As Colorado’s snowpack starts to melt, Nathan Elder of Denver Water is looking for one thing: numbers.
“The better data we have, the better decisions we can make. That’s pretty much the bottom line,” said Elder, a water resource engineer for the Front Range water provider, which serves 1.5 million customers.
In Colorado, water watchers spend the year looking at numbers that tell how dense snow is or that describe its reflectivity — which ties to how fast it melts. Reservoir managers seek out estimates of how much liquid water is in the state’s thick mountain snowpack, which currently sits at 101% of normal, to decide how much water to release to avoid floods. Farmers watch snow reports to gauge how much snow-produced irrigation water will flow into their fields.
When about 83% of the state’s water supply comes from surface water fed by winter snowpack and spring runoff, measuring that snowpack is a high-stakes science as prolonged drought and a changing climate make every drop count.
With better data, “there’s going to be more confidence in your decisions, a little bit less worry,” Elder said.
That’s where “snow pillows” and laser-bearing planes come into play.
Natural Resources Conservation Service gathers hourly data at 115 specific locations, called snow-telemetry stations, around Colorado. The SNOTEL sites stand at locations between 9,000 and 11,600 feet in elevation and look like tall sheds rigged with measurement gadgets, like large pillows that measure the weight of snow as it falls.
This Fresh Water News story is a collaboration between The Colorado Sun and Water Education Colorado. It also appears at wateredco.org/fresh-water-news.
But snow scientists are also taking to the air to gather basinwide snapshots of the volume of snow in a basin at a single point in time using planes equipped with lidar technology. This technique, started at NASA’s Jet Propulsion Laboratory, helps fine-tune the SNOTEL data.
The two techniques complement each other. For example, SNOTEL sites in southwestern Colorado may show that the region’s snowpack is 95% of the median from 1991 to 2020.
However because of their locations, SNOTEL sites miss snow that gathers in areas below 9,000 feet or above 12,000 feet, and that can throw off key data for water users.
On April 4, Airborne Snow Observatories Inc. flew over the Dolores River Basin to measure its snowpack. There, the actual amount of snow in the basin may not be as robust as it seems: lower-elevation snowpack has not materialized this year based on current measurements, said co-founder Jeff Deems.
“That’s the question I’m getting: Are we really at 100%, or are we going to see that we’re a bit shy of that?” Deems said.
Average snow with dusty problem
According to SNOTEL sites, snow has collected in all of Colorado’s major basins at near-average levels compared with the 30-year normal.
The southern basins — think south of Interstate 70 — received between 95% and 98% of their typical snowpack and have passed the time when their snowpack typically peaks, which means snow is beginning to melt and flow through the state’s streams and rivers.
The northern basins, from Grand Junction to Denver and northern communities, have 101% to 106% of their normal snowpack, compared with historical data. Snowfall in the South Platte, Laramie and North Platte basins typically peaks between April 21 and 24.
Airborne Snow Observatories began its data-gathering in March and has flown over river basins across the state, from the Roaring Fork to the Dolores, Upper Gunnison and Colorado River headwaters, to gather data that complements the data from SNOTEL sites.
Deems is also watching for dust layers buried in the snowpack and estimating how quickly spring runoff will peak.
Water users, like farmers and ranchers, want to see a long, slow runoff season, which helps in the late summer when irrigation water supplies start to dwindle.
But dark dust layers in the snowpack attract more solar radiation, warming the snow and melting it more quickly. Gusting winds laid down blankets of dust across Colorado in early March and April, according to the Center for Snow and Avalanche Studies.
“What’s this dust going to do to us? It’s pretty widespread; it’s pretty intense,” Deems said. “The gun is cocked. If we get a sunny spring without much additional snowfall, then this snowpack’s going to come out in a hurry.”
“It gives us more flexibility”
For water managers like Elder, the basinwide, aerial data has been a game changer.
Denver Water draws 20% of its supply from the Fraser River watershed on the Western Slope. Its collection system involves 34 miles of canals and 30 diversion points, where pipes siphon water into the Denver Water system. Eventually that water travels through Moffat Tunnel into South Boulder Creek and Gross Reservoir.
Each spring, water managers have to make decisions about when to open gates to the diversions and how much water to take.
In the past, they depended on two SNOTEL stations and a single stream gauge in the Fraser River near Winter Park. They used the stream gauge as a forecast point: Based on its measurements, they would try to predict the stream behavior at diversion points miles away based on years of historical data.
It was like using a blunt knife instead of a scalpel. The forecasting results were too uncertain to help the water managers, Elder said.
Without an accurate idea of the snowpack above each diversion intake, Denver Water had little choice but to divert as much as possible early in the season without letting streams go dry or allowing more water to go by the intake than was necessary.
Starting in 2019, Airborne Snow Observatories offered a more accurate, basinwide glimpse of the area. In 2023, Denver Water was able to use that data to take its share of water while leaving more on the Western Slope. For example, it did not divert any water from Cabin Creek and instead allowed a larger flow to flush out accumulated sediment and debris.
“We can decide, OK, we can leave these diversions off. Leave that water in the river. … Get what we need, and provide those benefits for the river where we didn’t have the ability to do that before,” Elder said. “It gives us a lot more flexibility and allows us to provide those benefits.”
Based on the aerial data gathered so far this year, Denver Water could again manage its operations to leave more water in Western Slope rivers while providing for its community. If it does not need to divert any water from a portion of its collection system, Elder’s team aims to coordinate with Fraser River communities to identify the best places to reduce diversions to benefit rivers and aquatic ecosystems on the Western Slope.
“Now that we’ve had one year under our belt, we’ll start getting their input,” Elder said. “Make sure the decisions we’re making are benefiting them, and where we’re making those bypasses is where they want to see those bypasses as well.”
For Deems, this kind of outcome is the whole point of what he’s doing.
There are 55 significant diversion projects that carry water from one basin to another in Colorado. With better data, water managers could be more flexible in how and when they divert water. They could balance certainty for Front Range communities that depend on the exported water while minimizing impacts to the Western Slope, where much of the water originates.
“I could speak for our whole crew on this: We built this out of our academic work, seeing that there was a ready application with huge potential for positive outcomes for society,” Deems said. “To see that manifest, it makes all the hard work and late nights totally worth it.”