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<br />Assessing salin~~-~~ct'8~~~O~.Ts on the Colorado RiYf~
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<br />SALINITY IN THE Colorado River Basin /7~1;~/?!r;:)}C"---.
<br />adversely affects more than 12 million . -. /r'''':' 1,"_
<br />people and I million irrigated acres in the . .'/ ,.., . ?~I < ! (
<br />Southwestern United States and a portion Colorado :':".':i -'. '
<br />of Mexico. The river's salt conten( in- ,_,
<br />c(reases from about 50 milligrams per liter River Basin c; :,(..,_,',),;,~_:;.:",<_.,...,._,..;".. . ',;__
<br />mg per liter) al"its headwaters to more _ " ~
<br />than 800 mg per liter at Imperial Dam, WYOMING' ,"', <.(, 1..,>-
<br />Arizona, the last major diversion point ScalulM"u . :.I.c.\:.:~?i:"f.'-
<br />before the river reaches Mexico. AI. 0 25 so 100 - "'::'7,q.~::)
<br />though salt springs, water leaching through _
<br />saline soil and rock formations, and other
<br />natural sources contribute to the salt load,
<br />salinity increases since 1900 mostly are of
<br />human origin. Society's increased con-
<br />sumption of relatively pure water causes
<br />salts to be concentrated in remaining
<br />stream flows, thus increasing salinity. Ad-
<br />ditional salts arc added by'irrigation re.
<br />turn flows. which often percolate through
<br />saline rock and soil before rejoining the
<br />river,
<br />In the 1960s saline waters discharged
<br />from the Wellton-Mohawk project in Ar-
<br />izona and the filling of Lake Powell be-
<br />hind the Glen Canyon Dam sharply in-
<br />creased the salinity of water delivered to
<br />Mexico, Concurrently, the perception of
<br />salinity damages grew, and Upper and
<br />Lower Basin water interests united to form
<br />a strong coalition to push for a federally
<br />funded salinity-control program. I
<br />The result was the Salinity Control Act
<br />of 1974 authorizing construction of a ma-
<br />jor desalinization plant under Title I and
<br />four salinity-control units and the inves-
<br />tigation of twelve others under Title n.
<br />Initially, $155 million was authorized for
<br />Title I and $125 million for Title II, but
<br />costs of Bureau of Reclamation and Soil
<br />Conservation Service salinity-control units
<br />under Title II ultimately may approach
<br />$500 million, Significantly, federal mon-
<br />ies will pay entirely for the desalinization
<br />plant to meet commitments to Mexico and
<br />for 7S percent of the domestic salinity-
<br />control program. The remaining 2S per.
<br />cent will nol be paid by project benefi-
<br />ciaries but by surplus power.generation
<br />revenues from the Colorado River Basin.
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<br />Hydrologic uncertainty
<br />
<br />Despite this large financial cornrpitmenr,
<br />considerable hydrologic uncertainty sur-
<br />rounds salinity control. At one time it was
<br />projected that by the year 2000 salinity
<br />levels at Imperial Dam would rise dra-
<br />matically to 10400 mg per liter from the
<br />1972 level of 879 mg per liter. Subse-
<br />quently. however. official projections have
<br />
<br />IAllen V, Knees(:. "Salinitv in the Colorado
<br />River," Resources no. 70 (July) 1982.
<br />
<br />10,RESOURCES
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<br />CALIFORNIA
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<br />been reduced to a current expectation of
<br />946 mg per liter by the turn of the century,
<br />without salinity control.~ Salinity at 1m.
<br />perial Dam has actually fallen in recent
<br />years to 816 mg per liter in 1981 and to
<br />732 mg per liter in 1983, This, of course,
<br />leads one to speculate about the efficacy
<br />of salinity.control investments.
<br />It also takes time for water and salls to
<br />pass from the Upper Basin through all the
<br />reservoirs to the Imperial Dam, The Bu-
<br />reau of Reclamation now assumes a hy-
<br />draulic retention time of five to seven years,
<br />~U.S. Bureau of Reclamation. Colorado River
<br />WaItT Quallry Improvemenl Program. Status
<br />Report. No. 12, Denver. Colorado. January
<br />1985.
<br />
<br />so that 90 percent of salinity-control ben.
<br />efits probably will be perceived at Im-
<br />perial Dam in that time. This is impor.
<br />tant. because the economic measure of
<br />damages avoided by salinity control must
<br />be discounted to establish a net present
<br />value for comparison CO program costs.
<br />Finally, both the relarive contributions
<br />to salinity by various sources and the
<br />amount of salt that must be removed from
<br />the river to achieve a given reduction re-
<br />main uncertain, The accepted estimates
<br />of the sources of salinity are from a \97l
<br />EPA study that attributes ~7 percenr of
<br />salt contributions to natural sources. 37
<br />percent to irrigation. (2 percent to res-
<br />ervoir evaporation. 3 percent to water ~:t-
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