9326

• UCREFRP Catalog Number: 9326
• Author: U.S. Fish and Wildlife Service.
• Title: Draft Biological Opinion for Ute Water/Plateau Creek Pipeline Replacement Project, Mesa County, Colorado.
• USFW Year: 1996.
• USFW - Doc Type: Denver.
• Copyright Material: NO

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as the average annual depletion for the years 1984 through 1987 in order to
provide a historic depletion figure which is more representative of the more
recent historic water use. The new depletion is defined as the average annual
depletion beyond the historic depletion calculated to occur in each year from
1988 through 2045. The historic and new depletions are each described in two
ways, as an overall depletion to the basin and as a depletion to the 15-mile
reach.
Quantification of depletion impacts have focused on the 15-mile reach for four
reasons. First, the Service considers the 15-mile reach to be especially
important habitat for the Colorado squawfish and razorback sucker. Second,
the Service has developed flow recommendations for the 15-mile reach against
which reductions of current flows can be compared. Third, the 15-mile reach
has the least flow of the four subreaches because it is located upstream of
the Gunnison River confluence and immediately downstream of the large
diversions at and above Palisade; consequently, a reduction in flow will
impact the 15-mile reach to a greater degree than the other reaches. Fourth,
almost any reasonable and prudent alternative which offsets depletion impacts
to the 15-mile reach will necessarily offset depletion impacts to the other
reaches.
To determine the effects of the Project on water quantity and alteration of
the hydrologic regime, an analysis of flow changes was conducted. This
analysis compared the post-Project conditions to the pre-Project section 7
baseline. These levels of development were simulated for the 1975 to 1993
period of record. Flows and flow reductions were calculated as monthly
averages for each month of each year of the 19-year period of record.
Each year of the 19-year period of record was classified according to the
Service's Flow Group classification as a 25, 50, 80, or 100 percent exceedance
flow frequency. For each year, the average monthly post-Project flows at the
top of the 15-mile reach were compared to the Service's flow recommendations
for that year's Flow Group to determine "make-up flows". Make-up flows were
calculated as the Project's reductions of baseline flows below the Service's
recommended flows. For a month in which the baseline flow is below the
Service's recommended flow, the make-up flow is equivalent to the Project's
flow reduction for that month. For a month in which the baseline flow is
above the Service's recommended flow and the post-Project flow is below the
Service's recommended flow, the make-up flow is the difference between the
Service's recommended flow and the post-Project flow. For a month in which
the post-Project flow is above the Service's recommended flow, the make-up
flow is zero.
The overall depletion to the basin, which is equivalent to the Persigo-Lake
Powell reach flow reduction, was calculated as the difference between the
Project's diversions and estimated return flows taking into account
replacement reservoir releases.
In the hydrologic analysis for the Project, the current level of depletion is
not completely represented in the baseline for all years of the period of
record. The baseline flows were calculated using the historic gage flows and
subtracting depletions resulting from pF~jects which have received successful