FLOOD03034

• County: Pueblo
• Community: Pueblo
• Stream Name: Fountain Creek
• Basin: Arkansas
• Title: Floodplain Analysis Report for Fountain Creek Overflow
• Date: 2/1/1983
• Prepared For: Pueblo
• Prepared By: MSM Consultants, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The 8th Street bridge was recoded based on your surveys. All
of the possible access points for water to enter the downtown
area were surveyed. The water surface elevations in that
area were compared to possible access points into downtown,
and only two points were found to be low enough for water to
pass through under 100 year flooding conditions (64,000
cfs). Rating curves were calculated for those two access
points.

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Using the revised HEC-2 data and the rating curves, the
amount of water flowing down the channel, through the left
overbank (Lower East Side area), and through the right over-
bank diversion access points was calculated for flows ranging
from 47,000 cfs to 64,000 cfs. At 47,000 cfs, the right bank
diversion was found to total approximately 510 cfs. At
64,000 cfs it was found to total approximately 1905 cfs.

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Comments on Methodology and Results

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The methodology used by MSM appears reasonable to us.
The rating curves assumed rectangular cross sections at the
two access points, and the calculations were correct. The
HEC-2 elevations were comparable to the results of the Army
Corps of Engineers for channel elevations. Given the rela-
tively shallow flows entering the downtown area (1 to 3 feet)
we feel that MSM's approach of selecting particular diversion
points is more refined than the Army Corps of Engineers'
approach of extending cross sections from the channel west
into the downtown area. With the accuracy of topographic
mapping being on the order of half the contour interval,
flooding of 1 to 3 feet can easily be estimated incorrectly
if diversion cross sections are estimated from mapping rather
than field surveys.

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Since the intent of this phase of analysis was not to
consider potential flooding on the east side of Fountain
Creek, we will not comment on the results for that area at
this time. However, we would like to note that we continue
to have serious concerns about that area and its potential
for flood damages, and we trust that everyone involve0 at the
ci ty, state, and federal levels will be able to arr ive at a
reasonable delineation of the flood potential of that over-
bank area.

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Based on our review of MSM's work, it appears reasonable
to assume that overbank flow into the downtown area from a
100 year flood on Fountain Creek would be on the order of
2000 cfs rather than the approximately 5000 cfs previously
calculated for the Flood Insurance Study. However, it should
be noted that these calculations are based on the assumption
that there will be no blockage at the 8th Street bridge which
is not a natural condition during a flood event. The

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