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 hydrologic model of the Fountain Creek drainage basin consists of 106
numbered sub-basins which are contained within 32 regional basins as shown on
Figure 4.3-1 (Volume II). Table 4.7-1 lists each regional basin, its
abbreviation and the corresponding numeric range for the sub-basins. Each sub-
basin has been assigned an alphanumeric designation corresponding to the regional
basin which it is located within. Each alphanumeric designator is unique to each
individual sub-basin that comprises the regional basins. Eleven of these
regional basins have previously been delineated as drainage basins by either the
City of Colorado Springs or E1 Paso County. Whenever possible, existing sub-
basin delineation was followed or consulted in the compiling of sub-basins in
this study. For the purposes of this study, sub-basins from the individual
studies were combined into larger basins in order to simplify the computational
procedures that arise when dealing with a large number of drainage basins.

In order to achieve maximum consistency between the Fountain Creek and the
Monument Creek studies, hydrologic parameters set forth in the companion analysis
of Monument Creek were followed in the Fountain Creek analysis. Within the
hydrologic computer model HEC-l (USACOE, September, 1990), the Soil Conservation
Service (SCS) Dimensionless Hydrograph model was used to develop runoff
estimates. Variables required for this procedure for each individual sub-basin
are the area, curve number (CN), and the lag time (Tlag). Sub-basin areas were
estimated, using a planimeter, from U.S.G.S quadrangle maps (I" = 4166.7').
Curve numbers were determined for each sub-basin utilizing the hydrologic soil
characteristics, ground cover and corresponding imperviousness, in addition to
Tables 5.4 and 5.5 of the City of Colorado Springs/El Paso County Criteria Manual
(Colorado Springs 1987). Soil hydrologic soil groups are illustrated on Figure

3.5-2, Volume II and corresponding CN values are presented in Tables 4.7-2 and
4.7-3 (Appendix A, Volume III). Lag time (Tt g) was calculated based on its
relationship with the time of concentration (Tej using the following equation:

T1ag = 0.6Te

Time of concentration for each sub-basin was determined by adding travel times
for overland flow, channel flow, and pipe flow from the hydrologically most
distant point in the basin to the outfall point. To estimate initial times of
concentration several expressions have been developed, including the following
form of Kirpich's equation:

Where:

Te = ((3.35 X 10-6 L^3)/(h))^O.385
Te = Time of concentration (minutes)
L = Stream length in feet
h = Difference in elevation in feet between the upper and
lower limits of the drainage basin.

4.0-10