Comparison of Water Year 2021 Streamflow to Historical Data at Selected Sites in the Snake River Basin, Wyoming

Fact Sheet 2022-3043
By: , and 

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Abstract

The headwaters of the Snake River are in the mountains of northwestern Wyoming on lands primarily administered by the National Park Service and the Bridger-Teton National Forest. Streamflow in the Snake River Basin has been measured at some sites for more than 100 years (U.S. Geological Survey, 2021). Water from this drainage basin is used for recreation, agriculture, municipal supply, and power generation. Comparison of streamflows in the basin in water year 2021 with historical data can increase understanding of how these multiple uses, along with the ongoing drought in the Western United States, affect water availability during different times of the year (U.S. Department of Agriculture, 2022). Historical streamflow data are defined as the operational period of the streamgage through water year 2020. A water year is named for the year in which it ends; therefore, water year 2021 is October 1, 2020, through September 30, 2021.

Snake River above Reservoir, near Alpine, Wyoming (station number 13022500), is located 100 miles downstream from the headwaters site of Leidy Creek at mouth, near Moran, Wyoming (station number 13012465). The annual streamflow at Snake River above Reservoir, near Alpine, Wyoming, is about 700 times the annual streamflow in Leidy Creek. Photograph by Jerrod D. Wheeler, July 15, 2020.

Streamflow Data Collected in the Snake River Basin

Sixteen streamgages were in year-round operation and one streamgage was operated from April 1 to September 30 during water year 2021 at sites on the main stem of the Snake River and its tributaries (table 1, fig. 1) (U.S. Geological Survey, 2021). The streamgages recorded streamflow at sites with drainage areas ranging from 5.13 square miles in the tributary Leidy Creek (station number 13012465; table 1) to 3,465 square miles on the main-stem Snake River, just upstream from Palisades Reservoir (station number 13022500; table 1) (U.S. Geological Survey, 2021). Streamflow in the Snake River in Wyoming is primarily a result of snowmelt runoff that typically begins in May and continues through July, depending on the area and elevation of the watershed upstream from the streamgage. Additionally, streamflow is regulated by dams and diversions at the more downstream sites (table 1) in the basin, which modifies natural streamflow patterns by storing and releasing water to meet downstream water needs.

Table 1.    

U.S. Geological Survey streamgages in operation during water year 2021 in the Snake River Basin upstream from Palisades Reservoir, Idaho (U.S. Geological Survey, 2021).

[mi2, square mile]

Station number Station name Period of record (water year) Number of years of record used to calculate daily mean streamflow Drainage area
(mi2)
13010065a Snake River above Jackson Lake near Flagg Ranch, Wyoming 1984–2021 37 486
13011000b Snake River near Moran, Wyoming 1904–2021 117 807
13011500a Pacific Creek at Moran, Wyoming 1917–2021 73–77c 169
13011820a Blackrock Creek below Split Rock Creek, near Moran, Wyoming 2018–21 3 32.1
13011900a Buffalo Fork above Lava Creek near Moran, Wyoming 1965–2021 55 323
13012465a Leidy Creek at mouth, near Moran, Wyoming 2019–21 2 5.13
13012475a South Fork Spread Creek at mouth, near Moran, Wyoming 2019–21 2 44.4
13013650d Snake River at Moose, Wyo. 1995–2021 26 1,677
13014300a Gros Ventre River above Upper Slide Lake, near Kelly, Wyoming 2017–21 2–3c 407
13014500a Gros Ventre River at Kelly, Wyoming 1917–2021 23-28c 622
13015000d Gros Ventre River at Zenith, Wyomingb 1917–18, 1987–2021 0–35c,e 683
13016305a Granite Creek above Granite Creek Supplemental near Moose, Wyoming 1995–2021 25 14.9
13016450d Fish Creek at Wilson, Wyoming 1994–2021 26 71.1
13018300a Cache Creek near Jackson, Wyoming 1963–2021 58 10.6
13018350d Flat Creek below Cache Creek, near Jackson, Wyoming 1989–2021 29 129
13018750d Snake River below Flat Creek, near Jackson, Wyoming 1976–2021 46 2,627
13022500d Snake River above Reservoir, near Alpine, Wyoming 1938–2021 70 3,465
a

Streamflow is unregulated.

b

Streamflow is primarily regulated.

c

Because the site did not operate year-round during some years, the daily mean calculation for individual days may be based on a different number of years of data. The range of years used for calculation are noted.

d

Streamflow is a combination of unregulated and regulated.

e

Seasonal site typically operated between about April 1 and September 30.

