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October 24-Month Study

Date: October 13th 2023 

From: Water Resources Group, Salt Lake City

To: All Colorado River Annual Operating Plan (AOP) Recipients

Current Reservoir Status

September Inflow

(unregulated) 

(acre-feet)

Percent of 

Average

(percent)

Oct. 12 Midnight

Elevation (feet)

Oct. 12, Midnight

Reservoir Storage

(acre-feet)

Fontenelle 50,100 125 6498.67 278,511

Flaming Gorge 66,800 145 6029.43 3,243,137

Blue Mesa 26,100 74 7494.84 616,067

Navajo 600 2 6047.04 1,137,300

Powell 223,600 65 3573.16 8,758,440

Expected Operations

The operation of Lake Powell and Lake Mead in the October 2023 24-Month Study is pursuant to the

December 2007 Record of Decision on Colorado River Interim Guidelines for Lower Basin Shortages and

the Coordinated Operations of Lake Powell and Lake Mead (Interim Guidelines) and reflects the 2023

Annual Operating Plan (AOP). Pursuant to the Interim Guidelines, the August 2022 24-Month Study

projections of the January 1, 2023, system storage and reservoir water surface elevations set the

operational tier for the coordinated operation of Lake Powell and Lake Mead during 2023. 

Consistent with Section 2.D.1 of the Interim Guidelines, a Shortage Condition consistent with Section

2.D.1.b is governing the operation of Lake Mead for calendar year (CY) 2023. In addition, Section III.B of

Exhibit 1 to the Lower Basin Drought Contingency Plan (DCP) Agreement will govern the operation of

Lake Mead for CY 2023. Efforts to conserve additional water in Lake Mead under a 2021 Lower Basin

Memorandum of Understanding (MOU) to facilitate near-term actions to maintain the water surface 

elevation of Lake Mead and additional conservation efforts under the Lower Colorado River Basin System

Conservation and Efficiency Program (LC Conservation Program) will also take place in CY 2023.

The August 2023 24-Month study projected the January 1, 2024, Lake Powell elevation to be less than

3,575 feet and at or above 3,525 feet and the Lake Mead elevation to be at or above 1,025 feet. Consistent

with Section 6.C.1 of the Interim Guidelines the operational tier for Lake Powell in water year (WY) 2024 

will be the. Mid-Elevation Release Tier and the water year release volume from Lake Powell will be 7.48

million acre-feet (maf). 

The 2022 Drought Response Operations Agreement (DROA) Plan1 for May 2022 through April 2023 was

amended to suspend 2022 DROA Plan releases as of March 7, 2023. A total DROA release of

1 For more information: https://www.usbr.gov/uc/DocLibrary/Plans/20220429-2022DroughtResponseOperationsPlanApprovalMemo-508-DOI.pdf. 
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approximately 463 thousand acre-feet (kaf) occurred under the 2022 DROA Plan. Reclamation will attempt

to maximize DROA recovery in the Upper Initial Units in WY 2023 and through April 2024. Reclamation

will provide monthly DROA accounting, including DROA releases and recovery, which can be found online 

at: https://www.usbr.gov/dcp/DROSummarySheet.pdf. 

In May of 2023, the DROA Parties agreed to the 2023 DROA Plan. The 2023 DROA Plan does not include

any DROA releases, but rather provides for recovery of prior DROA releases from the units upstream of

Powell.

Reclamation will continue to carefully monitor hydrologic and operational conditions and assess the need

for additional responsive actions and/or changes to operations. Reclamation will continue to consult with

the Basin States, Basin Tribes, Mexico, and other partners on Colorado River operations to consider and

determine whether additional measures should be taken to further enhance the preservation of these

benefits, as well as recovery protocols, including those of future protective measures for both Lakes

Powell and Mead. 

The August 2023 24-Month Study projected the January 1, 2024 Lake Mead elevation to be below 1,075

feet and above 1,050 feet. Consistent with Section 2.D.1 of the Interim Guidelines, a Shortage Condition

consistent with Section 2.D.1.a will govern the operation of Lake Mead for CY 2024. In addition, Section

III.B of Exhibit 1 to the Lower Basin DCP Agreement will also govern the operation of Lake Mead for CY

2024. Lower Basin projections for Lake Mead take into consideration updated water orders to reflect

additional conservation efforts under the LC Conservation Program.

