Stillwater Reservoir west of Yampa in need of expensive repairs

Stillwater Reservoir was drained in August 2021 for inspections to determine upgrades needed to the aging infrastructure.
Colorado Division of Water Resources/Courtesy photo

When the 75-foot dam for Stillwater Reservoir was built in 1939 by the Civilian Conservation Corps for the former Yampa Reservoirs Public Irrigation District, it was well constructed to meet engineering standards at the time.

But by today’s standards, the dam’s abutments would be addressed differently, said Dana Miller, dam safety engineer with the Colorado Division of Water Resources in Steamboat Springs. As a result, the aging dam infrastructure needs expensive upgrades to bring the structure up to current safety standards, Miller said.

Since it was constructed, the dam at approximately 10,300 feet elevation has experienced consistent seepage issues where the sides of the dam abut the hillsides. If not addressed, the seepage could eventually lead to a failure of the dam, Miller explained.

Although the seepage has been worked on through the years with minimal results, lasting improvements could cost millions, according to the owner Bear River Reservoir Co. The reservoir water is owned by 18 agricultural shareholders and the town of Yampa, and those southern Routt County hay growers have been affected financially due to lower water storage allowances, plus years of drought.

The Stillwater Reservoir was placed on a fill restriction by the state in June 2019 and currently is limited to approximately 80% capacity, which the water storage level may reach during wetter years. The structure is classified as a high-hazard dam, which is not based on its condition but because “loss of life and significant damage is expected downstream if the dam were to fail,” Miller explained.

The 129-acre reservoir, which is also known for the trailhead to popular Devil’s Causeway hike, was drained to a small dead pool in August 2021 for inspections of the upstream side of the reservoir outlet gates. The reservoir was drained again in October for work on the hydraulic operating system, said Andi Schaffner, secretary for Bear River Reservoir Co. 

Yampa resident Schaffner said the owners of the private, nonprofit reservoir company have contributed more than $100,000 to help with dam issues in the past 11 years, and total upgrades to the hydraulics are predicted to cost $300,000.

Workers with Marine Diving Solutions inspect the outlet to Stillwater Reservoir when it was drained in August 2021.
Colorado Division of Water Resources/Courtesy photo

This year, the reservoir company received grants toward the updates including $139,500 from the Yampa-White-Green Basin Roundtable, $125,000 from Colorado River District and $50,000 from Upper Yampa Water Conservancy District, Schaffner said.

Work began in October and November to upgrade the hydraulics system and will be completed by W.W. Wheeler & Associates water resources engineers in Englewood after the reservoir is drained again following the irrigation season in 2023, Schaffner said.

Workers inspect the internal hydraulics of Stillwater Reservoir dam in August 2021.
Colorado Division of Water Resources/Courtesy photo

With millions of dollars likely needed to fix the seepage issues, the timeline for that work is optimistically estimated for 2025, according to the reservoir company.

Dams and reservoir storage are critical to agriculture and the Routt County community, but they also create an inherent risk to those living downstream, Miller said. So providing financial resources to help dam owners repair and maintain the structures is essential. The 20 recommendations in the Yampa Integrated Water Management Plan released in September included the recommendation to “identify repairs for existing reservoirs and secure infrastructure funding to complete them” and “support owners of six large reservoirs with major infrastructure repair needs.”

The engineer said if the Stillwater Reservoir were allowed to fill to full capacity and did breach, some of the downstream reservoir dams “could not accept that type of flow, and the dams would fail as well.” However, the reservoir company noted engineering studies show the dam is not in danger of failing. Rather, the issue is being able to fill to capacity.

“We’ve done significant studies and investigative engineering work. We are happy for the grants that we’ve been able to procure so far, but we will be looking for many more for the final project,” Schaffner said. “We would just like to be able to see it return to full storage. You can’t replace the reservoir storage with other water; that’s why it’s so important to keep it operational.”

Another high-hazard dam in the region is Sheriff Reservoir, and town leaders in Oak Creek are currently searching for funding to complete necessary repairs. Four other smaller private dams within the water division are under state-ordered fill restrictions, including Rams Horn south of Yamcolo Reservoir in the Flattops, Drescher southeast of Craig, Nofstger southeast of Hayden and Sullivan south of Craig near Pagoda, Miller said.  

The engineer said the water division usually has six different reservoirs per year under fill restrictions until repairs are made, including one smaller dam that has been on a fill restriction since 1988.

Stillwater Reservoir located 15 miles west of the Town of Yampa was drained in August 2021 for inspection work and then drained again for the start of upgrade work in October 2022.
Colorado Division of Water Resources/Courtesy photo

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