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<br /> <br />1 <br />1 <br />1 <br /> <br />1 <br /> <br />1 <br />1 <br />TABLE 5 <br />YAMPA RIVER CROSS-SECTION IDENTIFICATION <br />REACH <br />NUMBER FLOW VALUES (CFS) <br />50-M 100-YR <br />(NEAREST <br />HYDROLOGIC POINT) CROSS- <br />SECTION CROSS-SECTION TYPE <br />NUMBER DERIVATION <br />OF FLOOD <br />DEPTHS <br />1 15800, 18300 (YI) NONE DETAILED STUDY <br />ALREADY PERFORMED FEMA STUDY <br />2 15800, 18300 (Y1) A-A' 3 CALCULATED <br />3 16651, 18791 (Y2) B-B' 2 (FROM F-F') CALCULATED <br />4 17102, 19052 (Y3) C-C' 2 (FROM F-F') CALCULATED <br />5 17102, 19052 (Y3) D-D'* I CALCULATED <br />6 17102, 19052 (Y3) NONE CANYON REACH N/A <br />7 18315, 19776 (Y4) F-F' I CALCULATED <br />8 18315, 19776 (Y4) G-G' I CALCULATED <br />9 18548, 20003 (Y5) H-H' 3 CALCULATED <br />10 18548, 20003 (Y5) 2 (FROM F-F') CALCULATED <br />11 18548, 20003 (Y5) 2 (FROM G-G') CALCULATED <br />12 18548, 20003 (Y5) NONE CANYON REACH N/A <br />13 19748, 21433 (Y6) K-K' I CALCULATED <br />14 35842, 40481 (Y7) L-L' 2 (FROM D-D') CALCULATED <br />15 36497, 41322 (Y8) M-M' 2 (FROM G-G') CALCULATED <br />* Map-derived cross-section E-E' was prepared, but it was not used. It was omitted because the <br />field- surveyed cross-section, D-D', located in the same reach, better represents that reach. <br />4.4 Computing Flood Depths <br />Flood depths were calculated at each cross-section through a computer program (QANY) which <br />uses Manning's equation. The input parameters for the calculation of flow included: x and y <br />coordinates for points on the cross-section, Manning's 'n' values (ranging from 0.03 to 0.035 for <br />the channel and 0.045 to 0.05 for the overbank) (Reference 7), the channel slope (interpreted <br />from USGS quadrangle maps), and depth values. The program calculated flow and velocity <br />values for each depth value entered. The target flow values were those values established in <br />1 Section 3.0 and shown on Table 3. Rating curves were established from the calculated depths. <br />From the rating curves 50-year and 100-year flood elevations were established at each location. <br />In performing the depth calculations the flow on the river the day of the survey was obtained <br />from the USGS and subtracted from the established 50-year and 100-year flows for each <br />particular hydrologic point. The depth of water on the day of the survey was estimated and <br />I added to the flood depth calculations to obtain the true flood depths shown in Table 6. The <br />18