The 2024 operational tier determinations for Lake Powell and Lake Mead will be documented in the 2024 

AOP, which is currently in development.

Current runoff projections into Lake Powell are provided by the National Weather Service’s Colorado Basin

River Forecast Center. The observed unregulated inflow into Lake Powell for the month of September was 

0.224 maf or 65% of the 30-year average from 1991 to 2020. The October 2023 unregulated inflow

forecast for Lake Powell is 0.400 maf or 88% of the 30-year average. The observed 2023 April through July

unregulated inflow is 10.62 maf or 166% of average. The preliminary observed WY 2023 unregulated 

inflow is 13.42 maf or 140% of average.

The draft 2024 AOP is available online at:

https://www.usbr.gov/lc/region/g4000/AOP2024/AOP24_draft.pdf

The 2023 AOP is available online at:

https://www.usbr.gov/uc/water/rsvrs/ops/aop/AOP23.pdf. 

The Interim Guidelines are available online at:

https://www.usbr.gov/lc/region/programs/strategies/RecordofDecision.pdf. 

The Colorado River DCPs are available online at:

https://www.usbr.gov/dcp/finaldocs.html. 

The 2021 Lower Basin MOU is available online at: 

https://www.usbr.gov/lc/region/g4000/2021_MOU.pdf. 

The Upper Basin DROA is online at:

https://www.usbr.gov/dcp/droa.html. 

The Upper Basin Hydrology Summary is available online at:

https://www.usbr.gov/uc/water/crsp/studies/24Month_10_ucb.pdf. 

Information on the LC Conservation Program is available online at: 
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https://www.usbr.gov/lc/LCBConservation.html. 

Fontenelle Reservoir 

As of October 02, 2023, the Fontenelle Reservoir pool elevation is 6499.40 feet, which amounts to 85 

percent of live storage capacity. Inflows for the month of September totaled approximately 51,177 acrefeet (af) or 128 percent of average. 

Current release rate is set at 1,100 cfs. Winter base flow release will be set in mid-November after 

receiving the November forecasts. Winter base flow will be set to a constant release rate from midNovember to approximately mid-March, depending on winter icing conditions. Pending hydrology, 

winter releases will be approximately 1,150 cfs. 

The October final forecast for unregulated inflows into Fontenelle for the next three months projects near 

average conditions. October, November, and December Most Probable inflow volumes amount to 50,000 

af (111 percent of average), 45,000 af (107 percent of average), and 35,000 af (109 percent of average), 

respectively.

The next Fontenelle Working Group meeting is April 18, 2024 at 10 AM MDT and location is pending. 

Details on the meeting will be provided as we get closer to the meeting date. Prior Fontenelle Working 

Group meeting minutes are available online on USBR’s website at 

https://www.usbr.gov/uc/water/crsp/wg/ft/ftcurrnt.html. The Fontenelle Working Group is an open public 

forum for information exchange between Reclamation and other parties associated with the operation of 

Fontenelle Reservoir.

Flaming Gorge Reservoir

As of October 3, 2023 (end of day), Flaming Gorge Reservoir pool elevation is 6029.67 feet, which 

amounts to 89 percent of live storage capacity. Unregulated inflow volume for the month of September is 

approximately 67,000 af, which is 145 percent of the average September unregulated inflow volume. 

Current average daily releases are approximately 1,700 cfs. 

Flaming Gorge Dam operations are in an average hydrologic classification for the month of October and 

are projected to remain in the average hydrologic classification through the remainder of the base flow 

period. The summer base flow period ended on September 30, 2023. The autumn average daily release 

decreased from 1,960 cfs to 1,700 cfs and remains within the average hydrologic classification range of 

1,500 cfs to 2,400 cfs in Reach 2, measured at the Jensen USGS Gage. This data is considered the most 

likely scenario given the current forecast, is general, and is subject to changing conditions.

The October unregulated inflows into Flaming Gorge for the next three months projects near average. 

October, November, and December forecasted unregulated inflow volumes amount to 60,000 af (113 

percent of average), 56,000 af (113 percent of average), and 39,000 af (118 percent of average), 

respectively.

