GENERAL31841

• Permit No: M1999002
• IBM Index Class Name: General Documents
• Doc Date: 7/22/1999
• Doc Name: FINAL ENVIRONMENTAL IMPACT STATEMENT VOLUME 2 APPENDIX L
• Media Type: D
• Archive: No

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recessional flows routinely dissect gravel bars and thereby produce
tertiary bars of clean cobble at the base of the riffles. These
tertiary bars are used by Colorado pikeminnow for spawning. The
importance of high magnitude, low frequency discharges is in forming
and maintaining the midchannel bars. Dissection of bars without
redeposition by high magnitude flows would lead to con3itions where
spawning habitat is no longer available (Harvey et al. 1993).
It is unknown whether tertiary bars similar to those used for Colorado
pikeminnow spawning in Yampa Canyon are available in the 15-mile reach
of the Colorado River. There, significant motion of bed material
occurs at near bankfull discharge of 22,000 cfs (Van Steeter 1996).
These flows occur on average once in 4 years. Van Steeter (1996)
concluded that flows of this magnitude are important because they
generally remove fine sediment from the gravel matrix which maintains
the invertebrate community and cleans spawning substrate.
Although the location of spawning areas in the Colorado River is not
as defined as in the Yampa River, the annual presence of larvae and
young-of-the-year downstream of the Walker Wildlife Area, in the Loma
to Black Rocks reach and near the confluence of the Dolores River,
demonstrates that spawning occurs every year. Osmundson and Kaeding
(1989, 1991) reported that water temperatures in the Grand Junction
area were suitable for Colorado pikeminnow spawning. In 1986, a year
of high runoff, suitable temperatures for spawning (20" C) occurred in
mid-August; in 1989, a year of low runoff, the mean temperature
reached 20° C during the last week of June. Tyua (1990) demonstrated
that Colorado pikeminnow often migrate considerable distances to spawn
in the Green and Yampa Rivers, and similar though more limited
movement has been noted in the mainstem Colorado River (MCAda and
Kaeding 1991).
Collections of larvae and young-of-year downstream of .known spawning
sites in the Green and Yampa Rivera indicate that downstream drift of
larval Colorado pikeminnow occurs following hatching (Haynes et al.
1984; Nesler et al. 1986; Tyus 1990, Tyus and Haines 1991). During
their first year of life, Colorado pikeminnow prefer warm, turbid,
relatively deep (averaging 1.3 feet) backwater areas of zero velocity
(Tyus and Haines 1991). After about one year, young are rarely found
in such habitats, though juveniles and subadults are often located in
large deep backwaters during spring runoff (USFWS, unpublished data;
Osmundson and Burnham 1998).
Larval Colorado pikeminnow have been collected in the 3unnison River
up- and downstream of the Redlands Diversion Dam (Anderson 1996;
Osmundson and Burnham 1998). Burdick (1997) reports that the capture
of larval Colorado pikeminnow in 1995 and 1996 upstream of the
Redlands Diversion Dam coupled with aggregations of adult fish during
the spawning season confirms that spawning occurs upstream of the dam.
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