9383

• UCREFRP Catalog Number: 9383
• Author: SWCA, I.
• Title: Recovery Goals for the four Colorado River Endangered Fish Species.
• USFW Year: 2000.
• USFW - Doc Type: Logan.
• Copyright Material: NO

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historic flows can jeopardize those species. The importance of flow maintenance to the

. ed Colorado River fishes is recognized throughout the Colorado River Basin (Stanford
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In the lower basin, flow regulation and habitat fragmentation have extensively altered
most riverine habitats, leaving few historic riverine habitats in tact (Marsh and Minckley 1985,
Minckley 1985). In the upper basin, flow regulation has generally reduced the peak of spring
runoff and increased the magnitude of base flows in historic habitat. Since 1950, annual peak
discharge of the u olorado River has decreased by 29-38% (Van Steeter and Pitlick 1998)
in occupied habitat ... Grand Valley. Flows of the Green River near Jensen, Utah, have
'i:;~

decreased by 13-35 o.d~ng spring and increased by 10-140% during summer and winter due to
regulation by Flaming Gorge Dam (Muth et a1. 2000). Overall, storage of spring flows have
reduced spring runoff by 28% in the Green River and by 37% in the Colorado River during May
and June (USGS flow records, 1906-1982). The effect of these flow modifications on the
endangered fishes is not clear, but a sudden and dramatic decline occurred in the Green River
shortly after completion of Flaming Gor am in 1963 (Vanicek 1967, Vanicek and Kramer
1969). It is hypothesized that stream ification reduced high-velocity flows that flush
sediments from spawning cobbles (Van Steeter and Pitlick 1998), reduced channel and habitat
complexity with concomitant losses in food production (Osmundson 1999), and reduced the
availability of flooded bottomlands during spring runoff, which are possibly used as nursery
habitats by newly-hatched larvae and young.
Streamflow modification in the Colorado River Basi esulted in depleted flow and
altered flow regimes. These changes have altered water tern e, sediment loads, water
quality, and habitat (see Section 3.1.1.2). Flow regulation is attributed primarily to dam
operations, irrigation diversions, transbasin diversions, riverside pumps, and instream industrial
and municipal pumping systems. In the lower basin, most of the main channel has been
extensively fragmented with dams and diversions, and there are few remaining riverine reaches.
In the upper basin, streamflow regulation has affected most of the remaining riverine habitat, and
little flexibility remains for reoperation of existing dams to provide flows to assist rec
Colorado River endangered fishes.

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