GCPBA River News Notes - Sept/Oct Canyon Flows Steady @ Fab Fun Level - 14,800 CFS - All You Need To Know About River Flows
Glen Canyon Dam / Lake Powell – The unregulated inflow volume to Lake Powell in July was 4.35 maf (279% of average). This year the unregulated inflow in July was the second wettest July since the closure of Glen Canyon Dam (1963). The April through July unregulated inflow to Lake Powell for 2011 was 12.92 maf (163% of average) and this was the third wettest April through July period since the closure of Glen Canyon Dam.
In terms of reservoir elevation and storage, Lake Powell reached its peak for water year 2011 on July 30, 2011 which was 3660.9 feet (39.1 feet from full pool) and 18.61 maf (76.5% of capacity), respectively. Releases now exceed inflows and the elevation and storage are now slowly decreasing each day. The peak reservoir elevation and storage that occurred in water year 2010 was 3638.8 feet (61.2 feet below full pool) and 15.86 maf (65.2% of capacity) and this occurred on July 5, 2010. As of August 11, 2011 the reservoir elevation and storage in Lake Powell was 3659.64 feet (40.36 feet from full pool) and 18.45 maf (75.8% of capacity), respectively.
Current Dam Operations
Releases from Glen Canyon Dam are approximately 24,600 cfs which is very near the full capacity of the powerplant. The release volume for August will likely be about 1.45 maf. In late August, releases from Glen Canyon Dam will be reduced over 3 days to approximately 14,800 cfs on September 1, 2011. During the transition to the lower level, releases will likely fluctuate for power generation.
Beginning on September 1, 2011 a steady flow experiment will begin and releases will be maintained steady at approximately 14,800 cfs until November 1, 2011. This will be the fourth year of a five year program of steady flows in September and October. The targeted release rate of 14,800 cfs is the current estimate of the maximum sustainable release rate for all 61 days during September and October given the current maintenance schedule for Glen Canyon Dam. It is possible that the actual maximum sustainable release rate during September and October could be somewhat higher. Reclamation will attempt to set the targeted release rate for the steady flow experiment at the highest level possible and
this will be determined near the end of August.
While the release rate from Glen Canyon Dam over the next several months will likely be near steady, the instantaneous releases from Glen Canyon Dam may fluctuate somewhat to provide 40 MW of system regulation. These instantaneous release adjustments maintain stable conditions within the electrical generation and transmission system and result in momentary release fluctuations within a range of about 1100 cfs above or below the targeted hourly release rate. The momentary fluctuations for regulation are very short lived and typically balance out over the hour.
Spinning and non-spinning reserve generation is also maintained at Glen Canyon Dam. In order for Colorado River Storage Project (CRSP) powerplants to participate in the electrical generation and transmissions system, these powerplants must maintain a level of generation capacity available in reserve to assist the local control area for when unanticipated generation outages occur. The current CRSP powerplant reserve requirement is 100 MW (equivalent to approximately 2,675 cfs of release from Glen Canyon Dam). When an electrical outage occurs within the control area, CRSP powerplants can be called upon to provide up to 100 MW of additional generation for up to 2 hours. Under normal
circumstances, calls for reserves are infrequent and for much less than the required 100 MW. Because Glen Canyon Powerplant is the largest facility of the CRSP powerplants, most of the CRSP reserve requirement is maintained at Glen Canyon Dam.
The Operating Tier for coordinated operations of Lake Powell and Lake Mead during water year 2011, pursuant to the Interim Guidelines has been the Upper Elevation Balancing Tier. In April, based on the projected end of water year elevation of Lake Powell, a shift was made such that the Equalization Tier has governed operation of Lake Powell since then. Reclamation has been operating Glen Canyon Dam with the intent of achieving Equalization by September 30, 2011. Due to significantly high inflows this spring and summer however, it is very likely that Equalization will not be fully achieved by September 30, 2011. Reclamation will continue to operate Glen Canyon Dam to release water at near full capacity of the Glen Canyon Powerplant until Equalization is fully achieved
Current Inflow Forecasts and Model Projections
The August 24-Month Study projects the annual release volume for water year 2011 will be 12.45 maf and the end of water year reservoir elevation and storage for Lake Powell will be 3656.91 feet (43.09 feet from full pool) and 18.092 maf (74.4% of capacity), respectively.
The hydrologic outlook forecast for water year 2012 projects that the most probable (median) unregulated inflow volume will be 12.6 maf (105% of average based on the period from 1971 through 2000). Based on this hydrologic outlook, the August 24- Month Study projects the annual release from Lake Powell during water year 2012 will be 13.57 maf and the end of water year 2012 reservoir elevation and storage for Lake Powell to be 3646.4 feet (53.6 feet from full pool) and 16.77 maf (69% of capacity), respectively.
Colorado River Basin Hydrology
Since water year 2005, hydrologic conditions in the Upper Colorado River Basin have been slightly below average with significant variability from year to year. The average unregulated inflow to Lake Powell during the period from 2005 through 2011, which is a good measure of the hydrologic conditions in the Colorado River Basin, were 11.2 maf which is slightly below the official average of 12.0 maf (based on the period from 1971 through 2000). The variability during this period has been from a low water year unregulated inflow of 8.4 maf (70% of average) in water year 2006 to a high of over 17.0 maf (141% of average) which is the projected for water year 2011.
Overall reservoir storage in the Colorado River Basin has increased by nearly 10 maf since the beginning of water year 2005 and this is a significant improvement over the drought conditions during water years 2000 through 2004. On October 1, 2004, the beginning of water year 2005, the total reservoir storage in the Colorado River Basin was 29.84 maf (50.2% of capacity). As of August 12, 2011, the total reservoir storage in the Colorado River Basin was 39.28 maf (66.1% of capacity).
Updated: Aug 12, 2011 Rick Clayton
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