FLOOD01887

• Designation Number: 261
• County: Routt
• Community: Oak Creek
• Stream Name: Oak Creek
• Title: Flood Hazard Identification Report - Oak Creek, Colorado
• Date: 9/1/1986
• Designation Date: 11/1/1986
• Floodplain - Doc Type: Floodplain Report/Masterplan

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HYDROLOGIC AND HYDRAULIC DETERMINATIONS

Flood History

It is known that significant flooding occured in 1914, 1939, 1950
and 1984 as well as other years (Ref. 14). The streamflow occuring
during the May, 1984 snowmelt flood was estimated 'by Dismuke and Dismuke
Consultants, Inc. at approximately 650 cfs at County Route 27 (at the
northern end of town). Local residents have indicated that the May, 1984
flood was the "flood of record". Streamflows for the other flood events
are not known.

Flood Characteristics

"Typical" flooding along Oak Creek is caused by snowmelt runoff.
However, at frequencies as rare as the lOa-year event, flooding can occur
from rainfall runoff.

Hydrologic Analysis

A hydrological analysis of flows in Oak Creek was performed for
snowmelt and/or rainfall runoff over the basin. There are no active
streamflow gage records on Oak Creek. A gage was formerly existent on Oak
Creek for only 5 years (water years 1953 to 1957). It was located 4.5
miles southwest of the Town of Oak Creek. The length of record of this
gage was insufficient to be analyzed and provide meaningful results. The
Soil Conservation Service's (SCS) unit hydrograph procedure (Ref. 9) was
then employed to determine the lOa-year peak streamflow. Significant
parameters used with this method were a lOa-year 24-hour rainfall of 2.8
inches and a SCS curve number of 70.

A lOa-year peak flow was computed using the assumed basin
parameters and compared with the flow values of other streams in the
region (Ref. 4). Through this comparison, the laO-year peak flow was
adjusted to reflect the runoff characteristics of the basin.

The la-year flood event was assumed to be the result of a snowmelt
event. This value was obtained from a regional analysis of streams which
had acceptable gage records and similar characteristics. A straight line
was then drawn between the two "known" points on log-probability paper
and flows were extrapolated for the 50- and 500-year events. A plot of
the frequency discharge curve for Oak Creek is shown in Figure 1.

Peak flows for Oak Creek at the Town of Oak Creek (drainage area of
22.7 square miles) are as follows:

Recurrence Interval
(years)
10
50
100
500

Peak Flow
--CCf~
300
750
1050
2100

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