FLOOD01718

• County: Montrose
• Community: Montrose
• Stream Name: Uncompahgre River
• Title: City of Montrose Flood Control and Drainage Plan
• Date: 5/1/1981
• Prepared For: Montrose
• Prepared By: Gingery Associates, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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100 YR. FLOOD HYDROGRAPH
MONTROSE ARROYO
CONFLUENCE WITH CEDER CREEK
1200
-110 '"
1000 \
UPSTREAM
BASIN
800 RUNOFF ,---
,
I ,
_600,
"
.
0 ~
- '"
.
0
.
.
> G "-..
0 coc^'
"
0400 "'-
RUNOff .~ ~
~,
200
, J -~
0 I
0 50 '00 '50 200 250
TIME(MiNUTES 1
FIGURE 5

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HYDRAULIC ANALYSIS
A hydraulic analysis was completed by Hydro-Triad Ltd. in April, 1979,
(Reference 1) to determine water surface profiles for tnelO-ye ar,SO-year,
lOo-year, and 5(}O-y~dr floods on l-1.:1ntrose Arroyo, Cedar Creek and Dry Ceddf
Creek. These water surface elevations were computed using theHEC-1Icom -
puter model for backwater analysis. The culvert crossings on Montrose
Arroyo are insufficient to pass the lOO-year flow; consequently, during
such an event a ccnsiderable amount of flow would be lost from thech annel
to flow overland. This shallow flooding wOl.l1d flow away f~om M::Introse
Arroyo west and northwest to the Uncompahgre Rlver. Some of this flow
would pond along the east side of the D&RGW Railroad embankment between
South 1st and North 2nd Streets. The previous hydraulic compl.ltations were
carried out based on the premise that imediate1y downstream of each cross-
ingall spilledflowisconsideredtObebackinthechannel,andanyex-
cess is again shown as spilling at the next inadequate crossing. This
procedure....as used by f1ydro-Triad Ltd. topreventtheanJlysi> fr ombecom-
ing superseeded each time an upstream culvert is improved, and to illustrate
a conservative situation.
In order to evaluate existing damages, it is necessary to have the
floodplain and flood profiles defined for the existing conditions. Therefore,
Gingery Associates conducted hydraulic analyses to determine flood elevations
andde1ineatefloodinglimitsthatref1ecttheactualsituationthat exists
in Montrose. The an<l.lyses were performed ln the followingrnanner: Proceed-
ing in a d?wnstream direction, at thp first inadequate crossing (SOuth 12th
Street). cal culatinn~ wprp nude based on cl.Ilvert rating curves and existing
topogrdphy to determine the amount of flow lost from thech<l.nnel. Downstream
of the crossing the discharge in the channel was reduced by this a 001.1111. This

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