Grizzly Reservoir, the high mountain lake above Aspen formed by the damming of Lincoln and Grizzly creeks, will be drained next summer for repairs to the dam, tunnel and outlet work.
After spring runoff next year, Twin Lakes Reservoir and Canal Company will lower the reservoir, so workers can install a membrane over the steel face of the dam, which was built in 1932, according to a May feasibility report rehabilitation of the dam. .
The report, prepared by RJH Consultants Inc. of Englewood, included an inspection and assessment of the infrastructure and presented various rehabilitation options. Half of the cost of the study – $50,000 – was funded by the Colorado Water Conservation Board (CWCB).
“The purpose of the dam rehabilitation is to address dam safety issues associated with the corroded and thinning steel liner of the upstream slope, uncontrolled seepage, and operational issues with the outlet structures,” the report said.
The project will also replace the gates that control water flow in the Twin Lakes Tunnel and repair the outlet structures that release water into Lincoln Creek. According to the report, the outlet works have problems with cracks, holes and seepage, and the gates of the over 80-year-old tunnel have problems with leakage, are difficult to operate and require major maintenance every year.
“This infrastructure is aging and it is time to rehabilitate it,” said Kalsoum Abbasi, chairman of the board of Twin Lakes Reservoir and Canal Company.
Twin Lakes officials expect the project to be completed in October 2023. They will also tap into the reservoir this month to weld a small test section of the dam membrane to see how it holds up in the winter. rigorous at 10,500 feet. This work should begin on August 22; the reservoir will be filled in October.
Grizzly Dam is considered a high-risk dam by the Colorado Division of Water Resources. This does not mean it is likely to fail, but it does mean that loss of life would be expected if the dam failed. Still, the state’s last inspection in 2021 found the dam satisfactory — the highest rating — and declared full storage capacity safe.
The report estimated the cost of the rehabilitation work at nearly $7 million. Twin Lakes plans to get a loan from the CWCB for part of the cost and will pay the rest with money from its water user assessments.
How the system works
Grizzly Reservoir is part of a complex system of storage buckets, tunnels, and canals that takes water from the headwaters of the Roaring Fork River Basin below the Continental Divide and delivers it to Front Range towns. The system collects runoff from 45 square miles of mountainous terrain, including the New York, Brooklyn, Tabor, Lincoln, Grizzly and Lost Man creek drainages and discharges it into the Grizzly Reservoir, which can hold 570 acre-feet. of water.
From there, the water flows into the 4-mile-long, hairpin-straight Twin Lakes Tunnel under the Continental Divide and into Lake Creek, a tributary of the Arkansas River. Twelve miles later, this water arrives at Twin Lakes Reservoir where it is stored before being sent to Front Range towns via pipelines and pumps.
Four municipalities own 95% of the water in Twin Lakes: Colorado Springs Utilities owns 55%; the Pueblo Waterworks Board has 23%; The Metropolitan District of Pueblo West owns 12% and the City of Aurora 5%.
The Twin Lakes system is such an integral part of the towns water supply that they employ two caretakers to live year-round in a cabin on the remote reservoir site to make sure everything is running smoothly. It is the largest water source on Colorado Springs’ West Slope and accounts for approximately 21% of its total water supply.
The project is capable of diverting up to 46,000 acre-feet per year, or nearly 40% of flows in the upper reaches of the Roaring Fork, according to figures from the Roaring Fork Conservancy. In recent years, Twin Lakes has diverted between about 31,000 and 38,000 acre-feet per year, according to data from the Colorado Division of Water Resources.
During next year’s rehabilitation work, most creeks – Lost Man, New York, Brooklyn and Tabor – will be able to flow downstream instead of being collected by a canal system that feeds the Grizzly Reservoir. As long as water rights take priority, Twin Lakes will likely continue to take and send through the tunnel any flows they get from Lincoln and Grizzly creeks, according to Abbasi. This means that a section of Lincoln Creek below the dam will be dry.
When irrigators in western Colorado’s Great Valley make the Cameo call—which occurs most summers and often commands the entire Colorado River and its tributaries upstream—those with junior water rights must cease. to divert, so that the irrigators can get their share. The Cameo appeal is made up of water rights from agricultural diverters near Palisade, including the Grand Valley Water Users Association and the Orchard Mesa Irrigation District. Under Colorado water law, the oldest water rights have first use of the river, and Cameo’s right is older than Twin Lakes.
“As long as we have priority, we can still bring water through the tunnel,” Abbasi said. “Whatever happens in the tank, we’ll have a way to get it through the tunnel for the majority of the project.”
Abbasi said overall, Twin Lakes will likely divert less water than normal in 2023.
Pitkin County Stored Water
Once work on Grizzly Dam begins next summer, there will likely be more water flowing into the upper Roaring Fork above Aspen when the creeks that usually flow into Grizzly are allowed. to descend downstream. But, there will also be a 200-acre hole where water stored by Pitkin County will not be released.
As part of a 2018 water court settlement, Pitkin County received 800 to 1,000 acre-feet of water from the Twin Lakes system, which is sent downstream rather than to the Front Range. Two hundred acre-feet of this can be stored in the Grizzly Reservoir for release in late summer.
“The reason Pitkin pushed for this was because that’s when we need the water the most,” said Pitkin County Assistant Attorney Laura Makar. “This is where streams matter, and every cfs makes the biggest difference.”
This year, the county used the 200 acre-feet to help boost flows between the end of the spring runoff and when the Cameo call came in this week.
“We timed it perfectly, so there’s no hole in the river,” Makar said. “The fish and the river have taken full advantage of it. We could somehow maintain the river until the Cameo call goes off.
But, next year, it will not be possible to release the 200 acre-feet of stored water because there will be no water in the Grizzly Reservoir at the end of the summer.
“It looks like next year we will be limited to whatever naturally exists in the system,” Makar said. “We’re making sure that when we plan for next year, we make sure we get the full benefit…but knowing that we won’t have 200 acre-feet at the end of the season that could actually come from the reservoir. “
Aspen Journalism covers rivers and water in conjunction with The Aspen Times. For more information, visit http://www.aspenjournalism.org.