The Science of Measuring Snow
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Much of the water that flows through the West originates high up in the mountains. Each winter, as snow accumulates there, hydrologists calculate how much of the water that melts from it will end up downstream. That information is critical to towns, power plants, and irrigators who depend on the water.
Near the summit of Interstate 80 in southeastern Wyoming, Matt Hoobler trudges through a scrubby open field on snowshoes, carrying a long hollow metal pipe. Reaching a marked spot near the trees, he carefully holds the metal tube perpendicular to the ground, then lets it drop through the snow, twists it, and pulls it out.
Hoobler, a snow surveyor with the Wyoming State Engineer’s Office, is taking a core sample of the snowpack. The specially calibrated cylinder measures snow depth, weight, and density.
“Water content at this site is 5.5 inches. That means if this snow was to melt instantaneously, there’d be 5.5 inches of water sitting in this meadow,” Hoobler said.
Hoobler collects snowpack information at sites throughout Wyoming, like his colleagues in 12 other Western states, including California, Washington and Alaska. Because these sites are often remote, they can travel up to 70 miles a day by snowshoe, skis, and snowmobiles on surveys, carrying survival equipment to protect them in the event of severe weather.
“The main reason we’re up here for snow survey is for river forecasting. In other words, once it all turns to water, how much water is going to exist in our rivers and our reservoirs,” Hoobler said.
The snow survey program started in the 1930s. Each year surveyors add new data to the collection, validating the record and improving accuracy. Hoobler said understanding the relationship between snowpack and water supply is critical.
“Society depends on water — whether it’s growing the crops we’re going to eat or producing hydroelectric power. Fifty to eighty percent of flows of North Platte River depend on this white stuff — snow,” Hoobler said.
One hundred miles southwest, in the South Platte River basin, Mage Hultstrand skis through deep snow just off the highway to get to the Joe Wright SNOTEL site on the top of Cameron Pass in Colorado.
SNOTEL stands for “snowpack telemetry,” or remote data transmission. Hultstrand is a hydrologist with the Natural Resources Conservation Service’s snow survey program in Denver. Every year more than 700 remote stations like this one track snowpack and climate data, including snow depth and temperature, across the West.
“We measure the water content of the snow here,” Hultstrand said, pointing out markers that border the snow pillow, an envelope filled with antifreeze that acts like a scale, weighing the snow and converting it to a measurement of total water content. SNOTEL data are combined with manual snow survey data, collected by people like Hoobler, and compiled into water supply forecasts. Hultstrand said those projections help water providers prepare for the season ahead, determining if they’ll have to apply restrictions in dry years.
“Water providers and agricultural users start paying attention early in the season to what’s going on. This is the headwater state, so this is where all of your water is coming from, with the exception of whatever precipitation is received in spring and summer,” Hultstrand said.
Downstream, Nebraska irrigators also rely on groundwater, which is affected by snowfall. But it takes time for that melted snow to travel through the underground aquifer and back to streams and reservoirs, which impacts central Nebraska irrigators. Tom Schwarz farms about 750 certified organic acres near Bertrand, Nebraska. In addition to row crops, he grows vegetables to supply supermarkets in Lincoln and Omaha.
Schwarz uses groundwater on most of his fields, but also depends on Platte River water stored in Lake McConaughy. Schwarz said he keeps an eye on snowpack but knows there’s a delay in what he and other central Nebraska irrigators will actually receive from the mountains.
“When the snow falls this year, it fills up the reservoirs in the mountains. Irrigators in the Panhandle use that water and, in turn, that water goes down into the aquifer and, hopefully, into the river and down to Lake McConaughy for use the following year,” Schwarz said.
That water is controlled by the Central Nebraska Public Power and Irrigation District. Spokesman Jeff Buettner said they take that delay into account and watch snowpack and river forecasts and levels at Wyoming reservoirs when planning their water supply. But inflows to Lake McConaughy have been declining for the last decade, partly due to groundwater development and conservation measures upstream. Buettner said 2014 will be the seventh time in the last 10 years that Central Irrigation’s customers will receive less than a full supply of water. This year’s allocation will only be half of what they could expect historically.
Still, Buettner said water conservation and efficiency is key. Some big snowpack years would help, too.
Back in Wyoming, Matt Hoobler reads the results of his snow survey report.
“Last year at this time, we had 17 inches of snow; we have 31 this year. Last year we had 2.7 water content inches; we have 5.5 this year. And our 30-year average is 5.4, so we’re just a hair above average. Any time you can have average, that’s a great day,” Hoobler said.
So far, most of the Platte River Basin snowpack reports are above average. But since it’s still midwinter, most water providers will wait to see what the April report brings before getting too excited.