FLOOD06275

• County: Moffat
• Community: Moffat County and Unincorporated Areas
• Basin: Yampa/White
• Title: FIS - Moffat County and Unincorporated Areas
• Date: 2/2/1982
• Prepared For: Moffat County
• Prepared By: FEMA
• Floodplain - Doc Type: Current FEMA Regulatory Floodplain Information

Peak discharge-drainage area relationships for all streams studi€'r1
in detail are shown in Table 1.

Tributalies 1 and 2 were studied by dppruximdce mei hod;:; U;:;illq
the Rational Method.

J.< Hydraulic Analyses

Analyses of the hydraulic characteristics of the. t !c'(hli_nq r:nlllC('S
studied in the county were carried out to p.t.ovitk (....-:~ imai ,'~;
of the elevations of floods of the selected recurr{~nc{~ :ll\LI~rV---1J ~':
along each of these flooding sources.

For detailed studied streams, the water-surface (?l{~val:inn:; l)f:
floods of the selected reCUrrence intervals were (;1 lrnpllt','li t- h'-''---~lJq1J
use of the U.s. Army Corps of Engineers HEC-2 s\.pp--b,Wi...\o,I,lh'l Cl)JllFltcr
program (Reference 7). The results obtained trnlil j h{~ tiEl' -.: UlllltY.JtJ"
program were adjusted on the profiles to within toi l~J. ,1lll't-'~' 1,1
the vicinity of bridges to more accurately repreB~'nl ,1\'1 U.ll 11~),-',ill~(;
conditions (Reference 8).

Cross sections used in the backwater analyses for Yalllpa F 1.V(~J' .
the lower portion of Fortification Creek, Bl:othertl)l1 GU.'-.dl, and
the portion of Cedar Mountain Gulch upstream of \I.~;. llHl!W,'l' ';0
were obtained from the Colorado Water Conservation Hc.rrd In l'er'~L t-:-;
prepared by the U. S. Army Corps of Engineers (Refel ,';)CE"C :1 and
4). Cross sections used ~n the backwater analyses 1"01 t.hE' \IPPCL
portion of Fortification Creek, Sand Gulch, Sand Gulch Tributary,
Lay Creek, and Big Gulch were obtained by aerial pllot.ogr"..ffi1etlY
(Reference 9). Cross sections for the lower portion of l~~'ddr
Mountain Gulch and all of Pine Ridge Gulch were fj eld FUivey,',;.
The below-water sections of all cross sections well' obt .lir'l.t..'0 hy
field measurement. All bridges, dams, and cuJvcru' Wt..'lC j iL~}d-
sur veyed to obtain elevati.on data and structUl dl 9~'L'n:\'{ l~'.

Locations of selected crOSS sections used in toile hydi J.U.L1C drL1'i~'~~',':-
are shown on the Flood Profiles (Exhibit 1). FOl ,;tll'im ,'esmCl","
for which a floodway is computed (Section. 4.2), sl2-1......ct.€d ....lO!:;S
section locations are also shown on the Flood Boundaj y ,jl1<.: ~-'~t'<-':(~\'-,::
Map (Exhibit 2).

Roughness factors (Manning's "n") used in the hydr,.n::il' CCC1~~Ut.-:::.~-l~~:'<-:'
for the study streams were chosen by engineering )l,igrc.c'c ,,;oj
based on field observations of the flooding sOuI....~es ai-,D tIc,',]
plain areas. Roughness values for the main channel ot alj S',~:"C2T:~~
studied ranged from 0.030 to 0.050; flood plain roughness values
ranged from 0.035 to 0.080.

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