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1 <br /> 1960 was selected as the basis for determining normal <br /> evaporation because this represents a period of consistent <br /> ' and complete records and includes both wet and dry intervals . <br /> These data are contained in Figure C-2. Because the rate <br /> ' of evaporation from small surfaces , such as pans, is more <br /> than for large open surfaces , such as lakes, it is necessary <br /> 1 to convert pan evaporation measurements to lake surface <br /> evaporation by application of a coefficient. A coefficient <br /> of 0. 78, which is generally applicable to a Colorado sunken <br /> ' pan, has been applied to the data of Figure C-2 to derive <br /> total lake surface evaporation which is contained in Figure C-3. <br /> Pan evaporation measurements are limited to the months of <br /> April through October because during the winter season the <br /> ' loss rate is relatively low and freezing of water in pans <br /> precludes accurate measurement. Information published by <br /> ' the U. S. Environmental Data Service indicates that for the <br /> Boulder area May-October evaporation represents 72 . 5% of <br /> the annual total. Using this figure the annual evaporation <br /> ' was computed as shown in Figure C-3. The evaporation for <br /> ' November through March was then determined by deducting the <br /> April through October amount from the annual total and is also <br /> ' shown in Figure C-3. <br /> ' Net water loss for normal dry and wet year conditions was <br /> ' determined by reducing total lake surface evaporation, as <br /> C-7 <br />