Floodplain Information Report Volume 2 White River from Rio Blanco Lake to the Utah-Colorado State Line

• Basin: Yampa/White/Green
• Title: Floodplain Information Report Volume 2 White River from Rio Blanco Lake to the Utah-Colorado State Line
• 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

P-1
u
n
C
TABLE 5
WHITE RIVER CROSS - SECTION IDENTIFICATION
.REACH
FLOW VALUES (CFS)
CROSS=
CROSS; .SECTIC3N TYPE
DERIVATION
NUMBER
SfI-- Yi2;:100 YR
SEGFI0NN
NUM$ER
OF FLOOD
(NEAREST
DEPTHS
HYDROLOGYC.POiNT) ,
1
6934, 8133 (WI)
Z -Z'
3
CALCULATED
2
9565, 12501 (W2)
A -A'
1
CALCULATED
3
10137, 13508 (W3)
NONE
CANYON REACH
N/A
4
11007, 15079 (W4)
B -W
1
CALCULATED
5
12051, 17021 (W7)
D -D'*
1
CALCULATED
6
12051, 17021 (W7)
E -E'
2 (FROM 13-13')
CALCULATED
7
13500, 20000 (W9)
NONE
DETAILED STUDY
FEMA STUDY
ALREADY PERFORMED
8
13500, 20000 (W9)
FA -FA'
3
CALCULATED
9
13500, 20000 (W9)
NONE
CANYON REACH
N/A
10
14539, 21873 (W10)
F -F'
4
FEMA STUDY
* Map - derived cross- section C -C' was prepared, but it was not used. It was omitted because the field- surveyed
cross - section, D -D', 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 0.045 to 0.065 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 accepted
methodologies used by state and federal agencies in performing detailed analyses, except that
there is no balancing of energy from one cross - section to the next.
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