9603

• UCREFRP Catalog Number: 9603
• Author: Clayton, R. and A. Gilmore.
• Title: Flaming Gorge Environmental Impact Statement Hydrologic Modeling Study Report - Results of Action and No Action Alternative Analysis.
• USFW Year: 2001.
• USFW - Doc Type: \
• Copyright Material: NO

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3
incrementing the beginning and ending years of the natural flows for the following input trace by
one year. For example, the fIrst trace of the model began with the natural flows for January 1921,
and ended 39 years later with the natural flows for December 1959. The second trace began
with natural flows for January 1922 and ended in December 1960. Subsequent traces were
developed in this manner until the end of the period of record was reached (December 1985).
Once the end of the period of record was reached, additional traces were created by incrementally
appending the initial natural flows from the period of record to the end of the trace so that the
length ofthe trace was 39 years long. For example, the 28th trace contained the natural flows for
January 1948 through December 1985. But this only equaled 38 years. To extend this trace to a
length of39 years, the natural flows for January 1921 through December 1921 were added to the
end of the 28th trace. The 29th trace required that 2 years of natural flows (January 1921 through
December 1922) be appended to the end of the trace to achieve a length of39 years. This
process was continued until all 65 traces were constructed. When the Green River model is run,
the model run is complete when all 65 input traces have been successfully routed through the
Green River system.

To evaluate how well each run ofthe model achieved the flow objectives of the
proposed alternatives, it was necessary to generate output at a daily time step for river flows in
Reaches One and Two. A daily post processor model was constructed for this purpose. The
daily post processor model generated the spring release hydro graph from the monthly model
results and processed it into daily results. The daily release hydrograph was then routed through
Reaches One and Two of the Green River. The historic daily flows of the Yampa River for the
period from January 1, 1921, to December 31, 1985, were taken from United States Geological
Survey stream flow records and were used as the input hydrology by the daily post processor.
There are no rules in the daily post processor that operate Flaming Gorge Dam that are unique to
the daily postprocessor model. All of the rules necessary to operate Flaming Gorge Dam to
achieve the proposed alternatives are present in the monthly model and the daily post processor
model.

Ruleset Development

The rules that operate Flaming Gorge Dam to achieve the objectives of the proposed
alternatives are referred to as rulesets. For each of the proposed alternatives, one ruleset has been
developed. The paragraphs below describe the specifIc objectives that each ruleset was designed
to achieve.

During the spring (April through July), the objectives ofthe Action Alternative require a
peak release magnitude of suffIcient duration to achieve flow targets in Reaches One and Two.
These objectives change depending on the hydrologic condition of the Upper Green River Basin.
Except for cases when the minimum release rate of 800 cfs is prescribed, the objectives for
Reach Two appear to achieve the objectives for Reach One as well. The spring objectives of the
Action Alternative for Reach Two that are achieved by the Action ruleset are described below.