WSP08437

• File Number: 8220.105.LJ
• Description: Navajo Reservoir
• State: NM
• Basin: San Juan/Dolores
• Date: 12/1/1983
• Title: Draft Hydrologic Determination - December 1983 - Water Availibility 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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from that of using the formula. Depletions are an input to the model rather

than an output. It was therefore necessary to specify a depletion level and

then verify other parameters such as shortages and storage used. Even the dep-

let ion level could not be specified exactly because the reservoir evaporation

portion of the depletion varies with the operation of the reservoir and is

dependent on water surface areas and evaporation rates. Another major dif-

ference between the model approach and the formula approach is that in the model

- just as in the real world, the streamflow and the demands are both spacially

and temporally distributed, i.e., there may not be water available to meet

demands at a given point in the basin at a given point in time. The formula

approach, however, assumes that all of the water is available to meet all of the

demands above Lee Ferry.

Cne model run was made in an effort to confirm the 5.8 HAF computerized formula

run. Bank storage release was restricted to zero and the maximum drawdown on

the reservoirs constrained to minimum power poolS. The atorage used by the

model was 20.7 HAF (vs. 26.2 in the formula approach) and the average shortage

was 264,000 AF/yesr or 4.6 percent over the 25-year critical period 1953-1977.

The results of the run indicate an actual depletion obtained of 5.775 HAF. If

an adjustment is made for the difference in storage values used between the two

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methods, the remaining storage would be about 1 1/2 percent. An annual release

of 8.27 HAF was made from Lake Powell in this run.

Another model rUn was made to verify the results of the 6.3 HAF computerized

formula run. The depletion level reached was only 6.187 HAF, short of 6.3 KAt.

With a Lake Powell annual release of 8.23 MAF and a critical period of 2S yeara,

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