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

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Hydrograph Analysis

A typical hydrograph resulting from an isolated period of rainfall consists of
a rising limb, crest segment, and falling limb, or recession. The shape of the
rising limb is influenced mainly by the character of the storm which caused the
rise. The SCS Type II storm distribution used during this study is evident in
the steep slopes along the rising limb of the hydrographs developed. With the
use of the SCS Type II storm distribution approximately 50% of the rainfall
occurs within a one-hour period.

Computed 10- and 100-year flood flows from the Fountain Creek watershed produced
relatively smooth hydrographs. The 100-year event hydrograph produced by the
companion study from the Monument Creek watershed is relatively smooth, however,
the 10-year hydrograph is multi-peaked with flows of 6698 cfs and 6697 cfs.
Combining the hydrographs within the HEC-l model at the confluence, the resulting
hydrograph resembles the shape and smoothness of the Fountain Creek watershed
hydrographs with the timing and peak flows controlled by the Monument Creek
Basin.

With time 0000 representing the commencement of rainfall, the time to peak (Tp)
for the Fountain Creek watershed upstream of the confluence occurs at 1345 and
1315 for the 10- and laO-year flood events, respectively. As was expected, the
TQ for the Fountain Creek watershed for the 100-year event is shorter than the
lu-year event. Tp val ues of 1310 and 1345 for the 10- and 100-year events,
respectively, were shown to occur for the Monument Creek basin according to the
analysis completed in the companion study. When the basins were combined the Tp
for the watershed downstream of the confluence developed were 1333 and 1358 for
the 10- and 100-year events, respectively.

It is interesting to note that the basin does have a characteristic of naturally
attenuating peak flows as they move downstream. This is dramatically obvious
from the 1965 flood on Jimmy Camp Creek which produced a peak of 124,000 cfs at
its confluence with Fountain Creek, but the Fountain Creek peak at Pueblo was
47,000 cfs wher~ the basin is 17 times as large, including Jimmy Camp Creek.
This is due to both the temporal and spatial spreading of the runoff volume and
the limited areal extent of even this major flood event.

4.8 REGIONAL HYDROLOGIC ANALYSES

Often individual drainage basins may have an insufficiently documented history
of flooding either in information available or the period of record for which
information is available. Transposition of information from other
meteorologically and physiographically similar areas is a commonly accepted
hydrologic technique of supplementing Site-specific information with data which
may be more statistically complete. This can be accomplished in a mathematically
precise method such as a multiple regression analysis or a single (or composite)
variable comparison such as peak flow per square mile of drainage area. This is
the third hydrologic procedure utilized for this study.

Pitlick (1988) developed a "Colorado Foothills" regional flood frequency curve
which can be used for developing estimated peak flows for selected frequencies
based upon the statistical value of 'the mean annual flood. This is based upon

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