USBR: June 2021 24-Month Study #ColoradoRiver #COriver #aridification

Colorado River “Beginnings”. Photo: Brent Gardner-Smith/Aspen Journalism

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The operation of Lake Powell and Lake Mead in this June 2021 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 2021 Annual Operating Plan (AOP). Pursuant to the Interim Guidelines, the August 2020 24-Month Study projections of the January 1, 2021, system storage and reservoir water surface elevations set the operational tier for the coordinated operation of Lake Powell and Lake Mead during 2021.

The August 2020 24-Month Study projected the January 1, 2021, Lake Powell elevation to be below the 2021 Equalization Elevation of 3,659 feet and above elevation 3,575 feet. Consistent with Section 6.B of the Interim Guidelines, Lake Powell is operating under the Upper Elevation Balancing Tier for water year 2021. With an 8.23 million acre-foot (maf) release from Lake Powell in water year 2021, the April 2021 24-Month Study projected the end of water year elevation at Lake Powell to be below 3,575 feet. Therefore, in accordance with Section 6.B.1 of the Interim Guidelines, Lake Powell will continue to release 8.23 maf through the remainder of the water year 2021.

Consistent with Section 2.B.5 of the Interim Guidelines, the Intentionally Created Surplus (ICS) Surplus Condition is the criterion governing the ope ration of Lake Mead for calendar year 2021. In addition, Section III.B of Exhibit 1 to the Lower Basin Drought Contingency Plan (DCP) Agreement is also governing the operation of Lake Mead in calendar year 2021.

The 2021 AOP is available online at: https://www.usbr.gov/lc/region/g4000/aop/AOP21.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 Upper Basin Hydrology Summary is available online at: https://www.usbr.gov/uc/water/crsp/studies/24Month_06_ucb.pdf.

Current runoff projections into Lake Powell are provided by the National Weather Service’s Colorado Basin River Forecast Center and are as follows. The observed unregulated inflow into Lake Powell for the month of May was 0.543 maf or 23 percent of the 30-year average from 1981 to 2010. The June unregulated inflow forecast for Lake Powell is 0.750 maf or 28 percent of the 30-year average. The 2021 April through July unregulated inflow forecast is 1.800 maf or 25 percent of average. [ed. emphasis mine]

In this study, the calendar year 2021 diversion for Metropolitan Water District of Southern California (MWD) is projected to be 1.087 maf. The calendar year 2021 diversion for the Central Arizona Project (CAP) is projected to be 1.359 maf. Consumptive use for Nevada above Hoover (SNWP Use) is projected to be 0.248 maf for calendar year 2021.

Due to changing Lake Mead elevations, Hoover’s generator capacity is adjusted based on estimated effective capacity and plant availability. The estimated effective capacity is based on projected Lake Mead elevations. Unit capacity tests will be performed as the lake elevation changes. This study reflects these changes in the projections.

Hoover, Davis, and Parker Dam historical gross energy figures come from PO&M reports provided by the Lower Colorado Region’s Power Office, Bureau of Reclamation, Boulder City, Nevada. Questions regarding these historical energy numbers can be directed to Colleen Dwyer at (702) 293-8420.

Runoff and inflow projections into upper basin reservoirs are provided by the Colorado River Forecasting Service through the National Weather Service’s Colorado Basin River Forecast Center and are as follows:

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