FLOOD09158

• Designation Number: 24
• County: Boulder
• Community: Unincorporated Boulder County
• Stream Name: Lower Saint Vrain Creek
• Basin: South Platte
• Title: Floodplain Information Report - Lower Saint Vrain Creek - Volume III
• Date: 6/1/1972
• Designation Date: 7/1/1993
• Floodplain - Doc Type: Floodplain Report/Masterplan

fighting steps to ~vold flood d~~ges ~nd the evacuation of Doople and
property from the flood plain. Any advance warning time In this event
m 19 ht be i mporta n t and s hou I <:I be heeded. I~ater I a I stora')e on the f I oed
plain at Longmontcould t>ea factor. The sewage treatment facilities
at Longmont are located on the flood plain and constitute a potential
pollutlonhaziJrd.

PASTFLOOOS

Flood warning ar><J torecastinq-TheCltyof Lonqmont
reliesontelephonecOTlmUnlcationfromupstreamlntheSt.\lrainCreek
bllsinforinformationonstormsandresultanthlghstraamtlow$. The
operation personnel at Button Rock Dam on North St. \lrain Creek is one
such ~urce ot Information.

Summary of Historical Floods
Theoldost kr>own Insta;lCeot flooding fr=St. 'IrainCraek
In the vicinity Of LO"9"'ont occurred in 1864. Otner fioodS ktrOwn to
causedarooge have occurred in 1876, 1894. 1919. 1'121, 1938, 1941,
1949,1951, 1957,and 1969. A storm In June 1864 resulted inatlood
theaffectsofwhichroportodly"wereteltseverely"lnthe_$t.\Irain
va I I ey. The Go I den, Co i or"do Tr i bune ot '~"\" 3 I, 1876 oeser i bed a
flood during th<>t month liS covoring farmlandS frcrn "bluff toblutf"
at too junction of St. \lralo and Left Hand Creoks, at Longmont. Tho
flood Of 31 May 1894 had enestimaTod PWkdisehargeof 9,800c.f.s.
at Lyons and washad away 20 homos thore. There are nO accounts avail.
able of spac1ficdar.'.lgtls in tile study raach for the lil94 flood t>utat
I east minor damages ""'y b<! d~,;u"",d. This assumption m"y "I so b", m<ldoJ
iloout the study ro"ch tor the flood Of late July 1919 \oIhen great
destruction was done to the LyOns vicinity by cloudburst storms.
Since the peak discharge at Lyons On 30 July 1919 was later computed

Flood fighting and energency evacuation plans - The
Boulder 80unty 8ivll Dofanse Director coordlnatos closely with the
Sherift's office and local police during tloodemergencles. Thesta-
tioning of stream watchors, the avallablllty of evacuation equipment,
and furnishing emergency communications are functions preplanned for
flood emergancies.

to ba 9,400 c.f.s. at least minor damages to rural areas in the studv
reaCh ware likely. The tlood Of September I':lStl was confined r'lostly
to rural areas <fownstream of Longmont.

Material storage on the flood plain-On the left bank
of St. ,rain Craek upstream from the Colorado and Southern bridge
there ara industrial develoome~ts In the flood plain where storage
vardsmlghtcontaln",uchfloatabla"",terl"I, irn:ludlngsrnallcorn-
pr~~~Qd g"~ t."n~ and stor"yt< wrrei cont,:,if)ifs. There "re a nunlber
of trailers in the flOOd plain that could ba s...apt ir.to tha channel
durln9<llargeflood. Floatablem<lTerialc1ln3CCumulateatoridces
and other constrictions I~reaslng t~ da~r of bridae destruction
and r"i,;ing w"tor surf,"e etev"tions In tha flood plain.

Flood Records
Thera are nodlre<;t recordS of streamtlowsor high water
n'Iilrksat Longmont for the past tloodsdls<;ussed.'Are. Tllbl" 3. p<lge
8, shows records ~t nearby locations.

Flood Oescriptions
2-7 June 1921 ~ Heavy r<llns combined with sno>m1elt runoff
-------
caused flood;ng '" the Longmontarea early '" JUnA 0' 1921. , total

of 5.87 Inches of rain ...as recorded at LO"9f"Ont frO"1 2 to 7 Juna.
The Boulder Camarll of 7 Juna 1921 rApOrted that St. 'Ira in Creek at
Longmant was "wav out of its D<lnkS" aM "throe~quarters of", ",ile

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