Bighorn Basin Water Supply and Utilization Report Wyoming Area Office Report for March 2021

The Wyoming Area Office of the Bureau of Reclamation is responsible for the operation of Reclamation reservoirs in Wyoming east of the Continental Divide except for Keyhole Reservoir. Four off-stream reservoirs in Nebraska commonly referred to as the Inland Lakes also fall within the Wyoming Area. The North Platte River Basin Reservoirs have a combined storage capacity of 2,800,000 acre-feet. The major reservoirs in the Shoshone and Wind/Bighorn Basins have a combined storage capacity of 1,600,000 acre-feet.

United States of America Department of the Interior Bureau of Reclamation P.O. Box 1630 Mills, Wyoming 82644-1630

Report for March 2021 WATER SUPPLY AND UTILIZATION REPORT BIGHORN RIVER BASIN WYOMING AREA OFFICE

This report concerns the operation of Reclamation facilities in the Shoshone and Wind/Bighorn River Basins.

Reclamation defines a water year as the time period of October 1 through September 30. Water year is abbreviated in this report as W. Yr.

Other organizations furnished information for the Water Supply and Utilization Report. Their cooperation is greatly appreciated.

This report is available on the Internet and can be accessed by following these steps:

1. Log on to the Great Plains Home Page at http://www.usbr.gov/gp 2. Select Water Operations. 3. Select Water Management Information. 4. Select Water Supply Report. 5. Under Bighorn Basin, select the current report or reports from the previous 12 months

1 BIGHORN RIVER BASIN INFLOW

(1000 acre-feet) End of March End of March Accumulated Inflow Inflow Historical Inflow October - March W. Yr. 30 Yr. % of W. Yr. W. Yr. W. Yr. W. Yr. 30 Yr. % of Reservoir 2021 Avg. ¹ Avg. 2020 2019 2018 2021 Avg. Avg. Bull Lake 2.2 2.0 111 0.9 1.5 2.7 13.7 18.1 76 Boysen 48.9 53.7 91 75.5 58.9 73.0 223.0 276.1 81 Buffalo Bill 19.6 21.7 90 20.6 21.7 23.8 124.2 120.4 103 ¹ Average is based on the 1991-2020 period.

BIGHORN RIVER BASIN RESERVOIR INFLOW End of March

40 FEET FEET 1000 X - 30 ACRE

0 Bull Lake Boysen Buffalo Bill RESERVOIR

Average 2021 2020 2019 2018

2 BIGHORN RIVER BASIN OUTFLOW

(1000 acre-feet) End of March End of March Cumulative Outflow Outflow Historical Outflow October - March W. Yr. 30 Yr. % of W. Yr. W. Yr. W. Yr. W. Yr. 30 Yr. % of Reservoir 2021 Avg. ¹ Avg. 2020 2019 2018 2021 Avg Avg. Bull Lake 1.5 1.8 85 1.2 1.9 2.6 9.3 16.6 56 Boysen 37.5 57.3 65 88.1 61.8 117.2 231.8 298.8 78 Buffalo Bill 13.8 26.3 53 29.8 34.1 67.8 117.0 142.2 82 ¹ Average is based on the 1991-2020 period.

BIGHORN RIVER BASIN RESERVOIR OUTFLOW End of March 120

100

40 ACRE-FEET X 1000 X 1000 ACRE-FEET

0 Bull Lake Boysen Buffalo Bill

RESERVOIR

Average 2021 2020 2019 2018

3 BIGHORN RIVER BASIN STORAGE

(1000 acre-feet) Total Storage End of March Total Percent End of March Historical Storage Conservation of Reservoir W. Yr. 30 Yr. % of W. Yr. W. Yr. W. Yr. Storage Capacity 2021 Avg. ¹ Avg. 2020 2019 2018 Capacity Bull Lake 79.5 78.5 101 92.1 81.0 104.5 152.5 52 Boysen 562.5 555.3 101 579.7 571.6 571.4 741.6 76 Buffalo Bill 457.3 422.8 108 455.7 431.0 423.4 646.6 71 Pilot Butte 27.6 28.7 96 27.6 27.8 27.9 33.7 82 ¹ Average is based on the 1991-2020 period. ² This does not reflect a long term average because in 1992 the capacity of the reservoir was increased to approximately 646,565 acre-feet as a result of raising the dam. The average used here reflects data from 1993 through 2020.

