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<br />river flm,s in Lake Head was increased in anticipation of the
<br />
<br />commencement of the filling of Lake Powell and flows available
<br />to dilute agricultural returns fell sharply. For the decade
<br />from 1951-60 the flow of the Colorado River at the northerly
<br />international boundary with Mexico averaged 4,240,000 acre-
<br />feet per year, while for the 1961-70 decade, the flow averaged
<br />only 1,521,000 acre-feet per year, a reduction of 2,719,000
<br />acre-feet per year.
<br />The Well ton-Mohawk Project, a system of diversion and
<br />distribution works for the irrigation of 75,000 acres along the
<br />Gila River near its confluence with the Colorado, was authorized
<br />by the Congress in 1947, and completed by' the Bureau of Recla-
<br />
<br />mation in 1952.
<br />
<br />Drainage problems soon developed and the
<br />
<br />Project was augnented to include a system of drainage wells and
<br />
<br />collection system discharging into the Gila River near its
<br />
<br />junction with the Colorado.
<br />
<br />The drainage system went into
<br />
<br />operation late in 1961, discharging 'approximately 300 second
<br />feet of waters averaging about 6,000 ppm of total dissolved
<br />solids into the Colorado River below the last point of diversion
<br />
<br />in the United States, but above Morelos Dam, the Mexican point
<br />of diversion for most of the water delivered under the Mexican
<br />Treaty of 1944. The average annual salinity of the waters
<br />received by Mexico increased from about 850 ppm to nearly 1500
<br />
<br />ppm.
<br />
<br />This marked increase in salinity of deliveries provoked
<br />
<br />the filing of a formal protest ,lith the State Depar'tment by the
<br />
<br />Mexican government.
<br />Of the 1,500,000 acre-feet annually guaranteed to Mexico
<br />under the 1944 Treaty, more' than 500,000 acre-feet is derived from
<br />
<br />drainage or return flows below Imperial Dam.
<br />
<br />Of this amount the
<br />
<br />Wellton-11ohawk Project contributes about 220,000 'acre-feet and
<br />the balance comes from return flows from other United States
<br />
<br />projects.
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