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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002561

Figure E9 shows how the 2,920 (365*8 years) mean daily releases of Figure E8 are ranked.
For example, 40 percent of the daily releases were less than 10,000 cfs.

Figure EI0 shows the average, maximum, and minimum mean daily Davis 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 6,000 cfs. The January maximum is the
highest of the 248 mean daily releases or 13,000 cfs and the minimum is the lowest of the
248 mean daily releases or 1,600 cfs. A visual inspection of the averages shows how
releases change during the year to meet downstream demands. Also noted is the maximum
instantaneous release for Davis of 28,000 cfs. The minimum instantaneous release that can
be expected under highly unusual circumstances is about 1000 cfs or less than the release for
1/2 of a generation unit output. Such low flows may be caused by downstream flooding,
construction, search and rescue, or for other emergencies. When comparing figure E3
Hoover average releases with figure EI0 Davis average releases, the difference is mostly due
to change in storage of Lake Mohave.

Figure Ell shows Davis Dam actual hourly releases for four days during 1994. The release
patterns for the different seasons show the pattern for power demand and that the 5
generating units are put on and off line as full units of approximately 5,000 cfs each down to
1 unit. As monthly releases for months of higher downstream water use increase, the
maximum hourly release tends to increase.

Figure E12 shows Lake Mohave midnight elevations. It shows that Lake Mohave tends to
reach its maximum elevation in. the spring and its minimum elevation in the fall to provide
flood control space for large hurricane type storms coming up river from Baja Mexico.
Actual elevations differ from target elevations of Figure 17, section II, as needed to regulate
Hoover releases and downstream demands for water. The Razorback Sucker backcove
rearing program began in 1994 set limits for drawdown to no more than 2 feet in a 10 day
period during the spawning season and that Mohave elevation be above elevation 640 feet
between March 15 and June 15 to provide sufficient depth for the backcove rearing areas.
Lake Havasu's limited operating range is currently used to help meet these operating
constraints as well as changing Hoover energy allotments and releases if needed.

Figure E13 shows the range and average Lake Mohave midnight elevations by month for
years 1982, 1989-1995. The maximum average occurs in February and the minimum
average occurs in October. As noted, the minimum elevation of Lake Mohave with out
resetting the intake stops is at elevation 630 feet. The maximum elevation is 646.5 feet
where wave action begins to leak into an inspection gallery.

Figure E14 shows monthly change in Lake Mohave elevation and is computed as end of
month elevation minus previous end of month elevation. The values for the period before
and after initiation of operational constraints for Razorback Sucker rearing are plotted
separately. The largest elevation monthly increase occurs in December and averages about
+5 feet before constrained operations is +7 feet after. The largest elevation monthly

Appendix E - 4