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Last modified
7/14/2009 5:02:30 PM
Creation date
5/17/2009 11:00:41 PM
Metadata
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UCREFRP
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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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />For the purposes of this investigation, the st.udy area was divided into five regions: <br /> <br />1. Green River above the confluence (RM 50.0 to 0) <br />2. Colorado River above the confluence (RM 50.0 to 0) <br />3. Colorado River from the confluence to Brown Betty (RM 216.5 to 212.5) <br />4. Colorado River in Cataract Canyon (RM 212.4 to 201.5) <br />5. Inflow of the Colorado River into Lake Powell (RM 201.4 to 195.0) <br /> <br />2.1 Region t: Green River above the Confluence <br /> <br />This region of the study area (Figure 3) encompassed the Green River from near the Mineral Bottom <br />boat launch (RM 50.0) downstream to the confluence of the Colorado River (RM 0). Included in this <br />region were the southern portion of Labyrinth Canyon and Stillwater Canyon. The two major drainages <br />within this region were Millard Canyon (RM 33.7) and Horse Canyon (RM 14.3); there were numerous <br />small ephemeral drainages such as Horsethief, Taylor, Deadhorse, and Jasper Canyons. <br /> <br />The Green River along this region was characterized by a low gradient of about 3 feet per mile, and <br />a meandering channel with predominantly silt and sand substrates. The river course flowed alternately <br />through wide floodplains and bottom lands with densely vegetated shorelines of tamarisk and willows, <br />and steep canyons with talus and cliff shorelines. Cobble, gravel, and some boulders occurred as <br />alluvial deposits at the mouth of tributary drainages. These deposits were particularly extensive below <br />Millard and Horse Canyons, where they formed large cobble riffles (Photos A-5 through A-8). <br /> <br />The shoreline and riparian zone of this region was dominated by a tamarisk/willow association. <br />Tamarisk is an exotic phreatophyte imported as an ornamental into California from Asia in the 1800's. <br />The invasion of the entire Colorado River Basin by this plant is dramatically illustrated in a book entitled <br />In the Footsteps of John Wesley Powell (Stephens and Shoemaker 1987), in which the authors <br />rephotographed areas of the river in 1968 which had been photographed by E.O. Beamon on the <br />second Powell Expedition of 1871-1872. These photographs clearly illustrate a change in the riparian <br />zone from willows and cottonwood trees with unvegetated sand bars to a dominance of tamarisk in <br />both riparian zones and sand bars in a period of about 100 years. Recent research (Graf 1978, <br />Andrews 1986) suggests that the bankfull channel width of the Green River in this region has decreased <br />by 10 to 27% within the past. 2 to 3 decades. Bank stabilization by tamarisk, in addition to a decrease <br />in the magnitude and duration of peak discharges due to flow regulation from Flaming Gorge Dam, <br />were cited as the principal factors contributing to the decreasing channel width. A continuation of this <br />trend could potentially decrease the number of backwaters in this region of river and subsequently <br />reduce its value as a nursery for Colorado squawfish. <br /> <br />Fish habitat in this region was provided by backwaters, cobble riffles, slow runs, eddies, and <br />shorelines. Backwaters were more abundant here than in any of the other four regions. Although <br />densities of backwaters varied on any given year depending on flow regimes, est.imated backwater <br />densities based on their availability for the Interagency Standardized Monitoring Program, known as the <br />ISMP (USFWS 1987) conducted by the UDWR in 1987 and 1988 were at least. two per 5 miles of river <br />(Personal communications with Mr. Miles Moretti, UDWR, February 1988). This included only backwaters <br />that met the st.andardized monitoring criteria of a minimum of 30 m2 in size and a maximum depth of <br />1 foot. Backwaters that did not meet these criteria occurred in the region but were considered marginal <br />as fish habitat. This high relative density of backwaters made this region the most important of the <br />st.udy area in terms of survival and recruitment of YOY Colorado squawfish and other native fishes. <br />These backwaters generally appeared during decreasing flows in mid to late summer and were typically <br />formed by large eddies over sand bars and in dewatered side channels (Valdez and Wick 1981). <br /> <br />5 <br />
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