting off a super-sized spigot: Denver Water shuts down key supply system to juggle critical construction projects,” The Denver Channel, October 26, 2021.

Michael Booth, “Environmental groups appeal court decision that would pave way for Denver Water to raise Gross Reservoir Dam,” The Colorado Sun, April 26, 2021.

Date2010 and 2011
LocationColorado (map)
CreditTed Wood/The Water Desk
RightsFree to reuse under Creative Commons license.

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