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<br />. <br /> <br />0760 <br /> <br />diversions during releases considerably greater or less than 400 ft3/s <br />may differ from that given in figure 7. They may be estimated by assum- <br />ing a direct relationship between reI ease discharge and inadvertent <br />diversions (inadvertent diversions during a 100-ft3/s release would be <br />about 25 percent of that given in fig. 7). <br /> <br />Although the detailed chart study involved only 14 of about 40 <br />diversions above the Colorado Canal, the brief examination of the charts <br />for many of the other ditches indicated only minor response to the res- <br />ervoir releases. <br /> <br />Data are not available to evaluate return flow as it might affect <br />inadvertent diversions and for this reason it was not considered in the <br />preceding analysis. However, return flow in general, and specifically <br />its effect on inadvertent diversions, is an area in which further study <br />is needed. <br /> <br />Evapotranspiration <br /> <br />Evapotranspiration is the process by which water is evaporated <br />from wet surfaces or transpired by plants (Veihmeyer, 1964). A brief <br />discussion of each of the two processes involved in evapotranspiration, <br />evaporation and transpiration, follows. <br /> <br />. <br /> <br />Evaporation losses <br /> <br />Evaporation takes place both from free-water surfaces and from soil <br />surfaces. The increase in evaporation from soil surfaces due to bank <br />storage during a reservoir release was assumed to be insignificant. <br /> <br />Evaporation from free-water surfaces is commonly determined from <br />estimates of lake evaporation. Lake evaporation can be estimated by a <br />number of methods. Three of these methods were used in this phase of <br />the study and are only briefly described herein: <br /> <br />Method 1. Standard pan evaporation method (Veihmeyer, 1964). <br />By this method, average monthly pan evaporation for the entire <br />reach was determined by correlating observed pan evaporation <br />with elevation and mean monthly temperature at appropriate U.S. <br />Weather Bureau stations. The average monthly lake evaporation <br />was then computed as <br /> <br />Elake = 0.7Epan' <br /> <br />(4) <br /> <br />Method 2. Modified pan evaporation method (World Meteorolog. <br />Organization, 1966). This method converts observed pan evapora- <br />tion to lake evaporation based on climatic and topographic con- <br />siderations. Calculations were made for both the Pueblo and Twin <br />Lakes U.S. Weather Bureau stations and averaged. <br /> <br />. <br /> <br />23 <br />