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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the assumption that streamflow gage analyses are sufficient in length to produce
a reliable mean annual flood and the assumption that more infrequent flows which
are not accurately represented at all gages are represented at some. Hi s
regional analysis produces the following values for peak flows at the Manitou
Gage:

Q'0 = 2.4 x 359 cfs = 862 cfs
Q'00 = 12.5 x 359 cfs = 4,488 cfs

This method was not felt to be particularly applicable to Fountain Creek
downstream of the confluence with Monument Creek due to the large percent of the
drainage basin located in the high plains versus the foothills. However, the
resulting peak flow values for the Tejon Gage have some relevance as another
piece of information:

Q,o = 2.4 x 3,072 cfs = 7,373
Q,oo = 12.5 x 3,072 cfs = 38,400

Muller (unpublished) developed an approximate regional analysis of peak
historical flows on similar foothills drainage basins and, separately, on adopted
design flow discharges for a similar group of streams which drain these areas.
Using the peak historical flow rates experienced at these gages, which have
records of from 72 to 104 years, the peak discharge in cubi~ feet per second per
square mile varied from 25 to 102 and provided an average of 57 cfs/mi2
(including the highest and lowest values) and an average of 54 cfs/mi2 (without
the highest and lowest values). Using 60 cfs/mi2 as reasonably representative
of a similar foothills stream at its mouth for a 100-year event produces an
estimated 100-year flood peak of 6,180 cfs at the Manitou Gage. Adopted lOa-year
peak flow unit discharge rates per square mile ranged from 42 to 84 and provided
an average of 56 (including the highest and lowest values). This provides
indirect confirmation of the 60 cfs/mi2 number described for the historical peak
comparison. This evaluation is not applicable to Fountain Creek below the
confluence with Monument Creek.

Among the regional hydrologic methods which were not utilized is Technical Manual
No.1 (Colorado Water Conservation Board 1976) which was judged not to be
applicable to foothills streams because of the lack of such streams in the data
sample used for development of this method, and the lack of recognition that such
streams represent a distinct category which is neither "mountain" or "plains".
The U.S. Army Corps of Engineers' unpublished hydrologic re-evaluation, for
Fountain Creek upstream of the confluence with Monument Creek was not accepted
by the City of Colorado Springs and therefore was also not included in this
analysis.

Paleohydrologic analyses have also been utilized to estimate the peak rate of
flow and related frequency from flooding evidence examined in the field. Precise
numerical information is not produced by this type of hydrologic method but it
can produce valuable information which in combination with other methods helps
describe extreme event hydrology.

Jarrett (1987) developed unit discharge values, in cubic feet per second per
square mile, based upon field paleohy~rologic evaluations of maximum experienced
floods or those floods which have occurred since the last ice age (10,000 year

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