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<br />3 <br /> <br />The amount Df water used by these plants in their transpiration varies <br /> <br />with many factors including the depth to the water table, climate, water <br /> <br />sal inity, density of growth of the species, etc. Measurements and some <br /> <br />reasonable estimates of the amount of water transpired by phreatophytes <br /> <br />are available. A single cottonwood tree three years old can use 10.3 <br /> <br />gallons per day, and a three-year old salt cedar used 13.5 gallons per day <br /> <br />during the growing season in Safford Val ley, Arizona.4 A more useful <br /> <br />measurement is on an acreage basis, which gives a better way to calculate <br /> <br />total water loss for large areas. Table 2 gives amounts of water used by <br /> <br />some phreatophytes under certain conditions in the Arkansas River Val ley <br /> <br />between Pueblo and the <br /> <br />5 <br />Co I orado-Kansas border.. For compar i son purposes, <br /> <br />Table 3 I ists typical \'Iater consumptive use by irrigated crops in the <br /> <br />Arkansas River Valley east of Pueblo.6 <br /> <br />TABLE 2 <br /> <br />ANNUAL WATER LOSS RATES IN RELATION TO WATER TABLE DEPTH <br />Water Loss Rates'" (Acre-ft. ,per Acre) <br />Depth from Surface in Feet <br /> <br />Vegetation 0-5 5-10 10-15 <br />Cottom,ood 3.3 3.0 2.5 <br />Heavy brush (salt cedar) 3.5 3.3 3.0 <br />O~,en b rus h and grass 2.0 1.6 1.2 <br />Open a re a 5 1.5 1.0 0.8 <br />Cattails to open \"a te r 4.0 <br />,', I nc 1 udes effective precipi tation <br /> <br />Althouth the above figures are high, it should be kept in mind that in <br /> <br />open areas \..,rith normal grass cover, or range lilnJ, evapotranspiration is <br /> <br />ai'proximatelyequal to the annual ~recipitation. or about I: to IS inches <br /> <br />per year. <br /> <br />,- <br />