FLOOD09445

• Designation Number: 53
• County: Larimer
• Community: Unincorporated Larimer County
• Stream Name: Cache La Poudre River
• Basin: South Platte
• Title: Floodplain Information Report - Cache La Poudre River, Colorado, Volume III
• Date: 10/1/1975
• Designation Date: 3/1/1976
• Floodplain - Doc Type: Floodplain Report/Masterplan

FLOOD SITUATION

DEVELOP~lENT ON THE FLOOD PLA 1 N
The Cache la Poudre River flood plain as defined in this reoort
Is used essentially for agricultural purposes. This tyoe of use has re-
sulted In open fields and intermittent farm or ranch buildlnqs. Some sand
and qravel mining is present on the flood plain especially upstream from
Interstate Highway 25. Because of the expected population increases as
indicated by table 3, development pressure can be expected to intensify
In the study reach especially at the upstream and downstream study limits
nearest Fort Collins and Greeley respectively.

SOURCES OF DATA AND RECORDS
Stream gaging records from United States Geological Survey
stream gages on the Cache la Poudre River were used to perform the hydro-
logic analysis for this study. These gages and pertinent data pertaining
to each gage are shown In table 4.

Table 4
Cache la Poudre Stream Gage Data

Ta b I e 3
POPULATION
LARIMER AND WELD COUNTY
(U.S. Census Rureau Fioures)

GaQe Location

Ora I naqe Area
(Sq. Miles)

GaQlnq Record

8 1/2 miles northwest
of Fort Collins

1,055

Continuous since
1882

1930
1940
1950

1960
1970
19AO
1990

~/eld

65,097
63,747
67,504
72,344
80,297
125 oool!
,
180 oool!
,

Larimer County
33,137
35,539
43,554
43,343
89,900

3 miles upstream from
South Platte River

1,877

March to October
1903; August to
November 1904;
January 1914 to
December 1919;
June 1924 to
present.

Year

!! Larimer-Weld Regional Plannino Commission projections.

The Larimer-Weld Regional Planning Commission, acting for the
Included jurisdiction of Larimer County, Weld County, the city of Fort
Collins, and the city of Greeley, provided topographic mapping and cross
section survey data which was used to compute water surface profiles and
to define flooded area limits. The cross section surveys were made by
photogrammetrlc methods in 1972. Additional bridge cross section Infor-
mation was provided In 1973. The aerial photographs used as a base for
the flooded area maps were flown In July 1969.

FLOOD SEASON AND FLOOD CHARACTERISTICS
Annual peak flows on the Cache la Poudre River In the study
reach normally occur In the period May through September, with the majority
of the high flows occurring In June. Although most floods result from
Intense rainfall In the basin, snowmelt runoff Is a factor'and the worst

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