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Last modified
8/11/2009 11:32:55 AM
Creation date
8/10/2009 3:09:05 PM
Metadata
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UCREFRP
UCREFRP Catalog Number
7171
Author
Meyer, C. W. and M. Moretti.
Title
Fisheries Survey of the San Juan River, Utah 1987.
USFW Year
1988.
USFW - Doc Type
Pub. No. 88-1,
Copyright Material
NO
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<br />Habitat Characteristics <br />At the flows observed in this study, the river within the canyon <br />areas consistently remained within a relatively homogenous, single ~ <br />channel, with few to no backwater habitats. Conditions were more <br />variable in the braided channel area because of the variable number <br />and sizes of channels. Backwater formation appeared restricted mainly <br />to low flow conditions in late summer and fall. The physical measure- <br />ments of the river, although limited, gave some indication of the <br />changing nature of the river, both longitudinally and seasonally. ~ <br />During spring, the average channel width of the river was greatest (80 <br />m) in the middle canyon area (RMI 78-6) and least (59 m) in the upper, <br />braided area (Table 15). As would be expected, the variation in chan- <br />nel width was greatest in the upper braided area (Table 15). Water <br />depths during spring were much greater in the lower canyon area (aver- <br />age=2.7 m) than in the braided channel area (average=l.2 m; Table ~ <br />15). Average channel widths in the lower canyon were narrower than in <br />the middle canyon area, and depths averaged at least one-half meter <br />deeper in the lower canyon versus the middle canyon (Table 15). <br />During summer the average channel width was about the same between the <br />middle canyon area (mean=41 m) and braided area (mean=41 m) of the <br />river; again the braided area was the most variable (Table 15). ~ <br />Average depths between the two areas of the river were quite similar <br />in summer (mean in both areas=0.5 m), as were maximum depths (mean in - <br />both areas=0.8 m; Table 15). The lower canyon averaged narrower (39 <br />m) and deeper (0.7 m) than either of the other two areas (Table 15). <br />Between spring and summer, at the flow levels observed, the braided - <br />area changed mostly in depth; the two canyon areas showed large <br />decreases in depth and, to a lesser degree, in width. <br />The number of backwater habitats (29) found in the braided <br />channel area was significantly greater than expected (X2=18.1, <br />P=0.05,df=2) based on the proportion of the 120 mi of river the area <br />encompassed. The number of backwaters (5) found in the lower canyon ~ <br />was significantly less than expected. <br />In addition to variability in the longitudinal distribution of <br />backwaters, the dimensions of backwater habitats varied among the <br />three geomorphologic areas of the river. The surf ace area of back- <br />waters decreased downstream. The average size of backwaters was r <br />largest in the braided channel area (Four Corners to Sand Island) and <br />smallest in the lower canyon area (Mexican Hat to Grand Gulch; Table <br />16). The mean values for maximum depths of backwaters were about the <br />same in the braided channel (0.37 m) and middle canyon (0.34 m) areas <br />(Table 16). Backwater depths in the lower canyon area were about <br />twice the depths of backwaters in the other two areas (Table 16). ~ <br /> <br />- 36 - . <br />
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