FLOOD02335

• Designation Number: 258
• County: Pueblo
• Community: Pueblo
• Basin: Arkansas
• Title: Flood Insurance Study - Pueblo
• Date: 9/1/1986
• Designation Date: 9/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

500-year floods, have a 10. 2. 1. and 0.2 percent chance. respectively,
of being equaled or exceeded during any year. Although the recurrence
interval represents the long term average period between floods of a
specific magnitude. rare floods could occur at short intervals or even
within the same year. The risk of experiencing a rare flood increases
when periods greater than 1 year are considered. For example, the risk
of having a flood which equals or exceeds the 100-year flood (1 percent
chance of annual exceedence) in any 50-year period is approximately 40
percent (4 in 10), and, for any 90-year period, the risk increases to
approximately 60 percent (6 in 10). The analyses reported herein reflect
flooding potentials based on conditions existing in the community at the
time of completion of this study. Maps 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 each flooding source studied in detail
affecting the community.

Basic hydrologic analyses for the Arkansas River and Fountain Creek
were developed for the Review Survey Report, Arkansas River
(Reference 7) and the Fountain Reservoir (Reference 6). Flood-
frequency data for these two streams were developed from discharge-
frequency relationships of historic floods and stage-discharge
records covering a 77-year period of gaging stations operated by
the USGS (Reference 8). These analyses followed the standard log-
Pearson Type III method (Reference 9).

Flow-frequency parameters for Dry Creek (East) and Wild Horse-Dry
Creek were developed from procedures outlined in a USGS manual
(Reference 10).

For the Arkansas River, Fountain Creek, and Wild Horse-Dry Creek,
discharges for the 500-year floods were determined by straight-
line extrapolation of a single-log graph of flood discharges computed
for frequencies up to 100 years.

Peak discharges for University park Tributary were calculated from
a methodology developed for small watersheds by the USGS (Reference 11).

peak discharge-drainage area relationships for the Arkansas River,
Fountain Creek, University Park Tributary, and Wild Horse-Dry Creek
are shown in Table 2.

The peak 100-year discharge for the outflow from Lake Minnequa was
developed by an independent rainfall-runoff determination for the
Lake Minnequa basin. This determination was accomplished using
the HEC-1 computer model (Reference 12). For this analysis. precip-
itation values for the 100-year storm were calculated from the
official City of pueblo depth-duration intensity curve and the

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