PROJ00040

• Contract/PO #: C153446
• Contractor Name: Grand Mesa Water Conservancy District
• Contract Type: Grant
• Water District: 0
• County: Delta
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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The data used for these operation studies included: 0) diversion requirements
computed for the l;l;-year study period according to their dry, normal or wet year
rank, (2) Tongue Creek basin generated stream flows entering the upper service
area and (3) the portion of streamflows from adjacent basins that were determined
to be available for transbasin diversion.

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Figure IV-l is a schematic diagram of the model showing the existing and the
proposed basin operations. In the existing operations, due to the location of the
majority of senior water rights in the lower service area, requests for water from
streamflows and from the Grand Mesa reservoirs are made first from the lower
service area. Shortages occur in the upper service area. In the proposed operation
of the basin, water supplies from streamflows and from the Grand Mesa reservoirs
are first allocated to the upper service area. In this way, the upper service area
shortages are greatly reduced and the return flows are proportionately increased.
The remaining stream flows augmented by the increased return flows are then
supplemented by water stored in a proposed reservoir to meet the lower area
demands. The change of sequence will allow more of the calls to be met, including
calls from junior rights holders in the upper basin, satisfy senior water right holders
as in the past, and also improve the usage of the return flows. The operation
studies are described in detail in Appendix B and the results of the operation
studies in Chapter V.

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Historical diversions were evaluated to establish monthly diversion patterns in
years of low, normal, and high stream flows. Historical diversions, however, are
poor indicators of how much water is needed to meet actual crop irrigation
requirements. These diversions often exceed CIR when water is abundant and they
fall short of CIR when water is scarce.

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To obtain a reliable indicator of water requirements, CIR was calculated by the

standard methods and procedures used by agricultural and irrigation specialists,

taking into account such factors as evapotranspiration, crop coefficients, effective

rainfall, conveyance loss, and on-farm irrigation efficiency. These calculated

requirements were designated, for purposes of this study, as "minimum water

requirements".

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