WSP07117

• File Number: 8276.130
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 11/1/1990
• Title: Final Environmental Assessment: Price and Stubb Ditch Improvements - Grand Valley Unit
• Water Supply Pro - Doc Type: EIS

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Chapter I II

AFFECTED ENVIRONMENT AND
ENVIRONMENTAL CONSEQUENCES

Table 5
Salt loading in the Grand Valley Unit
area from present ground water sources

Source
Irrigation sources
Canals
Laterals
On-farm ditches
Deep percolation from irrigated fields
Orchard Mesa Power Canal
Highline Lake 1
Natural sources
Total

Outflow
(tons/vear)

136,000
99,800
92,700
173,500
12,000
24,000
37,400
575,400

1 Tonnage attributed to Highline Lake. Estimated using
a separate Highline Lake budget.

Impacts

Surface Water.--No significant change in the salt loading from surface
sources is expected under any of the alternatives.

In the short term, sediment yields from construction material sites would
increase; however, properly planned excavations and revegetation would
reduce this problem. A section 402 permit would be required for any
discharges during construction and this would limit pollution of surface
waters.

Ground Water.--Under the no-action alternative, salt load reductions from
other segments of the Grand Valley Unit would continue. The salt loading
to the Colorado River is expected to decrease by 11,500 tons annually with
the recommended plan, all from ground water sources. The reduction would
be due to reduced canal seepage rates. Table 3 shows the expected salt
loading conditions of the alternatives.

VeQetation and Wildlife

Present Conditions

Veaetation.--Vegetation within the proposed project area can be
characterized as a mosaic of agricultural lands, wetlands, and shrubland
communities modified and supported by irrigation and water-use practices
over the last century. The development of irrigated agriculture has
created plant communities that differ from the salt-desert shrub
associations that historically occurred here, and still occur just north of
the stubb Ditch. Plant communities, including cultivated crops, maintained
by ditch water support wildlife historically restricted to natural washes
or the river bottom, or in cases such as the ring-necked pheasant, species
exotic to the Grand Valley. Wildlife species that evolved with, and are
dependent upon, salt desert vegetation have been reduced in the Unit area.

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