FLOOD10390 ‎(2)‎

• County: Moffat
• Community: Craig to Dinosaur National Monument
• Stream Name: Yampa River
• Title: Floodplain Information Report - Yampa River from Craig to Dinosaur National Monument
• Date: 4/1/1996
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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TABLE 5
YAMPA RIVER CROSS-SECTION IDENTIFICATION

15800, 18300 (YI) NONE DETAILED STUDY FEMA STUDY
ALREADY PERFORMED
2 15800, 18300 (YI) A-A' 3 CALCULATED
3 16651, 18791 (Y2) B-B' 2 (FROM F-F') CALCULATED
4 17102, 19052 (Y3) C-C' 2 (FROM F-F') CALCULATED
5 17102, 19052 (Y3) 0-0'. CALCULATED
6 17102, 19052 (Y3) NONE CANYON REACH NfA
7 18315, 19776 (Y4) F-F' CALCULATED
8 18315, 19776 (Y4) G-G' CALCULATED
9 18548, 20003 (Y5) H-H' 3 CALCULATED
10 18548,20003 (Y5) I-I' 2 (FROM F-F') CALCULATED
II 18548,20003 (Y5) 1-1' 2 (FROM G-G') CALCULATED
12 18548, 20003 (Y5) NONE CANYON REACH NfA
13 19748,21433 (Y6) K-K' CALCULATED
14 35842, 40481 (Y7) L-L' 2 (FROM 0-0') CALCULATED
15 36497,41322 (Y8) M-M' 2 (FROM G-G') CALCULATED
* Map-derived cross-section E-E' was prepared, but it was not used. It was omitted because the
field- surveyed cross-section, 0-0', 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 0.035 for
the channel and 0.045 to 0.05 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

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