WSP04979

• File Number: 8240.200.10.B
• Description: UCRBRIP - Riverine Fish Flow Investigations
• Basin: Colorado Mainstem
• Date: 6/1/1999
• Author: CDOW
• Title: Riverine Fish Flow Investigations 1999
• Water Supply Pro - Doc Type: Publication

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The results from subjective habitat typing indicated that riffles and runs were
more common at Duffy than at Sevens (Table 10), but these results are of little value in
quantitatively describing the two study sites. Mean wetted perimeter was fairly similar
between the two sites indicating a similar channel size. The only wetted perimeter that
was significantly different (alpha = 0.05) was at 200 cfs (Table 10), The percent of the
channel that was wetted tended to be higher at Duffy than Sevens at flows of 200 and
600 cfs (51 vs. 44% and 64 vs. 57 % respectively) but were fairly similar at 50 cfs (37
vs, 34 %, respectively).

Table 10. Percent habitat types and mean wetted perimeter at bankfull flow
(channel) and mean wetted perimeter at 50, 200 and 600 efs and
(95% C. I.). Sample size at DutTy is 32 and at Sevens is 29.

HABITAT FEATIlRE SEVENS DUFFY
Rifiles (%) 16% 21%
Runs (%) 64% 68%
Pools (%) 2% 1%
Backwater (%) 18% 9%
Mean wetted perimeter, bankfull (9000 cfs) 402.5 it (29.5 394.3 it (40.3)
Mean wetted oerimeter 50 cfs) 138.6 it 03.3 146.611(20.9)
Mean wetted oerimeter 200 cfs) l75.2 II (13.5 202.9 II (17.4)
Mean wetted perimeter 600 cfs) 230.3 II (16.2) 250.7 II (17.6)

The slope of both study areas was very flat. The energy grade line (water surface
slope) at Sevens 0.04% and it was 0.14% at Duffy. The flat nature of the river meant
that much of the river was comprised of run habitats. The substrate composition had a
higher percent of sands and fines at Sevens. At Sevens the substrate was 34% silt and
sand, 28% pea gravel, 27% gravel and 5% large gravel. At Duffy the substrate was 13%
silt and sand, 10% pea gravel, 32% gravel and 27% large gravel. Cobble and boulders
comprised 6% of the substrate at Sevens and 16% at Duffy.

At a flow of 200 cfs, Duffy had higher percentages of very shallow (less than 0.5
ft) and very deep (over 5.5 ft) habitats than Sevens (Figure 3). Sevens had a higher
composition of habitat between 1 and 4 feet of depth. The depth frequency distributions
were different for the two sites indicating that Duffy has a higher depth and habitat
diversity. However, without velocity data, shallow riffles could not be distinguished
from shallow runs. At flows of 50, 100 and 150 cfs it was felt that most of the area over
3.5 feet deep would have very slow velocities and could be considered pool habitat.

At a flow of 50 efs, 98.4% of the surface area was less than 3.5 feet deep at
Sevens compared to 91.7% at Duffy (Figure A3J). At flows of 50, 100, and 150 efs the
amount of area less than 2.5 feet in depth was fairly similar forthe two sites and about
87% of the total. However, Duffy had more area less than 0.5 feet while Sevens had
more area with depths between 0.5 and 2.5 feet (Figures A3.4 and A3.5).

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