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 change of sequence would allow the requests from senior water right
holders to be met as in the past and improve the usage of the return flows to
provide water to more junior rights holders.

3. The Potential Use of the Grand Mesa Reservoirs

A series of optimization studies were performed to evaluate the use of the
existing Grand Mesa Upper Basin reservoirs. First, the basin was operated
with virgin flows that would occur without the existing upper basin reser-
voirs. Then, the basin was operated with upper basin reservoirs in use under
the existing mode of operation. Finally, optimization of the upper basin
reservoir system was investigated by examining operational modifications to
define potential improvements. The consultant determined that revised
operation of the upper basin reservoir volumes available would only be a
small improvement over the historical operation. Therefore, it was
concluded that the existing reservoirs operate in an efficient manner and that
operation modifications would not provide substantial benefits to the project.

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4. Cactus Park Reservoir: The Stabilizing Factor

Releases are made from Cactus Park reservoir whenever streamflows and
return flows cannot meet the lower basin demands. Monthly evaporation
volumes are also taken into account to determine reservoir storage require-
ments. The results from a series of operation studies conducted for
Alternatives I, 2 and 3 show annual releases during the 4/;-year period to vary
from 0 to 19,900 acre-feet.

5. Runoff Forecasts: The Management Tool

Runoff forecasting is essential for the operation of the project and to predict
streamflow available and reservoir releases during the irrigation season.
Runoff forecasts are especially crucial during low flow years. The operation
of the reservoir is a function of the reservoir content at the start of the
irrigation season, the required release rates and the seasonal water supply.
The reservoir content at the start of the irrigation season is always known.

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