FLOOD03293

• County: Eagle
• Community: Gypsum
• Stream Name: Eagle River
• Basin: Colorado Mainstem
• Title: Floodplain Analysis
• Date: 11/1/1982
• Prepared For: Gypsum
• Prepared By: Eldorado Engineering
• Floodplain - Doc Type: Floodplain Report/Masterplan

RECEIVED
MAY 1 5 1997

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Introduction

Colorado Water
ConseMllian BDard
_@m~~~ n'
NO'! 15 1982 U '
COLORADOWATER
CONSERVAT!Of\! SO."RD

This flood plain analysis was conducted to deter~ine the flooding
characteristics of the Eagle River at Eagle River Estates. a new
subdivision in.the town of Gypsum. Filing Nos.l through 4 of the
subdivision and the study area of this report are shown in Figure
1. ' '

The results of this report"are to be used to' control construction,
in the fJood plain. It is the intention of the developer and of '
the town of Gypsum to minimize the flood, hazard to new residences
in the subdivision. "

FLOOD PLAIN ANALYSIS
EAGLE RIVER ESTATES
TO\~N OF GYPSUt-I
EAGLE COUNTY, COLORADO

Method of'Analysis

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November 1982

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The flood plain was analyzed' using the Hec-2 water surface 'profiles
computer program developed by the U. S. ArmY Corps of Engineers.
The water surface profile was determined for the 10, 50, 100 and 500
year flood events. ,An encroachment option was also used to deter-
mine the location of the floodway and of the floodway fringe of
the 100 year flood, plain; " " " ,',' ,

If the area of the floodway fringe was filled in to an elevation
above the flood water elevation so that no flow was permitted there,
the ~Iater surface elevation of the floodliay \'/ould not rise more
than one foot above the normal 100 year flood water elevation.

The following flows were used for the,various flood events:

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Flood Frequency

10 year
50 yeal'
100 year
500 year

Discharge. CFS
5904
7564
8223
9727

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Prepared by:

Eldorado Engineering Company
823 Blake Avenue - P.O. Box 669
Glenwood Springs, Colorado 81601

These flow values were obtained from the Water Resources Division
of the U. S. Geological Survey. The data I'/as based on flol'lS recorded
at a gauging'station at Gypsum from 1947 to 1978. 'The "expected"
probability" estimates were calculated using a Log Pearson Type,'
III analysis.

Cross sections of the river and flood plain were field surveyed
at intervals to obtain accurate representative topography of the
study area. Those cross sections ~/ere input for the Hec-2
program. The location of the sections are shown in Figure 2. The
existing grade of each cross section is shown in Figure 3. Elevations
are relative to UCS and GS Benchmark No. J-269 located on the NW
pier of the D & RG\~ Railroad Bridge crossing U. S. Highway 6 & 24
in the town of Gypsum. Benchmark elevation is 6319.725.'