Last Updated: March 15, 2021
The unregulated inflow volume to Lake Powell during February was 201 thousand acre-feet (kaf) (51% of average). The release volume from Glen Canyon Dam in February was 675 kaf. The end of February elevation and storage of Lake Powell were 3571.46 feet (128 feet from full pool) and 9.64 million acre-feet (maf) (39 %o of live capacity), respectively.
The six-month period from April to December 2020 is one of the driest periods on record. Current conditions resemble 2002, 2012, 2013 and the beginning of 2018, four out of the five driest years on record.
To view the most current reservoir elevation projections, click on: Lake Powell Elevation Projections.
To view the most current monthly release projections, click on: Lake Powell Release Projections.
To view the 2021 progession of snowpack above Lake Powell, click on Lake Powell Snow Chart.
To view the current inflow forecast relative to past inflows, click on Lake Powell Inflow Forecast.
The operating tier for water year 2021 (September 2020 through October 2021) was established in August 2020 as the Upper Elevation Balancing Tier, consistent with Section 6.B of the Interim Guidelines. Consistent with Section 6.B of the Interim Guidelines, Lake Powell’s operations in water year 2021 will be governed by the Upper Elevation Balancing Tier. With an 8.23 maf release from Lake Powell in water year 2021, the February 2021 24-Month Study projects the end of water year elevation at Lake Powell to be below 3,575 feet, and the end of water year elevation at Lake Mead to be below 1,075 feet. Therefore, in accordance with Section 6.B.1 of the Interim Guidelines, the February 24-Month Study projects that 8.23 maf shall be released from Lake Powell in water year 2021.
In March, the release volume will be approximately 700 kaf, with fluctuations anticipated between about 8,589 cubic feet per second (cfs) in the nighttime to about 14,647 cfs in the daytime, and consistent with the Glen Canyon Dam, Record of Decision (dated December 2016). The anticipated release volume for April is 628 kaf.
The Glen Canyon Dam Planning and Implementation Team, by consensus, recommends a Spring Disturbance Flow be implemented at Glen Canyon Dam March 15 to 26, 2021. This event supports maintenance needs of the facility and advances research goals of the Glen Canyon Dam Adaptive Management Program.
Technical experts at the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center and Western Area Power Administration have coordinated with Reclamation operations and maintenance officials to design flow releases to optimize benefits for both dam maintenance and the aquatic ecosystem throughout Glen, Marble, and Grand Canyons while minimizing negative impacts to hydropower.
The proposed spring disturbance flow releases of 4,000 cubic feet per second for 5 days is needed to conduct maintenance on the apron of Glen Canyon Dam. This low flow will be followed by an increase in flow culminating in a peak discharge of approximately 20,150 cubic feet per second for 82 hours.
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 1,100 cfs above or below the hourly scheduled release rate. Under system normal 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 800 cfs) of generation capacity in reserve in order to respond to a system emergency even when generation rates are already high. System emergencies occur fairly 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 2021 unregulated inflow to Lake Powell, issued on March 3, 2021, by the Colorado Basin River Forecast Center, projects that the most probable (median) unregulated inflow volume this year will be 5.13 maf (47% of average).
There is significant uncertainty regarding next season’s snowpack development and resulting runoff into Lake Powell. Reclamation updates the minimum and maximum probable forecasts four times a year: January, April, August, and October. Under the January minimum probable 24-Month Study, the forecast projected Lake Powell’s water surface elevation to fall below 3,525 feet in 2022. This model result initiates enhanced monitoring and coordination under the Agreement for Drought Response Operations at the Initial Units of the Colorado River Storage Project Act (Drought Response Operations Agreement “DROA”). This model result does not initiate operational changes to Reclamation facilities. The March minimum probable 24-Month Study continues to project elevations falling below the target elevation of 3,525 feet in 2022.
The Upper Division States and the Upper Colorado River Commission (UCRC) enhanced monitoring and coordination will involve a monthly meeting communicating monthly model results from the minimum, most, and maximum projected operations. Please note that 90% of the suite of results are expected to be above the minimum probable projections and there is currently a 10% expectation to be below elevation 3525 feet under the minimum probable scenario.
The minimum probable 24-Month Study will continue showing operations under the Lower Elevation Balancing Tier (LEBT) that is pursuant to the 2007 Record of Decision on the Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations of Lake Powell and Lake Mead (Interim Guidelines).
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.
The March forecast for water year 2021 ranges from a minimum probable of 3.49 maf (32% of average) to a maximum probable of 8.05 maf (74% of average). There is a 10% chance that inflows could be higher than the current maximum probable forecast and a 10% chance that inflows could be lower than the minimum probable forecast.
Based on the current forecast of 5.13 maf unregulated inflow, the March 24-Month Study projects Lake Powell elevation will end water year 2021 near 3,557.03 feet with approximately 8.10 maf in storage (33% of capacity). Note that projections of elevation and storage for water year 2021 have significant uncertainty at this point in the season. Projections of end of water year 2021 elevation and storage using the minimum and maximum probable inflow forecast from and results from the March 2021 DROA model runs are 3,543.92 feet (7.16 maf, 29% of capacity) and 3,578.99 feet (9.85 maf, 41% of capacity), respectively. Under these scenarios, there is a 10% chance that inflows will be higher, resulting in higher elevation and storage, and 10% chance that inflows will be lower, resulting in lower elevation and storage. The annual release volume from Lake Powell during water year 2021 is projected to be 8.23 maf under the March minimum and most probable inflow scenarios and 8.60 maf in the maximum probable scenario.
Upper Colorado River Basin Hydrology
Upper Colorado River Basin regularly experiences significant year to year hydrologic variability. During the 21-year period 2000 to 2020, however, the unregulated inflow to Lake Powell, which is a good measure of hydrologic conditions in the Colorado River Basin, was above average in only 4 out of the past 19 years. The period 2000-2020 is the lowest 21-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.62 maf, or 80 percent of the 30-year average (1981-2010). (For comparison, the 1981-2010 total water year average is 10.83 maf.) The unregulated inflow during the 2000-2020 period has ranged from a low of 2.64 maf (24 percent of average) in water year 2002 to a high of 15.97 maf (147 percent of average) in water year 2011. In water year 2018 unregulated inflow volume to Lake Powell was 4.6 maf (43 percent of average), the third driest year on record above 2002 and 1977. Under the current most probable forecast, the total water year 2021 unregulated inflow to Lake Powell is projected to be 5.13 maf (47 percent of average).
At the beginning of water year 2021, total system storage in the Colorado River Basin was 28.88 maf (48 percent of 59.6 maf total system capacity). This is a decrease of 2.77 maf over the total storage at the beginning of water year 2020 when total system storage was 31.64 maf (53 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 now current level of 48 percent of capacity at the beginning of water year 2021. Based on current inflow forecasts, the current projected end of water year total Colorado Basin reservoir storage for water year 2021 is approximately 24.81 maf (42 percent of total system capacity). The actual end of water year 2021 system storage may vary from this projection, primarily due to uncertainty regarding this season’s runoff and reservoir inflow.