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<br />003082 <br /> <br /> <br />T. W ROBINSON H <br /> <br />'&;'lW~ <br /> <br /> <br />..:f.:::,. ':.::<;{'}":;:' ',..,. <br /> <br />[;: C......>~;}:;\.). <br />..c...",..::.... '''';'':'1'''' <br />,'., "c'.Y.'., <br />."...... c.,','. ....,. ,.>,;'.;'J; <br />':;i?":" '.N'C" <br />,,'>c';;Jh' <br /><;\ \:':.<r' <br /> <br />;;'i;N;:t <br />:,:r <br /> <br />~}i~;{;~ <br /> <br />'C;' <br /> <br />. <br /> <br />THE ROLE OF PHREATOPHYTES IN THE HIDROLOGY <br />OF ARID REGIONS' <br /> <br />ABSTRACT <br /> <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. <br /> <br />INTRODUCTION <br /> <br />. <br />',i"'. ~ <br />:~ ,} :; <br /> ":'it~1;1;f ..r.. ,.; <br /> .' <br />;,;:.., :>;"" ( <br />.:' <br />i': ~~ <br />,~~;,. ~;t(:3'1 ~ <br />", ::" ;~;i~ <br />:, lie ~I!~, <br />:~~'s ;:~;~~JgrU:'; <br /> " <br /> <br />. <br /> <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 <br /> <br />.,:;-:.;'.';<.>/ .:;. '..:" <br />":'.::.;y,::'ci;.:.':;::-,/, <br />'.:', ,>("~.:~;;S:;i <br />C"::'".';::;,: :' <br /><:i", ~';:1':'''(; " <br /> <br />;'f~,"""i;!!s;{;;':; ::>'r.'':' .'.,'. .,...".. .;...'. '::/.;:......,0::.:,.'..:....:.:.:...:.'.;..' ..'.".;..., '....;..::.:'.-':".:::., ...:.,..,.,.<.;...,.;;:;;,:;;.... .\.; '.:, ,':";,"';':.,:: <br />.....,.:. ...'.;...:.;,.,... ..:;<;:;:"<':;::;:;:::: ::.,...;,:}'::..',.":,::X;,;; .;'....... ....' .;:,':,',':',<<;:." :":'\iit"'0;'.,:i::' <br />,:/,,""'\;:: ";}::::;(c"..,:::;', .'-;:i'. ;,', ..,:A><;" .j',i>...;';,.'ii.r.,',' .....,..;'.>C ~.;,:;i..<.. <br />;?:;.. ;;. ;:.: ":,','. ~,::; \>: ,;;'?;::; t:'\~,: ~...~:}..::;:\.,;t; ;\,,,:..:/::;.;};.;~:,:,','::,:~t::;;;.;: .' ....::,i>:J:..~.:;.b.G;:..::;;::~;'.::;i. <br />, ....' , ,:..'i; .,;<',;,*::...,.;.'):....,.. :;;:>'.... .:.,'..).;,. ;';i.:::)",;;'.. <br />.;;..',}' <}::.:,;';; ,,' ,.,,:t:: .:."..Ai, t;;:<::.:\i;~i;tP:::;;..;,.,:",:.... '.'c..:.;" :"'\ii':>:::<':;:':" ..'..:;:::.::..~,.;>;:>,;\ "i<;,.:',y,-'e}:;,r:'..::::;' <br />:""~'Cff:':; ;f:..~ . ':t' "'J..::t :.... '.:/ii"';i~i.;i';;':i;:..;i :t'.i'; .'.;'C.' ;'" \:' ':-:". "i.'C:;''':'.>. ....... ::'>>. "'''. .'. >,';>C;;".'. <:':<. .i,'.....'..'..> ;';"'.'\. ..;.5.):...,_...."'. .....'...3...i: :,:./. ','. <br />.'i .,!;;: ;<:) :;:;'t~t~; i;i'';'\;Tf;:'::;';; :1"".:. .W" :;~r., iJ'ir ",' <br />:". .' .'... . '. .,,' ../., "':";< '., .' ',;/ . <'; ;"";"!"':;~..;;,;i:' U ;;:', '.... <:';,,';::/0:':i'~ ;:\' . "d',;r .t ,t":; <br /> <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. <br /> <br />Division, U. S. <br /> <br />77 <br /> <br />" <br />:) <br />';:: <br /> <br />JL.;,.a <br />