Drought and dry soils again will diminish Colorado’s spring runoff
Forecasters: Streamflows down nearly 20% compared to snowpack for Colorado River headwaters, other basins
Water forecasting agencies in Colorado have released their April streamflow predictions, confirming what many already knew: Drought and dry soils will diminish rivers this spring.
“The main story of this water supply outlook season is the effect of last year’s drought going into winter,” said Karl Wetlaufer, a hydrologist and assistant supervisor with the Natural Resources Conservation Service Colorado Snow Survey. “We are anticipating significantly lower runoff compared with the snowpack because we entered winter with such dry conditions that the soils are going to have to soak up a ton of moisture before it actually makes it through the system into the river.”
The Colorado Basin River Forecast Center and NRCS both released streamflow forecasts this week for the months of April through July. This is the second year in a row parched soils will rob rivers of their water.
If soils were not so dry, streamflow predictions would track closely with snowpack. But this year, in many areas streamflows are predicted to be down by 15% to 20% compared with the snowpack, and streamflow for all river basins in the state are predicted to be below average.
NRCS relies heavily on data from SNOTEL (short for snow telemetry) sites for its water supply forecasts. These automated sensors collect snow and weather data from remote, mountainous areas around the state. At the beginning of the month, the snow-water equivalent, which is a measure of how much water is contained in the snowpack, was 90% of average for the Colorado River headwaters, which includes the Roaring Fork River basin. Warm weather the first few days of the month had dropped that number to 78% by Wednesday.
According to NRCS models, streamflow for the Roaring Fork River, measured at its confluence with the Colorado River in Glenwood Springs will be 70% of average. The CBRFC model predicts just 68% of average. Throughout the Colorado headwaters, streamflow predictions range from 57% to 77% of average.
According to CBRFC hydrologist Cody Moser, most river basins in Colorado were in the bottom five driest years for soil moisture going into the winter and some places, like the San Juan River basin in the southwest corner of the state, had record low soil moisture.
“We had poor soil moisture entering the season,” Moser said. “We also have below normal snow, so a lot of things are working against a good runoff season.”
The Lake Powell inflow forecast, at 3.2 million acre-feet, is just 45% of normal and a 2% decrease from the CBRFC March forecast.
Another tricky year for Ruedi
Tim Miller, a hydrologist at the Bureau of Reclamation, which operates Ruedi Reservoir, said predicting inflow into the reservoir from the Fryingpan River and surrounding tributaries is like “looking out into the crystal ball.”
It’s Miller’s job to release enough water from the reservoir to make room for the inflow. Filling it to capacity — roughly 102,000 acre-feet — requires precision and can be tricky. Last year Miller missed the mark by about 5,000 acre-feet, leaving reservoir levels a bit low. It was because streamflow forecasts didn’t fully account for the spring’s lack of precipitation, warmer-than-normal temperatures and dry soils, he said.
“We were over-forecasting until right at the very end,” Miller said. “It wasn’t until the end of May and early June that we realized we just weren’t going to get that volume. Last year, because of those forecasts, I was releasing quite a bit more water at this time because I was expecting a bigger inflow.”
This year, Miller said he plans on releasing just the minimum needed to meet the instream flow needs of the lower Fryingpan until he knows there will be enough runoff to fill the reservoir. Much of the water stored in Ruedi is either “fish water,” released for the benefit of endangered fish downstream or contract water, which has been sold by the bureau to cover the costs of building and operating the reservoir. Many different entities and water providers, including Ute Water Conservancy District and the Colorado Water Conservation Board, own some of this contract water.
The reservoir has a decent chance of filling this year, Miller said, but there is another factor that could negatively impact those chances. Ruedi is currently 57% full, down from where it was at this time last year, about 66% full, according to Miller.
“Ruedi is lower starting out than what it would have been starting out last year, so that’s going to be an issue,” Miller said. “There are just a lot of things to juggle.”
The bureau is predicting about 112,000 acre-feet of runoff for the upper Fryingpan River basin this year, but about half that will be taken through the Boustead Tunnel system to the Front Range, Miller said.
So how might low runoff affect local water providers and users? For starters, the city of Aspen is still in Stage 2 drought restrictions, a carry-over from last August. That means restrictions on washing sidewalks and vehicles, and outdoor watering. One of the biggest water uses in Aspen is outdoor watering of lawns and landscaping.
“We are going to do our damnedest to make sure people are responsible,” said Steve Hunter, utilities resource manager with the city of Aspen.
Hunter said he has been talking with other local water managers about creating a valley-wide unified message about the drought, to target residents and visitors alike. The next city drought response committee meeting is April 23.
Despite the bleak streamflow outlook, weather is still a big unknown. Late spring storms and summer monsoon season — which mostly failed to materialize in 2020 — could begin to turn things around.
“We are just going to be prepared,” Hunter said. “We need to be adaptable. It may get worse, it may get better, it may stay the same.”
Aspen Journalism covers water and rivers in collaboration with The Aspen Times. For more go to http://www.aspenjournalism.org.
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