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<br />S.TATE OF CALIFORNIA_THE RESOURCES AGENCY
<br />
<br />EDMUNO G. 6ROWN JR., Go.....rnor
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<br />COLORADO RIVER BOARD OF CALIFORNIA
<br />107 SOUTH BROADWAY, ROOM 8103
<br />LOS ANGELES, CALIFORNIA 90012
<br />(213) 620....80
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<br />March 15, 1982
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<br />Mr. Clifford I. Barrett
<br />Regi onal Dire ct or
<br />Upper Colorado Regional Office
<br />U.S. Bureau of Reclamation
<br />P.O. Box 11568
<br />Salt Lake City, Utah 84111
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<br />Mr. W.B. Plummer, Regional Director
<br />Lower Colorado Regional Office
<br />U.S. Bureau of Reclamation
<br />P. O. Box 427
<br />Boulder City, Nevada 89005
<br />
<br />Dear Messrs Barrett and Pl~mer:
<br />
<br />We have reviewed the draft Environmental Assessment for the
<br />proposed uprating of the Glen Canyon Powerplant, and have concerns
<br />with regard to the computer model of the Colorado River System used
<br />in analyzing the preferred plan.
<br />
<br />As stated on page 7 of the draft Environmen~al Assessment, the
<br />Bureau's computer program shows that there is an 85 percent probabi-
<br />lity of Lake Powell being at or above elevation 3641 (16,660,000 acre-
<br />feet of storage) in the year 2000, and a 60 percent probability of
<br />being at or above the same elevation by the year 2040. In response
<br />to our inquiry, . John Newman of the Upper Colorado Regional Office
<br />informed us that the hydrologic analyses performed to develop those
<br />probabilities used, as the basis for computing "602(a) storage"
<br />requirements, the most critical period of record. We are concerned
<br />since the operating criteria specify other hydrologic factors, such
<br />as the probabilities of water supply, t,o be considered in computing
<br />602(a) storage requirements.
<br />
<br />In the past, we have discussed with your offices our belief
<br />that the Bureau should use, in its computer simulation models, the
<br />water supply criteria specified in the operating criteria rather than
<br />only the most critical period of record in the computation of 602(a)
<br />storage requirements. The Bureau's use of the most critical period
<br />of record as the only water supply factor in computing 602(a) storage
<br />requirements, was stated in Assistant Commissioner Barrett's letter
<br />of March 20, 1979. The three Lower' Basin states jointly replied
<br />
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