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TABLE 5 COLORADO RIVER CROSS-SECTION SELECTION REACH l'LOWVALUCS(CFS) CROSS SECTION DERIVATION NUMBER JO-YR,IOONR SOURCB OFDEPTII (HYDROLOGIC POINT) , 38700,42900 DETAILED STUDY COESnrDV (Cl &0) AVAILABLE 2 311700,42900(0) DETAILED STUDY COESnmY AVAILABLE 2 C2-C6 DETAILED STUDY COE STIJDY AVAILABLE , 4IOJ4,45791(C6} DETAILED Snmy COE SnrDY AVAILABLE , 44400,49300 (C6-C8) CANYON REACH NIA , 44400,49300 (C8) A-A' FIELD CALO..rLA TED SURVEYED ; 44400,4't300(C8) CANYON REACH WA , 4JO~,50030(C9) DETAILED STUDY FEMA STUDY AVAILABLE , 7f619,80289(C9.Cll) DETAILED STUOY FEMA STUDY AVAILABLE " 73340,82262 (C12) CANYON REACH N/A " 74S6J,83668(Cl3) B-B'MAP CALCULATED DERIVED " 74)6J,g)btlg(C13J C,C' MA~ CALCULATI:::l> DERIVED' I I. . Reoch12c...Cany<>ll.u.ch,hul.map-<kriv.dcro"'-secl;on.."a/lu..dlhe...any....y, 4.4 ComrJl,l1inc Flood De[lths flood depths were calculated at each cross-section through a computer program (QANY) which u!\C~ Manning'~ equation, The input pa1'3mete~ for the calculation of flow included: ~ and y coordinates for points on the cross-section, Manning's '0' values (Reference 11), the channel slope (inlerpreted from USGS quadrangle maps), and depth values. The program ca1culalOO flow and velocity values ior each depth value entered, The target t10w values were those values established in Section 3.0 and showD on Table 3. Raring curves were established from the calculated depths. From the rating (;urves 50-year and loo-year flood elevations were established at each localion. " Inperfonning the depth calculations, the flow on the river the day of the survey was obtained from the USGS and subtracted from the established 50 and lOO-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 flood depths as shown in Table 6. The methodology used for computing flood depths at the cross-sections is similar to the accepted method ologiesused by state and federal agencies inperfonning detailed analyses except that there is no balancing of energy from one cross-section to the nexl. The one field-surveyed cross-section and the two map-derived cross-section are graphically represented in Figures 7A . 7C. An example 1'3ting curve was prepared for the field-surveyed cross-section, It is presented inPlaJel6, after the floodplain maps. 4.5 Delineatinl! Flood Boundaries The calculated flood depths for the unstudied stream reaches were rUSl ploned on the quadrangle maps at the cross-section locations. The resulting floodplain widths were compared to the floodplain widths on the cross-section plots. The floodplain boundaries between the cross- sections were then approximated by delineating flood depth contours and interpreting the relationship. between those flood depth contours and the ground contours. Consideration was given to the slope within each reach. For all of the previously studied reaches the detailed delineations were transferred directly onto the base mapping without any flood depth computations. The delineations for the previously unstudied reaches were blended with the existing detailed delineations on the base maps. The fmalized infonnation was displayed on the USGS 7.5' quadrangle maps (scale of l" = 2,000'). A table identifying the 4uadrangle maps used in each plate and the map scale is given in Figure 8. The location of each floodplain map plate is shown in Figure 9, and the t100dplain maps are shown in PlaJe$ 1-/5. "