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<br />, <br /> <br />The graphs on pages 27 and 28 illustrate some of the pertinent historical facts <br />related to the amounts of water produced by the Colorado River System above Lee Ferry, <br />Arizona, the compact division point between the Upper and Lower Colorado River Basins. <br />The first graph, on page 27, is entitled Colorado River Flow at Lee Ferry, Arizona The top <br />of each vertical bar represents the estimated virgin flow of the river, i.e., the flow of the <br />river in millions of acre-feet past Lee Ferry for a given year had it not been depleted by <br />activities of man. Each vertical bar has two components: The lower shaded part <br />represents the estimated or measured historic flow at Lee Ferry, and the difference <br />between the two sections of the bar in any given year represents the stream depletion, or <br />the amount of water estimated to have been removed by man from the virgin supply <br />upstream from Lee Ferry. It is worth noting that in 1977, and again in 1981, the historic <br />flow at Lee Ferry exceeded the virgin flow. Beginning in 1962, part of this depletion at Lee <br />Ferry was caused by the retention and storage of water in storage units of the Colorado <br />River Storage Project. The horizontal line (at approximately 15.0 million acre-feet) shows <br />the long-term average virgin flow from 1896 through 2002. Because the Colorado River <br />Compact is administered on the basis of running averages covering periods of ten years, <br />the progressive ten-year average historic and virgin flows are displayed on this graph. <br /> <br />The second graph on page 28, entitled Lee Ferry Average Annual Flow for <br />Selected Periods, is a graphical representation of historic and virgin flow averages for <br />several periods of record. The periods of water years selected were those to which <br />reference is usually made for various purposes in documents pertaining to the Colorado <br />River System. <br /> <br />Several important hydrologic facts are apparent from these two graphs on pages <br />27 and 28. <br /> <br />(1) A vast majority of the high flows occurred prior to 1929. <br /> <br />(2) Since the 1 924-1 933 decade, the progressive ten-year average virgin flow has not <br />exceeded the average virgin flow except in the 1941-1950 and the exceptionally <br />wet 1975-1984 through 1984-1993 decades <br /> <br />(3) For the period 1896-1921, which is prior to the Colorado River Compact of 1922, <br />the average virgin flow was estimated to be 168 million acre-feet per year, which <br />is considerably greater than for any other period selected, including the long-term <br />average. A stream-gaging station at Lees Ferry, Arizona was not installed until <br />1921. Thus, the virgin flow at Lees Ferry prior to the 1922 Compact is estimated <br />based upon records obtained at other stations, e.g. the stream gage on the <br />Colorado River at Yuma, Arizona for the period 1902-1921. <br /> <br />(4) For the longest period shown, 1896-2002, the estimated average annual virgin <br />flow is 15.0 million acre-feet and the average annual historic flow is 12.1 million <br />acre-feet. <br /> <br />(5) For the next longest period, 1906-2002, the estimated average annual virgin flow <br />is 15.1 million acre-feet and the average annual historic flow is 12.0 million <br />acre-feet. Many of the early records for this series of years, as well as for the <br />1896-2002 period, are based upon the estimates of flows made at other gaging <br />stations, as mentioned in (3) above. This average is about equal to the 15.0 <br />million acre-feet estimated forthe 1906-1967 period which was used as the basis <br /> <br />25 <br />