TWG

Basin Hydrology and Operations

October 14, 2020
Upper Colorado Basin

Water Year 2020 

Observed Hydrology 

and Projected October 

Hydrology

2
Upper Basin Storage (as of October 12, 2020)

3

Reservoir Percent 

Full

Storage

(maf)

Elevation

(feet)

Fontenelle 72 0.247 6,492.93

Flaming 

Gorge 85 3.18 6,025.55

Blue Mesa 50 0.417 7,467.24

Navajo 66 1.12 6,041.02

Lake Powell 46 11.22 3,594.34
WY2020 Precipitation and Observed Inflow

4

1 Percent of average based on the period of record from 1981-2010.

Reservoir

Unregulated 

Inflow

(kaf)

Percent of 

Average1

Fontenelle 997 92

Flaming Gorge 1,250 81

Blue Mesa 608 64

Navajo 430 40

Powell 5,847 54

as of October 1, 2020

Water Year 2020

Observed Unregulated Inflow
5
Seasonal Precipitation and WY2021 Forecast

6

1 Percent of average based on the period of record from 1981-2010.

Reservoir

Unregulated 

Inflow

(kaf)

Percent of 

Average1

Fontenelle 890 82

Flaming Gorge 1,115 77

Blue Mesa 755 84

Navajo 705 66

Powell 7,900 73

as of October 1, 2020

Water Year 2021

Forecasted Unregulated Inflow
7
Upper Colorado Basin

Projected Operations 

for Water Year 2021 

Based on September 

2020 Modeling

8
9
Powell Release Scenario

10
11
12
13

Most Probable End of WY 2022 Projection: 

3,595.04 feet (46% full)

Min/Max Range: 3,558.38 to 3,660 feet

Most Probable End of WY 2021 Projection: 

3,584.12 feet (39% full)

Min/Max Range: 3,567.54 to 3,656.19 feet
Lake Mead End of Month Elevations 

Projections from the August and September 2020 24-Month Study Inflow Scenarios

14

Most Probable End of CY 2020 Projection: 

1,085.16 feet (40% full)

Min/Max Range: 1,084.87 to 1,086.34 feet

Most Probable End of CY 2021 Projection: 

1,086.70 feet (40% full)

Min/Max Range: 1,067.28 to 1,086.70 feet

Most Probable End of WY 2022 Projection: 

1,083.62 feet (40% full)

Min/Max Range: 1,048.09 to 1,115.95 feet
Maintenance Schedule WY2021 Unit Number Oct 

2020

Nov 

2020

Dec 

2020

Jan 

2021

Feb 

2021

Mar 

2021

Apr 

2021

May 

2021

Jun 

2021

Jul 

2021

Aug 

2021

Sep 

2021

1

2

3

4

5

6

7

8

Units Available 5 6/5 6 6 6 6 6 6 6 6 6 6/4

Capacity (cfs) 16,500 20,100

/16,400 20,000 19,900 19,800 19,600 19,500 19,500 19,700 20,100 20,000 19,900/12,600

Capacity 

(kaf/month) 1,110 1,200 1,260 1,230 1,110 1,230 1,230 1,270 1,270 1,320 1,350 1,110

Max (kaf) 2 640 640 720 760 680 710 640 630 660 750 800 600

Most (kaf) 1 640 640 720 860 750 800 710 710 740 870 890 690

Min (kaf) 2 640 640 720 760 680 710 640 630 660 750 800 600

15

Glen Canyon Power Plant Planned Unit Outage Schedule for Water Year 2021

(updated 09-21-2020)

15

1 Projected release, based on August 2020 Most Probable Inflow Projections and 24-Month Study model runs

2 Projected release, based on August 2020 Min and Max Probable Inflow Projections and 24-Month Study model runs

3 Dependent upon availability to shift reserves, which will increase capacity by 40MW at current efficiency. 

9.0

8.23

8.23

SEP 

MOST3

AUG 

MAX
16
17
18
Water Quality

19
Sand Budget Model Results – October 7, 2020

As of this week, not sufficient 

sediment to support an HFE.

