<br />003082
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<br />T. W ROBINSON H
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<br />THE ROLE OF PHREATOPHYTES IN THE HIDROLOGY
<br />OF ARID REGIONS'
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<br />ABSTRACT
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<br />The vegetation of arid regions may be divided, on the basis of the source of its water
<br />supply, into two general classes, xerophytes and phreatophytes. Xerophytes, the more
<br />extensive group, are plants that subsist on meager, amounts of soil moisture j phreatophytes,
<br />which require more water, are plants that habitually obtain their water supply from
<br />ground water. In comparison to xerophytes, phreatophytes are more closely related to,
<br />and have the greater effect on, the water available for man's use. In addition to their
<br />effect on water supply, phreatophytes may grow so densely along -streams as to increase
<br />the flood hazard by choking the hormal overflow channels.
<br />The occ.urrence of phreatophytes may be used as a guide to indicate not only the
<br />presence of ground water hut also its approximate depth and qualit~. As these plants use
<br />large quantities of water and as most of them are of low economic value, they waste large
<br />quantities of ground water through the process of transpiration. .This draft -on the ground-
<br />water reservoirs of the arid regions depletes an already inadequate water supply. Much
<br />of this wasted water can he salvaged and therefore conserved hy methods that will put
<br />it to a higher beneficial use.
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<br />INTRODUCTION
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<br />The vegetation of arid regions may be divided, on the basic of its source
<br />of water supply, into two general classes, xerophytes and phreatophytes. Xero.
<br />phytes are plants that obtain their water supply from soil moistnre;' phreato-
<br />phytes are plants that tap ground water. Commonly, in arid regions, the soil
<br />moisture, which is derived from irregular and infrequent rains, is deficient
<br />for the plants' needs. As a consequence, xerophytes are adapted to subsisting
<br />on a scanty water supply, and during long dry periods they may become es-
<br />sentially dormant. This ability is connoted by the term xerophyte, which was
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<br />'" Publication authorized by the Director U:. S. Geological Survey.
<br />'" ... Hydraulic engineer, Grouml Water Branch, W ate~ Resources
<br />Geological Survey, Menlo Park, Calif.
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<br />Division, U. S.
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<br />77
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