WSP12636

• File Number: 8282.300
• Description: Colorado River Operations and Accounting - Lower Basin Administrative Procedures
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/1/1996
• Author: DOI-BOR
• Title: Description and Assessment of Operations-Maintenance and Sensitive Species of the Lower Colorado River - Volume II - Appendices-Etc - 08-01-96
• Water Supply Pro - Doc Type: Report/Study

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00255')

Mean Monthly: Average of the daily values for the month, may only occur 2 or fewer times
per day.

Mean Annual: Average of the 12 monthly values, may only occur 2 or fewer times per day.

Midnieht: Instantaneous value at midnight.

End of Month: Midnight value at end of month.

End of Year: Midnight value at end of year.

Historical Hoover Dam/Lake Mead Operations

Figure El shows the mean daily releases for Hoover Dam. There are 365 daily mean values
plotted for each year. The maximum non-flood year mean daily release is shown to be
25,400 cfs during March 1994 and is a result of the Hoover turbine uprating in 1993 making
higher releases possible. The increase in daily release due to uprating appears to increase
maximum mean daily release by up to 3000 cfs. The minimum mean daily release of
800 cfs occurred during January 1993 and was due to operations to limit flooding in Mexico
during the high flows on the Bill Williams River and Gila River. Typical minimum mean
daily flow appears to have decreased by 1000 cfs after the Hoover uprating. The change in
overall appearance of the pre and post 1993 uprating periods is due to the increase in turbine
capacity and also changes to target elevations and other operational constraints for Lake
Mohave for the 5-year backwater cove rearing program of Razorback Suckers.

Figure E2 shows how the 2,920 (365*8 years) mean daily releases of Figure El are ranked.
For example, 40 percent of the daily releases were less than 10,000 cfs.

Figure E3 shows the average, maximum, and minimum mean daily Hoover release in each
month for the 8 non-flood control years. For example, January average daily release is the
average of the 248 (8*31) mean daily releases or 7,500 cfs. The maximum is the highest of
the 248 mean daily releases or 15,500 cfs and the minimum is the lowest of the 248 mean
daily releases or 800 cfs. A visual inspection of the averages shows how releases change
during the year to meet downstream demands. Also noted is the highest possible
instantaneous power release for Hoover of 49,000 cfs. The minimum instantaneous release
that can be expected under highly unusual circumstances is about 500 cfs or the release for
1 station service turbine. Such low flows may be caused by downstream flooding,
construction, search and rescue, or for other emergencies.

Figure E4 shows Hoover actual hourly releases for four days during 1994. The release
patterns for the different seasons show the pattern for power demand and the amount of
water to be released for the month. As monthly releases for months of higher downstream
water use increase, the maximum hourly release tends to increase. The hourly min to max
flow change during the day will have different effects downstream depending on the elevation

Appendix E - 2