FLOOD11727

• Designation Number: 221
• County: El Paso
• Community: Manitou Springs
• Basin: Arkansas
• Title: FIS - Manitou Springs
• Date: 8/1/1983
• Designation Date: 1/5/1984
• Prepared For: Manitou Springs
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

.,

I

Water-surface llevations of floods of the selected recurrence
intervals were computed through use of the U.S. Army Corps of
Engineers HEC-; step-backwater computer program (Reference 7).

Cross section tata and additional flood plain data for Fountain
Creek upstream of the road to the Cave of the Winds was obtained
from the Flood I Insurance study for the unincorporated areas of
El Paso County I (Reference 8). Cross sections used for the backwater
analyses of su~'herland Creek, Williams Canyon, and Ruxton Creek
were obtained rom detailed field surveys of each stream reach.
Cross sections ,used for the backwater analysis of Fountain Creek
downstream of ~he Road to the Cave of the Winds were furnished
by the U.S. Arty Corps of Engineers from the Flood plain Information
report for the larea published in 1974 (Reference 3). For Fountain
Creek and suth~rland Creek, supplemental cross sections were develop-
ed from topogr~phic maps at a scale of l:1,200, with contour inter-
vals of 4 and 40 feet (Reference 9). All bridges, culverts, and
other hydraulidally significant structures were field checked
to obtain elevJtion data and structural geometry.
I

Locations of sJlected cross sections used in the hydraulic analyses
I
are shown on t~e Flood Profiles (Exhibit 1). For stream segments
for which a flqodway is computed (Section 4.2), selected cross
section locatidns are also shown on the Flood Boundary and Floodway
Map (Exhibit 2)1.
I
Roughness fact<~rs (Manning l s "n") used in the hydraulic computations
for Sutherland Freek, Williams Canyon, and Ruxton Creek were chosen
by engineer ing Ijudgment and based on field observations of the
st::eams and ovelrbank areas. Roughness factors for the main channels
ranged from 0.0120 to 0.035, and overbank factors ranged from 0.040
to 0.050 for flpods of the selected recurrence intervals. Roughness
factors for Fountain Creek downstream of the Road to the Cave
of the Winds we~e supplied by the u.s. Army Corps of Engineers
(Reference 3) ahd ranged from 0.020 to 0.040 for the main channel
and from 0.050 ~o 0.100 for the overbank areas for floods of the
selected recurrbnce intervals.
!

Starting water-~urface elevations for the streams studied in detail
were determinedl using the slope-area method or a critical depth
elevation.

It

I
I
Flood profiles ~ere drawn showing computed water-surface elevations
,
to an accuracy ~f 0.5 foot for floods of the selected recurrence
intervals (Exhibit 1).
I
\
Generally, the ~istances on the flood profiles correspond to distances
measured along the centerline of the designated watercourses.
,
Along Williams ~anyon, however, the low-flow is carried through
an 1,100-foot, ~oncrete box culvert under Canon Avenue near to
the confluence ,ith Fountain Creek. In this area, the divergence
of the 10W-flow\drainage necessitated the use of distances measured

I
!

.

11

l

I
J
L~