Drought conditions persist in the Colorado River basin. The basin has received some drought relief during the months of September and October, however. Basinwide precipitation in September, 2002 was 185 percent of average. This was the first month with above average precipitation in over a year. Precipitation in October was 110 percent of average. These autumn rain storms have dampened soils in the basin and have erased some of the soil moisture deficit caused by the drought. This is important for next spring's snowmelt runoff. Soil moisture deficits reduce runoff efficiency causing greater amounts of water to be lost to the soil.
Water year 2002 will be remembered as one of the driest years on record in the Colorado River basin. Unregulated inflow to Lake Powell in water year 2002 was only 3.06 million acre-feet or 25 percent of the 30 year average. This is the lowest unregulated inflow ever recorded since the completion of Glen Canyon Dam in 1963. The previous low occurred in 1977 when inflow to Lake Powell was 3.66 million acre-feet.
Inflow to Lake Powell continues to be significantly below average. Unregulated inflow into Lake Powell in September, 2002 was 58 percent of average, and unregulated inflow in October was 309,000 acre-feet or 56 percent of average. Inflow as of November 4, 2002 is about 7,500 cfs. Average inflow in early November is generally about 10,000 cfs. Inflow to Lake Powell is expected to remain below average through the fall and winter. Snowpack in the Colorado River basin is 90 percent of average as of November 5, 2002. It should be noted that early season snowpack figures are usually not indicative of runoff volumes the following spring.
On April 24, 2002, members of the Glen Canyon Adaptive Management Work Group (AMWG) recommended to the Secretary of the Interior that a two-year experimental flow test be made from Glen Canyon Dam beginning in water year 2003. The recommendation addressed the decline of two key resources in the Grand Canyon: sediment and population viability of endangered humpback chub. Reclamation, the National Park Service, and the United States Geological Survey have jointly prepared an Environmental Assessment (EA) under the National Environmental Policy Act to document the impacts of these proposed experimental flows. The EA can be found at: http://www.uc.usbr.gov/envdocs/ea/gc/gc_release.html
A total of 476,000 acre-feet will be released from Glen Canyon Dam during November, 2002, which is an average of 8,000 cfs. On Mondays through Fridays in November, daily fluctuations will likely vary between a low of about 5,000 cfs (during late evening and early morning off-peak hours) to a high of about 10,000 cfs (during daylight hours and early evening on-peak hours). On Saturdays during November, releases will likely vary between a low of about 5,000 cfs during off-peak hours, to a high of about 9,500 cfs during on-peak hours. On Sundays, releases will likely vary between a low of about 5,000 cfs during off-peak hours to a high of about 8,000 cfs during on-peak hours.
Releases in December, 2002 will likely be higher than November. Unless there is a very high flow event on the Paria River during November (in which case the December volume would be 492,000 acre-feet), the release volume in December will be 600,000 acre-feet.
Drier than average conditions have now prevailed for the past three years in the Colorado River basin. Total unregulated inflow into Lake Powell in water year 2000 and 2001 was 62 and 59 percent of average, respectively and only 25 percent of average in 2002. These low inflows have reduced water storage in Lake Powell. The current elevation of Lake Powell is 3,624.4 feet (75.6 feet from full pool). Current storage is approximately 14.2 million acre-feet (58 percent of capacity). The water surface elevation of Lake Powell will likely continue to decline for the remainder of this year. The current projection shows that the water surface elevation of Lake Powell will be about 3621 feet (79 feet below full pool) on January 1, 2003. Hydrologic conditions often change, however, and the actual end-of-year elevation of Lake Powell will depend, in large part, on weather conditions in the Colorado River basin from now through the end of the year.
Because of the draw down condition of Lake Powell, releases from Lake Powell in water year 2003 are being scheduled to meet the minimum objective release of 8.23 million acre-feet. This is consistent with the requirements of the 1970 Criteria for Coordinated Long-Range Operation of Colorado River Reservoirs.
This release courtesy Tom Ryan