WSP05341

• File Number: 8278.100
• Description: Title I - Yuma Desalting Plant
• Basin: Colorado Mainstem
• Date: 12/23/1992
• Author: USDOI/BOR
• Title: Yuma Desalting Plant - Alternatives for the Interim Period
• Water Supply Pro - Doc Type: Publication

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about 20 percent to approximately 3,600 ppm. There are sources of water
other than the bypass canal contributing to the Slough.

The creation of a wetland habitat was not anticipated. In the June 18,
1975, Final Environmental Impact Statement, Colorado River Salinity
Control Project, Title I, the potential for impacts to the Slough was
addressed. However, at that time, it was assumed that the Desalting
Plant would be operational within 3 years of completion of the Bypass
Drain and that there would not be sufficient bypass to create a major
wetland environment, nor would there be sufficient time for species to
become dependent upon the habitat.

Reclamation has proposed conducting studies of the Slough to the
United States Section of the IBWC to determine the degree of impacts and
to consider opportunities to minimize those impacts. Through
consultation with Mexico, Mexico has indicated that they have an
interest in studies in the Slough, to be conducted under the auspices of
the Mexican Government, and possibly with help from the United States.
A proposal has been submitted, through IBWC, to Mexico and we are
awaiting their response. The Fish and Wildlife Service has also been
contacted and is expected to cooperate in biological portion of the
studies. In the meantime, the one-third operation of the Desalting
Plant is not expected to significantly impact the wetland system.

CURRENT SITUATION

The United States has complied with the salinity differential of
Minute No. 242 since 1974. That is, the average annual salinity of
water delivered to Mexico at the Northerly International Boundary,
upstream of Morelos Dam, has not exceeded the average annual salinity of
the water arriving at Imperial Dam by more than 115 ppm plus or minus
30 ppm (maximum of 145 ppm).

The United States has achieved this compliance through bypassing all
WMIDD irrigation drainage to the Slough and substituting good quality
water from upstream storage for delivery to Mexico. For an interim
period which began in 1982, the United States has replaced the
additional water released from storage to meet the delivery obligation
to Mexico with the water conserved by lining the Coachella Canal. The
volume of WMIDD irrigation drainage bypassed has ranged from about
192,000 af per year to a low of 118,500 af per year over the past
10 years.

Table 1 shows the quality and quantity of river flows used to meet the
1944 Treaty obligations during calendar year 1991. As shown,
145,000 af per year of WMIDD irrigation drainage was bypassed and lost
from use, while additional releases from upstream storage were made to
meet the objectives of Minute No. 242. The annual average flo~-weighted
salinity differential is slightly greater than 115 ppm but within
145 ppm of the salinity of the Colorado River flow at Imperial Dam.
Mexico has insisted that the salinity differential be maintained as
close as possible to 115 ppm. To achieve as close of an approximation
as possible of the 115 ppm differential without the operation of the

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