FLOOD08078

• Designation Number: 169
• County: Eagle
• Community: Unincorporated Eagle County
• Basin: Colorado Mainstem
• Title: Flood Insurance Study - Eagle County, Colorado, Unincorporated Areas
• Date: 5/1/1980
• Designation Date: 12/1/1980
• Floodplain - Doc Type: Floodplain Report/Masterplan

3.1 Hydrologic Analyses

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

Discharges on Eagle River (at Minturn), Taylor Creek, Brush
Creek, Roaring Fork River, Eagle River (at Redcliff),
Turkey Creek, and discharges for approximate study areas were
determined using regression analysis based upon regional gage
analysis.

~

This regional analysis of streamflow data was completed, assuming a
log-Pearson Type III distribution (Reference 9). The streamflow
data were separated into snowmelt and rainfall peaks, and each type
was analyzed separately. A total of 15 stream gages located in
Eagle County were analyzed. The length of record of these gages
ranges from 6 to 43 years.

Drainage area-discharge curves were developed from these data for
the 10-, 50-, 100-, and SOD-year flood events. Snowmelt peaks were
found to produce the flood peaks for larger drainage areas, and
cloudbursts produced the peaks in smaller basins, generally less
than 20 square miles in area.

The discharges for Fryingpan River were obtained from a Flood
Plain Information report (Reference 10).

Peak discharge-drainage area relationships for Eagle River
(at Minturn), Fryingpan River, Taylor Creek, Brush Creek, Roaring
Fork River, Eagle River (at Redcliff), and Turkey Creek are
shown in Table 1.

3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of streams in the county
were carried out to provide estimates of the elevations of floods
of the selected recurrence intervals along each stre~ studied in
the county.

Water-surface elevations of 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 11).

The cross sections for Eagle Rlver (at Minturn), Eagle River
(at Redcliff), Fryingpan River, Taylor Creek, Roaring Fork River,
and Turkey Creek were obtained by field surveys. Cross sections
for the backwater analyses of Brush Creek, Reach 1, were also
obtained from topographic maps, (Reference 13) with below-water
data obtained from field surveys. Cross sections for Brush Creek,

9

REVISEO:l/25/83