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RRFW Riverwire – Glen canyon Dam Update
April 11, 2008

Lake Powell - Glen Canyon Dam - Current Status
Glen Canyon Dam Operations

Releases from Glen Canyon Dam in April 2008 will average 10,000 cubic feet per second (cfs) through April 14, 2008. During this period, on Mondays through Fridays, daily release fluctuations, due to load following, will likely vary between a low of 7,000 cfs (during early morning and late evening off-peak hours) and a high of 13,000 cfs (during late morning and early evening on-peak hours). On Saturdays and Sundays during this period, release fluctuations will likely vary between a low of 7,000 and a high of 12,500 cfs.

After April 14, 2008, to the end of April, releases from Glen Canyon Dam will likely average about 12,600 cfs. On Mondays through Fridays, daily release fluctuations will vary between about 9,500 cfs and 15,500 cfs while Saturday and Sunday fluctuations will likely vary between about 9,500 and 15,000 cfs. The total monthly volume released during the month of April 2008 will likely be about 680,000 acre-feet.

The monthly release volume in May 2008 will likely be higher than in April 2008. A total monthly volume of 755,000 acre-feet is scheduled to be released in May 2008 with a daily average release of about 12,300 cfs. This volume could be adjusted if forecasted inflows to Lake Powell change next month.

As discussed in the 2008 Annual Operating Plan, the Interim Guidelines for the Operation of Lake Powell and Lake Mead (Interim Guidelines) do provide for an April adjustment to the operational tier for the current water year if the current operational tier is Upper Elevation Balancing and specific conditions are projected in the April 24-Month Study. Specifically, if the April 24-Month Study projects the September 30 (current water year) Lake Powell elevation to be greater than the equalization elevation for the current water year, the Equalization tier will govern the operation of Lake Powell for the remainder of the water year.

Based on this April forecast and an annual release volume of 8.23 million acre-feet (maf), as established through the Interim Guideline B.1 (Upper Elevation Balancing Tier), the April 24-Month Study would project the end of water year elevation of Lake Powell to be approximately 3639. This projected elevation is above the equalization level for 2008 (3636 feet). Under the Interim Guidelines and based on this projected condition, the Equalization tier will govern for the remainder of water year 2008. Under the Equalization tier, the annual release volume from Glen Canyon Dam will likely be greater than 8.23 maf and for the April 24-Month Study is projected to be 8.88 maf. The projected end of water year elevation of Lake Powell is 3634.65 feet.

Upper Colorado River Basin Hydrology

Hydrologic conditions above Lake Powell have dried out somewhat during March. Precipitation in the Upper Colorado River Basin was 65% of average in March 2008 and is now 112% of average for the water year as of April 7, 2008. As of April 7, 2008 the snowpack conditions above Lake Powell are 116% of average. The climate outlook for the Upper Colorado River Basin indicates that the next 3 months will likely have below normal precipitation and above normal temperatures.

Inflow to Lake Powell is currently 14,500 cfs (April 6, 2008). Total unregulated inflow to Lake Powell so far in water year I thought 2008 (October through March) is 86% of average with March measured at 88 % of average.

Forecasted April through July unregulated inflow to Lake Powell in 2008 is 9.7 million acre-feet, 122 % of average (April final forecast). Typically by April 1st, the snow accumulation season is nearly complete in the Upper Colorado River Basin. Snowpack levels, on average, peak by about April 10th.

The current elevation of Lake Powell (March 2, 2008) is 3,590.5 feet, 109.5 feet from full pool elevation of 3,700 feet. Reservoir storage is currently 10.86 million acre-feet, or 44 percent of capacity. The water surface elevation of Lake Powell is now near its seasonal low. In April, anticipated snowmelt runoff will cause the water surface elevation to begin to increase. Under the current inflow forecast, Lake Powell would reach a peak elevation of about 3639 feet in July 2008. The peak elevation for Lake Powell in 2007 was 3,611.7 feet.

Upper Colorado River Basin Drought

The Upper Colorado River Basin is experiencing a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except one.
In the summer of 1999, Lake Powell was essentially full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. Inflow to Lake Powell in 1999 was 109 percent of average. The manifestation of drought conditions in the Upper Colorado River Basin began in the fall months of 1999. A five year period of extreme drought occurred in water years 2000, 2001, 2002, 2003, and 2004 with unregulated inflow to Lake Powell only 62, 59, 25, 51, and 49 percent of average, respectively. Lake Powell storage decreased through this five-year period, with reservoir storage reaching a low of 8.0 million acre-feet (33 percent of capacity) on April 8, 2005.

Drought conditions eased in water year 2005 in the Upper Colorado River Basin. Precipitation was above average in 2005 and unregulated inflow to Lake Powell was 105 percent of average. Lake Powell increased by 2.77 million acre-feet (31 feet in elevation) during water year 2005. But as is often the case, one favorable year does not necessarily end a protracted drought. In 2006, there was a return to drier conditions in the Colorado River Basin. Unregulated inflow to Lake Powell in water year 2006 was only 71 percent of average.

Water year 2007 was another year of below average inflow with unregulated inflow into Lake Powell at 68 percent of average. Over the past 8 years (2000 through 2007, inclusive), inflow to Lake Powell has been below average in all but one year (2005).

Reservoir storage in Lake Powell and Lake Mead has decreased during the past 8 years. Reservoir storage in Lake Powell is 45 percent of capacity. Storage in Lake Mead is 50 percent of capacity.

This release courtesy Rick Clayton, US Bureau of Reclamation

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