9469

• UCREFRP Catalog Number: 9469
• Author: Colorado Water Conservation Board.
• Title: Floodplain Information Report\
• USFW Year: 1995.
• Copyright Material: NO

TABLE 5
GL?NNISON RIVER CROSS-SECTION SELECTION
REACH
NUMBER FLOW VALUES {CFS) SQ-
1R, 100-YR {NEAREST '
HYDROLOGIC POINT) CROSS-
'SECTION CROSS=SECTION .TYPE
NUMBER DERIV~ITION
QF FLOOD
'DEPTHS
1 22000, 24700 (G2) NONE DETAILED STUDY
ALREADY
PERFORMED FEMA STUDY
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 (GS) D-D' 1 CALCULATED
8 24856, 27868 (GS) E-E' 3 CALCULATED
9 24856, 27868 (GS) NONE CANYON REACH N/A
fl0 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
* -Map- enve cross-section F-F was prepare , ut it was not use It was omitte ecause t e ie surveyed
cross-section, G-G', located in the same reach, better represents that reach.
1 4.4 Computing. Flood Depths
Flood depths were calculated at each cross-section through a computer program (QANY) which
t 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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