FLOOD00852

• County: Arapahoe
• Community: Arapahoe County
• Stream Name: Cherry Creek
• Title: Cherry Creek River Run Improvements
• Date: 9/1/1986
• Prepared For: Arapahoe
• Prepared By: Greiner Engineering Sciences, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

Mannings "n" values used in the calculations ..ere .04 for the channel and .065
for the overbank areas.

The technical data developed for use in the HEC-2 model and the HEC-2 computer
results are included in the back of this r'=port. A table of the computed
water surface elevations for the 100-y=ar existing conditions flood is in-
cluded in the floodway section of this report.

FLOODPLAIN DELINEATIONS

Based on the results of the HEC-2 comput er model, the boundary of the 1 DO-year
flood was determined at the cross sect 1. on locat ions. Between Se ctions, the
boundary was interpolated using the following topographic: information.

Sections 87790 to 90330
U. S. Army Corps of Engineers, Flood Plain Information ~erry Creek,
flown April 1975.

Sections 0.00 to 4,440
Northway - Gestalt, Topographic MaPE.!~Ciehmann, Martin Site 1
foot CI, 1981

lOO', 2

Sections 4840 to ll020
Analytical Surveys, Inc. Topographic Ma2ping, River Run Project, Digi-
tized Sections Only, 1984

Sections ll600 to l7300
Northway - Gestalt, Topographic Mapping.Ashbrook Site, l"=lOO', 2 foot
CI, 19 8l, and

U.S. Army Corps of Engineers and, ~:ry Creek Floodplain Information
Report Mapping, 1"=200' CI, flo,;n April, 1975.

FLOODWAY

Encroachment on floodplains such as art:Lficial fill, reduces the flood-carry-
ing capacity and increases flood heights, thus increas ing flood hazards in
areas beyond the encroachment itself. UsIng the floodway concept, the area of
the lOO-year floodplain is divided into two areas, f'loodway and floodway
fringe. The floodway is the channel of a stream, plus any adjacent floodplain
areas, that must be kept free of encroachment in order that the lOO-year flood
be carried without substantial increaseas in flood heights. For purposes of
this study, the allowable surcharge increase is 0.5' according to the guide-
Unes of Arapahoe County and the Urban Drainage and Flood Control District.
The less restrictive 1.0 foot floodway, which is enforced by FEMA, has not
been included as part of this study, bu: can be found in the previous letter
of map revision for River Run (Reference 1).

A schematic drawing which shows typical relationships between the floodway and
floodway fringe and their significance to flood plain development follows:

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