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<br />001497
<br />only a relatively small area subject to this loss is needed to furnish the
<br />requirements for stock use. Evaporation maps prepared by the United
<br />States Weather Bureau show that the average annual evaporation from a
<br />lake surface in the Pacific Southwest area varies from a minimum of
<br />about 30 inches in the no rthern mountainous area to a maximum of 86
<br />inches in lower parts of the Gila and Colorado River basins (U.S. W. B.
<br />1959). From 70 to 80 percent of this loss occurs in the 6 summer months,
<br />May to October" when most ranges are in use. Total stock water require-
<br />ments for 100 head of cattle during this period will be about 184,000 gal-
<br />lons, or 0.57 acre-feet. This is equivalent to the evaporation Irom 0.24
<br />acre of open water in the north where evaporation is at a minimum or to
<br />0.1 acre in the south where evaporation is at a maximum. 'The require-
<br />ments quoted are for stock use only and do not include anything for loss
<br />or waste resulting from storage in tanks or troughs.
<br />
<br />The amount of transpiration loss by vegetation varies in accord-
<br />ance with a number of factors, including plant species, density and height
<br />of vegetation, depth to the water table, temperature, and the number of
<br />daylight hours. The Subject has been discussed by several investigators
<br />and various ,methods for measuring or estimating the use of water by dif-
<br />ferent types of plants have been developed. One of the commonly used
<br />methods is the empirical Blaney-Criddle formula (Blaney, H. F., and
<br />Criddle, W. D., 1949). Examples of consumptive use of phreatophytes
<br />obtained by measurements, inlyst:rnete.rs or bye,stimates using th.., BLaney-
<br />Criddle Jprmula; or othe'rm,ethods,a:r,e 'sho\ml in'tlie:>ifollowing tabulat ion:
<br />
<br />Location
<br />
<br />Table 1
<br />Consumptive use of water by phreatophytes
<br />Consumptive
<br />use during
<br />indicated
<br />period
<br />(inches)
<br />Apr. -Sep.
<br />47
<br />
<br />Compiled by
<br />Blaney( 1957)
<br />Do.
<br />
<br />Depth to
<br />water
<br />
<br />Type of
<br />vegetation
<br />
<br />tabl e
<br />(inches)
<br />
<br />Remarks
<br />
<br />Bonsall Bas in, Cal.
<br />
<br />Cottonwoods
<br />
<br />Do.
<br />
<br />70
<br />May-Oct.
<br />31
<br />24
<br />
<br />36
<br />
<br />Do.
<br />
<br />48
<br />
<br />Santa Ana Basin, Cal. Salt grass
<br />Do. Willows
<br />Rio Grande Bas in, Tex. ,
<br />N. Mex. Do.
<br />Pecos Valley, Tex.,
<br />N. Mex. Salt grass
<br />
<br />Do.
<br />Do.
<br />
<br />25
<br />
<br />18
<br />
<br />Do.
<br />
<br />24
<br />
<br />70
<br />May-Dec.
<br />40
<br />
<br />Do.
<br />
<br />Safford Valley, Ariz.
<br />
<br />48
<br />
<br />Compiled by
<br />Blaney( 1951}
<br />Do.
<br />Do.
<br />Do.
<br />
<br />Bac charis
<br />
<br />Do.
<br />Do.
<br />Ft. Collins, Colo.
<br />
<br />Tamarisk
<br />Do.
<br />Sedge grass
<br />6
<br />
<br />48
<br />61
<br />18
<br />
<br />48
<br />24
<br />54
<br />
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