Update on Hydrology, Glen 

Canyon Operations and Water 

Quality

GCDAMP Technical Working Group

October 13, 2021
Upper Basin Storage (as of October 11, 2021)

Reservoir

Percent 

Current 

Live 

Storage

Current 

Live 

Storage

(maf)

Live 

Storage 

Capacity 

(maf)

Elevation

(feet)

Fontenelle 64 0.23 0.33 6,491.45

Flaming 

Gorge 78 2.93 3.75 6,018.71

Blue Mesa 27 0.22 0.83 7,433.06

Navajo 57 0.94 1.70 6,023.21

Lake Powell 30 7.24 24.32 3,545.13

UC System 

Storage 31 11.70 31.09

2
2021 Precipitation: September and Seasonal

3
2022 Precipitation: October and Seasonal

4
Current SWE and Observed UC Runoff

Available online at: https://waterwatch.usgs.gov/index.php?id=wwdur_cumrunoff

5
October 2021 30-Year Average Shift 1991-2020

• CRSP Initial Unit facilities will continue to operate according to their Records of Decision

• Moving to the 1991-2020 statistics will provide forecasted reservoir operations that are 

more reflective of the dry conditions we are currently experiencing

• The significant wet hydrology observed in the 1980s will be removed from the forecast 

probabilities and no longer influencing and overestimating forecasted water volumes.

• Incorporating the last decade of record dry hydrology from 2011-2020 includes the observed 

higher temperatures and drier conditions that have occurred with climate change.

• Upper Green Basin least amount of change because of 2011 and 2017 wet hydrology

• San Juan has greatest shift with continued dry hydrology over last decade

Reservoirs

1981-

2010 

AprilJuly Avg 

Volume 

(kaf)

1991-

2020 

AprilJuly Avg 

Volume 

(kaf)

April-July 

Volume 

Difference 

(kaf)

April-July 

Percent 

Difference

1981-

2010 WY 

Avg 

Volume 

(kaf)

1991-

2020 WY 

Avg 

Volume 

(kaf)

WY 

Volume 

Difference 

(kaf)

WY Percent 

Difference

Fontenelle 726 735 9 1% 1,082 1,074 (7) -1%

Flaming Gorge 979 966 (12) -1% 1,455 1,411 (43) -3%

Blue Mesa 676 636 (40) -6% 955 904 (51) -5%

Navajo 737 628 (109) -15% 1,075 911 (165) -15%

Powell 7,155 6,392 (763) -11% 10,831 9,603 (1,228) -11%

April-July Volumes Water Year Volumes

6
Most Probable August Forecast

Water Year 2021

April – July 2021

Observed Unregulated Inflow

as of October 11, 2021

Reservoir

Unregulated 

Inflow

(kaf)

1981-2010

Percent 

of Avg

1991-2020

Percent 

of Avg

Fontenelle 318 44 43

Flaming 

Gorge 380 39 39

Blue Mesa 317 47 50

Navajo 378 51 60

Powell 1,850 26 30

Water Year 2021

Preliminary Observed Unregulated Inflow

as of October 11, 2021

Reservoir

Unregulated 

Inflow

(kaf)

1981-2010

Percent 

of Avg

1991-2020

Percent 

of Avg

Fontenelle 561 52 52

Flaming 

Gorge 650 45 46

Blue Mesa 518 54 57

Navajo 403 37 44

Powell 3,502 32 36

7
Lake Powell Unregulated Inflow Chart

8
Most Probable August Forecast

Water Year 2022

April – July 2022

Forecasted Unregulated Inflow

as of October 4, 2021

Reservoir

Unregulated 

Inflow

(kaf)

1981-2010

Percent 

of Avg

1991-2020

Percent 

of Avg

Fontenelle 575 79 78

Flaming 

Gorge 732 75 76

Blue Mesa 550 81 86

Navajo 518 70 82

Powell 5,170 72 81

Water Year 2022

Forecasted Unregulated Inflow 

as of October 4, 2021

Reservoir

Unregulated 

Inflow

(kaf)

1981-2010

Percent 

of Avg

1991-2020

Percent 

of Avg

Fontenelle 830 77 77

Flaming 

Gorge 1,070 74 76

Blue Mesa 760 80 84

Navajo 705 66 77

Powell 7,400 68 77

9
Upper Colorado 

Basin

Projected Operations 

for Water Year 2022 

Based on October 

2021 Modeling

10
2021 DROA Timeline of Events

• January 2021: Minimum Probable 24 Month Study run projected 

Powell below 3,525’ 

