FLOOD03173

• County: Statewide
• Community: All
• Basin: Statewide
• Title: State of Colorado 2002 Flood Documentation Report
• Date: 1/1/2003
• Prepared For: CWCB
• Prepared By: ICON Engineering, Inc.
• Floodplain - Doc Type: Flood Documentation Report

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Hvdroloeic and Hvdraulic Conclusions

The Colorado River is the major river in the Glenwood Springs area. This river flows to
the west through the city where it receives inflow from several creeks and canals in the
area. Atkinson Canal flows from the south to the north through the heart of the city
emptying into the Colorado River. Mitchell Creek is on the western end of town and
flows to the south until it's eventual confluence with the Colorado River. Oasis, Cascade,
No Name, and Grizzly Creeks all have similar characteristics to Mitchell Creek flowing
from the north to the south until they empty into the Colorado River.

Hydrologic analyses were performed using available baseline data from NOAA Atlas 2 in
order to generate Intensity Duration Frequency, or IDF, curves for rainfall events within
the Glenwood Springs area. Using the rainfall amounts mentioned in the Storm
Characteristics and Information section of this report and the estimated storm duration
from the NEXRAD radar images (rougWy two hours), one could estimate the frequency
of this specific event. The results of this analysis are summarized below in Table 5.1.

Table 5.1 - Hydrologic Analysis Summa

A t 5, 2002 Storm

30
0.49
0.41

0.71
.3 (20-MINUTE DURATION)
0.30
0.48
0.28
0.67*

According to the Glenwood Springs Post Independent, "...across the Colorado River and
to the west the storm dropped 0.67 inch(es) near the head of SOB basin near South
Canyon" (McGregor, 1). This area is about 8 miles west of the city of Glen wood Springs.
Since this point rainfall amount occurred outside the Glenwood Springs area, and since it
is much greater than the other rainfall amounts, this precipitation amount was considered
an outlying data point and not used to estimate the event frequency.

There are no flow gages available for Mitchell Creek. Two gages were found for rivers
near Glenwood Springs but, since these rivers did not flood, they were not considered in
the hydrologic analysis. However, the information found is included in the Additional
Support Information section of this report.

ICON Ergineering, Inc

43

January 2003