Reclamation is planning to hold Flaming Gorge Working Group meetings tentatively on March 21, 2024 

and April 17, 2024, at 10:00 am (and Teams virtual meeting). The location is TBD. The Flaming Gorge 

Working Group is an open public forum for information exchange between Reclamation and the 

stakeholders of Flaming Gorge Dam. The public is encouraged to attend and comment on the operations 
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and plans presented by Reclamation at these meetings. Meeting notes from past Working Group 

meetings are posted on the Working Group webpage. For more information on this group and these 

meetings please contact Alex Pivarnik at (385) 475 – 8329.

Aspinall Unit Reservoirs

As of September 10, 2023, releases from Crystal Dam are approximately 1,750 cfs. Flows of the Gunnison 

River in the Black Canyon are being maintained at about 690 cfs while the Gunnison Tunnel is diverting 

1,045 cfs. Flows in the Whitewater Reach of the Gunnison River are about 1,570 cfs.

The unregulated inflow volume in September to Blue Mesa was 26,100 af (86 percent of average). 

Unregulated Inflow volumes forecasted for Blue Mesa for the next three months (October, November and 

December) are projected to be: 29,000 af (78 percent of average), 28,000 af (93 percent of average) and 

26,000 af (104 percent of average), respectively. The October 24-Month Study will be reflective of these 

new forecasted inflows.

The forecasted 2024 water year unregulated inflow volume to Blue Mesa is projected to be 845,000 af (93 

percent of average). The water supply period (April-July) for 2024 is forecasted currently for an 

unregulated inflow volume of to be 595,000 af of unregulated inflow (94 percent of average).

Blue Mesa elevation has increased dramatically between April and the end of June in water year 2023. On 

April 9, 2023 the elevation of Blue Mesa was 7444.46 feet above sea level and Blue Mesa was 36.3% full. 

On June 25, 2023, the elevation of Blue Mesa reached its peak for the year at 7512.47 feet above sea level 

and Blue Mesa storage reached 92 4% of full. Blue Mesa ended water year 2023 (September 30, 2023) at 

an elevation of 7496.50 feet with about 629,478 acre-feet of storage which was 76 percent of capacity.

The Aspinall Unit Operations Group is an open public forum for information exchange between 

Reclamation and the stakeholders of the Aspinall Unit. The public is encouraged to attend and comments 

on the operations and plans presented by Reclamation at these meetings. Meeting notes from past 

working Group meetings are posted on the Operations Group webpage. For more information on this 

group and these meetings please contact Erik Knight in the Grand Junction Area Office at (970) 248-0629.

The next Operations Group meeting will be held January 18, 2024 at 1:00 p.m., in person in Montrose 

Colorado. This will be an in-person meeting with an option for remote participation. Contact Erik Knight 

in the Grand Junction Area Office at (970) 248-0629 to get more information regarding this Operation 

Group meeting.

Navajo Reservoir

On October 2nd the daily average release rate from Navajo Dam was 564 cfs while reservoir inflow was 

averaging 375 cfs. The water surface elevation was 6047.70 feet above sea level. At this elevation the live 

storage is 1.14 maf (69 percent of live storage capacity) and the active storage is 519 maf (51 percent of 

active storage capacity). An average of 178 cfs is currently being diverted to Cutter Reservoir for the 

Navajo Indian Irrigation Project (NIIP). Due to streamflows below minimum bypass, 0 cfs is being diverted 

to the San Juan-Chama Project (SJC) above Navajo Reservoir. So far this calendar year, NIIP has diverted

190 kaf and SJC has diverted 142 kaf.
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Releases from Navajo Dam are made for authorized purposes of the Navajo Unit and are pursuant to the 

Record of Decision for the Navajo Reservoir Operations. Releases target the San Juan River Recovery 

Implementation Program's (SJRIP) recommended downstream baseflow range of 500 cfs to 1,000 cfs 

through the critical habitat reach of the San Juan River (Farmington, NM to Lake Powell).

Preliminary modified unregulated inflow (MUI) into Navajo in September was 0.4 kaf (1 percent of 

average). The release averaged 690 cfs and totaled 42.3 kaf, which was 87 percent of average for the 

month. The release averaged 770 cfs (according to USGS at Archuleta) and totaled 45.9 kaf, which was 

102 percent of average for the month. Of that total release, 5.3 kaf was part of the Jicarilla Apache 

Nation's subcontractor's project water release request (New Mexico State Interstate Stream Commission 

and The Nature Conservancy).