BIGHORN RIVER BASIN RESERVOIR STORAGE End of March

700

600

500

400

FEET X 1000 - 300 ACRE 200

100

0 Bull Lake Boysen Buffalo Bill Pilot Butte RESERVOIR

Average 2021 2020 2019 2018

4 BIGHORN RIVER BASIN GENERATION

(Energy in giga-watt hours) End of March End of March Accumulated Gross Gen. Gross Generation Historical Generation October - March Powerplant W. Yr. 30 YR. % of W. Yr. W. Yr. W. Yr. W. Yr. Accum % of 2021 Avg. Avg. 2020 2019 2018 2021 Avg. Avg. Boysen ¹ 2.9 4.0 72 6.7 4.9 5.6 16.9 21.6 78 Pilot Butte ² 0.0 0.0 n/a 0.0 0.0 0.0 0.0 0.1 n/a Heart Mtn. ³ 0.0 0.1 n/a 0.0 0.0 0.5 1.7 1.1 155 Buffalo Bill ³ 0.5 3.5 13 3.8 5.5 12.8 2.8 14.8 19 Shoshone ³ 1.8 1.4 125 1.8 1.2 1.0 8.3 8.6 97 Spirit Mtn. 4 0.0 0.0 n/a 0.0 0.0 0.2 1.7 1.1 155 1 Average is based on the 1991-2020 period. 2 Average is based on the 1991-2020 period. Pilot Butte Powerplant is currently in "mothballed" status and does not generate electricity. 3 Average is based on the 1993-2020 period. 4 Average is based on the 1996-2020 period.

BIGHORN RIVER BASIN GROSS GENERATION End of March 14.0

12.0

10.0

8.0

6.0 GWH

4.0

2.0

0.0 Boysen Pilot Butte Heart Mtn. Buffalo Bill Shoshone Spirit Mtn. RESERVOIR

Average 2021 2020 2019 2018

5 BIGHORN SNOWPACK WATER CONTENT

SWE in inches ¹ April 1st Comparative April 1st Snow-Water Equivalent Snow-Water Equivalent WATERSHED W. Yr. 30 Yr. % of W. Yr. W. Yr. W. Yr. 2021 Median Median 2020 2019 2018 Bull Lake Reservoir 10.3 11.9 87 11.4 11.9 9.7 Boysen Reservoir 12.3 13.0 95 14.4 12.6 11.3 Buffalo Bill Reservoir 16.4 17.1 96 19.1 17.2 16.1

Boysen Reservoir Watershed Buffalo Bill Reservoir Watershed SWE in inches ¹ SWE in inches ¹ Snotel Stations Water 30 Yr. Snotel Stations Water 30 Yr. (Elevation) Content Median ² (Elevation) Content Median ² Burroughs Creek (8,750) 10.4 13.1 Blackwater (9,780) 19.7 22.1 Hobbs Park (10,100) 11.8 13.4 Evening Star (9,200) 26.3 23.9 Kirwin (9,800) 9.2 9.4 Marquette (8,760) 5.2 8.0 Little Warm (9,620) 9.8 10.2 Sylvan Lake (8,420) 17.6 19.2 Togwotee Pass (9,580) 21.7 21.6 Sylvan Road (8,120) 10.1 11.1 Townsend Creek (8,700) 9.2 9.0 Togwotee Pass (9,580) 21.7 21.6 Younts Peak (8,350) 14.1 14.1 Younts Peak (8,350) 14.1 14.1 Watershed Average 12.3 13.0 Watershed Average 16.4 17.1

Bull Lake Reservoir Watershed SWE in inches ¹ Snotel Stations Water 30 Yr. (Elevation) Content Median ² Elkhart Park (8,400) 9.3 12.1 Hobbs Park (10,100) 11.8 13.4 Little Warm (9,620) 9.8 10.2 Watershed Average 10.3 11.9

¹ SWE (Snow Water Content is the amount of water in the snowpack expressed in inches) ² Median for the 1981-2010 period

6 BIGHORN WATER SUPPLY FORECAST

(1000 acre-feet) April 1, 2021 Actual 30 Yr. Comparative Actual Forecast April-July Runoff ³ April-July Expected April - July Runoff Points Reasonable Reasonable Runoff % of Avg. W. Yr. W. Yr. W. Yr. W. Yr. Minimum¹ Expected Maximum¹ Avg. ² 2020 2019 2018 2017 Bull Lake 80 120 160 144.0 83 123.0 160.5 175.0 263.0 Reservoir Wind River above 225 350 475 437.6 80 424.1 475.6 817.9 913.9 Bull Lake Creek Boysen 250 450 700 621.4 72 439.3 823.1 1,007.0 1,636.2 Reservoir Buffalo Bill 500 700 900 749.0 93 791.2 901.1 1,299.7 1,262.0 Reservoir ¹ The probability is estimated to be 9 chances in 10 that the actual volume will fall between the reasonable minimum and reasonable maximum. ² Average is based on the 1991-2020 period.

(1000 acre-feet) April 1, 2021 Forecast of April-July Runoff 30 Yr. Forecast April-July Points Probability of Exceedance Runoff 90% 70% 50% % of Avg 30% 10% Avg. ¹ Bull Lake 80 104 120 83 136 160 144.0 Reservoir Wind River above 225 299 350 80 401 475 437.6 Bull Lake Creek Boysen 250 368 450 72 552 700 621.4 Reservoir Buffalo Bill 500 618 700 93 782 900 749.0 Reservoir ¹ Average is based on the 1991-2020 period.

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