FLOOD10401

• County: El Paso
• Community: Colorado Springs
• Stream Name: Fountain Creek
• Basin: Arkansas
• Title: Fountain Creek Drainage Basin Planning Study - Volume 1
• Date: 7/1/1994
• Prepared For: Colorado Springs
• Prepared By: Muller Engineering Company, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
I
I
I.
I
I
I
I
I
I

frequency). This relationship produces the following values for peak flows at
the following gages:

Manitou:
1,075 cfs/mi2 x 103 mi2 = 110,725 cfs

Tejon: .
1,075 cfs/mi2 x 392 mi2 = 421,400 cfs

Using a straight-line relationship, with the mean annual flood as the second
point, a linear relationship is produced as shown on FiQures 4.8-1 and 4.8-2
using paleohydrologic evidence.

Jarrett (1987) also studied in detail paleohydrologic evidence along Fountain
Creek and its tributaries and while little flood flow frequency numerical
information was developed, the following conclusions can be reached:

1. Streams above 7,500't show little evidence of large floods in terms of
peak unit discharge per square mile.

2. Many individual basins in the elevation range of 6,000 - 7,500' show
very high unit di scharges per square mil e but not for the same
meteorologic events. This illustrates that the largest floods were
caused by intense rainfall which was very localized, possibly due to
orographic characteristics and other factors.

3. There is a preference for flood~ on basins facing southeast toward the
prevailing flow of moisture.

4.9 HYDROLOGIC SUMMARY AND DESIGN FLOW RECOMMENDATION

Rationale

In consideration of the size of the Fountain Creek drainage basin, its regionally
unique geographic position. along the Front Range of Colorado, the site specific
basin characteristics, and the lack of consistent, reliable rainfall/runoff
information, no one hydrologic method can be depended upon to be uniquely
correct. As such, the results of the methodologies described in the previous
sections have been compiled on discharge/frequency Figures 4.8-1,4.8-2 and 4.9-1
for the purpose of comparing the estimated IO-year and 100-year flows for each
of the hydrologic index locations previously described. This provides a summary
of information in a visual format which assists the responsible entity in
choosing values and/or a method which is acceptable for the purposes for which
those values are to be used. The following paragraphs discuss Figures 4.8-1,
4.8-2 and 4.9-1 and interpret the results of the various methods. The final
section makes recommendations on design flows to be adopted.

Early in the hydrologic evaluation it was discovered that the U.S. Army Corps of
Engineers, authors of the currently adopted flood peak information (used also in
the FEMA flood insurance studies), consider that information obsolete and the
numbers too high for the reach of Fountain Creek upstream of the confluence. The

4.0-23

.
.
.
.
.
I
I
I
I
I
I
I
I
I
I
i

...
C
~

a.:
c(
IX

...
iil
j