7046 ‎(2)‎

• UCREFRP Catalog Number: 7046
• Author: Valdez, R. A., W. J. Masslich and A. Wasowicz.
• Title: Final Report\
• USFW Year: 1992.
• Copyright Material: NO

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Reach VI (RM 128.7 - 177.0) This reach traversed a large canyon through its entirety. The
channel was primarily pool-drop in native, interspersed with short sections of rime-run habitat. Data
collected by CDOW showed that cobble was the dominant substrate followed by boulder, silt and
sand, with finer substrates occurring in pools and other slow velocity areas. CDOW data showed that
channel widths range from less than 30 feet to more than 90 feet.

4.3.1.4 Potential Spawnint! Habitat. Thirteen potential spawning sites for Colorado squawfish
were identified on the Dolores River during the study. Classification of these sites was based on
criteria previously described including the presence of deep pools and eddies in proximity to and
interspersed with cobble riffles and run habitat. Three of these sites were selected as representative
of potential spawning sites in the Dolores River. Detailed maps of these sites are presented in
Figures 13-15. All mapping was conducted during low flows and emphasis was placed on
characterizing substrate sizes and embeddedness. Data collected from each of the three potential
spawning areas are presented in Appendix A

4.3.1.5 Nurse" Habitat. Backwater densities on the Dolores River ranged from 0.2 to 0.8
backwaters per mile at flows observed during the study. Backwaters ranged in size from 150 ft2 to
32,000 ft2. Maximum depths of backwaters ranged from 6 inches to 4 feet. Substrates were generally
composed of organic fines, silt, sand and cobble. The majority of backwaters were formed in
dewatered side channels. Highest backwater densities were found in Reaches II and ill at flows of
approximately 200 - 300 cfs. It was noted during the study that the stochostic nature of the
hydrograph during the summer months frequently inundated and desiccated backwater habitats. This
ephemeral character of backwaters reduced the value of the system as a nursery. However, the
Dolores River confluence was located immediately upstream of the Professor Valley nursery area on
the Colorado River, where dispersing larvae and age-O fish find ample habitat. A similar situation
exists on the Yampa River, where larval Colorado squawfish drift into nursery areas in the Green
River downstream of their confluence.

Other potential nursery habitats included ephemeral isolated pools and trickle fed side channels.
Ephemeral isolated pools were uncommon in the Dolores River, although several large isolated pools
were located with an array of both native and non-native species. Trickle fed side channels were also
identified as potential nursery habitat. This habitat was characterized by a side channel isolated from
inflow except for a small trickle of water flowing through cobbles. Current was generally not
perceptible and temperature was similar to that observed in backwaters. This habitat type was
common in much of the study area

4.3.2 Chemical Attributes

Water quality of the Dolores River was represented by grab samples collected at points in time.
Because of the variable nature of the river, these water samples were not necessarily representative
of the full range of water quality. Flood events or spates, particularly those associated with runoff
of high intensity summer storms, greatly influenced water quality. Water quality data for Trips 1
through 6 are presented in Tables 3641.

In addition to water quality samples for laboratory analysis, field measurements were taken for
conductivity, salinity, pH, alkalinity and dissolved oxygen. Water quality data collected afield are
presented in Table 35. A historical comparison of water quality is presented in Table 42

4.3.2.1 Alkalinity. Alkalinity is a measure of the buffering capacity of water. Buffering capacity
is important to water quality (EP A 1986) since pH has a direct effect on organisms as well as an

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