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Show Since seldom is there an actual record of observation of evaporation at a proposed reservoir site, it was determined to use some form of geographic and topographic reference by which to estimate evaporations. In this study of the problem, the elevation and latitude of the Weather Bureau Stations in the basin where climatolo-gical data have been collected, were found to give remarkably satisfactory results. From these data for 18 localities in the Colorado River Basin the following preliminary relation was derived, hereinafter referred to as formula (1)- E = 90 + 48cos 2x - 10A (1) In this formula E is the annual evaporation in inches depth from the free water surface of the reservoir x is the latitude of the given location A is the altitude or elevation of the station or water surface at the reservoir site in units of 1,000 feet A most comprehensive study and tabulation of evaporation data was compiled by the late Robert B. Horton, eminent civil engineer and hydrologist. The tabulation which Mr. Horton compiled for the Natural Research Council was published in the Transactions of the 24th Annual Meeting of the American Geophysical Union, Part II, April 1943, and contains data for some 150 Weather Bureau Stations throughout the United States. Mr. Horton adjusted these data in all cases giving results equivalent to those for the standard Class O Weather Bureau pan while data covering only short periods were further adjusted to the most probable long time means. The validity and reliability of these data is above question and they constitute a most valuable reference source which has been frequently consulted and was used in checking the data used in this study. With this evaporation formula, a table was prepared to show the approximate mean annual evaporation in acre-feet for several combinations of alternative reservoir sites suggested as substitutes for Echo Park and Split Mountain Reservoir sites. Considerable additional study was given to this subject after the computation of the first table, and records from two additional Weather Bureau stations in or very near the Colorado River Basin were utilized for additional basic data. Formula (1) was then revised with the following slight change in the numerical coefficients and is hereinafter referred to as formula (2) - E = 86.4 + 46cos 2x - 10A (2) E, x and A have the same significance as before. Analysis of -44- |