WSP07975

• File Number: 8278.100
• Description: Title I - Yuma Desalting Plant
• Basin: Colorado Mainstem
• Date: 10/1/1987
• Author: USDOI/BOR
• Title: Yuma Desalting Plant Operations Study - Draft Special Report
• Water Supply Pro - Doc Type: Publication

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ESTIMATE OF YDP OPERATING YEARS

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Over the years, a number of studies have addressed the question:
Ho~ often would production from the YDP be required? Since
existing estimates were made before the recent years of surplus
flows on the Colorado River, they are no longer considered valid.
The most logical means of determining years of required
production would be from salinity differentials projected by the
Colorado River Simulation System (CRSS) computer model.
Unfortunately, the data bases currently lack the refinement
necessary to make the projections. (The eRSS data base is being
extended to provide the capability in the near future.) However,
eRSS has been able to project the occurrence of surplus flows
each year during the time period 1991 through 2050 for 80
different sequences (traces) of hydrologic events. This analysis
assumes that the salinity differential is acceptable during years
of surplus flow. Thus, based upon these 80 traces, the
probability of the occurrence of surplus flow conditions can be
estimated for future years.

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The concept that acceptable salinity differentials are associated
with occurrences of surplus flows assumes that Wellton-Mohawk
drainage flows can be bypassed without requiring YDP production.
Thus, The higher the probability of surplus flows occurring, the
lower the probability that YDP production will be required.

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An analysis of the eO-trace data indicates that YDP production
would be required for 59 years out of the 60-year period between
the year 1991 and the year 2050 assuming a 50 percent probability
of surplus flows. If the probability of surplus flows is reduced
to 40 percent, YDP production would be required for 53 out of 60
years for the same period. If the probability is further reduced
to 30 percent, production would be required for 47 out of 60
years. Thus, YDP production would be required 10 out of 10
years, 9 out of 10 years, and 8 out of 10 years for 50, 40, and
30 percent probability of surplus flows, respectively. For
Simplicity of analysis, the probability of surplus flows was
assumed to be 50 percent and that the YDP would be operated. every
yea~ during the period 1991 to 2050.

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Because of the high projected operating cost of the YDP and
requirements to budget for operating expenses 2 years in advance,
management would probably be willing to assume a higher level of
risk under actual operating conditions than was used for this
analysis. Thus, the YDP would probably only be in production 7
or 8 out of 10 years. As a result, the actual average annual
operating cost of the YDP would be slightly less. A somewhat
reduced YDP annual operating cost would make some of the plans,
now considered to be marginally feasible, infeasible. As will be
shown later, none of the plans recommended for further study fall

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