Hydrology

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Current Status The unregulated inflow volume to Lake Powell in May was 2,294 thousand acre-feet (kaf) (98 percent of average). The release volume from Glen Canyon Dam in May was 700 kaf. The end of May elevation and storage of Lake Powell were 3,604 ft (96 feet from full pool) and 12.1 maf (50% of full capacity), respectively. The reservoir reached a seasonal low elevation on April 15th near elevation 3591.14 feet. Since that time the reservoir elevation has been increasing and will continue to increase throughout mid-summer as runoff from snowmelt and precipitation enter the reservoir. Inflow Forecasts and Model Projections The operating tier for water year 2016 was established in August 2015 as the Upper Elevation Balancing Tier. The April 2016 24-Month Study established that Lake Powell operations will be governed by balancing for the remainder of water year 2016. Under balancing, the contents of Lake Powell and Lake Mead will be balanced by the end of the water year, but not more than 9.0 maf and not less than 8.23 maf shall be released from Lake Powell. Based on the most probable inflow forecast, this June 24-Month Study projects a balancing release of 9.0 maf in water year 2016; the actual release in water year 2016, however, will depend on hydrology in the remainder of water year and will range from 8.23 to 9.0 maf. The projected release from Lake Powell in water year 2016 will be updated each month throughout the remainder of the water year. Reclamation will schedule operations at Glen Canyon Dam to achieve as practicably as possible the appropriate total annual release volume by September 30, 2016. In June, the release volume will be approximately 800 kaf, with fluctuations anticipated between about 9,000 cfs in the nighttime to about 17,000 cfs in the daytime and consistent with the Glen Canyon Operating Criteria (Federal Register, Volume 62, No. 41, March 3, 1997). The anticipated release volume for July is 950 kaf with daily fluctuations between approximately 11,500 cfs and 19,500 cfs. The expected release for August is 900 kaf with daily fluctuations between approximately 10,000 cfs and 18,000 cfs.

Table- Hydrology of the Colorado River	---	---

Reservoir Elevations Inflows to Lake Powell USBR Weekly Water Report USBR Water Report USBR -LC Region Hourly Forecasts USBR- Historic Use Records Water Accounting Reports Snow Pack Reports Bureau of Reclamation- Snow Pack Report SNOWTEL Report The snowtel report is a calculating report, and takes approximately 3 minutes to run. Select the report under "Public", listed as "Colorado River above Lake Powell" (116 snowtel sites). Data source is updated at least daily. U.S. Drought Monitor U.S. Drought Monitor Tree Flow Data

Water Flow Gages Lake Powell Water Level Graphs Colorado River at Lees Ferry Paria River at Lees Ferry Colorado River at 30 mile Colorado River above LCR LCR at Colorado River Colorado River at Bright Angel Creek Bright Angel Creek Shinumo Creek Colorado River abv Lava Canyon rm66 Colorado River bl rm127 Kanab Creek Havasu Creek Colorado River abv National Canyon Colorado River bl Diamond Creek Colorado River abv Spencer rm246 Lake Mead Water Level Graphs Presentations and Papers 2016 TWG: Basin Hydrology, Operations, and 2017 Hydrograph AMWG: Basin Hydrology, Operations, and 2017 Hydrograph Glen Canyon Dam Operations During Equalization 2015 California Drought Monitor Lake Mead Issues and Lower Basin Shortage Preparedness Lake Mead Issues and Lower Basin Shortage Preparedness - Presentation Basin Hydrology Operations, and 2016 Hydrograph Basin Hydrology Operations, and 2016 Hydrograph 2016 Annual Operating Plan AMWG: Basin Hydrology and WY 2016 Hydrograph TWG: Hydrology Update and 2016 Hydrograph Water Quality in Lake Mead and Upstream Influences: Dissolved Oxygen during 2014 Basin Hydrology, Operations, and 2016 Hydrograph Hydrology Update and 2016 Hydrograph 2014 AIF: Basin Hydrology, Operations, and 2015 Hydrograph Proposed 2015 Hydrograph AIF: Basin Hydrology, Operations Other Stuff Operational Flexibility 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 typically maintains 30 mw (approximately 880 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. Hydrologic Variability The Upper Colorado River Basin regularly experiences significant year to year hydrologic variability. During the 16-year period 2000 to 2015, 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 16 years. The period 2000-2015 is the lowest 16-year period since the closure of Glen Canyon Dam in 1963, with an average unregulated inflow of 8.51 maf, or 79% 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 2000-2015 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. The water year 2015 unregulated inflow volume to Lake Powell was 10.174 maf (94 percent of average), which, though still below average, was significantly higher than inflows observed in 2012 and 2013 (45% and 47 percent of average, respectively).