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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The East River at A1mont gage was chosen to expand the data set for the Gunnison River near Gunnison
daily stream gage flows. The East River at Almont gage has a continuous record from 1935 through
2000. The East River gage was chosen since it had the highest degree of correlation, the longest
available period of record, and unprocessed results. Other gages had been processed to remove the
effects of the Taylor Park Reservoir. The resulting family of flow records is presented in Appendix A-
Table A.8.

Figure 5.8.2.1 Peak to Daily Flow Relationship - Gunnison River near Gunnison Gage
14,000

~ 12,000
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.~
2 10,000
::J
o

,;

.

...
:g 8,000
s:::
s:::
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6,000

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:: 4,000
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11l
&. 2,000

o
o

2,000 4,000 6,000 8,000 10,000
Daily Peak Flows Gunnsion near Gunnison (cfs)

12,000

5.8.3 Results for Reach 9

Before any analysis was completed, the data record for both the East River at Almont and Gunnison
River near Gunnison gages were filtered for rain on snow events, using the 0.5 inch criteria discussed in
Section 4.1.1. Six rain on snow events were found in the record of the Gunnison River near Gunnison
gage. The East River at A1mont results 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.8. Prior to using the REGFREQ program, HEC-FFA was used on both the East
River at Almont and Gunnison River near Gunnison 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 both gages was determined to be a low outlier. The results from the analysis
are presented in Figure 5.8.3.1. Additionally, the adopted statistics and the 10, 2, 1, and 0.2 percent
chance exceedence flows are presented in Table 5.8.3.1.

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