Mountains are our Reservoirs

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(March 2019) Written by Zane Ashford, Big Sky Watershed Corps Member – In the arid Rocky Mountain West, snowpack is critical. The heavy snowfall observed from October through May is stored in the mountains and then slowly released to our rivers in the spring and summer. This runoff contributes not only to the municipal water supply that we rely on for drinking each time we turn on our tap, but it supplies water to the fisheries, recharges our groundwater aquifers, and it provides for the irrigation ditches across the valley, too. In fact, high elevation snowpack and the subsequent runoff feeds 50-80% of Montana’s water supply. In the Gallatin Watershed, our livelihoods rely on the snowpack accumulated in the Gallatin and Bridger Ranges throughout the winter. Without a substantial snowpack built up over the winter and spring, irrigation ditches across the Gallatin Valley are more likely to run dry in July, greatly affecting farmers and ranchers ability to water their crops and cattle. A below-average water year could also have detrimental effects on both the Gallatin and East Gallatin Rivers, as low water levels often result in increased water temperatures that can be lethal to fish. However, snowpack monitoring and water supply forecasting can aid in predicting and preparing for these events.

Lauren extracting a core from the snowpack.

BSWC members, Lauren & Julia, measuring snow density.

Big Sky Watershed Corps (BSWC) members from across the state traveled to McAllister, at the foot of the Tobacco Roots, on March 1st to help the Natural Resources and Conservation Services (NRCS) monitor the snowpack at the Four Mile snow course. This manual monitoring is crucial for forecasting water availability for the upcoming season. Snowpack monitoring has been performed at Four Mile every year by the NRCS and dedicated volunteers since the 1940s. Starting in the 1980s, the NRCS implemented advanced snowpack telemetry (SNOTEL) sites across the state, which record real-time snowpack data. These SNOTEL sites measure Snow Water Equivalent, snow depth, and temperature. These data from snow courses and SNOTEL sites are critical for predicting water availability and are publicly available on the NRCS website if you’d like to see what’s going on at SNOTEL sites near you.

Figure 1. February precipitation percentage of normal (NRCS, 2019).

After a warm and dry January with stream flows reading at just below normal, February brought hope for the Gallatin Watershed. Cold air from the Arctic pushed down and settled over Montana, providing record breaking low temperatures for most of the month. Coupled with moisture coming over from the Pacific, the entire region was blanketed by snow and the storms persisted for the greater part of February. As you can see in Figure 1, the Gallatin Watershed received 210% of its average monthly precipitation in February.

All of this snow brought a lot of water to the watershed, with one site near the headwaters of the Gallatin gaining over an inch of snow water equivalent each day for the last week of February. Snow water equivalent, or SWE, can be thought of as the depth of water contained within the snowpack. February’s snow storms brought the Gallatin Watershed SWE from 83% to 122%, providing hope for a good water year for all of those in the region. While March and April, known as very wet months, will determine the fate of our water supply, it is expected that the watershed will see above average streamflow volumes for much of the summer, as seen in Figure 2. This is great news for all of us who live and recreate in the Gallatin Watershed; it means that there will be water flowing in our rivers and streams for us to play in and water flowing in the ditches to irrigate with.

Figure 2. Snow water equivalent percentage of normal in the Gallatin Watershed (NRCS, 2019).

For more detailed information on the current state of our snowpack, view the Water Supply Outlook Report.