Into the dark, under the Divide and out the other side

Inspecting Roberts Tunnel: What it’s like going through a 23-mile concrete tube thousands of feet underground.

November 14, 2016 | By: Jay Adams

This is not your typical road trip. Twenty-three miles long and more than 4,000 feet underground, navigating Roberts Tunnel is more like driving a convertible through a car wash in the dark.

And for the Denver Water team that inspects this critical piece of infrastructure, it’s a big task, and not for the faint of heart.

Inspection Team left to right: Nate Soule, Lithos Engineering inspector; Tim Holinka, West Slope operations supervisor; Garret Miller, Roberts Tunnel supervisor; Doug Sandrock, safety specialist; Jay Dankowski, mechanic; Erin Gleason, dam safety engineer.
Inspection team (left to right): Nate Soule, Lithos Engineering inspector; Tim Holinka, operations supervisor; Garret Miller, Roberts Tunnel supervisor; Doug Sandrock, safety specialist; Jay Dankowski, mechanic; Erin Gleason, dam safety engineer.

Starting in Summit County, Roberts Tunnel carries water from Dillon Reservoir, under the Continental Divide and into the North Fork of the South Platte River in Park County before heading on to customers in Denver. Completed in 1962, the tunnel took 16 years to build and can deliver more than 480 million gallons of water a day to the Front Range. It’s nearly as long as the Chunnel under the English Channel.

“It’s an impressive piece of engineering,” said Erin Gleason, a Denver Water dam safety engineer. “We inspect the tunnel every five years to check for debris and look for any structural issues.”

On Sept. 21, a six-person inspection team went into the tunnel entrance at Dillon Reservoir and spent four hours driving through the 10-foot-diameter passageway to the tunnel’s east portal, near the town of Grant in Park County.

“When we do tunnel inspections, we’re looking for shifts and cracks in the concrete lining,” Gleason said. “We compare notes from past inspections to see if there are any changes that could lead to future problems.”

The inspection team arrives at the Roberts Tunnel east portal near Grant in Park County.
The inspection team at the Roberts Tunnel east portal in Park County.

Before the inspection begins, Denver Water drains the tunnel so the team can go through, but it’s not completely dry — especially at the entry point where the tunnel runs under Dillon Reservoir.

“It’s definitely wet at the beginning,” Gleason said. “Pressure from the water in the reservoir seeps through the rock and concrete and drains into the tunnel.”

While the water makes for a soggy ride, Gleason said seepage is not unusual to see inside tunnels and is not considered a major problem. The tunnel is basically dry after the first mile.

“We didn’t find any defects,” said Garret Miller, Roberts Tunnel supervisor. “It was a long ride, but this is something we have to do to make sure the tunnel can deliver water to our customers.”

A tunnel engineering consultant rode with the inspection team and declared the tunnel’s concrete lining to be in excellent condition.

“It’s really a team effort to pull off inspections like this, and we had an outstanding team,” Gleason said. “With regular inspections and maintenance, this tunnel will last well into the future.”

5 thoughts on “Into the dark, under the Divide and out the other side”

  1. Do you guys treat this as a confined space entry? And do you need gas detectors? Just curious thanks for the video.

    1. Great question, Phillip.

      Safety is always our No. 1 priority during these inspections, which is why a member of the Denver Water safety team was on the vehicle during the trip.

      We do treat the tunnel as a confined space during our inspections, and also continually monitor the air and other physical and environmental safety factors throughout the duration that the team is inside.

  2. How do you test those who go through the tunnel for any hints of claustrophobia?

    May customers or simply interested parties volunteer to ride along? Perhaps help out with holding lighting in place, writing documentation (I presume you don’t use paper & a pencil/pen), etc.

    How have computers and underwater cameras improved monitoring of the Roberts Tunnel?

    Who was Roberts?

    What angle or drop per mile is the Roberts Tunnel? Since the Tunnel is said to travel under Dillon Resevoir, what sort of intake site lies under the reservoir?

    1. Thank you for your interest! While we can’t answer every one of your questions with specifics for security reasons, the following should help answer most of your questions.

      Everyone who goes on the inspection is asked if they feel comfortable and is aware of the length of the tunnel and how long they will be inside during the inspection.

      In the interest of safety and security, only Denver Water personnel or contracted maintenance crews and inspectors are allowed in the tunnel.

      The tunnel is named for Harold D. Roberts, a member of the Denver Board of Water Commissioners in 1955, who was responsible for leading the rapid design and construction of the tunnel.

      The tunnel runs 23.3 miles and starts at an elevation of 8,845 feet above sea level at Dillon Reservoir and ends in Grant at 8,670 feet.

Post a Comment

Your email address will not be published. Required fields are marked *