The Colorado River basin has received some drought relief this past week. Significant precipitation throughout the basin occurred the weekend of September 7. This precipitation was particularly heavy in the "four corners" region and Southern Utah with numerous sites recording over 1 inch of precipitation over the weekend. Additional rain, primarily in the southern portion of the basin has continued through the September 9th work week. Very heavy precipitation was observed September 10 and 11 in the eastern portions of Arizona. While the moisture is welcome, drought conditions still prevail in the Colorado River basin. The Colorado River basin has not had a month with above average precipitation in over a year. It's likely that September, 2002 will be the first month with above average precipitation since August 2001.
April through July unregulated inflow to Lake Powell during 2002 was only 1.11 million acre-feet. This is only 14 percent of 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 April through July inflow to Lake Powell was 1.28 million acre-feet. Much below average precipitation with a poor snowpack this past winter contributed to this year's very low inflow. Water year unregulated inflow in 2002 will likely be 2.9 million acre-feet. This is only 24 percent of average and is also lower than the previous water year low which also occurred in 1977.
A total of 480,000 acre-feet will be released from Glen Canyon Dam during September, 2002. On Mondays through Fridays in September, 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 September, releases will likely vary between a low of about 5,000 cfs during off-peak hours, to a high of about 9,000 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 8,100 cfs during on-peak hours.
Releases in October and November, 2002 will likely be similar to September. A total of 492,000 acre-feet is currently scheduled to be released in October with 476,000 acre-feet in November.
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. Water year 2002 unregulated inflow will be about 24 percent of average. These three consecutive years of below average hydrology have reduced water storage in Lake Powell. The current elevation of Lake Powell is 3,627 feet (73 feet from full pool). Current storage is approximately 14.5 million acre-feet (60 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 3618 feet (82 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.
Observed inflow into Lake Powell has increased in the past week due to rainstorms. Inflow as of September 10, 2002 is 7,500 cfs. Inflow as September, 2002 began was only 3,000 cfs. Increased flow on the San Juan River accounts for the majority of this recent rise in Lake Powell inflow. The historic average inflow into Lake Powell in mid-September is about 9,000 cfs.
Because of the draw down condition of Lake Powell, and this years low runoff, releases from Lake Powell in water year 2002 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