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Barbara Giedraitis, of Westminster, fishes along the shoreline of Old Dillon Reservoir Monday. Pine-beetle killed trees contributed to the deterioration of the dam.0
SUMMIT COUNTY — The earthen dam at the Old Dillon Reservoir is not safe and the reservoir must be drained immediately, the Town of Dillon announced Monday.
Increased pine-beetle infestation of the trees around the reservoir — located on a ridge between the Dam Road and Interstate 70 — has contributed to significant deterioration of the aging dam’s condition, engineers from the Colorado Division of Water Resources discovered during their yearly inspection in early July.
Dead trees standing on the steep side of the dam could topple, uproot and threaten the integrity of the structure’s water-holding capacity, Dillon public works director Eric Holgerson said.
If the dam were to fail, uncontrolled drainage from the hill-top reservoir would most likely cause damage to both I-70 and commercial establishments in Silverthorne, the inspection report stated.
With plans in the works for an $8 million expansion of the existing reservoir, Dillon had hoped to meet the state’s safety requirements when construction started on the expansion next year.
“They’ve known there’s been problems associated with the reservoir,” Holgerson said. “But they were giving us time to do the enlargement.”
The July inspection found that immediate action couldn’t wait.
“Because the condition of this dam poses a significant threat to public safety, the Town of Dillon is ordered to install pumps and drain the reservoir,” read the letter from the state engineer.
Water stored in the 10-acre reservoir — built in 1939 by the original Town of Dillon — originates from Salt Lick Creek in the Wildernest area and passes under I-70 by a reverse-siphon process through what’s known as the Dillon Ditch.
The reservoir has been maintained principally as a recreation area since the town’s relocation to its current site in the early 1960s.
The expansion plan still undergoing final review by the Forest Service calls for a four-fold increase in the reservoir’s capacity, as well as construction of two modern 20- to 25-foot earthen dams.
Finalized renovation plans may not have required drainage of all the water, but the state has now ordered the reservoir 100 percent empty.
“We do not have a choice,” Holgerson said.
The morning after he received the state’s letter, Holgerson closed off the flow in the Dillon Ditch, so no new water can enter the reservoir.
Within the next few days, the town will install a siphon by the dam’s existing outlet pipe which will start a controlled drainage of water back into the Salt Lick Creek on the north side of the Interstate.
Holgerson expects the siphon process to take a month or so. Any remaining water will be removed with pumps.
The advantage of siphoning is that it’s a passive process and, unlike mechanical pumping, doesn’t require constant attention.
“I hope the siphon will do most of it,” Holgerson said.
In addition to draining water, the town plans to cut down from 20 to 25 dead lodgepoles standing on the dam’s contours as early as today or tomorrow, leaving their stumps in place to provide as much stability as possible to the structure.
Despite the state’s assessment of potential integrity problems, there is no visible seepage from the dam at present, Holgerson emphasized.
And with a storage capacity of only 46 acre-feet, compared to the 255,000 acre-feet contained in the “new” Dillon Reservoir, the threat of a breach is more cause for concern than alarm, he added.
Once construction on the new dam — expected to start next year — is completed, the reservoir will be refilled and again be accessible for fishing.
For now, town and Division of Wildlife officials are encouraging the public to catch and keep as many fish as possible.
Harriet Hamilton can by reached at (970) 668-4651, or at hhamilton@summitdaily.com.
Increased pine-beetle infestation of the trees around the reservoir — located on a ridge between the Dam Road and Interstate 70 — has contributed to significant deterioration of the aging dam’s condition, engineers from the Colorado Division of Water Resources discovered during their yearly inspection in early July.
Dead trees standing on the steep side of the dam could topple, uproot and threaten the integrity of the structure’s water-holding capacity, Dillon public works director Eric Holgerson said.
If the dam were to fail, uncontrolled drainage from the hill-top reservoir would most likely cause damage to both I-70 and commercial establishments in Silverthorne, the inspection report stated.
With plans in the works for an $8 million expansion of the existing reservoir, Dillon had hoped to meet the state’s safety requirements when construction started on the expansion next year.
“They’ve known there’s been problems associated with the reservoir,” Holgerson said. “But they were giving us time to do the enlargement.”
The July inspection found that immediate action couldn’t wait.
“Because the condition of this dam poses a significant threat to public safety, the Town of Dillon is ordered to install pumps and drain the reservoir,” read the letter from the state engineer.
Water stored in the 10-acre reservoir — built in 1939 by the original Town of Dillon — originates from Salt Lick Creek in the Wildernest area and passes under I-70 by a reverse-siphon process through what’s known as the Dillon Ditch.
The reservoir has been maintained principally as a recreation area since the town’s relocation to its current site in the early 1960s.
The expansion plan still undergoing final review by the Forest Service calls for a four-fold increase in the reservoir’s capacity, as well as construction of two modern 20- to 25-foot earthen dams.
Finalized renovation plans may not have required drainage of all the water, but the state has now ordered the reservoir 100 percent empty.
“We do not have a choice,” Holgerson said.
The morning after he received the state’s letter, Holgerson closed off the flow in the Dillon Ditch, so no new water can enter the reservoir.
Within the next few days, the town will install a siphon by the dam’s existing outlet pipe which will start a controlled drainage of water back into the Salt Lick Creek on the north side of the Interstate.
Holgerson expects the siphon process to take a month or so. Any remaining water will be removed with pumps.
The advantage of siphoning is that it’s a passive process and, unlike mechanical pumping, doesn’t require constant attention.
“I hope the siphon will do most of it,” Holgerson said.
In addition to draining water, the town plans to cut down from 20 to 25 dead lodgepoles standing on the dam’s contours as early as today or tomorrow, leaving their stumps in place to provide as much stability as possible to the structure.
Despite the state’s assessment of potential integrity problems, there is no visible seepage from the dam at present, Holgerson emphasized.
And with a storage capacity of only 46 acre-feet, compared to the 255,000 acre-feet contained in the “new” Dillon Reservoir, the threat of a breach is more cause for concern than alarm, he added.
Once construction on the new dam — expected to start next year — is completed, the reservoir will be refilled and again be accessible for fishing.
For now, town and Division of Wildlife officials are encouraging the public to catch and keep as many fish as possible.
Harriet Hamilton can by reached at (970) 668-4651, or at hhamilton@summitdaily.com.
