9344

• UCREFRP Catalog Number: 9344
• Author: Camp Dresser & McKee Inc.
• Title: Replacement of the Plateau Creek Pipeline.
• USFW Year: 1996.
• USFW - Doc Type: Denver.
• Copyright Material: NO

3.3.2 Historical Colorado River Flows
'~ The USGS has recently installed a gaging station on the Colorado River near Palisade which should
be representative of flows at the top of the 15-mile reach. However, the four years of record
currently available are insufficient to provide the range of flows expected under varying hydrologic
conditions expected over the life of the project. Therefore, existing gages upstream of Palisade with
Long-term records were used in conjunction with diversion records of intervening water rights to
develop a flow record under a wider range of hydrologic conditions.
Figure 3.3 is a schematic of the Colorado River system from just upstream of Plateau Creek to the
top of the 15-mile reach. The flows at the top of the 15-mile reach were determined by summing
the flows recorded by the Colorado River and Plateau Creek gages at Cameo with estimated inflows
from Rapid Creek. Diversions by the Government High Line Canal (Grand Valley Project) and the
Grand Valley Canal were deducted. Finally, the returns from the Orchard Mesa Powerplant tailrace
were added. This calculation is consistent with the methodology used in the USFWS 1995 report,
which forms the basis for flow recommendations in the 15-mile reach. The results of these
calculations are summarized in Table 3.7. Average monthly flow values for all 19 years of the
analysis are provided in Attachment A. As the USFWS found in its evaluation of streamflows
(USFWS 1995), negative values were generated using this algorithm (see 1977 results, Table 3.7);
~l the three months with negative values generated in this analysis were set to zero in subsequent
analyses.
Actual records for the two Cameo gages were used in the flow calculations, with the exception of
1984-1985 when the Plateau Creek gage was not functioning. Flows for those years were estimated
based on correlation with the Colorado River gage. No gage records were available for Rapid Creek.
Based on information provided by Ute Water and verified by the BLM, these flows were estimated
as shown in Table 3.7, with 1 cubic foot per second (cfs) flowing into the Colorado River from July
through March, increasing to 20 cfs in May and decreasing back to 1 cfs by July.
Diversion records for the Government High Line Canal and Grand Valley Canal, obtained from the
Colorado Division of Water Resources, were used to develop the values shown in Table 3.7 and
Attachment A for both canals and the Orchard Mesa tailrace return flows. Information reported in
the diversion records required some adjustment in order to portray accurate flow values. Diversions
by the Grand Valley Canal were occasionally reported in excess of its capacity of 640.28 cfs, in
which case such values were set to that capacity. Likewise, diversions by the Government High Line
Canal were reported as total diversion by the Grand Valley Project, which also includes any
diversion for the Orchard Mesa component of the project. To properly generate canal diversions and
powerplant return flows, the diversions were first limited to the physical capacity of the Government
High Line Canal at 1620 cfs. Irrigation diversions under the Government High Line component of
the project are available in the diversion records, so these were then subtracted from the adjusted
total diversions to compute the flows diverted to the Orchard Mesa system (limited to the 800 cfs
capacity of the Orchard Mesa siphon). Of this remaining flow, it was assumed that the first 188.2
cfs (the capacity of the Orchard Mesa irrigation delivery system) during the irrigation season would
be used for irrigation, with the remainder going to the powerplant and returning to the Colorado
CDM Camp Dresser & McKee
0:8047-1101DOC1APPEND-B.DOC B-lO