FLOOD10363 ‎(2)‎

• County: Gunnison
• Community: Gunnison County
• Stream Name: East River, Cement Creek, Alkali Creek, Ohio Creek
• Title: Gunnison County Flood Hydrology, Contract # W99-D-0018 Final Report
• Date: 11/1/2004
• Prepared For: US Army Corps of Engineers, CWCB and Gunnison County
• Prepared By: Tetra Tech, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Figure 5.2.2.1 Reported Peak Flow as a Ratio of the Reported Daily Average Flow - East River
near Crested Butte and Slate River near Crested Butte

1400

: ::
: ::
East River near Crested Bulle
"I Drainage Area = 90 sq mi

:
:
1
r
r

-'

1200

1/
~
~:
J.
.r..'.....
'it'.:..'..:....':
y = 1.2067xr~:....,:..~:... .............
l~2 = 0.9485l.L...i~,: .. ,...!.:;;/
....j,..,:;...::~..,..;:;'i/ ..;,
:/
~ './
./ ~
~ ,..

i .
----f----1
......l.....-.1

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-....

1000

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......----.--.-...............
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..............n.____......
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.._._~----_.--_.............
. ,.

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.... ........_-.-:.....~......
~; = 1 ~~:;:;..:':':': :':':':I::':':T:':'::E:':':':t:':J
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o 800
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Q.
"i 600
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CD
a:

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::':'.:;':':':':',;,',.',',.r,','.',r.',.,.,'

"__~"'h'_____.___ ."
. . . .
: .

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Slate River near Crested Bulle
Drainage Area = 70 sq.mi

. . -- __ni.u..:____.:___...: h _u__'_nn_'_____. '._________',__.h __ ____:__...~_____l____;
. : : : : . ~ :
.................~ .. ,t .:.....~... .~.....:
\\l' ..,.. ....:: ....)....+...+....4...., ....:...-+....;.....),...,~
. ............ -. .. ..:.....~.....:.....~. (: ..."":....~.....:... --r....":

f~Ll!i;jtlI!rTiJTIiiit;T!ii

. .. .... ". I . . : . .

i~]~[JlJri;fLttTLI:TITrJ

400

200

o
o

200

400 600 800 1 000
Reported Daily Average Flow (efs)

1200

1400

The REGFREQ program was then used to determine the correlation of the newly created flow data to
nearby gages on the Gunnison River system. A predictably high degree of correlation (>0.9) between the
Slate River gage and East River atAlmont (09112500) was found. The East River at Almont gage was
used to expand the data set for the Reach 3 daily stream gage flows. The resulting expanded data set is
listed in Appendix A - Table A.2.

5.2.3 Results for Reach 3

Before any analysis was completed, the data record for both the Gunnison River at A1mont and East
River at Almont gages .were filtered for rain on snow events, using the 0.5 inch criteria discussed in
Section 4.1.1. Two rain on snow events were found in the Reach 3 combined data set. (The East River at
Almont results represent the downstream end of Reach 5 and are described in Section 5.4.).

The REGFREQ and HEC-FFA programs were used to perform the analysis on the flow record in
Appendix A - Table A.2. Prior to using the REGFREQ program, HEC-FFA was used on both the East
River at A1mont and East River below Cement Creek data to test for low and high outliers based on a
methodology described in Bulletin 17B. Any outliers were manually removed from the REGFREQ data
set. The 1977 flow for the East River at Almont and the 1940 flow for the combined Reach 3 data set
were determined to be low outliers. The results from the analysis are presented in Figure 5.2.3.1.
Additionally, the adopted statistics and the 10,2, 1, and 0.2 percent chance exceedence flows are
presented in Table 5.2.3.1.

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