FLOOD03562

• County: Eagle
• Community: Eagle County
• Stream Name: Roaring Fork, Frying Pan
• Basin: Colorado Mainstem
• Title: Floodplain Information Report
• Date: 2/1/1978
• Prepared For: Eagle County
• Prepared By: Wright-McLaughlin Engineers
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Hydr.lulicAnalysis
The w;,ter surface elevations for floods of the selected recurrence Intervals
were computed through uSe of the Corps of Engineers' HEC-2 backwater computer
program (Reference 4). Sixty-four cross sections for the hydraulic analysis
of the Roaring Fork and Fryingpan rivers were secured from the topographiC
"",ps. The locations of these cross sections are shown by reference polnts
on the flooded area maps and the flood profiles in the ba~k of thIs report.
The 10,50, 100,and500-year flood elevatIons and discharges are iisted
in Table]. Channel rOllghness fa~tors (Manrllrlg' s n) for these computations
were assigned on the basis of field Irlspectlonof the floodplain areaS.

20

No area redllctlons at existlrlg bridge, were used in the hydrallllc analysis
to a~count for probable debris blockage.

A detai led compllter I isting of hydralll ic analysis showing all parameters
is included In the Technical Addendum (Reference 11}.

-

The flooded area maps, whiCh show the bOllndarles of the lOa-year flood, are
~ubd ivlded into the high hazard area and the low hazard area. As set forth
by the regulations of Eagle County, the high hazard area Is that portion
of the floodplain where the water depth can be expected to be greater than
\ foc>t, or the velocitles Can be exoected to be 3 feet per second or hi gher.
The low hazard area is the remaining portion of the flOOdplain. The low
halard are~ as plotted on the flooded area maps was determined by delineatIng
that Orea where the depth of flow was less than I foot, then checking th~
velocltle, In these areas to see rf they were less than 3 feet per second.
The t low velocl ty a~ross the rl ver at each ~rO$$ sect ion waS determined by
the HEC-2 backwater compllter program. If the velo~itles exceeded] feet
per second the low h<lzard reg;"n "d' ",,,,Jified, .u<;h thd( il indlllled o"ly
tho,e are~s where the de~th, were le~s than I foot and the velocl t ie, were
I e~' than 3 reet per .<,cond. The low hJJ.ard Jr"a is shown on the flooded
area maps by CrOSS hat~hing.