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<br />003095
<br />90
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<br />CONGRESO GEOLOGICO INTERNACIONAL
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<br />The term "consumptive waste" has been suggested -(Thomas, 1951, p. 217)
<br />to denote all the water that returns to the atmosphere without benefiting man.
<br />Whem restricted to apply only ot the water used by plant life, the term aptly
<br />describes the water used by plants that have little utility for man, Under this
<br />condition, .consumptive waste is defined as that part of consumptive use that
<br />is without considerable benefit to man. As defined and used in this paper, it
<br />is a part of rather than a complement to consumptive use. It connotes the opposite
<br />of beneficial consumptive use and becomes synonymous with nonbeneficial
<br />consumptive use.
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<br />SALVAGE OF CONSUMPTIVE WASTE
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<br />The water consumptively wasted by phreatophytes is available for salvage.
<br />Salvage with respect to consumption of water by phreatophytes means converting
<br />consumptive waste to beneficial consumptive use. The extent to which salvage
<br />may be effected will vary, depending upon the economic and physical condi<
<br />tions of the area under consideration. In favorable localities it may be possible
<br />to effect nearly 100 percent salvage, in others less, and under adverse condi.
<br />tions adverse conditions perhaps none at all.
<br />The quantity of water available for salvage in any locality is equal to the
<br />total water used by the nonbeneficial phreatophytes. It is their aunual consum-
<br />tion per unit area, times the area of the plants. It has been estimated that, in
<br />the arid and semiarid regions of the western United States (roughly the area
<br />west of about the 97th degree of longitude), there are about 16 millions acres of
<br />phreatophytes (Robinson, 1952, p. 60) and that they annually discharge 20
<br />to 2:5 million acre.feet of water into the atmosphere. This amount of water
<br />is equivalent to about twice the average annual flow of the Colorado River.
<br />The virtual loss of such a vast quantity of water in a water-short region points
<br />up the importance of salvage.
<br />Salvage may be accomplished in two ways: reducing consumptive waste,
<br />and increasing the efficiency of water consumption by plant life, Both these
<br />methods require a knowledge of the occurrence of and annual consumption
<br />of ground water by the phreatophytes occupying a given area.
<br />Reduction of consumptive waste may be accomplished by taking the water
<br />away from the plants, by loweriug the ground-water level below the root zone
<br />through pumping from wells or by drainage, and subsequently using the
<br />water elsewhere. The lowering in order to be effective must be rapid; other~
<br />wise the roots may keep pace with the decliuing water level, keeping the plant
<br />alive until conditions again become stable. Another way of reducing consumptive
<br />waste is by intercepting ground water upgradient from the" area of plant dis-
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