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flow of the river in millions of acre-feet past Lee Ferry for a given year had it not been depleted by activities of man, The shaded vertical bars, adjacent to the white bars, represent the estimated or measured historic flow at Lee Ferry, and the differ- ence between the two bars in any given year represents the stream depletion, or the amount of water estimated to have been removed by man from the virgin supply upstream from Lee Ferry. It is worth noti ng that in 1977 and again in 1981 the his- toric flow at Lee Ferry exceeded the virgin flow. Beginning in 1962, part of this depletion at Lee Ferry was caused by the retention and storage of water in storage units of the Colorado River Storage Project. The horizontal line (at approximately 15 million acre-feet) shows the long-term average virgin flow from 1896 through 1987. The second vertical line (at approximately 14.4 million acre-feet) shows the average virgin flow since 1922, after the adoption of the Colorado River Compact. Because the Colorado River Compact is administered on the basis of running averages covering periods of ten years, the pro- gressive ten-year average historic and virgin flows are displayed on this chart. The second chart on page 26, entitled Lee Ferry Average Annual Flow for Selected Periods, is a graphical representation of historic and virgin flow averages for several periods of record. The periods of water years selected were those to which reference is usually made for various purposes in documents per- taining to the Colorado River System, Several important hydrologic facts are apparent from these two charts on pages 25 and 26. (1) A vast majority of the high flows occurred prior to 1929. (2) Since the 1924-1933 decade, the progressive ten-year average virgin flow has not exceeded the average virgin flow except in the 1941-1950 and the exceptionally wet 1975-1984 through 1978-1987 decades. (3) For the period 1896-1921, which is prior to the Colorado River Compact of 1922, the average virgin flow was estimated to be 16.8 million acre-feet per year, which is considerably greater than for any other period selected, including the long- term average. A stream-gaging station at Lees Ferry, Arizona was not installed until 1921. Thus, the virgin flow at Lees Ferry prior to the 1922 Compact is estimated based upon records ~ 27