WSP07975

• File Number: 8278.100
• Description: Title I - Yuma Desalting Plant
• Basin: Colorado Mainstem
• Date: 10/1/1987
• Author: USDOI/BOR
• Title: Yuma Desalting Plant Operations Study - Draft Special Report
• Water Supply Pro - Doc Type: Publication

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reservoirs on the mainstem of the Colorado River and its
tributaries store runoff for later release when natural flows are
inadequate to meet downstream demands.

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A series of interstate compacts, court decrees, legislative acts,
and water delivery contracts, collectively known as the "Law of
the River," divides the water among the Upper and Lower Basin
States (Basin States), with each group of states receiving about
7.5 million acre-feet annually, and further specifies the amount
of water each state receives. In addition, the 1944 Mexican
Water Treaty provides for an annual delivery of 1.5 million acre-
feet from the United States to Mexico.

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Since normal flows are insufficient to meet all commitments when
all the states are using their apportionments, the Federal
Government has been given the responsibility of augmenting flows
in the Colorado River to ensure adequate water supplies needed
for delivery to Mexico. The "Law of the River" does not provide
for Federal use of state water to meet delivery requirements to
Mexico.

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Water quality is generally good near the headwater of the system
but deteriorates as the water flows toward the Gulf of
California. As the Basin States approach full utilization of
their apportionments, water quality deterioration is anticipated
to become mo~e pronounced. Without additional salinity control
efforts, the projected salinity at Imperial Dam could reach as
high as 970 milligrams per liter (mg/L) by the year 2010.
However, salinity control measures are intended to maintain
salinity at or below the standard of 879 mg/L at Imperial Dam.

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In the mid-1960's, the quality of water being delivered to Mexico
became so poor that Mexico filed a formal protest. As a result,
Minute No. 242 (Minute) of the International Boundary and Water
Commission (IBNC) was adopted. The Minute requires that the
United Statea shall adopt measures to ensure that the water
arriving at Moreloa Dam have an average annual salinity of no
more than 115 (~30) parts per million (p/m) u.s. count, of total
dissolved solids (TDS), above the average annual salinity of
water arriving at Imperial Dam (at anticipated levels of
concentration, p/m and mg\L are the same). This is referred to
as the salinity differential. Based on provisions of the Minute
and the assumptions that water quality standard would be met, the
quality of water arriving at Morelos Dam would range from 964 p/m
to 1,024 p/m. This maintains the water quality at a level
equivalent to the next user on the Colorado River with the
effects of Wellton-Mohawk return flows"removed.

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The YDP is being constructed as a part of the permanent solution
to meet the salinity differentials specified by the Minute and to

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