20
21
7

8

9

10

11

12

13

14

15

16

17

Temperature, °C

Lake Powell Release Temperature 

Projected Temperature based on September 2020 Forecast

Sept 2020 Most Probable Hydrology Aug 2020 Min Probable Hydrology Aug 2020 Max Probable Hydrology

Monthly average Temp LF Monthly average Temp CRBD

#Projection start date is based on initial conditions (Dec 2019)

Historic Projected

22
23
24

Upper Colorado Basin

Statistical Out-Year 

Update to 24-Month 

Study
24-Month Study Mode MTOM Mode

Primary Use

AOP tier determinations 

and projections of current

conditions

Risk-based operational

planning and analysis

Probabilistic or 

Deterministic

Deterministic – single 

hydrologic trace

Probabilistic 35 (or more) 

hydrologic traces

Simulated Reservoir

Operations Operations input manually Rule-driven operations

Time Horizon 

(years)

Frequency of 

Publication Monthly Monthly

1 - 2 1 - 5

25

Integrated Mid-term Modeling System
26

Month 

Issued Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

Jan RFC RFC RFC

Official 

A-J

Official 

A-J

Official 

A-J

Official 

A-J

ESP 

Jan

ESP 

Jan

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Feb RFC RFC RFC

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Mar RFC RFC RFC

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May RFC RFC RFC

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Jun RFC RFC RFC

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Nov RFC RFC RFC

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interpolateinterpolate

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Dec RFC RFC RFC

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interpolateinterpolate

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* Light grey text indicates that the model is run in this month, however, only results for the first 24 months of the model run (black text) are published in the 24 Month Study report

ESP monthly values are generated using the RFC ESP forecasted volume for the water year using the current month's initial hydrological conditions. The RFC provides monthly volumes consistent with the 3-month forecast and the water year ESP volume.

April-July 

Unregulated Inflow

Interpolated values are calculated by UCBOR and are based on percent of the 81-15 median. The method takes the precent of median of the previous month's forecast value and interpolates over two months to the percent of median for the 

month following the interpolation period. This is done to smoothly transition between the end of the current water year and the next water year. 

WY 2021 Source of Monthly Unregulated Inflow for Upper Colorado Reservoirs in the 24 Month Study

RFC values are issued by the Colorado Basin River Forecast Center (RFC) as the official forecast values for the next three-month period of time. The values are calculated using Ensemble Streamflow Predictions (ESP) modeling. This official forecast has the least 

amount of error associated with it. 

Official A-J values are official forecast values issued by the RFC for the April-July runoff period using ESP. Apr-Jul water supply forecast volume is disaggregated by the RFC. 

81-15 Med values are the monthly median inflow values generated from water years 1981-2015 calculated using the database maintained by the Bureau of Reclamation Upper Colorado Region (UCBOR). A water year begins October 1 and ends 

September 30.

Most Probable
27

Month 

Issued Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

Jan RFC RFC RFC

Coord 

A-J 

10th 

%ile

Coord 

A-J 

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%ile

Coord 

A-J 

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%ile

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A-J 

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%ile

interpolateinterpolate

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%ile of 

81-15

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%ile of 

81-15

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

81-15

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%ile of 

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%ile of 

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%ile of 

81-15

interpolateinterpolate81-15 

Med

Feb

Mar

Apr

Coord 

A-J 

10th 

%ile

Coord 

A-J 

10th 

%ile

Coord 

A-J 

10th 

%ile

Coord 

A-J 

10th 

%ile

interpolateinterpolate

25th 

%ile of 

81-15

25th 

%ile of 

81-15

25th 

%ile of 

81-15

25th 

%ile of 

81-15

25th 

%ile of 

81-15

25th 

%ile of 

81-15

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%ile of 

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%ile of 

81-15

25th 

%ile of 

81-15

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%ile of 

81-15

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%ile of 

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%ile of 

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interpolateinterpolate81-15 

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81-15 

Med

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Med

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Med

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Med

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Med

May

Jun

Jul

Aug RFC RFC RFC

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

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%ile 

Aug 

ESP

10th 

%ile 

Aug 

ESP

10th 

%ile 

Aug 

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10th 

%ile 

Aug 

ESP

interpolateinterpolate

25th 

%ile of 

81-15

25th 

%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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25th 

%ile of 

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25th 

%ile of 

81-15

25th 

%ile of 

81-15

Sep

Oct RFC RFC RFC

10th 

%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

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%ile 

Oct 

ESP

10th 

%ile 

Oct 

ESP

interpolateinterpolate

25th 

%ile of 

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%ile of 

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25th 

%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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Nov

Dec

Interpolated values are calculated by UCBOR and are based on percent of the 81-15 median. The method takes the precent of average of the previous month's forecast value and interpolates over two months to the percent of 

median for the month following the interpolation period. This is done to smoothly transition between the end of the current water year and the next water year. 

