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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drain water with additional water released from upstream storage; and constructing more wells
at Well ton-Mohawk to pennit selective pumping of drainage.

The Basin states were initially unwilling to make any concessions to Mexico on water quality.
They pointed to the language and legislative history of the treaty as proof that Mexico was
compelled to accept drainage water of any quality (except brine aquifers) as part of its
allotment. 4 In the eyes of many western U. S. water users, the provisions in the treaty were
consistent with their own state water laws. Water law in the western United States recognizes
the right to appropriate water for beneficial consumptive use-with some inevitable decrease in
quality-and decrees that "first in time is first in right." International water law, however,
generally follows the doctrine of riparian rights, under which downstream users have the right
to receive water that has not been degraded by upstream users.

By the late I 96Os, the states were convinced of the need to reach an accommodation with
Mexico. U.S. interests proposed a new basis for settlement: "equivalent salt balance," based
on a concept from agronomy and irrigation engineering.s An irrigation system that is in "salt
balance" returns the same amount of salt in its drainage waters as was applied to the land. Salt
neither accumulates in nor is leached from its soil.

Proponents of the equivalent salt balance position recommended that the U.S. dilute
Wellton-Mohawk drainage with a quantity of purer water sufficient to reduce the differential in
salinity between Imperial and Morelos Dams to that which would exist if the project were in salt
balance-about 280 ppm. In theory, as excessively salty waters were gradually drained from
beneath Wellton-Mohawk, the amount of dilution water needed would decrease. Once the
project reached salt balance, substitution for drain flows would no longer be necessary. 6 The
salinity of the water reaching Mexico would be that which the next downstream user would be
entitled to under U.S. water laws.

Myron B. Holburt, a member of the Committee of Fourteen from California, explained the
assumptions on which the equivalent salt balance concept rested as follows: "(I) water users in
the United States have a right to irrigate lands below Imperial Dam, (2) Mexico has to receive
drainage water under the Treaty, (3) creating a situation of ideal return flow conditions below
Imperial Dam with respect to salinity would be the best Mexico could expect, (4) the total
deliveries should be water of a quality that would be usable for irrigation of the type of crops
grown by Mexico, considering its soil conditions. ,,7

In the last days of the Diaz Ordaz administration, the U.S., with the support of the Colorado
Basin states, offered to negotiate a new Minute based on salt balance equivalence. The Mexican
government called the proposal constructive, but chose not to enter negotiations on a long-term
agreement until a new president, Luis Echeverria Alvarez, took office in December 1970.

The Search for a "Permanent, Definitive and Just Solution"

During 1971, the U.S. and the new Mexican administration discussed a settlement based on the
equivalent salt balance concept. By November, U.S negotiators believed that they were close

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