The total April-July modified unregulated inflow into Navajo in WY 2023 was 1.028 maf (164 percent of 

average). Total Modified Unregulated Inflow into Navajo for WY 2023 was 1.218 maf (134 avg). Total 

downstream release was 564 kaf (92 percent of avg).

The most probable MUI forecast for October, November, and December is 15 kaf (39 percent of average), 

25 kaf (93 percent of average), and 20 kaf (97 percent of average), respectively.

Reclamation conducts Public Operations Meetings three times per year to gather input for determining 

upcoming operations for Navajo Reservoir. Input from individuals, organizations, and agencies along with 

other factors such as weather, water rights, endangered species requirements, flood control, hydro power, 

recreation, fish and wildlife management, and reservoir levels, will be considered in the development of 

these reservoir operation plans. In addition, the meetings are used to coordinate activities and exchange 

information among agencies, water users, and other interested parties concerning the San Juan River and 

Navajo Reservoir. The next meeting will be held on Tuesday, January 16th 2024 at 1:00 PM. This meeting is 

open to the public, and will be held at the Farmington Civic Center, 200 West Arrington, in Farmington, 

New Mexico (subject to change based on guidance at the time). The meeting will also have a virtual 

option.

Glen Canyon Dam / Lake Powell 

Current Status

The unregulated inflow volume to Lake Powell during September was 224 kaf (65 percent of average). 

The release volume from Glen Canyon Dam in September was 474 kaf. The end of September elevation 

and storage of Lake Powell were 3,573.58 feet (126 feet from full pool) and 8.79 maf (38 percent of live 

capacity), respectively. 

Current Operations

The August 2023 24-Month study projects the January 1, 2023, Lake Powell elevation to be less than 3,575 

feet and at or above 3,525 feet and the Lake Mead elevation to be at or above 1,025 feet. Consistent with 

Section 6.C.1 of the Interim Guidelines the operational tier for Lake Powell in water year 2024 is the MidElevation Release Tier and the water year release volume from Lake Powell is 7.48 maf. 

October release volume will be 480,000 acre-feet and hourly releases will fluctuate from a low of 

approximately 5,000 cubic feet per second (cfs) during the early morning hours to a high of 9,320 cfs 
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during the afternoon and evening hours. The anticipated monthly release volume for November is 

anticipated to be 500,000 acre-feet and will be confirmed toward the end of October.

In addition to daily scheduled fluctuations for power generation, the instantaneous releases from Glen 

Canyon Dam may also fluctuate to provide 40 megawatts (MW) of system regulation. These 

instantaneous release adjustments stabilize the electrical generation and transmission system and 

translate to a range of about 1,300 cfs above or below the hourly scheduled release rate. Under normal 

system conditions, fluctuations for regulation are typically short lived and generally balance out over the 

hour with minimal or no noticeable impacts on downstream river flow conditions.

Releases from Glen Canyon Dam can also fluctuate beyond scheduled releases when called upon to 

respond to unscheduled power outages or power system emergencies. Depending on the severity of the 

system emergency, the response from Glen Canyon Dam can be significant, within the full range of the 

operating capacity of the power plant for as long as is necessary to maintain balance in the transmission 

system. Glen Canyon Dam currently maintains 30 MW (approximately 1,300 cfs) of generation capacity in 

reserve in order to respond to a system emergency even when generation rates are already high. System 

emergencies occur infrequently and typically require small responses from Glen Canyon Dam. However, 

these responses can have a noticeable impact on the river downstream of Glen Canyon Dam.

Inflow Forecasts and Model Projections

The forecast for water year 2024 unregulated inflow to Lake Powell, issued on October 2, 2023, by the 

Colorado Basin River Forecast Center, projects that the most probable (median) unregulated inflow 

volume in water year 2024 will be 9.40 maf (98 percent of average). 

