FLOOD09993

• County: Eagle
• Community: Eagle
• Basin: Colorado Mainstem
• Title: FIS - Eagle
• Date: 9/1/1979
• Prepared For: Eagle County and CWCB
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

flooding potentials based on conditions existing in the community at the
time of completion of this study. "'1aps and flood elevations will be
amended periodically to reflect future changes.

3.1 Hydrologic Analyses

Hydrologic analyses were carried out to establish the peak discharge-
frequency relationships for floods of the selected recurrence inter-
vals fGr each stream studied in detail in the community.

Flood discharges for the 10-, 50-, 100-, and 500-year floods on
Brush Creek Were calculated using regression equations based upon a
regional gage analysis for all of Eagle County (Reference 5).
Fourteen gages were employed in the county study, representing a
combined total of 318 years of record. The analysis was performed
using log-Pearson Type III methodology (Reference 6). The IOO-year
flood discharges for the approximate study reaches were also taken
froM these equations.

Peak discharge-drainage area relationships for Brush Creek are shown
in Table 1.

1'able 1.

Summary of Discharges

Flooding Source
and Location

Drainage Area
(Square Ililes)

Peak Discharges
(Cubic Feet per Second)
la-Year 50-Year lOa-Year 500-Year

Brush Creek
At Upstream and
Downstream Corporate
Limits of Eagle

150

875

1150

1225

1400

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of streaMS in the commu-
nity were carried out to provide estimates of the elevations of
floods of the selected recurrence intervals along each stream
studied in the community.

Water-surface elevations for floods of the selected recurrence intervals
were computed through use of the u.s. Army Corps of Engineers HEC-2
step-backwater computer program (Reference 7). Cross sections for
the backwater analyses of Brush Creek were obtained from topographic
maps at a scale of 1:1200, with a contour interval of 2 feet (Refer-
ence 8). All bridges were field checked to obtain elevation data
and structural geometry.

Locations of selected cross sections used in the hydraulic analyses
are shown on the Flood Profiles (Exhibit 1). For stream segments
for which a floodway is co~puted (Section 4.2), selected cross
section locations are also shown on the Flood Boundary and Floodway
j\l'lap (Exhibit 2).

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