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In water year 2021 — October 2020 to September 2021 — the streams feeding the Snake River in northwestern Wyoming carried roughly half to three-quarters of their usual water. The U.S. Geological Survey compared that year's flows at seventeen stream gauges with their full records, some more than a century long, to see how drought and the river's many uses shape the water available through the year.
The seventeen gauges, and each one's 2021 flow against its history. USGS.
The basin
The Snake rises in the mountains of northwestern Wyoming, on land run mostly by the National Park Service — Yellowstone and Grand Teton — and the Bridger-Teton National Forest. Its water is used for recreation, farming, towns and power. Almost all of it comes from snowmelt, which usually runs from May through July. At the lower gauges, dams and diversions store spring water and release it later for users downstream.
The gauges measure everything from Leidy Creek, draining 5 square miles, to the main stem above Palisades Reservoir, draining 3,465. The longest record, the Snake near Moran, goes back to 1904.
2021 against the record
"Historical" means each gauge's whole record up to 2020.
| Kind of site | 2021 flow as a share of the historical average |
|---|---|
| Unregulated streams | 49–78% |
| Regulated, or partly regulated | 79–113% |
Selected gauges:
| Gauge | Regulation | 2021 (million ft³) | Historical average (million ft³) | Share |
|---|---|---|---|---|
| Pacific Creek at Moran | none | 4,080 | 8,381 | 49% |
| Gros Ventre River above Upper Slide Lake | none | 6,587 | 11,530 | 57% |
| Snake River above Jackson Lake | none | 16,110 | 27,940 | 58% |
| Buffalo Fork above Lava Creek | none | 13,500 | 17,210 | 78% |
| Snake River at Moose | partial | 82,210 | 91,830 | 90% |
| Snake River below Flat Creek, near Jackson | partial | 103,900 | 114,900 | 90% |
| Snake River above Palisades Reservoir, near Alpine | partial | 123,800 | 142,500 | 87% |
| Snake River near Moran, below Jackson Lake Dam | mostly regulated | 51,130 | 45,240 | 113% |
The one gauge above its average sits below Jackson Lake Dam, where releases from storage, not that year's snow, set the flow.
When the water came
- Start of the melt: about on time at most unregulated streams.
- Peak: about on time too — but it did not last. Flows fell to summer low levels by midsummer.
- Regulated sites: peaked like the unregulated ones, then held closer to their usual flows afterward, as reservoirs released stored water.
- The spring share: on unregulated streams, April to June usually carries more than half the year's water; at regulated sites, less than half, because reservoirs hold it back. In 2021 those shares were close to normal nearly everywhere — there was less water, not a different season.
Sources
Written from Comparison of water year 2021 streamflow to historical data at selected sites in the Snake River Basin, Wyoming, U.S. Geological Survey Fact Sheet 2022–3043, a work of the United States government in the public domain. Gauge data are from the USGS National Water Information System.
Licence : CC0 1.0 (domaine public) · Adapté de pubs.er.usgs.gov
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