• Formal notification to parties

• Enhanced monitoring and coordination 

• Monthly analysis of min/most/max 

• May 2021: Most Probable 24 Month Study run projected Powell 

within inches of 3,525’ 

• DROA planning formally initiated

• July 2021: Continued declining hydrology and declining Powell

• Consultation and initiation of DROA releases under emergency provision of agreement

11
Upper Basin DROA Initial Unit Drought Response 

Releases that started in July 2021

• July WY2021 forecast decreased 

140 kaf from the June forecast

• Continued drought conditions 

exacerbated already parched soil 

moisture conditions

• WY2022 most probable forecast 

decreased 1.84 maf (17%)

• Prospects of future monsoon 

events unknown

Jul Aug Sep Oct Nov Dec

(kaf) (kaf) (kaf) (kaf) (kaf) (kaf) Sum

Flaming Gorge 13 42 43 27 0 0 125

Blue Mesa 0 14 18 4 0 0 36

Navajo 0 0 0 0 10 10 20

Sum: 13 56 61 31 10 10 181

DROA Releases for the July 24MS Model Run

12
Lake Powell & Lake Mead Operational Table

Operating Determinations for Water Year/Calendar Year 2022

3,535.40 ft

Jan 1, 2022

Projection

1,065.85 ft

Jan 1, 2022

Projection

13 1 Lake Powell and Lake Mead operating determinations are based on August 2021 24-Month Study projections consistent with the 2007 Interim Guidelines 

and 2019 Drought Contingency Plans. These determinations will be documented in the 2022 Annual Operating Plan for Colorado River Reservoirs.
Potential Lake Powell Monthly Release 

Distribution for Water Year 2022

14
Lake Powell End of Month Elevations Chart

Most Probable End of CY 2021 

Projection: 3536.62 feet (27% full)

Min/Max Range: 3536.01 to 3538.59 

feet

Most Probable End of CY 2021 

Projection: 3537.26 feet (28% full)

Min/Max Range: 3496.56 to 3614.20 

feet

15
Lake Powell Probabilistic End of Month Elevations Chart

16
Lake Mead water shortages

17

The Secretary of the Interior will take affirmative actions to implement programs designed to create or conserve 100,000 acre-ft per annum or more 

of Colorado River System water to contribute to conservation of water supplies in Lake Mead and other Colorado River reservoirs in the lower basin. 

All actions taken by the United States shall be subject to applicable law, including availability of appropriations. 
Lake Mead End of Month Elevations

Lake Mead End of Month Elevations 

Projections from the September 2021 24-Month Study Inflow Scenarios

Most Probable End of CY 2022 

Projection: 1,050.68 feet (30% full)

Min/Max Range: 1,047.90 to 1,061.19 feet

Most Probable End of CY 2021 Projection: 

1,066.09 feet (34% full)

Min/Max Range: 1,065.82 to 1,066.76 feet

18
Lake Mead Probabilistic End of Month Elevations Chart

19
Upper Colorado Basin

Hydropower 

Maintenance

20
Glen Canyon Dam Power Plant Unit Outage Schedule for 2021

21
Glen Canyon Dam Power Plant Unit Outage Schedule for 2022

22
Glen Canyon Dam Hourly Release Pattern September 

2021

23
Glen Canyon Dam Hourly Release Pattern October 2021

24
Glen Canyon Dam Hourly Release Pattern November 2021

25
Glen Canyon Dam Hourly Release Pattern December 2021

26
Water Quality

27
Water quality profiles of the San Juan Arm, temperature and 

DO Sept. 2021

28
Water quality profiles of the Escalante Arm temperature and DO

Sept. 2021

29
Lake Powell temperature profiles by year in Sept. 2019-2021

30
Lake Powell forebay temperature profiles and elevations from 

2000 to 2021.

31
Lake Powell projected temperature releases @ 6 months

32
Lake Powell projected temperature releases @12 months

33
Historic Projected

> 16 C HBC Spawn

> 12 C HBC Growth

34

Projected Water Temperatures in Grand Canyon 2021
Lake Powell September DO profiles for 2019-2021

35
Lake Powell release DO levels for 2019-2021

36
Daily temperature and DO values for September releases at GCD

37
15-min Temperature and DO data for 9/20-10/4 releases at GCD

38
Lake Powell forebay DO profiles and elevations from 2000 to 2021

39
Tributary flow data and precip data showing monsoonal events

40
Photograph looking towards Lake Powell showing a cut through 

the delta at Cha.

41
Photograph looking up the delta at Cha showing the channel cut.

42
Questions?

43