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<br />
<br />TABLE 5
<br />WHITE RNER CROSS-SECTION IDENTIFICATION
<br />
<br />
<br />.'.',.',..,.', ,."....,', "d''''
<br />, .......'.'----,.
<br />,-, - ..". - -.
<br />.".1?muV. ATI9N..........'.',.....,'.,..'...
<br />'O..'F'" ""."',,"'....'"
<br />tig~$
<br />
<br />The three surveyed cross-sections, the one surveyed cross-sections transferred to reaches other
<br />than the reach where they were surveyed, the two cross-sections that were hybrids of map cross-
<br />sections and field data, and the one cross-section which used FEMA depths from an upstream
<br />location are graphically represented in Figures 7A-F. Example rating curves were prepared for
<br />the three field-surveyed cross-sections. They are presented in Plates 10-12, after the floodplain
<br />maps.
<br />
<br />. ..,- -.. ,..--.. "
<br />','__ """" __n_ _ 'd....,',',..'_'__...,.,
<br />,. ,....- -.-""".-'-- -....,-.'.' ,'..-,."
<br />...,-, ....,.,...---,.,---,.,....--,----...,....,--, ..
<br />1c9~y~~tgl1
<br />.$IA.}\'& .'lll.. 0.;. .'.'~' '...........,.......
<br />,.:. "'.- ":.-, '.. ---,".',.'"",,,'.',:--,.'."','"
<br />:<,' . n,.::, _', C:,:_':"':'_'_'_:"';'_'_:':_,:,:_","':__':"
<br />",._'_._:.-',.,',..,.,:_,:.,.:-,..,_,_.._..:.:'_.,:_....':0"..:.:-.:"':-'-'-':':"',-,
<br />"'~"'.,."..""""S'..T'...'.'..."'.,.............
<br />.. . . - - ...,',.,.,..,.,'..-....,...,',',.,.",..,.',
<br />.... . """',',' ......,..
<br />/"""._ '_,' ',d_ ',...,'. ,'._ _.:-.:. :,t.:.;;;:;:;,;::.:;:;:;,;,;,;::::::,,:>,:.::::;:.,,:::;::-,':,~:
<br />'.,......RYl)"R\'.O..LQ'..'(J' I'C".''PO.. '.'INJ)'.' .,".'...
<br />','."-- -' ,,'- '-,,-, ''''''', - ',,-,---:..-,.
<br />,'---"" ",' -;,'-:' ,.'-::".:,'"
<br />. '-, - -, -,- -" -,'--,--"
<br />",,-,,_, '_- '__"_"-"-'.'. ,. ._'s.,.,'.__,'_-__-_ "-"-'-_.' '. "
<br />.,,, - ---'".-- -.... -..
<br />
<br />8
<br />9
<br />10
<br />
<br />6934, 8133 (WI) Z-Z' 3
<br />9565, 12501 (W2) A-A' I
<br />10137, 13508 (W3) NONE CANYON REACH
<br />11007, 15079 (W4) B-B' I
<br />12051, 17021 (W7) D-D" I
<br />120$1,17021 (W7) E-E' 2 (FROM B-B')
<br />13500, 20000 (W9) NONE DETAILED STUDY
<br /> ALREADY PERFORMED
<br />13500, 20000 (W9) FA-FA' 3
<br />13500, 20000 (W9) NONE CANYON REACH
<br />14539,21873 (WIO) F-F' 4
<br />
<br />CALCULATED
<br />CALCULATED
<br />NIA
<br />CALCULATED
<br />CALCULATED
<br />CALCULATED
<br />FEMA STUDY
<br />
<br />4.5
<br />
<br />Delineating Flood Boundaries
<br />
<br />I
<br />2
<br />3
<br />4
<br />5
<br />6
<br />7
<br />
<br />The calculated flood depths for the various stream reaches were fIrst plotted on the quadrangle
<br />maps at the cross-section locations. The resulting floodplain widths were compared to the
<br />floodplain widths on the cross-section plots. The floodplain boundaries betweep. the cross-
<br />sections were then approximated by delineating flood depth contours and interpreting the
<br />relationship between those flood depth contours and the ground contours. Consideration was
<br />given to the slope within each reach. The fmalized information was displayed on the USGS 7.5'
<br />quadrangle maps (scale of I" = 2,000'). A table identifying the quadrangle maps used in each
<br />plate and the map scale is given in Figure 8. The location of each floodplain map plate is shown
<br />in Figure 9, and the floodplain maps are shown in Plates 1-9.
<br />
<br />CALCULATED
<br />NIA
<br />FEMA STUDY
<br />
<br />· Map-derived cross-section C-C' was prepared, but it was not used. It was omitted because the field-surveyed
<br />cross-section, D-D', located in the same reach, better represents that reach.
<br />
<br />4.4 Computing Flood DeDths
<br />
<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 0.032 for
<br />the channel and 0.045 fa 0 065 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 />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 />
<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 />added to the flood depth calculations to obtain the true flood depths shown in Table 6. The
<br />methodology used for computing flood depths at the cross-sections is similar to accepted
<br />methodologies used by state and federal agencies in performing detailed analyses, except that
<br />there is no balancing of energy from one cross-section to the next.
<br />
<br />18
<br />
<br />19
<br />
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