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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Using the historic water supply and present 15,700 irrigated acres,
the present on-farm efficiency is about 39 percent with a project
efficiency of 32 percent. In addition, the water and salt budgets show
that during the past few years, salt contributions were greater than the
1960-1977 18-year average. Using the present irrigated acreage and a
balanced water budget, the revised annual salt budget would produce a
157,570-ton output into the Big Sandy River, Under present conditions,
it is estimated that 142,250 tons of salt are a result of irrigation and
15,320 tons are a result of runoff, erosion, and natural seeps. If
irrigation in the project area were completely eliminated, it is
estimated that the contribution of salt from runoff, erosion, and
natural seeps would increase to 32,720 tons, The increase from
15,320 tons to 32,720 tons is a result of lowering the water table,
allowing the natural interaction of the river and the aquifer flow to
occur.

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Improved water management is needed throughout the irrigation
conveyance, distribution, and application systems. Emphasis would be
directed toward diverting the correct amount of water for plant
requirements and avoiding seepage and resulting deep percolation losses.
Because salt pickup to the Big Sandy River is from the underlying
soluble sediments, the overall system analysis for improvement would be
geared to efforts toward reducing deep percolation and return flow to
the stream system.

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Diffused Area Watershed Management

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The evaluation indicates that contribution of salt to the Colorado
River system by the rangeland areas above the irrigated cropland is
generally low. Since only minimal salinity reduction benefits from
improving range areas could be expected, no treatment measures have been
proposed for this area.

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