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<br />Method 3. Empirical method (Harbeck, 1962). <br />reservoir evaporation in feet per day can be <br />equation <br /> <br />. r, . <br />Accot'd !ng "to Harbeck, <br />calculated using the <br /> <br />. <br /> <br />E = Nuz(eo-ea) <br /> <br />(5) <br /> <br />where N is 0.00028 for a I-acre surface area, uz is wind speed <br />at 2 meters above water surface in miles per hour, eo is the <br />saturation vapor pressure in millibars, corresponding to the <br />temperature of the water surface, and ea is the vapor pressure <br />of the air, in millibars. Mean monthly river temperatures were <br />estimated from data provided by the following: <br /> <br />Northside Waterworks, Pueblo; <br />Southern Colorado Power Company, Canon City; <br />Colorado Game Fish and Parks Department, Salida; <br />Otero Pumping Station, Homestake Project, Granite. <br /> <br />The evaporation rates determined by this method were much <br />lower during midsummer than rates determined by the other <br />methods. The reason is the importance of the wind factor <br />in this method and the fact that May, early June, and late <br />September are relatively windy above Canon City. <br /> <br />All lake evaporation rates determined by these methods were <br />multiplied by a factor of 1.7 which, according to Delay and Seaders <br />(1963), allows for higher evaporation rates from streams. Table 6 <br />shows the results of these determinations for the five common irri- <br />gation months. <br /> <br />. <br /> <br />Table 6.--Summary of Arkansas River evaporation aa~au~ations <br /> <br /> Mean monthly river evaporation, <br /> Method in feet per day <br /> May June July August September <br /> - <br />Standard pan evaporation-- 0.026 0.030 0.030 0.026 0.022 <br />Modified pan evaporation-- .030 .032 .032 .027 .021 <br />Empirical----------------- .034 .026 .018 .018 .022 <br />Average-------------- .030 .029 .027 .024 .022 <br /> <br />24 <br /> <br />. <br />