The rapid melting of snow quickly creates high flows in South Fork Spread Creek at mouth, near Moran, Wyoming (station number 13012475). Photograph by Cheryl Eddy-Miller, June 23, 2020.

Map showing sites and graphs showing streamflow data collected on Snake River and
                     its tributaries, Wyoming.
Figure 1.

Sixteen streamgages were in year-round operation and one streamgage was operated from April 1 to September 30 during water year 2021 in the Snake River Basin. Streamflow at each site was dependent on the drainage area and the timing of snowmelt, as well as upstream water regulation (U.S. Geological Survey, 2021).

Streamflow from water year 2021 at each site was compared graphically (fig. 1) to the streamflow for the period of record that predates the 2021 water year (historical data) (U.S. Geological Survey, 2021). The water year 2021 data are the daily mean streamflow at that site (fig. 1). The historical data are the mean daily streamflow (mean of all the daily means for the period of record through water year 2020) (U.S. Geological Survey, 2021). The daily mean and mean daily streamflow data are useful for observing the timing of streamflow and how large the flows are each day.

Comparison of Streamflow During Water Year 2021 to Historical Data

Cumulative streamflow is useful to determine the total amount of streamflow that flowed past each site during the entire month or each season and was calculated at each site using the daily streamflow data (table 2) (U.S. Geological Survey, 2021). Annual streamflow during water year 2021 tended to be lower than historical annual streamflow for the period of record through the 2020 water year (U.S. Geological Survey, 2021). At unregulated sites, the annual streamflow during water year 2021 ranged from 49 to 78 percent of the historical mean annual streamflow for the period of record through the 2020 water year (table 2). At sites with some level of regulation (table 2), the streamflow during water year 2021 ranged from 79 to 113 percent of the historical mean annual streamflow for the period of record through the 2020 water year (U.S. Geological Survey, 2021).

Table 2.    

Annual streamflow during water year 2021 and period of record through water year 2020 at U.S. Geological Survey streamgages, Snake River Basin (U.S. Geological Survey, 2021).

[Mcf, million cubic feet; POR, period of record; NA, not applicable]

Station number Station name Annual streamflow water year 2021
(Mcf)
Annual streamflow POR through water year 2020
(Mcf)
Percentage annual streamflow water year 2021 compared to mean annual streamflow POR through water year 2020 April, May, June streamflow, water year 2021
(Mcf)
April, May, June streamflow, POR through water year 2020
(Mcf)
Percentage mean annual streamflow during April, May, June during water year 2021 Percentage annual streamflow during April, May, June for POR through water year 2020
13010065a Snake River above Jackson Lake near Flagg Ranch, Wyoming 16,110 27,940 58 9,868 18,130 61 65
13011000b Snake River near Moran, Wyoming 51,130 45,240 113 13,530 15,170 26 34
13011500a Pacific Creek at Moran, Wyoming 4,080 8,381 49 3,026 6,270 74 75
13011820a Blackrock Creek below Split Rock Creek, near Moran, Wyoming 1,278 1,934 66 955 1,525 75 79
13011900a Buffalo Fork above Lava Creek near Moran, Wyoming 13,500 17,210 78 8,517 9,488 63 55
13012465a Leidy Creek at mouth, near Moran, Wyoming 154 208 74 70 106 45 51
13012475a South Fork Spread Creek at mouth, near Moran, Wyoming 1,019 1,439 71 535 828 53 58
13013650c Snake River at Moose, Wyoming 82,210 91,830 90 30,860 42,480 38 46
13014300a Gros Ventre River above Upper Slide Lake, near Kelly, Wyoming 6,587 11,530 57 4,082 7,439 62 65
13014500a Gros Ventre River at Kelly, Wyoming 11,300 15,910 71 6,148 9,229 54 58
13015000c Gros Ventre River at Zenith, Wyoming. NAd NAd NAd 3,483 5,803 NA NA
13016305a Granite Creek above Granite Creek Supplemental near Moose, Wyoming 840 1,248 67 580 767 69 61
13016450c Fish Creek at Wilson, Wyoming 5,854 6,118 96 2,197 2,287 38 37
13018300a Cache Creek near Jackson, Wyoming 272 403 68 124 211 45 52
13018350c Flat Creek below Cache Creek, near Jackson, Wyoming 2,187 2,764 79 715 919 33 33
13018750c Snake River below Flat Creek, near Jackson, Wyoming 103,900 114,900 90 39,540 52,960 38 46
13022500c Snake River above Reservoir, near Alpine, Wyoming. 123,800 142,500 87 51,790 67,770 42 48
a

