Spring management of multi-use Stagecoach Reservoir is challenging

White water can be seen rushing out of the outflow below the dam at Stagecoach Reservoir on Wednesday, April 24, 2024.
John F. Russell/Steamboat Pilot & Today

As snowpack melts rapidly this spring, reservoir managers have their hands full with challenging work, especially at the multi-faceted Stagecoach Reservoir.

“Springtime is always a challenging time for reservoir operation,” said Emily Lowell, district engineer for the Upper Yampa Water Conservancy District that owns and operates Stagecoach Reservoir. “We are working with a volume of water that is stored in the snowpack, and there are just a lot of variables about how the snowpack comes off.”

Holly Kirkpatrick, conservancy district public information officer, said the current runoff timeframe is the “most volatile” time of year for reservoir management, noting “we only get one shot at capturing the snowmelt.”

Lowell said such factors as temperature, snow-water equivalent levels and possible dust-on-snow events that may accelerate melting can all impact the annual spring runoff.

Stagecoach is a dynamic reservoir to manage with all the moving pieces of a water body that serves multiple purposes including industrial, recreational, municipal, agricultural and environmental, Lowell said.

“In the spring time, we are looking at all of components on a daily basis that we are adjusting based on conditions real time,” the engineer said.

That includes managing the high-elevation reservoir’s spring level as the ice cover melts. On average the reservoir remains about 4 feet below full capacity until the ice melts completely, which on average has landed on April 20 since 2011, according to the district. Then in the fall, water may need to be released to leave room for freezing water.

Water rushes out the outflow below the dam at Stagecoach Reservoir on Wednesday, April 24, 2024.
John F. Russell/Steamboat Pilot & Today

“Obviously we want to maximize the volume of water storing in the reservoir for later summer use,” Kirkpatrick said. “Because it’s a roller-compacted concrete dam with a hydro plant it has to be managed very carefully to protect the structure itself and the health of the river downstream.”

The outflow of the reservoir during high spring runoff can roar out of the back of the dam, and on Thursday the outflow was releasing at 169 cubic feet per second into the Yampa River. In past years on the same date, the outflow ranged from a low of 38 cfs in 2004 to a high of 293 cfs in 1998.

The water from the 819-acre reservoir also powers an 800-kilowatt hydroelectric power plant at the dam that provides enough electricity for about 100 homes each year.

Reservoir managers also work to limit the amount of time water runs over the concrete stairstep spillway so that invasive and predatory northern pike do not escape downstream to further impact the native fish population.

Kirkpatrick said the reservoir from 2012 to 2023 averaged almost 10 days a year when water passed over the spillway.

A group tours the dam at Stagecoach Reservoir in 2023 as water flows over the stairs of the concrete spillway. Water spills an average of almost 10 days a year.
Upper Yampa Water Conservancy District/Courtesy photo

“Unexpected late season events like the 2019 snow storm in late June can also cause spilling as runoff increases quickly during a time when the reservoir is already full,” Kirkpatrick said.

Water released from the reservoir is monitored for temperature and dissolved oxygen levels to protect the health of the river below the 36,000 acre-feet water body. The intake tower at the dam has three six-foot by six-foot openings at different elevations so that water of different temperatures can be mixed to an optimal temperature.

“We use a blend of each of these intakes so that the outflow coming out of the reservoir is balanced to meet our permitting requirements,” Lowell explained.

The district has produced a five-minute Stagecoach Reservoir Tour video that is posted on the webpage to give residents a peek at the dam operations. The district also offers in-person tours for student groups, including Colorado Mountain College students who visited Friday morning.

This year, officials at the conservancy district will benefit from new data to consider amid their spring runoff forecasting model. Airborne Snow Observatories based in California conducted LIDAR flights across the Yampa Valley on April 11 and will do so again in early May, Kirkpatrick said. The expensive LIDAR flights were funded by the Upper Colorado River Commission.

LIDAR, which stands for Light Detection and Ranging, is a remote sensing method that can show snowpack information across an entire river basin. In past years the runoff modeling was informed by historical records and the Natural Resources Conservation Service SNOwpack TELemetry monitoring sites at Ripple Creek and Lynx Pass.

A soil moisture data monitoring station added in September 2022 on private land south of Stagecoach Reservoir also is assisting with runoff modeling, Lowell said.

The engineer said the most common question she is asked is, “How are we looking for water this year?”

“Last year’s snowpack helped the reservoir recover after several years of drought,” Lowell said. “Things are looking pretty good for water. I anticipate it will be a hot, dry summer, so we’ll see.”

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