WSP06290

• File Number: 8277.600.10
• Description: Big Sandy River Unit - Colorado River Salinity Control Program
• State: WY
• Basin: Colorado Mainstem
• Date: 5/1/1986
• Title: U.S.D.A. Selected Plan - Big Sandy River
• Water Supply Pro - Doc Type: Definite Plan Report

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percolation to the underground aquifers. Of the total Big Sandy River
salt output, it is estimated that through the base period of 1960-1977
return flows from the irrigation delivery system seepage and deep
percolation from on-farm irrigation practices contribute about
133,860 tons annually. Natural runoff, erosion, and seeps contributed
an additional 15,320 tons annually.

The initial work for the Big Sandy River salinity study was done
from 1977 through 1979 with a USDA report being published November 1980.
A large range of alternatives was evaluated during the course of the
salinity study. A summary of alternatives evaluated is listed on pages
S-2 and S-3 with a summary table S-1 on page S-4 of the Big Sandy River,
Colorado River Basin Salinity Control Study, USDA Report dated November
1980. The USDA report did not identify a viable alternative which could
be supported by the State of Wyoming, the Soil Conservation Service, and
the irrigators in the area.

Early in 1984, the State of Wyoming asked that the Soil
Conservation Service evaluate an additional alternative and update the
landowner benefits that might be derived from installation of a low
pressure sprinkler irrigation system. The economic evaluation and
development of a low pressure sprinkler irrigation project was completed
in 1984. This alternative was presented to the State of Wyoming in
November and at a public meeting December 17, 1984, of the Eden Valley
Irrigation and Drainage District. Consensus was favorable to the low
pressure sprinkler alternative. The State of Wyoming and Irrigation and
Drainage District asked the SCS to prepare a USDA Selected On-farm Low
Pressure Sprinkler Plan. This report addresses that alternative. The
Low Pressure Sprinkler Alternative is essentially the same as
Alternative 3B as described in the 1980 USDA report. Alternative 3B was
a High Pressure Sprinkler Irrigation System using on-farm pumping
stations. The display of Alternative 3B is shown in chapter 3,
pages 3-5 and 3-6, and in appendix C, page C-3 of the 1980 USDA report.

On February 27, 1986, a meeting was held with the representatives
of various State agencies to explain the contents of the USDA Selected
Salinity Control Plan. As a result of this meeting, the State has
indicated its continued support and willingness to participate in
finalization and implementation of the plan. On April 2, 1986, an
informational meeting was held in Farson to explain in detail the USDA
Selected Plan and its impacts on the local irrigators and irrigation
district. Reaction of the local irrigators continues to be favorable
and the consensus of those attending is that the USDA Salinity Control
Plan on the Big Sandy River be finalized.

Implementation of the Selected Plan (low pressure sprinkler
irrigation with individual on-farm pumping) for 15,700 acres will
increase the present average on-farm efficiency from 39 percent to
68 percent and average project efficiency from 32 percent to 50 percent.
The change in on-farm efficiency would result in less deep percolation
from the farm area and resulting return flow from the saline seeps along
the Big Sandy River. This would result in a reduction of 52,900 tons of
salt annually entering the river system. This reduction would translate
to a decrease in salinity concentration in the Green River at the town

S-2

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