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Why we collect snowpack data up the Cottonwood Canyons
Salt Lake County monitors snowpack depth and density to inform streamflow forecasting and prepare for spring runoff.
The big picture
On the Wasatch Front, the potential for big spring flows is always highest in Big and Little Cottonwood Creeks.
Monitoring realtime stream flow is critical to prepare for spring runoff and any flooding that may occur.
In order to inform and improve our predictions for estimated streamflow and the timing of peak runoff, Salt Lake County's Watershed Planning & Restoration Program also monitors the snowpack in both canyons.
Photo: For safety, the Watershed Program uses a QBoat to collect flow data in the high flows during spring runoff. Shown here at Tanners Flat in Little Cottonwood Canyon (June 2019).
Collecting snowpack samples
Salt Lake County monitors snowpack depth and density at various elevations and aspects in Big and Little Cottonwood Canyons.
Starting at 8,500 feet, Watershed Program staff collect snow core samples at several locations selected as representative of the overall snowpack and precipitation conditions.
How much water is contained in the snowpack?
At each measuring point a hollow aluminum tube (up to 24' long) is pushed down to the ground surface to measure the depth of the snowpack.
The snow depth and weight of the core sample inside the tube are used to calculate the snow water equivalent (SWE) of the snowpack. SWE is used by hydrologists and water managers to gauge the amount of water contained in the snowpack. It is the amount of water that would be released if the snowpack were to melt all at once.
Streamflow forecasting
Snowpack density has significant implications for the spring melt scenario. Heavy, dense snow holds more water as compared with a light, dry snowpack. Dry snow is light with lots of air pockets. This lower density insulates itself well, which slows down the melt when temperatures start warming up in the spring.
There are many other variables that play into the timing of spring runoff, not just the consistency of the snowpack. Cloud cover, sun angle, and air temperature all play a part. Daytime highs and nighttime lows are particularly important. In the ramp-up to runoff, the Watershed Program keeps a close eye on the lows, checking every day to see if overnight lows are below freezing overnight at the 9,000' elevation.
Snowpack dashboard
Our snowpack monitoring data dashboard provides real time updates of the SWE (water content inches) calculated for each core sample.
Up to four core samples are collected per site per visit, at each of Salt Lake County's six snowpack sampling locations. Three in Big Cottonwood Canyon and three in Little. Watershed Program staff will visit each location multiple times throughout the season, typically February through May.
And now, for your viewing pleasure....
Salt Lake County's Watershed team measuring streamflow during spring runoff