8157

• UCREFRP Catalog Number: 8157
• Author: Pitlick, J., M. V. Steeter, B. Barkett, R. Cress and M. Franseen.
• Title: Geomorphology and Hydrology of the Colorado and Gunnison Rivers and Implications for Habitats Used by Endangered Fishes.
• USFW Year: 1999.
• USFW - Doc Type: \
• Copyright Material: NO

DATA SOURCES AND METHODS
Streamflow
The U.S. Geological Survey (USGS), along with other federal and state agencies, has operated
gauging stations in the Colorado River basin since the late 1800s. We have examined streamflow
records from many gauging stations on the main-stem of the Colorado River, and other gauges on
regulated and unregulated tributaries in western Colorado (Van Steeter, 1996). For the purpose of
illustration, this report discusses trends from six gauges that have relatively long records and are
relevant to our work. These gauges are: East River at Almont, Yampa River at Maybell, Colorado
River at Glenwood Springs, Colorado River near Cameo, Gunnison River near Grand Junction,
and Colorado River near the Colorado-Utah State Line. The first two sites are representative of
rivers with little flow regulation, while the latter four are representative of rivers with significant
flow regulation. Table 1 lists information on these gauges and Figure 1 shows their locations.
Table 1. Summary information on gauging stations used to evaluate long-term trends in
streamflow of the Colorado River and selected regulated and unregulated tributaries.
USGS Period of Qp Qm Stat. Sign.1
Gauge Number Record
--
-
= (m3/s)
----------------- (m3/s)
------------- (p< 0.05)
----------------
---------------------------
East River -------------------
09112500 -------
--
------------
1911-1949 79 10
at Almont 1935-1949 66 9
1950-1995 64 9 N,N
Yampa River 09251000 1916-1949 299 46
at Maybell 1950-1995 282 42 N,N
Colorado River 09072500 1899-1949 504 82
at Glenwood Springs 1950-1995 286 61 Y,Y
Colorado River 09095500 1934-1949 725 116
near Cameo 1950-1995 517 107 Y,N
Gunnison River 09152500 1902-1949 490 73
near Grand Junction 1950-1995 306 71 Y,N
1. Statistical significance determined using a T-test; Y indicates the difference in peak discharge (Qp) and mean
annual discharge (Qm) for pre- and post-1950 periods is statistically significant at the a = 0.05 level; N indicates the
difference is not statistically significant.
Discharge records from these gauging stations were partitioned into "unregulated" and "regulated"
time periods on the basis of when there were major changes in the amount of water stored in
reservoirs. Plots of cumulative reservoir storage capacity vs. time (Fig. 4) show that the greatest
increase in storage capacity in the upper Colorado River basin occurred in 1950, when Granby
dam was completed; on the Gunnison River, a large increase in storage occurred in 1966, when
Blue Mesa Reservoir was completed. Based on these results, we partitioned the discharge records
of the Colorado River and Gunnison River at 1950 and 1966, respectively. One additional reason
for splitting the records in mid-century, rather than in the 1930s when the first large reservoirs
were built, is that, typically, the regulated portion of the streamflow record is longer than the
unregulated portion. By splitting the data as such it-increases the number of years indicative of
unregulated or slightly regulated conditions, which increases the sample size and strength of our
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