FLOOD10404

• Designation Number: 128
• County: Larimer
• Community: Larimer County and Unincorporated Areas
• Basin: South Platte
• Title: FIS - Larimer County and Unincorporated Areas
• Date: 9/1/1978
• Designation Date: 1/31/1979
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

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Dry Creek is a tributary of the Cache La Poudre River which flows in
a southeasterly direction through Larimer County to its confluence
east of the City of Fort Collins. Development along the stream
consists of sparsely populated farm and range lands north and east
of Fort Collins. The channel is approximately 3 to 4 feet deep and
10 to 15 feet wide through the lower part of the study and 6 to 12
feet deep and 60 to 80 feet wide in the upstream areas. The stream
channel gradient within the section studied is approximately 18 feet
per mile. The soils within the Dry Creek flood plain are of the
Fluvaquents-Fluvents and Otero-Nelson Associations (Reference 3).

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Fish Creek flows north through Larimer County to its confluence with
the Big Thompson River at Lake Estes in the Town of Estes Park.
Fall River flows southeast through the county and joins the Big
Thompson River in Estes Park. The channels of both streams are well
defined and generally narrow, with cobble streambeds and heavy
vegetation encroaching upon channel banks. The flood plains are
largely undeveloped for both streams and the soils are of the
Argiborolls-Rock Outcrop and Cyroboralfs-Rock OUtcrop Associations
(Reference 3).

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The Cache La Poudre River flows in a southeasterly direction through
Larimer County. Development along the Cache La Poudre River flood
plain is minor at the present time with only a few residential and
commercial structures. The channel in the studied section is
approximately 160 feet wide and 7 feet deep, with the gradient
varying from 28 feet per mile in the upper parts of the study area
and 16 feet per mile in the lower parts. The soils within the Cache
La poudre River study area consist of the Fluvaquents-Fluvents
Association (Reference 3).

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2.3 Principal Flood Problems

Major floods on the streams are caused by intense rainfall from
localized thunderstorms over the basins. The floods caused by such
events will characteristically have high peak discharges of short
duration for all of the mountain area streams. The streams in the
plains areas are normally of a longer duration with less velocity
and considerable channel storage.

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Significant floods have occurred on the streams within the county in
past years. The most significant flood within the county occurred
on the Big Thompson River on July 31-August 1, 1976. This flood was
one of the worst natural disasters in the history of Colorado.
Intense precipitation over an approximate 60-square mile area between
Lake Estes and Drake, with rainfall depths up to 12 inches, generated
a flood discharge of approximately 31,200 cubic feet per second
(cfs) at the mouth of the canyon. This flood is known to have taken
139 lives. Property damage was estimated at $16.5 million, while
hundreds of people were left homeless. Over 200 residential struc-
tures were damaged or destroyed by the flood, while nearly 1200 land

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