WSP06981

• File Number: 8276.110
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/16/1978
• Title: Negative Determination of Environmental Impact: Stage One of the Grand Valley Unit - Colorado River Basin Salinity Control Project
• Water Supply Pro - Doc Type: EIS

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A Water Systems Improvement (WSI) program would be conducted by the
Bureau in which about 185 miles of canals would be lined and about 450
miles of laterals would be lined or placed in pipe to reduce seepage into
the ground water system. Land would be acquired for wildlife management
areas, and watering ponds would be provided above the Government Highline
Canal. These measures would compensate for wildlife losses expected to
result from loss of edge vegetation along existing canals and laterals
and the restricted access to the canal for wildlife watering. Since the
wildlife measures and pipe laterals were not included in the unit plan
at the time of authorization, the approval of funding by appropriate
congressional committees would be required. An Irrigation Management
Services (IMS) program is presently being conducted by the Bureau as part.
of the unit to provide irrigators with precise data concerning optimum
timing and application of irrigation water. On-farm Improvements, includ-
ing upgrading of irrigation systems by cost-share assistance, improvement
of irrigation management, and improvement of grazing lands and practices
on private rangeland, would be conducted by the Soil Conservation Service
to reduce seepage and deep percolation from farm operations.

The unit would be developed in stages to allow analysis of construc-
tion in a portion of the valley where plans and designs are complete and
where sufficient hydrologic data are available to measure and analyze the
changes that occur as a result of Stage One development. The Stage One
area was selected because it includes the Reed Wash Study Area which is
hydrologically isolated from most of the valley by impermeable shale
ridges and provides a sampling base which can be considered free of out-
side influences such as ground water recharge from aquifers outside the
area.

A program has been undertaken to monitor the flows and quality of
ground and surface water systems in the Grand Valley and to evaluate the
effects of the Grand Valley Unit on those systems. . By measuring surface
flows and salinity concentrations at the upper and lower ends of the
valley and surface and ground water flows and salinity concentrations at
several points within the valley, the relationship between surface and
ground water flows and salt loading within the valley can be calculated.

3. Stage One Development

The 3-year Stage One development would involve concrete lining and
rehabili tation of structures along a 6. 7-mile section of the Government
Highline Canal between Big Salt Wash and Mack Wash (see Stage One map).
The lined canal would have a capacity of 360 cfs, a bottom width of 8
feet, a maximum water depth of 6.6 feet, side slopes of 1.5 to 1, and a
lined height of 7.7 feet. Fourteen laterals totalling 34.2 miles that
now serve the area under the canal section to be lined would be consoli-
dated into 12 and placed in pipe sections totalling 29.7 miles. The
laterals would vary in diameter from 4 to 36 inches and would be designed
for self-cleaning velocities. The service area in the Stage One area
totals 6,300 acres. About 6.5 miles of interceptor ditch and three small
detention ponds with n total surface area of about 10 acres would be

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