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<br />OJ1823 <br /> <br />produced unreasonable variations in quality at downstream sta- <br />tions. Standard deviations were generally 100 percent greater <br />than expected. (See "Fundamental Difference Between Network <br />~Iodel and Biennial Report Method" for discussions related to <br />this problem.) <br /> <br />Consequently, data developed in the dissertation by Jjendrick <br />[6, Chapter VI and Chapter VII] were used to replace the ungaged <br />tributary inputs based on the simple mass b~lance approach. Gaged <br />data, information from previous studies, and correlation were used <br />to include inputs by Bright Angel, Tapeats, and Havasu Creeks, the <br />Muddy and Virgin Rivers, and Las Vegas Wash. Estimates of histor- <br />ical evaporation were based on a constant relationship between <br />annual evaporation at Lake Mead and the Boulder City pan. Tech- <br />niques used to distribute annual values by months were estimated <br />to produce a maximum error of 3 inches for any month., with a maxi- <br />mum annual error of 12 inches, equivalent to about 10 percent. <br /> <br />Inflows at the Grand Canyon station were adjusted for sediment con- <br />centration to provide an estimate of the actual volume of water <br />entering Lake Mead. Reservoir storage was adjusted to reflect <br />changes in both area-capacity curves and sediment volumes. r~ethods <br />used in estimating bank storage produced an equivalent bank storage <br />coefficient of approximately 6 percent. [6, p 89] <br /> <br />The sum of the true ungaged inputs, streamflows other than the Colo- <br />rado River, and the resultant mass balance errors after evaporation <br />and bank storage are estimated, are contained in Tables C-14 through <br />C-16 and in Figures C-15 through C-17. Data in the dissertation <br />were only developed through 1968. To extend the information through <br />1970, it was assumed that the 1968 data would repeat. <br /> <br />Comparing the original mass balance monthly results to those of <br />Hendrick: [6] <br /> <br />Item Original Hendrick <br />Mean flow 35,000 acre-feet 35,000 acre-feet <br />Standard deviation <br />flow 385,000 acre-feet 34,000 acre-feet <br />Mean salinity 46,000 tons 66,000 tons <br />Standard deviation <br />salini ty 904,000 tons 22,000 tons <br /> <br />It is noted that although the mean values compare favorably, vari- <br />ance of the original data is much greater. This is also apparent <br />from an inspection of corresponding tables. There are no negative <br />values in the dissertation data while there are many such values <br />in the original data. Consequently, the dissertation data were <br />used for all runs described in this report. <br /> <br />13 <br />