Glen Canyon Dam / Lake Powell
The unregulated inflow volume to Lake Powell in June was 3,039 thousand acre-feet (kaf) (114% of average). The release volume from Glen Canyon Dam in June was 598 kaf. The end of June elevation and storage of Lake Powell were 3,609.2 feet (91 feet from full pool) and 12.65 million acre-feet (maf) (52% of full capacity), respectively. The reservoir elevation is nearing its seasonal peak and will begin decreasing as inflow from spring runoff transitions to baseflows.
To view the most current reservoir elevation, content, inflow and release, click on: Lake Powell Data.
To view the most current reservoir elevation projections, click on: Lake Powell Elevation Projections.
To view this season's progession of snowpack above Lake Powell, click on Lake Powell Snow Chart.
The operating tier for water year 2014 is the Mid-Elevation Release Tier with an annual release volume of 7.48 maf, as established in August 2013 and pursuant to the Interim Guidelines, Section 6.C.1. Reclamation will schedule operations at Glen Canyon Dam to achieve as practicably as possible a 7.48 maf annual release by September 30, 2014.
In July, the release volume will be approximately 800 kaf, with fluctuations between about 10,000 cfs in the nighttime to about 18,000 cfs in the daytime and consistent with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997). In August, the release volume will likely be approximately 800 kaf with daily fluctuations between about 9,000 cfs and 17,000 cfs. The anticipated release volume for September is about 600 kaf with fluctuations between approximately 7,000 cfs and 13,000 cfs.
In addition to daily scheduled fluctuations for power generation, the instantaneous releases from Glen Canyon Dam may also fluctuate to provide 40 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 typically maintains 41MW (approximately 1,200 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 the 2014 April to July water supply season for Lake Powell, issued on July 1, 2014, by the Colorado Basin River Forecast Center, projects that the most probable (median) unregulated inflow volume will be 7.09 maf (99% of average based on the period 1981-2010). The April-July most probable forecast decreased by 460 kaf since last month. The seasonal snowpack peaked on April 7, 2014 at 111% of median and now all of the measurable snowpack has now melted.
Based on the current forecast, the July 24-Month study projects Lake Powell elevation will peak near approximately 3,610 feet in July and end the water year near 3,605 feet with approximately 12.25 maf in storage (50% capacity). Note that projections of elevation and storage have uncertainty, primarily due to uncertainty regarding the inflow to Lake Powell. Under the minimum probable inflow scenario, last updated in April, the projected summer peak was 3,599 ft and end of water year storage was 11.0 maf (45% capacity). Under the maximum probable inflow scenario, updated in April, the projected summer peak was 3,632 ft and end of water year storage was 14.9 maf (61% capacity). 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 minimum and maximum probable model runs will be updated in August. The annual release volume from Lake Powell during water year 2014 is projected to be 7.48 maf under all inflow scenarios.
Consistent with Section 6.C.1 of the Interim Guidelines, the Lake Powell operational tier for water year 2014 is the Mid-Elevation Release Tier with an annual release volume of 7.48 maf. This was determined in the August 2013 24-Month Study and documented in the 2014 Annual Operating Plan signed by Secretary Jewell in December 2013.
Upper Colorado River Basin Hydrology
The Upper Colorado River Basin regularly experiences significant year to year hydrologic variability. During the 14-year period 2000 to 2013, 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 3 out of the past 14 years. The period 2000-2013 is the lowest 14-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.25 maf, or 76% 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 2000-2013 period has ranged from a low of 2.64 maf (24% of average) in water year 2002 to a high of 15.97 maf (147% of average) in water year 2011. Under the current most probable forecast, total water year 2014 unregulated inflows to Lake Powell is projected to be 10.31 maf (95% of average).
Updated July 11, 2014
Email comments/inquires to: ResourceMgr@usbr.gov