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Last modified
7/14/2009 5:02:33 PM
Creation date
5/17/2009 11:27:48 PM
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UCREFRP
UCREFRP Catalog Number
8117
Author
Modde, T. and G. Smith.
Title
Flow Recommendations for Endangered Fishes in the Yampa River.
USFW Year
1995.
USFW - Doc Type
Denver, CO.
Copyright Material
NO
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<br />Because of the evolutionary relationship of native fish biology to natural <br />flows, virgin flows were used as a standard to compare deviations from historical <br />records. A modified version of the Indicators of Hydrologic Alteration (IHA) (Richter et <br />al. in review) was used to compare differences in virgin and historic hydrographs. <br />Based on hydrological modeling, a trend exists between virgin and historic flow <br />scenarios in which peak flows have been reduced and baseflows have increased since <br />water development began in the Yampa basin (Figure 12 and Table 1). The <br />difference between peak flow volumes under virgin and historic flows is seen in the <br />monthly means for March (-5.3%), April (-15.2%), May (-13.5%), and June (-8.6%) <br />(Table 2). During the low flow months, irrigation return flows were apparently <br />increasing low flow volumes, as seen in monthly means for August (+4.7%), <br />September (+25.6%), October (+34.3%), November (+16.0%), and December (+9.5%). <br />Similar effects were seen in the 7- to 90-day high and low flow averages listed in <br />Table 2 (for historic flows). High flow averages are reduced by 8.4% for annual one- <br />day maximums (as described in Table 1) to 11.3% for 90-day highs. Low pow <br />averages are increased by 79.2% for annual one-day minimums to 25.9% "for 90-day <br />lows. The slight moderation historic flows from virgin conditions was also observed in <br />the slight reduction of low flow duration, and the increase of high flow duration. The <br />standard deviations associated with virgin and historic flows were similar, even for low <br />flow measures in which mean values were considerably different (Le. Annual <br />minimum, 7, 30, and 90 day lows). <br /> <br />Habitat Maintenance and Geomorphol~ <br /> <br />Although information concerning the distribution, relative abundance, and <br />spawning requirements exist, little information exists on the habitat availability and <br />needs of the endangered fishes of the Yampa River relative to flow. Given this <br />shortcoming, the physical character of the Yampa River as formed by virgin flows <br />represent the best target to meet environmental needs of endangered fishes. The <br />physical character, and hence habitat for endangered fishes, of the Yampa River is <br />maintained by the magnitude of the hydrograph. O'Brien (1984) estimated that the <br />effective discharge (transportation of greatest sediment over a long period of time) of <br />the Yampa River near Cleopatras couch (RK 28 in Yampa Canyon) was 11,500 cfs <br />and that bankfull discharge (Le. channel changing capability) was 21,500 cfs. The <br />discharge that would be effective in scouring the channel to prevent encroachment of . <br />the river channel by vegetation occurs approximately every 1.5 years (O'Brien 1984). <br />Fisher et al. (1983, in Stanford 1994) provided evidence that vegetation along the <br />shoreline of the Yampa River has not changed substantially because of its unregulated <br />flows. Conversely, riparian vegetation, primarily nonnative species including reed <br />canary grass (Phalaris arundinacea), salt cedar (Tamarix spp.), and Russian olive (Elaeagnus <br />angustifolia) have modified channels in regulated reaches of the Upper Colorado River Basin <br />(Stanford 1994). The higher bankfull discharge, necessary to periodically reshape the river <br />channel historically occurs on a frequency of about every 20 years (O'Brien 1984). Mussetter <br />and Harvey (1994) estimated that flows necessary for bar formation at two known Colorado <br />squawfish spawning sites, Cleopatras Couch (RM 17) and Mathers Hole (RM 18), was <br />approximately 17,500 cfs and 25,000 cfs respectively. <br /> <br />21 <br />
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