Streamflow is unregulated.

b

Streamflow is primarily regulated.

c

Streamflow is a combination of unregulated and regulated.

d

Annual streamflow is not computed for the seasonally operated streamgage.

Snowmelt runoff began near the same time of year at most unregulated sites when comparing the increase in streamflow in the spring of water year 2021 to the historical spring streamflow increase. At most unregulated sites, the peak snowmelt streamflow for water year 2021 occurred near the same time as historical flows, but the duration of the peak flows was shorter in 2021, with streamflow dropping to base flow, or low flow, conditions in midsummer. Peak streamflows at sites that were primarily regulated or partially regulated were similar to unregulated sites, but the decrease in flow after the peak and base flow tended to resemble historical streamflow in magnitude and timing (U.S. Geological Survey, 2021).

Streamflow in Leidy Creek at mouth, near Moran, Wyoming (station number 13012465), located in the mountainous headwater of Snake River Basin is relatively consistent throughout the winter months owing to base flow as the area snowpack accumulates. Photograph by Jerrod D. Wheeler, February 23, 2020.

Snake River near Moran, Wyoming (station number 13011000), monitors regulated streamflow releases from the Jackson Lake Dam. Photograph by James R. Campbell, November 20, 2020.

Streamflow at unregulated sites indicates that the snowmelt runoff in April, May, and June typically accounts for more than 50 percent of the annual flow (table 2). Streamflow during the same 3 months, at sites with year-round data collection that are regulated or partially regulated, is less than 50 percent of the annual flow, which indicates the effect of storing the water from spring runoff. At most sites, regardless of the amount of regulation, during water year 2021 the percentage of annual streamflow during April, May, and June was similar to the percentage during the historical period of record (table 2) (U.S. Geological Survey, 2021).

References Cited

U.S. Geological Survey, 2021, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed December 6, 2021, at https://doi.org/10.5066/F7P55KJN.

For more information about this publication, contact:

Director, USGS Wyoming-Montana Water Science Center

521 Progress Circle, Suite 6

Cheyenne, WY 82007

307–775–9162

For additional information, visit: https://www.usgs.gov/centers/wy-mt-water/

Publishing support provided by the

Rolla Publishing Service Center

Suggested Citation

Law, R.M., Campbell, J.R., Wheeler, J.D., and Eddy-Miller, C.E., 2022, 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, 5 p., https://doi.org/10.3133/fs20223043.

ISSN: 2327-6932 (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Comparison of water year 2021 streamflow to historical data at selected sites in the Snake River Basin, Wyoming
Series title Fact Sheet
Series number 2022-3043
DOI 10.3133/fs20223043
Year Published 2022
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Wyoming-Montana Water Science Center
Description 5 p.
Country United States
State Wyoming
Other Geospatial Snake River Basin
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details