Laserfiche WebLink
<br />seepage of excess irrigation water from fielcs. d1tc~es and canals onto ancient <br /> <br />c <br /><;> <br />J:>, <br /> <br />marine depos1ts tleneath t~e 1rrigated lands. <br /> <br />Extremely saline aquifers <br /> <br />:-:; <br /> <br />(ground'Water deposits of concentraticns reaching 10.000 m;/l> overlying a <br /> <br />marine-deposited formation known as Mancos Shale are the primary source of <br /> <br />farm-cerivee salinity. Salts contained 1n the format1on are dissolved b)' water <br /> <br />enterin; aquifers and coming into chemical equllibrium with t~e shale en route <br /> <br />to the river's channels. The number of sa11n1ty sources (largel)' nonpo1nt}, <br />the variety of potential technical and institutional solutions for their <br /> <br />abatement, and the fact that those adversely affected by this externality are <br /> <br /> <br />separated spatfally, temporally. and administratively from the principal <br /> <br />pollutant sources create a un1que and complex cas1n-w1de water Gual1ty <br /> <br />management problem. <br /> <br />(Miller, Weat/'lerford. anc Thorson prov1de an excellent <br /> <br />overview of the Colerado River salinity issue.) <br />Salinity err.erged as a major policy 1ssue in the Colorac:o Rtver Bastn 1n <br /> <br />the early 1960's. An irr1gation project in ",estern Arizona began discharging <br /> <br />highly saline waters from a new drainage system. The f111109 of lake Po....ell, <br />the reservoir beh1nd Glen Canyon Dam, sharply curtailed water supplies <br /> <br />available to d1lute salts do....nstream. These t.o events drastically reduced the <br /> <br />qua11ty (and quant1ty) of ..ater aval1able to those rece1v1ng Colorado River <br /> <br />supp11es in Mexico and in parts of the U.S. <br /> <br />The Environmental Protection <br /> <br />Agency (1971) reported a signff1cant level of econom1c damages from salinity. a <br /> <br />conclusion supported hter by the U.S. Bureau of Reclamation (1980). Concerns <br />over potential furtner ..ater qua11ty decline on both sides of the bor~er led ~o <br />the Sal1n1ty Contrel Act of 1974. Th1s act prov1~e~ for abatement of bot.h <br /> <br />natural and agricultural sources, an<l authorized construction of four Upper <br /> <br />8as1n salinity control units and the stu~y of twelve others. <br /> <br />me 5011 <br /> <br />2 <br />