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<br />00309G <br /> <br />SECCION IV - GEOHlDROLOGiA <br /> <br />85 <br /> <br />,.'~,'.: .,;c. d"';. ',-,' "'-' <br /> <br /> <br /> <br /> <br /> <br />:; ~~1~~ <br />: l:,," ',>,;';1;':;.':"';":;;8:';; <br />/'" .\,:,:.:,.:::;g:;~"';'!"i'; <br />.',." '..c"..c: ":?;'; <br />[;}::": .:', . tie: <br />,(,>::?;"',:;;;.:;~,..:).:....:;.~~{:,; <br /><' <;<> J'~':>, ..",):, <br />r')!i;l~;':;""': :;; :", <br />,.:..,,: :,', (';:'.i;:; <br /> <br />;' ::<(:"'~i~~;ij: ;' <br />.> ,:,.. <br />::;:, <br />iF <br /> <br />The e!fect of humidity is the reverese of that of temperature. Experiments <br />in the Safford Valley of the Gila River of the southwestern United States show <br />that, as the relative humidity increases, the use of water by the plants decreases, <br />and as the relative humidity decreases the use increases (Gatewood, Robinson, <br />Colby, Hem, and others, 1950, p. 143). <br />The effect of wind movement is to increase the use of water, owing to removal <br />of the air or high humidity next to the plant leaves and replacement with air <br />of lower humidity from the adjacent desert areas, For the 'other elements of <br />climate, it has been found that. the plants' use of ground water is greatest when <br />the growing season and daylyght hours are long and the rainfall canty. In <br />arid regions generally, during the growing season, the temperature is' high, <br />the humidity low, the wind movement substantial, and the rainfall scanty. This <br />combination of climatic conditions is conductive to a high rate of water use <br />by phreatophytes, and, hence, to a substantial depletion of the groundwater <br />reservoir. <br /> <br />,: <br /> <br />(,:; it: ...,'...., !],; <br />,)~:,,::: 'OC c.; :.:~, <br />"x.,'.,"",..", :,..::";';"'::.,,,,..., <br />.:'.........,}.:: :,/ "r\,y <br />"./.:: ',,',.,' <<~"\.;..';\' <br />':""';'.:":::"""'. <br />/"'/:'~)"',:;"" :'" <br /> <br />. .:.. ..:.'..;.....'..',,<:\..... """?:;;:r;%"{ '~}'J".....".;..:,.I" ..,.,.:t;~I<.." :.:;'::"X>, <br />" '.' '. ,', ":'\':"5\i';>;":",,':/':.<:i> ,'i"" ,:f,',I,:D., :,::'<<:"';'",: .' .,;':;.;> <:':;",:";",,,,:;,)"'" <br /><,,;'';'''',< . . ..,; ":'/,;:'''-);'\'';;':;,:,,:;<~Y< ;" "':;' .,:,., . X:';;," ','.,: . ",::::..:y:.y.. ,,:<<',:::.;.'i :::0' <br />'..:.' ':::,V,'r';:~::;,:iX'{;:,;: ',::\0'1;"';; ';>~.J::.':'.,': .",;:I)!';;:{:i::>'<.:, .::. ",<iii';';:?';: i,:.:;!~"t :" <br />::;'::r":>',::"',;}'/\' ....,',;",t;,,ii::~i;:',;.,,f '-:.": '..:i.;, ,,'.;,:,:>," .,,:';;: ',."';> ',.: ~t;. <br />',',.,', :'.:..: ,,/:T ';ir:.",:}{<'.;,. /';""i,S:::;";'iWi:::::.i\':":;,;;.,r\',/\( '.,. ,j..,;::::; ::;''' .:i" >:,:. "',,:,, ~:5 <br />;';';.:!'>'''Vii.~\t~ .....':,/,.;(',::;"i:,;:j;.:::.:~\.... \~/"""':"';'....."".:L~~';.2;::" .;,:., >'.... ;:i;,~~;~b:;'~~~\*~ifKt;f~~(,t~~it?,;;'" f,ti~t{~:i~~t~;f';~~ <br /> <br />The density of phreatophyte growth is not uniform but may differ widely <br />from place to place, the plants raging from a dense jungle, like forest to a few <br />scattred individuals. The height or' size of the plant and the amount of. foli- <br />age affect the quantity or ground water transpired. The variations in density <br />and size of the plants may be evaluated in terms of areal density and vertical <br />density, and expressed as a product of the two, volume density. Areal denshy <br />relates to the density of growth of the plants with respect to the maximum <br />possible, Vertical density relates to the depth or thickness of the foliage with <br />respect to the maximum possible, The conditions of growth may be described <br />in terms of percentage of density by assigning a value of 100 percent to the <br />maximum possible, and zero to essentially no growth. A density of 100 percent <br />indicates growth so thick that the addition of a new growth .would caU3e an <br />equivalent amount of old growth to he choked out and to die, <br />It has been found that the use of water by phreatophytes is proportional <br />to the quantity of the transpiring material (Gatewood, Robinson, Colby, Hem, <br />and others, 1950, p. 27), As volume density is a measure the transpiring mat- <br />erial, the draft on the ground water varies as the volume density. The draft <br />is greatest where the growth is dense and the plants large, and least where the <br />growth is small and scattered. <br />Data on the annual rate of consumption of water by the different specie. <br />of phreatophytes are scanty, The data that are available indicate that the con- <br />sumption varies widely between species, even when growing in the same locality <br />and under essentially the same conditions. Data have been obtained for the <br />use of water by 8 common species of phreatophytes at different localities in <br /> <br />'..., ,.,,' <br /> <br />";:":/;;;:i~~if':' \,.:'" <br />.....,::..;,,:,;i~;.;;, <br /> <br />'f' <br /> <br /> <br />""'~rJ'~i~f.ffil~~;1' <br />[fi~;~I~~?l;.J,,;~ <br />)./j,": <br />(, :;;'[; :0. ;'\;::;JBf <br />; :':""'>"".'\)i?jEt <br />:':<1': } <br />\:, <br /> <br />JL~"; <br />