FLOOD04160

• County: Gunnison
• Community: Gunnison County
• Stream Name: Gunnison River
• Basin: Gunnison
• Title: Floodplain Information Report - Gunnison River From Delta to the Confluence with the Colorado River
• Date: 4/1/1996
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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TABLE 5
GUNNISON RIVER CROSS-SECTION SELECTION

~~~~~'J~~t;

22000, 24700 (G2)

.,-"-'-'.-'..._---.,..-.-.-.-,-..-.....
.""y~~ ..__.,..,"V""',','...
..,.,.............,.-,.,-,.,-.,-..-,-,.-..................
])1O~yA.-p9~)i
.....OFFLOOb....)..........//
...'.".........................'-"-,.......
... .. .....
DEPTHs... ......//.... .......
__"..'n........ ....
. ...

NONE

DETAILED STUDY
ALREADY
PERFORMED

FEMA STUDY

2 23093, 25893 (GJ) A-A' CALCULATED
3 23093, 25893 (GJ) 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 (Gs) 0-0' CALCULATED
8 24856, 27868 (Gs) E-E' 3 CALCULATED
9 24856, 27868 (G5) NONE CANYON REACH N/A
10 26162,29334 (G6) G-G" CALCULATED
11 26162,29334 (G6) NONE CANYON REACH N/A
12 27000, 30000 (G7) H-H' 2 (FROM E-E') CALCULATED
· - Map- enve cross-sectIOn F- was prepar , ut It was not use . It was omltte
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], 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 IOO-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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