9413

• UCREFRP Catalog Number: 9413
• Author: Osmundson, D. B.
• Title: Flow Regimes for Restoration and Maintenance of Sufficient Habitat to Recover Endangered Razorback Sucker and Colorado Pikeminnow in the Upper Colorado River.
• USFW Year: 2001.
• USFW - Doc Type: Grand Junction.
• Copyright Material: NO

In determining optimum flows for spring, a primary goal was to assure that high
runoff flows provide the sediment transport function necessary for channel maintenance
such that important habitat types remain available and fine sediment deposition problems do
not develop. Thus, flow recommendations for spring are aimed more at maintaining and
enhancing these effects than for maximizing rare fish habitat used during the spring months
as was the case for the summer and winter periods. The exception to this is to assure that
certain key habitats (i.e., flooded bottomlands) used by razorback suckers during the spring
spawning period are provided periodically. The bankfull discharge is a critical level during
spring because it is a threshold for important sediment transport processes as well as the
level at which over-bank flooding appreciably begins, thereby providing razorback sucker
larvae with critical nursery habitat. Reach-specific geomorphic studies indicated that the
magnitudes of the bankfull discharges in De Beque Canyon and in the floodplain upstream
of De Beque were very similar to the bankfull discharge in the downstream 15-mile reach.
It is recommended that this bankfull discharge be reached in all above-average and wet
years. Mean monthly flows for all years and peak flows for below-average and dry years
follow those previously recommended for the 15-mile reach.
Although the recommendations presented here are a best estimate of flows that will
most benefit future populations of the endangered fish, there are constraints to
implementing these recommendations. These constraints are due to the demands of the
irrigation and power canals that divert large amounts of water from the river during summer
and, to a lesser extent, during winter. As long as current operations at these diversions
continue, flows required at Cameo must be high enough to supply the canals and satisfy the
15-mile reach needs as well. During the summer this can result in more water in the river
than is optimum' for the endangered fish upstream of Cameo. Conversely, during the
winter, flows in the reach between the diversions can get too low for the fish. These
constraints are discussed and the flows that satisfy all needs to the greatest extent possible
are described.
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