Board Meeting 02/16/1984

• Board Meeting Date: 2/16/1984
• Description: Minutes, Agenda, Memorandums February 16, 1984
• Board Meetings - Doc Type: Meeting

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the formula, only annual values at Lees Ferry have been used. It is felt that
these data may be somewhat more accurate than the Virgin Flows mentioned above.
The formula along with the two hydrology data sets were computerized in order
to allow any combination of variables and values and their effects on allowable
depletions to be examined. To validate the use of the formula in the present
study, successful attempts to verify the previous (1965) studies were made.
These are discussed in the next section. After verification was obtained, runs
using the new period of record were made to determine values of allowable deple-
tions values by use of the formula, the values were further verified by runs
using the Colorado River Simulation System (CRSS) computer model.
Representative determination runs for the formula method and the model method
are presented in Tables 4 and 5 respectively.
B. Discussion and Results
An analysis of a similar study of Upper Basin depletion level by Tipton and
Kalmbach in July 1965, for the Upper Colorado River Commission revealed that
they too used the Bureau' s Virgin Flows as a basis for the determination. In
essence, they used a similar approach but solved the equation for Useable
Storage. They did this using two delivery assumptions - 7.5 MAY and 8.25 MAF,
and varied the depletion level in each one. They then plotted Upper Basin
depletion vs. required storage. With an assumed available storage of 29.0 MAY,
their plotted curves yielded a 5.6 MAY depletion with a delivery of 8.25 MAF to
the Lower Basin and 6.3 MAY with a delivery of 7.5 MAF. Using the computerized
formula with the Virgin Flows, zero shortage, 29.0 MAF of available storage and
a 7.5 MAY delivery, an allowable depletion of 6.3 MAY was derived; with a deli-
very of 8.25 MAY the depletion was computed at 5.6 MAY thus verifying the Tipton