WSP10281

• File Number: 8278.300
• Description: Title I - Mexican Treaty
• Basin: Colorado Mainstem
• Date: 9/1/1991
• Author: Anne DeMarsay CRBSCF
• Title: The Brownell Task Force and the Mexican Salinity Problem - A Narrative Chronology of Events
• Water Supply Pro - Doc Type: Publication

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used-and still uses-most of its Colorado River water to support irrigated agriculture in the
Mexicali Valley, this silence seems odd. The history of the treaty suggests that the u.s. and
Mexico drew different inferences about quality from the phrase "any and all sources."

Before the completion of Hoover Dam in 1935, destructive spring floods swept through the
Colorado Basin almost every year, followed by dangerously low flows in the summer. When
the river was in its natural state, Mexico could capture and use only about 750,000 acre-feet of
water per year. Hoover Dam made possible the storage of floodwaters and year-round flow
regulation, and Mexico stood to receive much more usable water-but the legislation authorizing
the dam's construction barred foreign governments from receiving any benefit from it! The
1944 treaty contained an apparent compromise: the U.S. would deliver approximately twice as
much water to Mexico as it would have been able to use had the Colorado River not been
regulated (1.5 million acre-feet) but Mexico would have no say in the source of that water within
the Basin, nor in its qua1ity.2

Until 1961, no problems arose from the salinity of water deliveries. In that year, the
Wellton-Mohawk Irrigation and Drainage District in Arizona, near the Mexican border, began
to operate a pumped drainage system. To lower the high water table beneath the project, it
began to pump highly saline water into its drains-water that was laden with salts that had
accumulated in the soils beneath the project from decades of irrigation without drainage. These
drainage waters, or "return flows" carried about 6,000 parts per million (ppm) of dissolved salts,
and entered the river just above Morelos Dam, the main Mexican diversion point.

In the same year, the U.S. sharply reduced upstream releases-which would have diluted the
brackish drainage waters from Wellton-Mohawk-in order to begin filling Lake Powell behind
the newly completed Glen Canyon Dam. These two events caused the average annual salinity
of water delivered to Mexico at Morelos Dam to jump dramatically, from about 800 ppm in
1960 to 1,340 ppm in 1961, to more than 1,500 ppm in 1962. Salinity levels in some months
exceeded 2,500 ppm. In November 1961, the government of Mexico filed a formal diplomatic
protest, charging the U.S. with violating international law. The International Boundary and
Water Commission (IBWC), thejoint U.S.-Mexican agency charged with administering the 1944
treaty, began negotiations on a practical solution.

For the next ten years, Mexican and U.S. scientists, diplomats, and Federal and state officials
debated the intent of the 1944 treaty, technical issues, and equities under international law
without reaching a permanent solution.3 The Committee of Fourteen-composed of two
representatives from each of the seven Basin states- had been created in 1938 to consider basin-
wide problems, including the prospective treaty. At the State Department's request, the
Committee was revived in the early 1960s to advise the U.S. Section of the IBWC on the
salinity issue.

In 1965, the U.S., under Minute No. 218 of the IBWC, agreed to several temporary measures
to reduce salinity: extending the Well ton-Mohawk Drain to permit drainage to be bypassed
around Morelos Dam (where it would flow to the Pacific Ocean without being diverted for use)
during periods of unusually high salinity; replacing about 40,000 acre-feet per year of bypassed