FLOOD01761

• Designation Number: 83
• County: Larimer
• Community: Unincorporated Larimer County
• Stream Name: Big Thompson River
• Title: Floodplain Information Report - Big Thompson River, Loveland to the Larimer-Weld County Line, CO, and the Little Thompson River, Boulder and Larimer Counties, CO
• Date: 6/1/1977
• Designation Date: 11/1/1977
• Floodplain - Doc Type: Floodplain Report/Masterplan

FLOOD SITUATION

Cross section data and topographic mapping having a
contour lnte.....al of 2 feet and a scale of I InCh equals 200 feet
~ere established by photogrammetrlc methods from flights made in
Apri 1 1975. These d"ta ~ere furni shed by Larimer County and
Boulder County in cooperation with the Colorado Water Conservation
Board. U. S. G<lologlca! Survey 7.5 minute quadr"ngle m"ps ~I th
10 foot contour Interv"ls at a scale of I Inch equalS 2,000 feet
were Illso usod In the study. Bridge and roadway survey data were
provided by the ColoradO Water COnservation Board.

SOtJRCESOF DATA AND RECORDS
Stream gaging records from the United States Geological
Survey stream gages on the Big Thompson and Little Thompson Rivers
were used in the hydrologic analysis for this study. The gage
locations and pertinent data pertaining to them are shown In table

2.

StrMm

Big Thompson
River

Dig Thompson
River

little
Thompson River

Table 2
Stream Gaging Data

Gllqe Location

At mouth of canyon,
500 feet upstream
from Handy Ditch
diversion dam and
6mlles east of
Qr"ke.

On left bank 0.7
mile upstream from
hlghwaybrldge, 1.6
miles upstream from
mouth, and 4 mi les
west of La Sail...

At mouth of canyon,
7.5mllessouthwest
of &>rthoud.

Approximate
Oralnaqe ....rea
(sq. mi.}

'"

828

'"

FLOOD SEASON AND FLOOD CHARACTERISTICS

GaqlnqRecord

The Big Thompson River basin Is located within an area
...hlehcanreceiveverylntenseralnfallofcloudburstmagnltude.
Floods have resulted from storms covering large areas receiving
heavygena....al raInfall aSlolel1 as f..om storms covering sm1l1 I areas
but producing extremely Intenserainf1lll. Floods generally occur
in the period from May through July. Annual peak discharges In
the ~tudy rellch, however, h1lve been experienced from March through
September.

COntInuous since
1867 "xcept for
periods between
1892 to 1895.
1904 to 1926,
1953 to 1938, and
1949 to 1951.

COntinuous since
IQ:4 except for 0
period trom 1915
to 1927.

floods in the 81g Thompson River baSin can hllVC consld-
"rably different characteristics depending upon the location within
the b1lsln. Floods In the mountlllnous region of the basin typically
have rapid ..Ises, high maximum discharges, and relatively short
du....atlons. floods In tho plains region, generally, are of lower
peak discha....ge and have longer du....atlon. Floods ...ithin the study
reaches generally have a duration of about I day. Flood peakS
fromthundar.,torm5covaring5m..11 llreilSilregener"llyr"pld:yaHcn.
Ullted Inthestudy....""chesbyvlllleystorageoffloodlolaters.

Continuous since
1929 except for a
period between 1950
and 1947. Wls-
contlnutldin 1961.)

Information on past floodS ...as obtained from Corps of
Engineers flood records, LarImer County. the U. S. Geologlclll Survey,
the ColoradO wate.... COnservation Board, and local newspapers.

"

F^CTORS AFFECTING FLOODING ....ND ITS I~~ACT
Obstructions to floodflolol5 - There arP. 6 roadlolllvs and
13 noadwllYs ...hlch cross the 81g Thompson River flood Olaln and

"