FLOOD09982

• County: Garfield
• Community: Battlement Mesa
• Stream Name: Colorado River
• Basin: Colorado Mainstem
• Title: Battlement Mesa Storm Drainage and Floodplain Study
• Date: 3/1/1975
• Prepared For: CWCB
• Prepared By: Frasier & Gingery, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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Page Seven
Battlement Mesa Development Storm Drainage and Flood Plain Study

The rational method was reviewed utilizing C factors of
0.10, 0.20, 0.30 and 0.40. The results of this sensitivity
analysis are shown in Table II.

Tl\BLE II
Pl'TIONJlL METHOD SENSITIVITY ANALYSIS
Return
Frequency C = 0.10 C = 0.20 C = 0.30 C = 0.40
2 year 143 cfs 289 cfs 432 cfs 578 cfs
10 year 230 cfs 460 cfs 577 cfs 921 cfs
100 year 400 cfs 800 cfs 1200 cfs 1600 cfs

The Colorado Unit Hydrograph Procedure ~Ias evaluated
varying the infiltration rate between 0.50 inches per hour and
0.75 inches per hour. The results of this sensitivity analysis
are shown in Table III.

TABLE III
COLOPl'DO UnIT HYDROGRl'PH PROCEDURE SENSITIVITY ANALYSIS

Return
Frequency Infiltration Rate Infiltration Rate
= 0.50 Inches/Hour = 0.75 Inches/Hour
2 year 51 cfs 51 cfs
10 year 173 cfs 86 cfs
100 year 773 cfs 496 cfs

Consideration was given to the relative accuracy of the
basic assumptions of the three procedures. The rational method
normally is applicable only to drainage basins less than 200
acres in area and finds its oreatest application in the design
of typical urban storm sewer systems. The SCS method is designed
primarily for use in rural areas and results in a peak rate of
runoff only. That is, a storm water runoff hydro graph is not
developed. The Colorado linit Hydrograph Procedure is applicable
to both rural areas and developed areas. The Colorado Unit
Hydrograph Proc,ec1ure also has the advantaoes of developing a
runoff hydrograClh which can be routed through reservoirs for