9493

• UCREFRP Catalog Number: 9493
• Author: Gaeuman, D., P. R. Wilcock and J. C. Schmidt.
• Title: High Flow Requirements for Channel and Habitat Maintenance of the Lower Duchesne River between Randlett and Ouray, Utah.
• USFW Year: 2003.
• USFW - Doc Type: \
• Copyright Material: NO

FINAL REPORT, November 2003
High-jlow Requirements for the Duchesne River

sediment transport capacity through a river reach is sufficient to transport the sediment load
supplied to the reach.
Loss of sediment transport capacity also impacts the quality and availability of physical
habitat used by aquatic biota. Gravel substrates can become choked with fine sediment,
impacting macro invertebrate production and the availability of spawning sites for some fish
species (Giller and Malmqvist 1998), while increased sediment deposition in backwaters and
side channels can reduce channel complexity and habitat diversity (Van Steeter and Pitlick
1998). Flow regimes needed to maintain these elements of physical habitat must exceed certain
discharge thresholds, in addition to transporting the imposed sediment load. Maintenance of a
productive gravel substrate requires discharges sufficient to mobilize the stream bed so that fine
sediment can be flushed from the subsurface (Petts and Maddock 1996). Maintenance of
backwater and side channel habitats requires discharges capable of accessing and scouring
sediment from these areas.
Numerous authors have stressed the importance of the natural flow regime, including
relatively large floods, for maintaining stream and riparian health (Hill et al. 1991; Richter et al.
1997; Poff et al. 1997). Higher flows are necessary to maintain channel and flood plain form and
function (Kondolf and Wilcock 1996; Stanford 1996; Milhous 1998; Trush et aI. 2000).
Discharges adequate to cause bank erosion and re-distribute bed sediment are needed to create
disturbance and maintain the structural elements that provide the basis for diversity in aquatic
and riparian habitat (Stanford et al. 1996). The ongoing deformation of channel pattern that
accompanies active meander migration may lead to the formation of meander cutoffs, i.e., the
main flow cuts a new path that bypasses part or all of a meander bend (Lewis and Lewin 1983).
Growing point bars may develop chutes and swales through a variety of processes, some of
which are discussed by Bridge et al. (1986), Hooke (1986), and Howard (1996). The resulting
islands, backwaters, side channels, and oxbow lakes comprise the elements of a complex aquatic
habitat.
Such physical complexity has been shown to be important factor for habitat use among
Colorado pikeminnow (Ptychocheilus lucius), an endangered endemic species found throughout
the lower Duchesne River. Osmundson (2001) reported that 84 percent of adult pikeminnow
located by radiotelemetry during spring runoff in the upper Colorado River were observed in
protected off-channel areas. Backwater habitats were also observed to serve as nursery habitat

2