May 2003. Dam Operations
Releases from Glen Canyon Dam the last two days of May are being moderately increased from the original May release schedule. Releases on May 30 and May 31 will vary from a low of about 9,000 cfs to a high of about 15,000 cfs. This is an increase of about 15 percent.
Releases from Glen Canyon Dam in June will average about 14,100 cubic feet per second (cfs) with a total of 840,000 acre-feet scheduled to be released. On Mondays through Fridays in June, daily fluctuations due to load following will likely vary between a low of about 10,160 cfs (during late evening and early morning off-peak hours) to a high of about 18,160 cfs (during late afternoon and early evening on-peak hours). On Saturdays, releases will likely vary between a low of about 10,160 cfs during off-peak hours to a high of about 16,500 cfs during on-peak hours. On Sundays, releases will likely be steady throughout the day at 10,160 cfs.
July and August releases will be moderately higher than June. A total of 900,000 acre-feet is scheduled to be released in July and August of 2003, which averages out to 14,600 cfs.
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.
Basin Hydrology
Record breaking high temperatures have persisted over the Colorado River basin in the latter part of May. This very warm weather has resulted in substantial late May snowmelt and runoff, especially in the Yampa River basin and the headwaters drainages of the Colorado River. Some streamflow gages are even recording record high flows for this time of year (the Eagle River in Colorado for example). Unfortunately, the remaining snow in the basin is disappearing fast, and these healthy river flows will not persist. Unless there is significant monsoonal activity this summer, river flows in the basin in July, August and September of this year will likely be much below normal levels. As of May 30, inflow to Lake Powell is 36,000 cfs, about 90 percent of what would normally be seen on this date. Inflow will continue to increase over the next few days, perhaps reaching a peak of 45,000 cfs the first week of June.
Even though river flows are quite high in the basin right now, drought conditions continue in the Colorado River Basin. River flows will likely drop dramatically in mid-June. Inflow volumes are expected to be substantially below average this year with water year 2003 being the 4th consecutive year with below average inflow to Lake Powell. The May mid-month inflow forecast issued by the National Weather Service is calling for 4.3 million acre-feet of unregulated runoff into Lake Powell during the 2003 April through July runoff period. This equates to 54 percent of average. Total unregulated inflow for water year 2003 will likely be about 60 percent of average. A revised inflow forecast will be issued by the National Weather Service the week of June 2.
While inflow to Lake Powell picked up considerably the last week of May, inflow was sluggish for most of the month. Total unregulated inflow in May, 2003 will likely be about 1,150,000 acre-feet (50 percent of average). Total inflow to Lake Powell has been significantly below average throughout 2003. Unregulated inflow in January, February, March, and April was 58, 62, 62, and 42 percent of average, respectively.
Total unregulated inflow into Lake Powell in water years 2000 and 2001 was 62 and 59 percent of average, respectively, and only 25 percent of average in 2002. Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963. These low inflows have reduced water storage in Lake Powell. Lake Powell reached a low water surface elevation this year of 3605 feet (95 feet from full pool) on May 1, 2003. The current elevation of Lake Powell is 3,609 feet (91 feet from full pool). Current storage is approximately 12.7 million acre-feet (52 percent of capacity). The water surface elevation at Lake Powell should continue to increase in June. However, there will not be a large rebound in water storage this year with projected inflow being so low. Under the current inflow forecast, Lake Powell will reach a peak water surface elevation of about 3,615 feet this year, in late June or early July.
Experimental Flows
Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, were completed on March 31, 2003. From January through March 2003 releases ranged between a high of 20,000 cfs to a low of 5,000 cfs each day. These same high fluctuating releases are scheduled to be repeated in January through March of 2004.
The January through March high fluctuating releases were intended to benefit the endangered humpback chub. Scientists have recognized that the humpback chub population has been in general decline since highly fluctuating flows were curtailed in November of 1991. Those flows helped keep the non-native fish, especially the rainbow and brown trout, in check. The trout are thought to prey upon and compete with native fish such as the endangered humpback chub.
The experimental flows from Glen Canyon Dam received environmental clearances in December 2002. The flows were analyzed in an environmental assessment in accordance with the National Environmental Policy Act. The experimental flows are the result of ongoing studies by scientists from the United States Geological Survey and were recommended by the Glen Canyon Dam Adaptive Management Work Group, a Federal advisory committee. The experimental flows address the decline of two key resources in the Grand Canyon: sediment and population viability of endangered humpback chub. The Finding of No Significant Impact on the experimental flows can be found at http://www.uc.usbr.gov/amp/flow_fonsi.pdf.
This release courtesy Tom Ryan