In addition to the October 2023 24-Month Study based on the Most Probable inflow scenario, and in 

accordance with the Upper Basin Drought Response Operations Agreement (DROA), Reclamation has 

conducted model runs in October to determine a possible range of reservoir elevations. The October 2023 

24-Month Study probable most, minimum and maximum probable inflow scenarios were used to 

determine the range of probable outcomes. The probable minimum and probable maximum model runs 

are conducted simultaneously in January, April, August, and October, or when necessary to incorporate 

changing conditions. The probable minimum inflow scenario reflects a dry hydrologic condition which 

statistically would be exceeded 90 percent of the time. The most probable inflow scenario reflects a 

median hydrologic condition which statistically would be exceeded 50 percent of the time. The probable 

maximum inflow scenario reflects a wet hydrologic condition which statistically would be exceeded 10 

percent of the time. There is approximately an 80 percent probability that a future elevation will fall inside 

the range of the minimum and maximum inflow scenarios. Additionally, there are possible inflow 

scenarios that would result in reservoir elevations falling outside the ranges indicated in these reports. 

The DROA coordination will continue until either (i) the minimum probable projected elevation remains 

above 3,525 feet for 24 months or (ii) the process moves to the next step when the most probable 

projected elevation indicates Powell elevations below 3,525 feet and a Drought Response Operations Plan 

is developed. This current Plan is described above and available for review here: 

https://www.usbr.gov/dcp/droa.html. 

The October forecast for WY 2024 ranges from a minimum probable of 6.00 maf (62% of average) to a 

forecasted October 24-Month Study maximum probable of 17.60 maf (183 percent of average) with the 

most probable forecast for water year 2024 of 9.40 maf (98 percent of average). There is a 10 percent 
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chance that inflows could be higher than the current maximum probable forecast and a 10 percent chance 

that inflows could be lower than the minimum probable forecast.

Based on the current forecast for water year 2024 of 9.40 maf unregulated, the October 24-Month Study 

projects Lake Powell elevation will end calendar year 2024 near 3582.86 feet with approximately 9.52 maf 

in storage (41 percent of capacity). Note that projections of elevation and storage for calendar year 2024 

have significant uncertainty at this point in the season. Projections of end of calendar year 2024 elevation 

using the October minimum and maximum inflow forecast results are 3,549.44 feet and 3,657.44 feet, 

respectively. The annual release volume from Lake Powell during water year 2024 is 7.48 maf under the 

Mid-Elevation Release Tier as determined under Section 6.C.1 of the Interim Guidelines as determined by 

the Department of the Interior as described above.

Upper Colorado River Basin Hydrology 

Upper Colorado River Basin regularly experiences significant year to year hydrologic variability. The 30-

year average was updated in October 2022 from 1981 through 2010 to 1991 through 2020. Shifting the

period of record decreased the average unregulated inflow 1.20 maf. The period 2000-2022 is the lowest 

23-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.29 

maf, or 93 percent of the 30-year average (1991-2020). (For comparison, the 1991-2020 total water year 

average is 9.60 maf.) The unregulated inflow during the 2000-2022 period has ranged from a low of 2.64 

maf (28 percent of average) in water year 2002 to a high of 15.97 maf (166 percent of average) in water 

year 2011. In water year 2021 unregulated inflow volume to Lake Powell was 3.50 maf (36 percent of 

average), the second driest year on record above 2002. Under the current most probable forecast, the 

total water year 2024 unregulated inflow to Lake Powell is projected to be 9.40 maf (98 percent of 

average).

At the beginning of water year 2024, total system storage in the Colorado River Basin was 25.27 maf (43 

percent of 58.48 maf total system capacity). This is an increase of 5.72 maf over the total storage at the 

beginning of water year 2023 when total system storage was 19.55 maf (33 percent of capacity). Since the 

beginning of water year 2000, total Colorado Basin storage has experienced year to year increases and 

decreases in response to wet and dry hydrology, ranging from a high of 94 percent of capacity at the 

beginning of 2000 to the beginning of water year 2023 with 19.55 maf (33 percent of capacity). Based on 

current inflow forecasts, the current projected end of water year 2024 total Colorado Basin reservoir 

storage is approximately 25.84 maf (44.2 percent of total system capacity). The actual end of water year 

2024 system storage may vary from this projection, primarily due to uncertainty regarding this season’s 

runoff and reservoir inflow.