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<br />THE PROBLEM
<br />
<br />The Colorado River Basin encom~ portions of
<br />seven states. The river flows ova, r 1, ,mi'~ from Its
<br />headwaters tn Wyoming and Co jol~ with
<br />tributaries In Utah and N9IN Mexico, flQws through the
<br />Grand Canyon, provides state bounda.fies for Nevada.
<br />Arizona, and California, and terminateS In the Gulf of
<br />California in the Republic-of Mexico. :
<br />Use of the river's water now and in futUre years has been
<br />allocated through a long history of apQroprlatlons and
<br />negotiations that include compacts.l~atlon, legislation,
<br />and an International treaty. ,
<br />About half of the present satlnlty COl)centretlon In the
<br />Colorado River at Hoover Dam near Lfs VeQas Is
<br />attributed to natural sources. The remalnlng half Is man-
<br />Induced as Indicated In the Chart.' .
<br />
<br />
<br />47% N~tural Sources
<br />37% IrrJgation
<br />12% REI~ervoit Evaporation
<br />--3%exp~rt$
<br />
<br />1%M&t
<br />
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<br />
<br />For irrigators, the higher salinity con~tratiOns cause
<br />decreased crop yields, altered crop patntms, locreased
<br />leaching and drainage requirements, 8~ .I~c~
<br />management costs. AgriCulturallosses~lther through
<br />lower yields or incmasOO productJonlm ' nt costs)
<br />begin when salinity levels of applied lnig Ion w~terreach
<br />700 to 850 mgIL, depending upon soil l;Pndltlons and
<br />type of crop grown. A summa!)' of the ettdcts is presented
<br />below: '
<br />
<br />mgiL
<br />
<br />Effect,
<br />
<br />Below 500
<br />Above 500
<br />700-850 and
<br />above
<br />
<br />Good drinking watet
<br />Municipal and Indus,trial losses
<br />Agricultural losses
<br />
<br />The Colorado River, at its headwaters 10 the mountains
<br />of north-central Colorado, has a salinity (dissolved
<br />minerals) concentratfon of only about 50:- ~glL. The
<br />salinity concentrations progressively incl1tase down-
<br />stream as a result of water diversions anQ salt
<br />contributions fromavarietyofsources.ln \981, ttlesalinity
<br />concentration averaged about 616 mglL I'jt Imperial Dam,
<br />the last major diversion point on the CoIorfdo RIver in the
<br />United States. Without control measures,~ the
<br />concentration is projected to increase, pos;ibly reaching a
<br />level of 1089 mglL. at Imperial Dam by 4bout -2010.
<br />
<br />~
<br />
<br />Salinity concentration increases result from two
<br />processes: salt loading and salt 'concentration. Salt
<br />loading increases the amount,of salt1ar a given amount of
<br />water, and salt concentration decf8l.l;Ses the amount of
<br />diluting water for a given amount of,salt.
<br />Salt loading is the addition to the river system of minerai
<br />salts from natural and manmade sources, Salt
<br />concentration results from the rise in salinity through
<br />streamflow depletions which concentrate the salt burden
<br />into a lesser volume of water in the rlversystam. Generally,
<br />the application of irrigatIon water reSults in Increased salt
<br />concentrations because of salt loading and concentrating
<br />effects of consumptive use: The total salt load In the river
<br />fluctuates annually with the overall Basin water supply.
<br />M the following ,graph illustrates, since 1949, the
<br />gen_el'lll trend In salinity concentrations at Imperial Dam
<br />has been upward, and the projectad level. through the
<br />year 2010 (without water quality Improvement program)
<br />, are 'eXpecred to fOllOW the ~rall rising trend.
<br />, The losses'asSoclated with municipal8!nd Industrial use .
<br />occur primarily from Increased water treatment costs;
<br />accelerated pipe corr.Osion and appliance wear, increased
<br />soap and detergent needs, and decreased watar
<br />palatability. The Environmental Protection Agency
<br />recommends drinking. Water contain no more than
<br />5:00 mglL of IDS (total dissolved solids). .
<br />
<br />
<br />TOTAL LOSSES
<br />$513,300 per mg/L (1982 dollars)
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<br />,
<br />,
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<br />-1f""""'W,,,,o.~"""'''~~'"'''....m
<br />
<br />floco<dOd..llnilV i....' " ImPGl'i.1 O.m, wilh""'lOOt;on.th"'''llhlh'V...20IO
<br />
<br />
<br />
<br />The hIgh salt load of about 9 mimon tons annually
<br />entering lake Mead in .the Lower ColoraddJUver' 6asih
<br />adversely affects more than 12 million peopJe~d 1 million
<br />acres of irrigated fa'nntand In the United States.Damages
<br />in the amount of $513,300 are projected to oCcur for each
<br />increase of 1 mgIL at Im~,rial Dam when _Salinity !
<br />concentrations reach the 875 to 1225 mglb range._ln
<br />1962, damages were approximately $113 mUllan, Unless
<br />controls are implemented, the damages could riseb$267
<br />million annually by the year 2010.
<br />In the late 1960's and early 1970'$, leaders at the regional
<br />and national level began to recognize the problem and
<br />seek solutions.
<br />
<br />"Current projection from QualllyofWaler, Colorado River
<br />Basin, Progress Report No. 11, January 1983,.Oepartment
<br />01 the Interior, '
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