Glen Canyon Dam
(Last Updated: November 15, 2018)
The Department of the Interior completed a High Flow Experiment from Glen Canyon Dam in November 2018. High Flow Experiments (HFE) below Glen Canyon Dam are driven by weather, sediment inputs, and other resource conditions, in accordance with the Long-Term Experimental and Management Plan (LTEMP). The HFE began on November 5, 2018, for a duration of 60 hours with flows surrounding the HFE fluctuating between 6,500 and 9,000 cfs during the evening and daylight hours for hydropower.
The April to July 2018 unregulated inflow to Lake Powell was 2.6 maf (36 percent of average). The unregulated inflow in October was 351 thousand acre-feet (kaf) (69 percent of average). October precipitation in the Upper Colorado Basin was 135 percent of average, but the extremely dry soil conditions decreased the amount of observed runoff. The release volume from Glen Canyon Dam in October was 625 kaf. The end of October elevation and storage of Lake Powell were 3,590.46 feet (110 feet from full pool) 10.86 maf (45 percent of full capacity).
The HFE will not impact the total annual amount of water released from Lake Powell to Lake Mead in water year 2019. Releases, both before and after the November experiment and throughout the remainder of the water year, will be adjusted to compensate for the higher volume released during this high flow experiment.
To view the most current reservoir elevation projections, click on: Lake Powell Elevation Projections.
To view the 2018 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 2019 was established in August 2018 as the Upper Elevation Balancing Tier. As described in the Interim Guidelines, under balancing, the contents of Lake Powell and Lake Mead are to be balanced by the end of the water year, but not more than 9.0 maf and not less than 8.23 maf is to be released from Lake Powell. Under this Tier the initial annual water year release volume is 8.23 maf but there is potential for an April 2019 adjustment to equalization or balancing releases. Based on the current forecast, an April adjustment to balancing releases is projected and Lake Powell is currently projected to release 8.85 maf in water year 2019. This projection will be updated each month throughout the water year.
In November, the release volume will be approximately 657 kaf, with fluctuations anticipated between 6,500 cfs in the nighttime to about 9,000 cfs in the daytime and consistent with the Glen Canyon Dam, Record of Decision on LTEMP (dated December, 2016). The anticipated release volume for December is 740 kaf with daily fluctuations between approximately 8,415 cfs and 15,165 cfs.
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 1,200 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 28 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 2019 unregulated inflow to Lake Powell, issued on November 1, 2018, by the Colorado Basin River Forecast Center, projects that the most probable (median) unregulated inflow volume next year will be 7.5 maf (69 percent of average). There is significant uncertainty regarding next season’s snow pack development and resulting runoff into Lake Powell. The forecast ranges from a minimum probable of 4.6 maf (42 percent of average) to a maximum probable of 15.4 maf (142 percent of average). There is a 10 percent 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, the November 24-Month Study projects Lake Powell elevation will end water year 2019 near 3,583 feet with approximately 10.16 maf in storage (39 percent of capacity). Note that projections of elevation and storage for water year 2019 have significant uncertainty at this point in the season. Based on the current forecast, the November 24-Month Study projects Lake Powell elevation will end water year 2019 near 3,573.43 feet with approximately 9.39 maf in storage (39 percent of capacity). Note that projections of elevation and storage for water year 2019 have significant uncertainty at this point in the season. Projections of end of water year 2019 elevation and storage using the minimum and maximum probable inflow forecast from October 2018 are 3,556 feet (8.027 maf, 33 percent of capacity) and 3,636 feet (15.54 maf, 64 percent of capacity), respectively. Under these scenarios, there is a 10 percent chance that inflows will be higher, resulting in higher elevation and storage, and 10 percent chance that inflows will be lower, resulting in lower elevation and storage. The annual release volume from Lake Powell during water year 2019 is projected to be 8.922 maf under the most probable scenario, and 9.0 maf under the maximum probable inflow scenarios and 8.23 maf under the minimum probable inflow scenario.
Upper Colorado River Basin Hydrology
The Upper Colorado River Basin regularly experiences significant year to year hydrologic variability. During the 19-year period 2000 to 2018, 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 2000-2018 is the lowest 19-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.54 maf, or 79 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 2000-2018 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 2019 unregulated inflow to Lake Powell is projected to be 7.6 maf (70 percent of average).
At the beginning of water year 2019, total system storage in the Colorado River Basin was 28.01 maf (47 percent of 59.6 maf total system capacity). This is a decrease of 4.91 maf over the total storage at the beginning of water year 2018 when total system storage was 32.92 maf (55 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 47 percent of capacity at the beginning of water year 2019. Based on current inflow forecasts, the current projected end of water year total Colorado Basin reservoir storage for water year 2019 is approximately 25.47 maf (42 percent of total system capacity). The actual end of water year 2019 system storage may vary from this projection, primarily due to uncertainty regarding this season’s runoff and reservoir inflow.
Please contact the Operations Group via e-mail at ResourceMgr@usbr.gov for additional information.
Last Updated: 11/15/18