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Last modified
7/14/2009 5:02:33 PM
Creation date
5/22/2009 7:38:47 PM
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UCREFRP
UCREFRP Catalog Number
8160
Author
Trammell, M. and T. Chart.
Title
Aspinall Studies
USFW Year
1999.
USFW - Doc Type
Evaluation of Nursery Habitat Availability and Colorado Pikeminnow Young of Year Habitat Use, in the Colorado River, Utah, 1992-1996\
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<br />Relationship of flows to habitat availability <br />The relationships between peak runoff flows, sampling flows and habitat area and volume ~ <br />were tested with Peazson's correlations. High peak flows during spring runoff were negatively <br />correlated with habitat availability in the following summer and fall (Figure 5). In the upper <br />section, high spring flows were significantly negatively correlated with summer habitat azea and <br />volume (p = 0.10), and in the lower section, high spring flows were significantly negatively <br />correlated with fall habitat area and volume (p= 0.10 and 0.07)(Table 11 and 12). Total habitat i <br />azea was highest in 1992, which was a low flow year preceded by several low flow years. Habitat <br />azea decreased by half during the relatively high flow year of 1993. The following year was <br />another low flow year, and habitat azea increased, but did not return to 1992 levels. The next <br />year, 1995, was another year with high flow and low habitat azea. In 1996, flows were moderate <br />and habitat area again increased, but not to pre-high flow quantity. / <br />Rakowski and Schmidt (1996) studied asand-bedded reach of the Green River similar to <br />the Colorado River reaches. They suggested that habitat quantity may decrease in the year of a <br />high peak flow, but that the following year or years may benefit as lower floods in succeeding <br />years scour bazs created during a high flow year, thereby increasing habitat complexity and <br />quantity. This effect was not seen in this study from 1993 to 1994. The relationship between / <br />peak flow offset by 1 and 2 yeazs and the habitat availability in summer and fall was also tested <br />using Pearson's correlations. There was no correlation between a 1-year previous peak flow and <br />habitat, r2 values were low, and p values were greater than 0.50. A slight negative correlation <br />observed on the 2-year offset was an aztifact of the similarity between the patterns of peak flows <br />offset by two years, 1990-1994 and 1992-1996. / <br />Although the flows at the time of sampling were not closely related to total habitat area in <br />the summer and fall, there was a trend towazds less habitat at the higher sampling flows. Habitat <br />area was quite variable, but appeared to be m~ximi~ed at flows below 4000 cfs (Figure 6). <br />The total area in four of the habitat types appeazed to decrease at high sampling flows (Figure 7). <br />Scour channel habitat area decreased less than migratory sandwave habitat area. There was a / <br />small increase in flooded ixibutary habitat as sampling flows increased, particulazly in the spring. <br />However, we did not sample at flows high enough to flood large areas of the tributaries. We <br />observed lazge sandbars plugging the mouths of the tributaries after the runoffhad receded. The <br />tributary mouths were not available to flooding at most sampling flows unless a flash flood had <br />removed the obstruction after the runoff. / <br />In the upper section, scour channel habitat decreased from 1992 to 1993, but then <br />increased in succeeding years. In the lower section, scour channel habitat decreased each year, <br />except for 1996. The two reaches were very similaz in terms of gradient and substrate, and flows <br />at sampling times. The difficulty of pinpointing an optimal flow to maximize habitat area is <br />demonstrated by the opposition of the relationships of habitat area to various flow levels at these / <br />two similar sites. <br />/ <br />14 / <br />
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