10th %ile Jan/Apr/Aug/Oct ESP values are generated using the RFC ESP forecasted volume for the water year using the monthly initial hydrological conditions. Monthly values are disaggregated from the total water year ESP volume 

using the median 81-15 statistical monthly distribution, consistent with the 3-month forecast. ESP forecasts are issued for each month of the base flow period to the end of the current water year for the 24-month study. 

* Light grey text indicates that the model is run in this month, however, only results for the first 24 months of the model run (black text) are published in the 24 Month Study report

WY 2021 Source of Monthly Unregulated Inflow for Upper Colorado Reservoirs in the 24 Month Study

Minimum Probable

April-July 

Unregulated Inflow

RFC values are issued by the Colorado Basin River Forecast Center (RFC) as the official forecast values for the next three-month period of time. The values are calculated using Ensemble Streamflow Predictions (ESP) modeling. This official forecast 

has the least amount of error associated with it. 

Coord A-J 10th %ile values are the official forecast of the total April-July volume issued by the RFC for the April-July runoff period using SWS and ESP. Monthly values are disaggregated using the 81-15 average monthly distribution.

25th %ile of 81-15 values are the monthly 25th percentile (75% exceedance) inflow values generated from water years 1981-2015 calculated using the database maintained by the Bureau of Reclamation Upper Colorado Region 

(UCBOR). A water year begins October 1 and ends September 30.
28

Month 

Issued Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov

Jan RFC RFC RFC

A-J 

Coord 

90th 

%ile

A-J 

Coord 

90th 

%ile

A-J 

Coord 

90th 

%ile

A-J 

Coord 

90th 

%ile

interpolateinterpolate

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%ile of 

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%ile of 

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interpolateinterpolate81-15 

Med

Feb

Mar

Apr

A-J 

Coord 

90th 

%ile

A-J 

Coord 

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%ile

A-J 

Coord 

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%ile

A-J 

Coord 

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%ile

interpolateinterpolate

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%ile of 

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75th 

%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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interpolateinterpolate81-15 

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May

Jun

Jul

Aug RFC RFC RFC

90th 

%ile 

Aug 

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90th 

%ile 

Aug 

ESP

90th 

%ile 

Aug 

ESP

90th 

%ile 

Aug 

ESP

90th 

%ile 

Aug 

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90th 

%ile 

Aug 

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%ile 

Aug 

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%ile 

Aug 

ESP

90th 

%ile 

Aug 

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%ile 

Aug 

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90th 

%ile 

Aug 

ESP

interpolateinterpolate

75th 

%ile of 

81-15

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

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%ile of 

81-15

Sep

Oct RFC RFC RFC

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

90th 

%ile 

Oct 

ESP

interpolateinterpolate

75th 

%ile of 

81-15

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%ile of 

81-15

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%ile of 

81-15

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%ile of 

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%ile of 

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%ile of 

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%ile of 

81-15

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%ile of 

81-15

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%ile of 

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%ile of 

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Nov

Dec

Interpolated values are calculated by UCBOR and are based on percent of the 81-15 median. The method takes the precent of average of the previous month's forecast value and interpolates over two months to the percent of 

median for the month following the interpolation period. This is done to smoothly transition between the end of the current water year and the next water year. 

90th %ile Jan/Apr/Aug/Oct ESP values are generated using the RFC ESP forecasted volume for the water year using the monthly initial hydrological conditions. Monthly values are disaggregated from the total water year ESP 

volume using the median 81-15 statistical monthly distribution, consistent with the 3-month forecast. ESP forecasts are issued for each month of the base flow period to the end of the current water year for the 24-month study. 

* Light grey text indicates that the model is run in this month, however, only results for the first 24 months of the model run (black text) are published in the 24 Month Study report

WY 2021 Source of Monthly Unregulated Inflow for Upper Colorado Reservoirs in the 24 Month Study

Maximum Probable

April-July 

Unregulated Inflow

RFC values are issued by the Colorado Basin River Forecast Center (RFC) as the official forecast values for the next three-month period of time. The values are calculated using Ensemble Streamflow Predictions (ESP) modeling. This official forecast 

has the least amount of error associated with it. 

Coord A-J 90th %ile are the official forecast of the total April-July volume issued by the RFC for the April-July runoff period using ESP. Monthly values are disaggregated using the 81-15 median monthly distribution.

75th %ile of 81-15 values are the monthly 75th percentile (25% exceedance) inflow values generated from water years 1981-2015 calculated using the database maintained by the Bureau of Reclamation Upper Colorado Region 

(UCBOR). A water year begins October 1 and ends September 30.
Questions/Discussion

29