FLOOD05377

• County: Arapahoe
• Community: Littleton
• Stream Name: South Platte River
• Basin: South Platte
• Title: Floodplain and Floodway Delineation for the ABM Riverfront Property
• Date: 3/1/1980
• Prepared For: Littleton
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The U.S. Army Corps of Engineers water surface profile computer
program HEC2 was used to compute the necessary floodplain and flood-
way information. The HEC2 program was also uaed in the City of

Littleton Flood Insurance Study.

Channel roughness coefficients

(Manning's

It

The roughness coefficients for each cross section

"nil)

were

selected based on a field inspection of the

floodplain

area.

can be reviewed. in the computer input summary provided i.n~be

appendix. rfo,.jl ~ ~ Co",,", 9~;;n
~\" f" 'f~ ~ I

A plot of the lOO-year water surface prOfile for present con-

ditions is shown in Figure-2.

The resulting floodplain is delin-

(P1N-9rA\~ vii V\~ f')-h L ?~

eated on Plate-I.

0~JJ do~'> ~~

The floodway encroachments were computed using standard aethods

recommended in the Flood Insurance Study. The floodway limits are

also shown on Plate-I. Basic floodway data is given in Table-l and

the supporting HEC2 computer output is included in the appendix.

Encroachment immediatly downstream of Belleview Avenue was reduced \~
~ ~ 1l'.J:t
in order to facilitate a smooth transition~to the Belleview Avenue ~~ ~-
o~ fJ

bridge. Such a
~
as compared to

reduction increased the floodway width in this area
--- -

the computed width shown in the HEC2 computer runs.

VI. COMPARISON WITH FLOOD INSURANCE STUDY

The results Of this study have been compared with information
provided in the Flood Insurance Study (FIS). A number of differences
have been noted which are explained in this section.

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