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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Runoff

In accordance with the City of Colorado Springs/El Paso County Drainage Control
Manual, the Corps of Engineers HEC-l Flood Hydrograph computer model (September
1990) was used to develop storm runoff hydrographs for the Fountain Creek
watershed. The HEC-l model simulates the surface runoff response of a river
basin to precipitation by representing the basin as an interconnected system of
hydrologic and hydraulic components.

Hydrographs were developed for existing and future development condition
an initial storm recurrence interval of la-years and a major storm rrenc
interval of lOa-years, following the SCS unit hydrograph procedure w' hin HEC-I.
This synthetic unit hydrograph method is based on a dimensionless uni hydro graph
developed from an analysis of a large number of unit hydrographs for
watersheds. An equation for the peak discharge of a unit hydrograph is derived
on the basis of the assumption that the dimensionless unit hydrograph can be
represented by an equivalent triangular unit hydrograph. The rising limb of the
hydrograph accounts for 35.7 percent of the runoff. The ordinates of the unit
hydrograph are determined through interpolation of the dimensionless unit
hydrograph curve at points defined according to the specified computational
interval, which is also the duration of the rainfall excess.

Routing for six significant reservoirs was accomplished with the Modified Puls
Routing Method found within HEC-1. This method applied to a reservoir consists
of a repetitive solution of the continuity equation. The individual and net
impact of smaller detention facilities is not reflected within the model as
previously described.

The Muskingum-Cunge routing technique was chosen to route stream flow within the
computer model. This routing technique can be used to route either lateral
inflow from either kinematic wave overland flow plane or lateral inflow from
collector channels and/or an upstream hydrograph through a main channel.

The result of the modeling process is the computation of stream flow hydrographs
at desired locations and design points in the river basin. The 10- and laO-year
hydrographs developed in the companion study for Monument Creek were input into
the Fountain Creek analysis at the Monument and Fountain Creek confluence. The
composite hydrographs are presented on Figures 4.7-1,4.7-2 and 4.7-3, previously
presented in this text.

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