WSP08576 - Laserfiche WebLink

Home Browse Search

Jl " I 2.a.b't WATER QUALITY Salinity at Northerly International Boundary Detailed information on negotiations between the United Stares and Mexico concerning the problem of high salinity of the Colorado River at the Northerlv International Boundan' was presented in the'I964--65 Annual Report 'of the Board. That report also described the participa- tion bl' the sevCll-state COlllmittee of 14, of which' the Chief Engineer is a melllber, in the deliberations which led to the international a!l:recment framed in Minute No. 218 of the l~1ternational Boundarv and \Vater Commission, approved March 23, 1965. 1n broad tcrms, the Minute provides that as an interim solution to the problem the United States construct, at its expense, an extension to the \\lellton-Mohawk drainage works with a C<lpacity of ,5) cubic fcet per second. Provi- sions for the operation of the drain extension arc spelled ont in the Minute. The Extension Channel can conve.I' drainage \I'ater from the \VeUton-Mohawk VaileI' to the Colorado River either above or below i\1orelos Dam, the Mexican diversion structurc. Con- srruction of the Extension Channel along the left hank or Arizona side of the river, was COIll- pleted in time for use during a major portion of the critical winter period of 1965-66. The wi"nter period is defined in the Mexic'lIl "''!,'ter Treatl. as October I throngh the following F ebn.iary. Generally during that period the Mexican warer orders arc near or at the T reatl' minimum of 900 cfs., so that the proportion (;f the total delivery composed of the relatively uni- form drainage returns from the Yum" area is greater and hence the salinity problem more acllte than in the other months. On November 16, 1965, drainage from the \Vellton-Mohawk VaileI' in Arizon'a was dis- charged intn the newl;' constructed 13-mile ExtensiOli Channel (formallv named by the Bureau of Reclamation as Main Outlet Drain Extension Channel). That date marked the be- ginning of the five-year period that the Minute will be openltive and also the end of four years of effort to find an interim physical solution to the salinity problem. . Drainage from the \\lellton-Mohawk Project increased from 36,900 acre-feet during the No- vember 15, 1964--Februarv 28, 1965, period to 6\,7()() acre-feet dming th~ companlb\e \965-(,(, period, However, the bypassing of \Vellron- Mohawk drainage waters to the river below Morelos Dalll resulted in reduction of the aver- age salinirv of the water in the river at the northerly' bound"rv of Mexico from about 1,470 p'pm during' the 191\4--1965 period to 1,190 ppm Juring the c<>mparable 1965-66 period. The Commissioner of the United States Sec- tion of the I nternarional Boundarv and \Vater Commission reported that during 'the first year of operation, fn)]ll November 16, 1965, through November 15, 191\6, a total of 105,830 acre- feet W,IS discharged from the bypass channel into the river below Morelos Dam, all account- able as Treatl' water. Of this amount, 47,170 ;lcre feet (45 percent) were disch'argd 'at the re- quest of Me.\ico during rimes when the scheduled deliveries were above the Treatv minimum of 900 cis. The remaining 58,660 'aere-feet were discharged below Morelos Dam during times of Treatl' minimum winter deliveries. About 15,- 000 icre-feet had to be m;lde up b~' releases from slorage in the United States in order to deliver in accurdance with Minute No. 218, the Tr~at\' minimum in the limitrophe section of the rh'er exclusive of \Vellton-Mohawk drainage waters. Plate 11 shows tbe salinin' and flow of the \Vellton-i'vlohawk drain, ami" of Colorado River ar Imperial Dam and at the northerly boundary of Mexico. Effect of Salinity on Agriculture It is generally recognized that increased use of Colorado River water by Upper Basin states will result in higher salinit~; of the already poor quality Colorado River water available to Cali- fornia, unless there js a major water augmenra- 31