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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002504

Mohave for the Razorback Sucker backcove rearing program.

Figure E20 shows the range and average Lake Havasu midnight elevations by month for
years 1982, 1989-1995. The maximum average occurs in May and the minimum average
occurs in December. As noted, the minimum elevation expected by boat marina operators is
at elevation 445.8 feet. The maximum elevation is 450.5 feet.

Figure E21 shows monthly change in Lake Havasu 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 the Lake Mohave Razorback Sucker rearing
program are plotted separately. The largest elevation monthly increase occurs in April and
averages about + 1 feet before constrained operations is + 1 feet after. The largest elevation
monthly decrease occurs in September and averages about -1 feet before constrained
operations and occurs in July and averages -1.5 feet after.

Comparison of Projected vs Historical Operations for Lake Mead/Hoover Dam

Projected values were computed using the CRSSez Colorado River reservoir simulation
computer program. The period 1996 through 2010 was simulated with 1000 traces or 15,000
annual values and 180,000 monthly values for each parameter were generated. Only values
for non-flood release years or about 120,000 monthly values were used in this analysis. The
Lower basin consumptive uses are shown on table E10 but for simulations the agricultural
users varied year to year using a variable use pattern. The hydrologic natural water supply
used is stochastically generated values that have the same statistical properties of the
historical 1906-1990 values. The stochastic hydrology has greater range in flows than the
historic data but on average has the same long term mean flows. The intermittent flow of
the Gila River is also included in the stochastic hydrology and also adds to the variability of
required releases to meet Mexican water delivery. There were no required reductions to
California uses and so recovery of the Mexican bypass of 120,000 acre-feet per year by the
Yuma Desalting Plant was not needed. There were essentially no reductions needed in CAP
uses to protect Lake Mead elevation of 1050 feet.

Figure E22 compares the average, maximum, and minimum monthly release as a monthly
volume in units of 1000 acre-feet, for Hoover Dam for non-flood control years for the past
15 years versus the projected next 15 years. The overall comparison shows that within the
accuracy of the simulation model, the projected 15 year period is very similar to the past
15 year period in both range in monthly release and average release for the two periods.
This should be expected given the high variability of both water use and hydrologic gains
below Hoover Dam including the Gila and Bill Williams Rivers of the past 15 years. Figure
E33 shows Parker Dam mean monthly projected releases to be very similar to the historic
period, indicating that the differences at Hoover are probably due mostly to different
historical storage in Mohave and Havasu from targets and increases in CAP diversions for
the projected period. Also the lack of need for any appreciable surplus uses or shorted uses

Appendix E - 6