Floodplain Information Report Volume 3 Gunnison River from Delta to the Confluence with the Colorado River

• Basin: Gunnison
• Basin: Colorado Mainstem
• Title: Floodplain Information Report Volume 3 Gunnison River from Delta to the Confluence with the Colorado River
• Date: 3/1/1995
• Prepared For: The Recovery Implementaiton Program for Endangered Fish Species in the Upper Colorado River Basin
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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TABLE 5
GUNNISON RIVER CROSS - SECTION SELECTION
REACH
FL OWN LU ES {CFS) SO
CROSS
CROSS- SECTION TYPE
AT
NUMBER
YR, I00 -YR (NEAREST
SECTION
NUMBER
OF FLOOD
HYDROI OGIC> POINT
DEPTHS
1
22000, 24700 (G2)
NONE
DETAILED STUDY
FEMA STUDY
ALREADY
PERFORMED
2
23093, 25893 (G3)
A -A'
1
CALCULATED
3
23093, 25893 (G3)
NONE
CANYON REACH
N/A
4
24004, 26914 (G4)
B -B'
3
CALCULATED
5
24004, 26914 (G4)
C -C'
3
CALCULATED
6
24004, 26914 (G4)
CA -CA'
2 (FROM B -B')
CALCULATED
7
24856, 27868 (G5)
D -D'
1
CALCULATED
8
24856, 27868 (G5)
E -E'
3
CALCULATED
9
24856, 27868 (G5)
NONE
CANYON REACH
N/A
10
26162, 29334 (G6)
G -G'*
1
CALCULATED
11
26162, 29334 (G6)
NONE
CANYON REACH
N/A
12
27000, 30000 (G7)
H -H'
2 (FROM E -E')
CALCULATED
* - Ivlap- derived cross - section F -F' was prepared, but it was not used. It was omitted because the field surveyec
cross - section, G -G', located in the same reach, better represents that reach.
4.4 Computing Flood Depths
Flood depths were calculated at each cross - section through a computer program (QANY) which
uses Manning's equation. The input parameters for the calculation of flow included: x and y
coordinates for points on the cross - section, Manning's 'n' values (ranging from 0.03 to 0.032 for
the channel and 0.04 to 0.055 for the overbank) (Reference 7), the channel slope (interpreted
from USGS quadrangle maps), and depth values. The program calculated flow and velocity
values for each depth value entered. The target flow values were those values established in
Section 3.0 and shown on Table 3. Rating curves were established from the calculated depths.
From the rating curves 50 -year and 100 -year flood elevations were established at each location.
In performing the depth calculations the flow on the river the day of the survey was obtained
from the USGS and subtracted from the established 50 -year and 100 -year flows for each
particular hydrologic point. The depth of water on the day of the survey was estimated and
added to the flood depth calculations to obtain the true flood depths shown in Table 6. The
methodology used for computing flood depths at the cross - sections is similar to the accepted
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