WSP09055

• File Number: 8281.100
• Description: Colorado River Studies and Investigations -- Availability of Water-Hydrologic Determination
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1988
• Title: Hydrologic Determination - 1988 - Water Availability from Navajo Reservoir and the Upper Colorado River Basin for Use in New Mexico
• Water Supply Pro - Doc Type: Report/Study

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compared to 25 years of annual streamflow as well as the difference in the
amount of storage used in the monthly study as opposed to that which would
be used in just 25 years. Both of these adjustments were then applied to
the storage value used in the mass balance program. The adjustments were
as follows:

Storage Adjustment
a) ,25 year 7 month storage
b) Adjusted amount for 25 years

= 24.762 MAF
= 24.762 x 25/25.5833= 24.197 MAF

Streamflow Adjustment
a) 25 year critical period average streamflow = 12,.97 MAF
b) 25 year 7 month critical period average streamflow - 12.81 MAF
difference - 0.16
for 25 years: 0.16 x 25 = 4.00

Total Adjustment

24.197 - 4.00 - 20.197 MAF of "adjusted" storage.

The adjusted storage includes the effects of sedimentation and bank
storage. Use of this value along with the annual natural flow record at
Lees Ferry and a minimum delivery to the Lower Basin from Lake Powell of
8.25 MAF produced a firm yield for the Upper Basin of 5.55 MAF. The yield
varied from 5.55 MAF with no shortages to the Upper Basin to 6.03 MAF with
an eight percent overall shortage as shown in Table 1.

The liklihood and magnitude of other shortages or "calls on the river" are
discussed in Section 5.

4. probability Analysis

In addition to calculating the firm yield of the upper Basin, the mass
balance model also calculated the probabilities of various higher yields
for given levels of shortages. These probabilities are simple plotting
positions or percent frequency and were determined by dividing the number
of times an interval of critical period length produced at least the
specified yield, divided by the total number of times an interval of
critical period length could occur in the total record (from 1906 to 1986).
The results are tabulated in Table 1 which also indicates the length of the

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