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Colorado: Roberts Tunnel turns 50 this year

23.3-mile aqueduct the key to Front Range development

On February 24, 1960, Roberts Tunnel construction crews from east and west “hole through” and meet. View is from the grant heading toward the east portal. Photo courtesy Denver Water.

By Bob Berwyn

SUMMIT COUNTY — As much as we here in the high country like to grumble about “our” water going to the Front Range, the diversions are one of those facts of life that isn’t going to change anytime soon.

And while Dillon Reservoir is the visible symbol of that reality, that water wouldn’t be going anywhere without the Harold D. Roberts Tunnel, a 23.3-mile aqueduct that carries the water under the Continental Divide, as deep as 4,500 feet below the spine of the continent.

In Park County, the water empties into the South Platte River, feeding the Front Range Reservoirs that have enabled Denver to grow into a thriving metropolis at the cusp of the Great Plains and Rocky Mountains. Water diverted from the Blue River Basin in Summit County provides nearly 40 percent of Denver Water’s supply.

The tunnel turns 50 this year, and Denver Water is commemorating the birthday with an invitation-only two-hour ceremony at the Roberts Tunnel headquarters near Grants. Denver Water employees, retirees who worked at the tunnel and Park County commissioners will take a journey through the history of the Roberts Tunnel, with presentations and discussions highlighting the past 50 years.

At the time the tunnel was built, it was the third-longest water supply tunnel in the world, behind the 96-mile Thirlmere Aqueduct (completed in 1925) that supplies water to Manchester, and the 85-mile Delaware aqueduct that brings more than 500 million gallons of water per day from upstate reservoirs to New York City.

Denver Water engineer Erik Holck said the Roberts Tunnel is still in great shape on its golden anniversary. Major infrastucture projects are often built to last 100 to 200 years, but with good maintenance, Denver Water expects the Roberts Tunnel to last indefinitely.

Holck said Denver Water spent several years studying different alignments for the tunnel, which cost $40.4 million in 1956 dollars, the equivalent of $340 million in 2012.

The Roberts Tunnel was built without the massive drill machines commonly used in tunneling today. Some of the biggest challenges included keeping water out of the work area while tunneling was in progress. The complex faults and joints in the Rockies allowed a lot of water to flow into the tunnel, Holck said.

Learn more about the history of Denver Water at this website.

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