WSP01703

• File Number: 8276.450
• Description: McElmo Creek Unit - Colorado River Salinity Control Program
• State: CO
• Basin: Colorado Mainstem
• Water Division: 7
• Date: 1/1/1983
• Title: Onfarm Irrigation Improvements - McElmo Creek Unit Salinity Control Study
• Water Supply Pro - Doc Type: Report/Study

1. SUMMARY

This USDA salinity control study was carried out under Public Law
93-320, the Colorado River Basin Salinity Control Act (88 Stat. 266), dated
June 24, 1974. Section 201(c) of the Act directs the Secretary of the
Interior, the Administrator of the Environmental Protection Agency, and the
Secretary of Agriculture to cooperate and coordinate their activities
effectively to carry out objectives of Title II of the Act as the basin
states continue developing their compact apportioned water. The McElmo
Creek Unit, known locally as the Montezuma Valley, is one of five diffuse
source control units designated in the Act for expeditious completion of a
planning report as a means to implement the salinity control policy adopted
for the Colorado River.

The USDA has two primary purposes in the McElmo Creek study:
determine the contribution of salt loading from the irrigated farm
(2) to determine the opportunity for reducing salt loading through
improvements in irrigation systems and practices.

(1) to
land; and

The scope of the study was limited to inventorying and analyzing
current irrigation systems and practices on a sample of the irrigated land
and off-farm group ditch. Results of these analyses were expanded to be
representative of the approximately 29,100 acres of irrigated land and about
235 miles of off-farm group ditchs in the Montezuma Valley. Canals in the
Montezuma Valley Irrigation (MVI) Company's distribution system are being
evaluated by the Bureau of Reclamation and were not studied by USDA.
Results of investigations were discussed at joint meetings throughout the
study where areas of common concern were identified and issues were
resolved.

Coordination of study activities leading to analysis of the salt
loading problem in the McElmo Creek Unit was accomplished through a
Multi-Objective Planning Team under leadership of the Bureau of Reclamation.
Participants in this team effort included personnel from the Bureau of
Reclamation, Soil Conservation Service, U.S. Fish and Wildlife Service, U.S.
Geological Survey, Colorado Division of Wildlife, Colorado Water
Conservation Board, Colorado Department of Health and the Dolores Soil
Conservation District.

Mancos shale, a marine formation with high salt content, underlies much
of the valley (See Figure 111-2) and is the principal source of salt in the
McElmo Creek Unit. Lenses of crystalline salt often are exposed during
excavation into shale. Because of the arid climate, salts have not been
leached naturally and applying irrigation water to the soil greatly
accelerates the leaching process.

The McElmo Creek contributes about 115 000 tons of salt annuall to the
Colorado River. About 54,0 present condition) tons are attributed to the
onfarm portion of current irrigated agriculture. Additional water from the
.poio,res Pro; ect will increase this salt T(;ading to about 60 ,000 tons"JU!t,!r~
without condition). Most of the salt is leached from the soil and
.. underlying Mancos -~hale and carried to the river by deep percolation from
irrigation and by seepage from unlined earthen ditches. (See Table I-I)

(')01 S'J)

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