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Work under way to diagnose trouble at Grizzly Reservoir

Brent Gardner-Smith
Aspen Journalism
Water from Lincoln and Grizzly creeks flows through the sediment at the bottom of Grizzly Reservoir, which was drained in August after a tree in the outlet gate caused problems.
Courtesy Twin Lakes Reservoir and Canal Co. |

As steps are taken to figure out the extent of the problem with the outlet in the dam that forms Grizzly Reservoir, it’s possible that rain could wash more sediment from the bottom of the recently drained reservoir down Lincoln Creek and into the upper Roaring Fork River.

“Unfortunately, there is the potential for that,” said Scott Campbell, the general manager of the Twin Lakes Reservoir and Canal Co., which owns and manages the dam and reservoir located about 16 miles southeast of Aspen. “My goal is to minimize the potential, but it is there.”

Campbell said last week that a channel was being dug through the recently exposed dirt at the bottom of the reservoir to direct flows from Lincoln and Grizzly creeks away from the dam outlet and directly into the diversion tunnel that runs under the Continental Divide.

Campbell that should make it possible to see if the seal around the outlet gate at the bottom of the dam simply needs to be repaired, or if there is more serious damage to the outlet works and the dam, which sits astride Lincoln Creek and is officially called the Lincoln Gulch Diversion Dam.

“We’ve got a dam that we can’t control, that we can’t regulate, and we don’t know what the issue is on the outlet yet,” Campbell said. “I’m fairly confident what the problem is, but I won’t really know if there is an additional problem there until we can get it dewatered and really give it a close look.”

In the meantime, it is possible a heavy rain could swell the flow of Grizzly and Lincoln creeks and water could flow over the newly formed channel, through the mud in the bottom of the reservoir, and out of the dam’s outlet. Or rain could simply soak the exposed sediment at the bottom of the reservoir and send more muddy water through the outlet.

According to the Roaring Fork Conservancy, officials with the U.S. Forest Service and the city of Aspen are monitoring the situation.

And April Long, the stormwater manager for the city, has let Campbell know the city wants to collect sediment samples from the drained reservoir to check for toxicity.

Piles of mine tailings from the old Ruby Mine and the Lincoln Mining District are visible upstream of the reservoir, but Campbell said he was not aware of issues that have arisen from the tailings.

TREE IN THE WORKS

Earlier in the month, operators at the reservoir went to close the outlet gate in the dam to stop sending water out of the reservoir down Lincoln Creek.

However, the gate wouldn’t close, and a tree was found in the works.

“After we removed the tree, we operated the gate up and down, and we still couldn’t get it to seal, so we knew had some kind of other problem,” Campbell said. “It’s not a good situation on a dam.”

Since he couldn’t control the water flowing out of it, Campbell made the call to drain the relatively small reservoir, which can hold 570 acre-feet of water and primarily serves as forebay to the transmountain diversion tunnel, which was built in the 1930s.

“I didn’t take the decision lightly,” Campbell said. “But I wanted to make sure I was providing for safety first.”

Inflows to Grizzly Reservoir from Lost Man Creek; the Roaring Fork River; and Tabor, Brooklyn and New York creeks were re-directed out of their diversion canals and back into natural stream channels.

Then about 200 acre-feet of water remaining in the reservoir was sent through the tunnel.

That left about 20 acre-feet of water in the silty bottom of the reservoir, along with the incoming flow from Lincoln and Grizzly creeks.

Starting early Aug. 10, that water began flowing slowly out of the reservoir, carrying mud with it.

By Monday afternoon, people in the Roaring Fork River valley noticed their local river had changed color, much like the Animas River near Durango had done in the wake of the Gold King mine spill.

PUBLIC NOTIFICATION

Campbell said that in retrospect he should have had a protocol in place to let people know that the reservoir had to be drained, which has not happened since the mid-1990s.

“One of the lessons I’ve learned from this is that we will have a protocol next time,” said Campbell. “I talk about trying to be a good neighbor, and I didn’t do that this time. But if we get in that position again, we’ll have a list where we let folks know. That would be more responsible of us as a company, and we’ll do that going forward.”

After the water from the reservoir was released, Campbell did contact Erin Gleason, a dam safety engineer for the state based in Glenwood Springs.

Gleason said Thursday she plans to inspect the dam once the outlet works are exposed.

If the situation requires more than a maintenance-level job, a storage restriction could be put in place on the dam until repairs are made.

If so, that could affect water deliveries to Colorado Springs, Pueblo, Pueblo West and Aurora, each of which owns a portion of the water that normally flows out of Grizzly Reservoir.

Editor’s note: Aspen Journalism is collaborating with The Aspen Times and the Glenwood Springs Post Independent on coverage of rivers and water. More at http://www.aspenjournalism.org


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