FLOOD07952

• County: Fremont
• Community: Canon City
• Stream Name: Four-mile Creek, Mud Gulch
• Basin: Arkansas
• Title: Floodplain Management Study - Four-Mile Creek and Mud Gulch at Canon City
• Date: 10/1/2002
• Prepared For: Canon City, Fremont County
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Floodplain Report/Masterplan

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* Precipitation P. The historical station precipitation data were used as input

to the TR-20 model. No areal adjustments were made because of the small drainage

areas involved. The Natural Resources Conservation Service (NRCS) 24-hour Type

IlA rainfall distribution was selected for use in the model to generate frequency peak

discharges.

* Runoff Curve Numbers CN's: Hydrologic runoff curve numbers (CN's) were

developed from the NRCS soil map, land use information, and field observations. CN

values for the TR-20 watersheds reflect weighted average CN's for a variety of land

uses and soils \\1thin each watershed.

* Time of Concentration Tc. Time of concentration values were computed for

the Mud Gulch sub-basins from an empirical equation in the Natural Resources

Conservation Service's Engineering Field Manual, Chapter Two, intended for small

rural watersheds.

Tc
Where,
Tc
L
CN
Y

=

(L08x [(1OooICN)-9]o7) 1 (1140 X yos)

=

Time of concentration (in hours)
Flow length (in feet)
Runoff curve number
100CII A

=

=

=

and
Where,
Y
C
r
A

=

Average watershed slope (in percent)
Total contour length (in feet)
Contour interv'al (in feet)
Drainage area (in square feet)

=

* Base Flow. A base flow value of 25 cfs was obtained from the local irrigation

annual record. This base flow accounts for the inflow from the Oil Creek Ditch that

enters Mud Gulch at a point 6,700 feet upstream from the Arkansas River.

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