FLOOD03938

• County: Jefferson
• Community: Lakewood
• Stream Name: McIntyre Gulch
• Basin: South Platte
• Title: Flood Hazard Area Delineation
• Date: 10/1/1977
• Prepared For: Lakewood
• Prepared By: UDFCD
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

CHANNEL CHARACTERISTICS SUMMARY

CHAPTER IV
HYDRAULIC ANALYSIS

Channe 1
Reach

Section

Degree of
Irregularity

Effect of
Obstruction

Roughness
Coefficient

A. General

Confl uence Main chan. smooth to minor minor .032
to Carr St. Overbank minor appreciable .051
Carr St. to Main chan. mod. to severe mi nor .045
Garri son St. Overbank minor moderate .051
Garrison St. Main chan. minor negl . to apprec. .030
to West DFC Overbank minor moderate .046
West DFC to Main chan. smooth to minor negligible .028
study 1 imits Overbank mi nor negligible .030
South of DFC Main chan. mi nor negl. to mod. .032
along Alameda Overbank minor negl. to mod. .032
C. Flood Plain Determination
The flood plain for a majority of the channel in the study area was

A hydraulic analysis was performed for the major drainageways of
McIntyre Gulch and consisted of determining the flood plain, the water
surface profile, and the floodway for the 100 year flood. The water
surface profile was obtained by performing backwater calculations using
a computer program. The data were then plotted on the 1" = 100' scale
mapping for the study and the flood plain outline defined. The basic
input data and methodology used in the analysis is presented in this
chapter.
B. Channel Characteristics

To estimate the channel and overbank roughness coefficients,
several field investigations were made to establish the basic channel
characteristics. The coefficients were then estimated taking into aCCount
the degree of irregularity, cross-section variation, obstructions,
vegetation, and meandering. The entire drainageway was subdivided into
four reaches with similar channel characteristics. A summary of the
channel characteristics for the various reaches is presented below. All
the channel reaches were considered to have minor meandering, low degree
of vegetal effects and cross-sections which alternate overbank flow zones
occasionally. The roughness coefficients were used as baseline values and
were adjusted accordingly for local conditons.

determined using a computerized backwater program. The program is called
"Multiple Backwater Profiles with Provisions for Bridge and Weir Losses",
Program No. 22G1M405 and written by William A. Thomas of the Little Rock
District, Army Corps of Engineers. The methodology used for the backwater
calculations is "Method II, EM 1110-2-1409" and the program is commonly
referred to as "HEC-II". The required input to the program is the channel
cross-section coordinates, the hydraulic properties of each sub-section
within the cross-section, and the discharge value. The backwater calculations
are initiated by inputting a known water surface elevation and discharge
value. The longitudinal spacing of the cross-sections varies with channel
condition, but generally the spacing was less than 300 feet. The starting

7