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and to d~termine what is actually represented in the flow and quality data for: each of the reaches. Until such an analysis is made, all represen~ations of a data base for the Basin should only be considered ~ as only reasonable representations of flow and quality in the Basin, ~ Decisions based upon the data bases (whether historical, the present 00 modified flows now being used, or stochastic data bases) should tv recogniz~ that the data bases are at best only a reasonable representation of the Basin. 3.3 Adjustments to Upper Basin Flows The recehtly completed Comprehensive Framework Study, June 1971, developed estimates of historical flows at key stations and estimates of historical outflows and depletions for three subregions within the Basin, the total 1965 level of depletion was estimated to be 2,807,700 acre-feet, including 45,000 acre-feet of evaporation from Fontenel~e and Navajo Reservoirs and omitting the losses at Flaming Gorge and Lake Powell Reservoirs. A major part of this depletion began before 1914, the year selected for the start of the study period, For example, the total of the yearly d~pletions estimated for the 52-year period in the Green River subregio~ was 47.867 million acre-feet. If the 1965 level of develop- ment had,been in existence for the entire period, the estimated total depletio~ would have been 51,584 million acre-feet, Thus, while the total average annual depletion in the subregion is about 1 million acre-fee~, the net average change for which the data must be modified is only about 70,000 acre-feet, Similarly in the other subregions, the chan$e for within-Basin depletions has been relatively minor except f6r recent projects, reservoirs, and diversions out of the Basin, t~e effects of which are fairly well documented. I \ These mi~or changes along with those that are documented can be used to obtain very good estimates of means and variances for use in the data gen~ration computation. The major problem is that only a few of the stat~ons were in operation during the entire 1914-65 period. Thus, th~ major area of concern in the data base would be the adjustments made in short periods of records to reflect the total 1914-65 period. . Rather than take the approach of correlating flows at-two stations with different periods of record to estimate the mean of the shorter record from the longer one, a more direct method was used, Where possible; either ratios between long and short period averages or known depletions were applied to adjust mean flow values to reflect the chos~n common period. Much of the upcoming discussion is an explanation of exactly what adjustments were made to the historical data, 19