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

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I. INTRODUCTION

The United States of America and the United Mexican States in 1944
adopted a Treaty for the Utilization of Waters of the Colorado and
Tijuana Rivers and of the Rio Grande. The Treaty allotted to Mexico
1,500,000 acre-feet annually "...of the yaters of the Colorado River,
from any and all sources...."

Of the total, approximately 1,360,000 acre-feet annually are
delivered to J.lexico in the limitrophe section of the Colorado River
upstream from :10relos Dam.* The remaining approximately 140,000 acre-
feet annually are delivered at the Southerly International Boundary,
17 miles to the south, and in the limitrophe section of the river beloy
/.lorelos Dam.

Although the Treaty permits the United States to include drainage
Yaters from irrigation projects beloy Imperial Dam as part of Mexico's
allotment, it does not settle the question of the quality of Colorado
River yaters to be delivered. Therein lay the difference betyeen the
tYO Governments in the interpretation of the Treaty and the requirements
of International lay.

The delivery of Treaty yaters to Mexico began in 1950 Yith the
completion of Morelos Dam, Mexico's major diversion structure on the
Colorado. Eleven years later, tYO events occurred to make Yater quality
a serious issue betyeen the tyO countries. There yere delivered to Mexico
above Morelos Dam highly saline drainage yaters, pumped by the Wellton-
Mohs.yk Irrigation and Drainage District from an aquifer that underlies
the District. These yaters, initially averaging 6,000 ppm TDS,** yere
pumped to maintain ground-Yater levels belay the crop root zone. In
addition, excess flays yhich Mexico had received prior to 1961 came to
a near end in that year. These floys had diluted the more saline drainage
Yaters that yere then being discharged to.the river beloy Imperial Dam,
Yith the result that the quality of wter delivered to /.lexica above
Moreloa Dam YaS very nearly the same as that used in the Loyer Colorado
River Basin of the United States.

The effect of these developments yaS to increase the salinity of
Colorado River wters made available to Mexico at the Northerly
International Boundary from an annual average of about 800 ppm TDS to
nearly 1,500 ppm TDS in 1962.

.Temporary emergency deliveries of less than 20,000 acre-feet of Mexico's
allotment of Colorado River wters are being made to the City of Tijuans.,
11exico.
*.All stated salinity concentrations are based on U.S. methods of
analysis and reporting unless otheryise noted. The references are to
parts per million of total dissolved solids.

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