WSP03378

• File Number: 8276.300
• Description: Lower Gunnison Basin Unit - Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 4
• Date: 7/1/1981
• Title: Lower Gunnison Basin Unit Status Report
• Water Supply Pro - Doc Type: Report/Study

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The alternative calling for concrete lining all canals and laterals
warranted for salinity control (Plan A-2) had received the most public
support and was therefore designated the public's recommended plan,
although it received only slightly more support than the alternative
for concrete lining adobe area canals and laterals indicating little
distinct preference of one over the other.

The planning team and members of the Uncompahgre Valley Water Users
Association recommended that Plan A-2 be adopted as the plan of develop-
ment for the Lower Gunnison Basin Unit. Public recommendation, operational
characteristics, impact on the environment, and other technical and economic
factors were considerations in plan selection.

Plan refinement

To determine the extent and range of lining, comparative analyses
were conducted. These analyses were based on a comparative estimate of
cost effectiveness for concrete lining varying components of the canal
and lateral system. Preliminary estimates of cost effectiveness for the
components were developed by apportioning the water and salt budget to
specific portions of the study area and estimating construction costs for
lining varying portions of the system analyzed. Three categories of
canal and lateral components were established by the planning team:
Category I, which included all components which individually had a
cost effectiveness at or below $450,000 per mg/L of salinity reduction;
Category II, which contained all components contributing to a combined
cost effectiveness of $450,000 per mg/L of salinity reduction; and
Category III, which consisted of all identified canal and lateral compo-
nents in the study area. The planning team members and representatives
of the water users board evaluated the categories and noted problems with
each. Of the three, Category III had the least support and was thereby
eliminated from further consideration. After careful study, the planning
team and water user board representatives recommended that a Category IV
analysis be developed which would place the limit of concrete lining at a
suitable break-point developed by graphing cumulative incremental cost
effectiveness against cumulative salt reduction. It was expected that
this break-point would fall between the limits of Category I and
Category II. As a result of the comparative analyses, about 335 miles
of canals and laterals were proposed for lining at this phase of the
planning process. Included were all the components on the east side of
the valley as well as about 80 miles on the west side.

However, with completion of feasibility-level designs and cost
estimates and refined salinity measurements, the cost effectiveness of
the recommended plan was found to be unacceptable and Plan A-2 was modi-
fied by successively withdrawing canal and lateral increments to improve
the cost effectiveness. The result was essentially the distribution
system on the east side of the valley, which would result in a construc-
tion cost of $137,800,000 and a salinity reduction at Imperial Dam of
15.2 mg/L, including adjustments for depletions. The cost effectiveness
of the modified plan, which is outlined in detail in the following section,
was $685,000. In the table on the following page, features, costs, and
cost effectiveness of each of the candidate plans are summarized.

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