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<br />Salinity in the Colorado River Basin <br /> <br />A <;o:riou~ ...."ater-quality issue in the Colorado River Basin is salinity defined <br />as the concentration of dissolved mineral salts or total di~sol\'ed solids in <br />water. Salinity increases in the Colorado River in a downMream direction: the <br />disso(ved~solids concentration is about 50 mgIL in the upstream mountain <br />areas and averages about 850 mgIL at Imperial Dam. Arizona (Kircher. 1984). <br />In the VeOL. annual dissolved-solids loads in the Colorado River ranged <br />from about 17.700 tons at HOI Sulphur Springs in the Southern Rod:}' ~h)Un~ <br />lains 10 more than 3..300.000 tons near the Colorado-Utah State line, <br />~Iajor 'murce... of salinity in the Colorado Rh'cr Basin are mineral springs <br />and nonpoint-source runnff. The major human influence is irrigated agricul- <br />lure. About II percenl of the salt load in the Colorado River near the U.5.- <br />~texico border is contributed from Ihe Grand Valley and Uncompahgre Valley <br />(lower Gunnison River Basin) agricultural areas (U.S. Depaflment of the <br />Interior. 1999). Much of the soil in these areas is derived from and overlies the <br />i\1ancos Shale, a saline marine deposit Deep percolation of irrigation water <br />and seepage losses from irrigation systems leach salt from the '>oil and .shale. <br />increasing tht. salinity of return t10ws. Salinity-control projects have been con- <br />su"Ucted throughout the Colorado River Ba..;in. including two projects in the <br />UCOL-thc Grand Valley Unit and the Lower Gunnison Basin Unit. <br />As part of the study of salinity in the Colorado River Basin. trends in dis. <br />solved-solids concentrations in tht' basin have been investigated in numerous <br />studies (Vaill.md Butler. 1999; Bauch and Spahr. 1998; Butler. 1996: Lieber- <br />mann and others. 1989: Kircher. 1984). The most recent study (Va.ill and <br />c Butler. 1999) detennilled that <br />',"" S <br />CoIoflldQ.... since the 19605 there have <br />Plateau' ] <br />6.000 ill been. in general. downward <br />,\ . <br />~ trends in flow.adjusted annual <br />" <br />I 5,000 ~ and monthly dissolH'J-solid:. <br />,t ~ concelllrations and loads in the <br />.,000 '!: <br />U Colorado River Basin upMream <br />, <br />3.000 ~ from Lake Powell in U1.1h. <br />~ e.""cepl in the Yampa River <br />2.000 '" Basin. In the UeOL. there <br />1-1 ~ were downward trends both <br />I " ',"" . J \ <br />,i ! upstream an lownSlfeam <br />" 0 i from the salinity.control <br />I ~ ~ 'i projects in the Grand Valley <br />i ~ ~ and the lower Gunnison River <br />~ ,~ Basin. With the downward <br />trends as e....idence. it appears <br />that both natural processes and <br />human etIorts such as salinity- <br />control projects may be <br />decreasing salinit)' loading in <br />the Colorado Rher Basin. <br /> <br />... <br />"'" <br />I'-' <br />..., <br /> <br />3,500,000 <br /> <br />~ 3.000,000 <br />, <br />~ <br />~ <br />~ <br />~ <br />. <br />~ <br />z <br />z <br />< <br /> <br />2,500.000 <br /> <br />2.000.000 <br /> <br />l.soo.ooo <br /> <br />1.000.000 <br /> <br />""""," <br /> <br />o 'CAD <br />. STREA""FlOW <br /> <br />, <br /> <br />. <br /> <br />,,,,,,"'m <br /> <br />"""" <br /> <br />Ml)IJnlBlrI$ <br /> <br />. <br /> <br />n <br /> <br />t) tj <br />I' I' <br /> <br />. <br /> <br />= <br /> <br />~ <br /> <br />~. OOWl';5mEAAAOIf'lECT1ON- <br /> <br />U <br />is <br />!~ <br />I <br /> <br />Mean amUBl d<SSOlveO-so/Ids 108-d$11'lCf&BSe greatly <br />befWeen~&SintheSouthllmRockyMoun!alnsand <br />$lIef; in Ihe CoIonw:lo Plateau. 0.18 based on WBle.- <br />ye.ars 197010 1993. (Butler.l996; BaltChand Spaht, <br />1998) <br /> <br />20 <br /> <br />\\'~Her Qualit~ 1Il1lle t"p~r COll1f.ldl) Rl\er Ba"!n <br />