7400

• UCREFRP Catalog Number: 7400
• Author: Valdez, R. A.
• Title: The Endangered Fish of Cataract Canyon
• USFW Year: 1990.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

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when most of the rapids were separated by short st.retches of relatively calm water, ranging from several
hundred yards to 1.2 miles in length. These reaches were often composed of large, deep shoreline
eddies immediately below the rapid and sections of swift runs leading to the next rapid. Fish sampling
was difficult at flows of 10,000 to 30,000 cfs, when the increased swiftness of the intervening runs and
the strength of the eddies reduced available sampling area Sampling was particularly inefficient at
flows of over 30,000 cfs because of the swiftness and turbulence.

Two freshwater springs were located in this region providing additional habitat for fish. One was
located at Rapid #3 (RM 211.5) and the other was at Rapid #11 (RM 207.2). At flows of under 10,000
cfs, a large side channel at each of these sites became cut off from the main channel forming a large
isolated spring-fed pool and a spring-fed backwater at each location. The backwaters became isolated
pools at flows of under 5,000 cfs but continued to support fish throughout the hot summer. Although
young Colorado squawfish and humpback chub were commonly found in these pools, the icthyofauna
was dominated by non-native species. These springs may have additional significance to the
endangered fish. Tyus (1985) has suggested that the groundwater seepage hypothesis, proposed by
Harden-Jones (1981), be considered as a possible olfactory imprinting mechanism for Colorado
squawfish en route to spawning sites. Colorado squawfish may spawn in Cataract Canyon using the
two identified springs for imprinting.

Because of the swiftness of most. habitats in this region, most sampling was conducted in a 3-mile
reach between Rapids #10 and 13. This area was informally known as "Cataract Lake", and at flows
of under 10,000 cfs consisted of many eddies, one side channel, large cobble bars, and several
backwaters. Below Cataract Lake was a 4-mile reach of closely spaced rapids that made sampling
nearly impossible at levels of over 10,000 cfs. The few samples taken in this reach did not yield
endangered fish, although the area contained favorable habitat. This region had the fewest backwaters
of any in the study area; no backwaters occurred at flow levels greater than 20,000 cfs, while only fIVe
typically occurred at lower flows. Three of these backwaters were in Cataract Lake. Flows during this
investigation ranged from about 3,000 to 70,000 cfs (See Section 2.6).

2.5 Region 5: Lake Powell Inflow

This region of the st.udy area (Figure 7) was the transitional zone between the Colorado River and
Lake Powell. It extended from 'Ten Cent Rapid' (RM 201.5) downstream to below Palmer Canyon (RM
195.0). The character of this area was dependent on the water level of Lake Powell. When the lake
was full (surface elevation of 3,700 feet), its inundation effect reached upst.ream to the base of Rapid
#25 ('Repeat Rapid'). At this lake level, Rapid #26, (Ten Cent Rapid) was mostly inundated, consisting
of a series of small standing waves, and noticeable current usually extended downstream to Palmer
Canyon. As the lake level receded in late summer and fall, Ten Cent Rapid emerged and noticeable
current extended further downst.ream to Clearwater Canyon (RM 192.0).

This region underwent dramatic changes during the span of this investigation. Expansive silt/sand
bars were deposited along the shoreline during the spring of 1983, 1984, and 1985 when the Colorado
River Basin experienced record runoff in combination with a maximum lake level of 3708.34 feet above
sea level on July 14, 1983 (Ferrari 1988). A large volume of sediment was transported by the Colorado
River and deposited into this region during these years. ..... Ferrari (1988) found average sediment depths
in Lake Powell ranging from 1 foot in several channels to 182 feet in Cataract Canyon (RM 181,
between Dark and Sheep Canyons). At the present sedimentation rate, it was est.imated that it would
take more than 700 years for sediment to fill Lake Powell to an elevation of 3700 feet.

The high lake levels allowed sediment deposits to reach higher levels on the shoreline. Beginning
in 1986, the lake level subsided with more normal water years, and large Silt/sand bars became
exposed, particularly along the shoreline. These covered the former rocky shoreline, and filled small