WSP09883

• File Number: 8273.100
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - BOR
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 9/1/1973
• Title: Colorado River International Salinity Control Project - Special Report - Executive Summary
• Water Supply Pro - Doc Type: Report/Study

.

.

.

.

.

.

.

.

.

.

.

l\)
o
W
""1

In a note dated November 9, 1961, Mexico formally protested that
".. .the delivery of _ter that is harmful for the purposes stated in
the Treaty constitutes a violation of the Treaty." Mexico continued to
press its case thereafter.

In response to the Mexican protest, the United States began in
1963 to alter river operations to reduce the salinity of Colorado River
_ter delivered to Mexico. By 1965, a 5-year agreement _s reached by
the two Governments, referred to as Minute No. 218 of the International
Boundary and Water COllllllission (IBWC).

This Minute, which became effective on November 16, 1965, provided
for practical measures to further reduce the salinity of waters reaching
Mexico. Under the Minute, each country reserved its legal rights. The
measures consisted of the construction and operation of a 12-mile-long
channel known as the Main Outlet Drain Extension to enable the United
States to discharge Well ton-Mohawk drainage waters to the Colorado River
either above or below Morelos Dam, and the installation and operation of
additional drainage wells in the Wellton-Mohawk area to make possible
selective pumping. During periods when scheduled deliveries to Mexico
were the Treaty minimum of 900 cfs,. the United States discharged all
Wel1ton-Mohawk drainage below Morelos Dam, amounting to about 50,000
acre-feet per year. These bypd.sS _ters were replaced by other waters
largely from above Imperial Dam. By the end of 1971, these operations,
coupled with a gradual ilnprovement in the quality of Well ton-Mohawk
drainage _ters, had reduced the average annual salinity of waters made
available to Mexico to about 1,245 ppn TDS, with monthly averages varying
from 1,105 to nearly 1,500 ppn TDS.

Meanwhile, Mexico concluded that it would not use _ters with
salinity greater than about 1,240 ppm TDS (1,300 ppm, Mexican method of
analysis) in the Mexicali Valley and asked the United States under terms
of Minute No. 218 to bypass an additional 40,000 to 75,000 acre-feet of
Well ton-Mohawk drainage flows annually. .The effect was to further reduce
the average salinity of waters diverted by Mexico at Morelos Dam in 1971
to about 1,160 ppm TDS.

Before Minute No. 218 _s to have expired on November 15, 1970, the
United States proposed a new 5-year agreement to further reduce salinity.
The United States offered to bypass additional volumes of Wellton-Mohawk
drainage and to substitute equal volumes of better waters to reduce the
average annual salinity of waters delivered to Mexico at the Northerly
International Boundary to about 1,140 ppm TDS, subject to increases in
salinity at Imperial Dam. This salinity would approximate that of

.Cubic feet per second.

2