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<br />FLOC!) SITUATIO,~
<br />
<br />Flood Se~son ~nd Flood CharacteristiCs
<br />Floods In the study reach of St. Vrain Creek ~~9 occurred
<br />In each of the fi~e months May through September. Higher flows occur
<br />annu~ Ily In May and June because of the rnounta I n snowmelt runoff but
<br />seriousflexxlingdoesootoc:curunlessrainfallaccomPaniesthesoow_
<br />melt. Table 3 lists some past peak discharges on St. VralnCreek,
<br />
<br />Sources of D.,taand RfJcords
<br />Thore are no stream flow records for the stud~ reach. The
<br />U. S. Geological Sur~ey Maintains a surface water recorder 9aoe on St.
<br />Vr"jn Creok at Lyons, i>bout 9milesupstrea.... from Lonqrnont. The Lyons
<br />gage is located downstream trom the confluence of North and South St.
<br />Vr~l n Creeks and has a dral na~e area of 21'9 square mi les. Records are
<br />available for August 1887toSeotember 1891 and from Juno 1895tot he
<br />present. The location of tho Lyons q391ng station Is shown In the
<br />basin ~p on the Inside front cover of this report.
<br />
<br />A sacond<}aqe IsmaintalnednearPlattevllle, near the mouth
<br />of the stra~m, ~bout 16 miles downstream from Longmant. This gage has
<br />"dr<lin.,ge area of nG SquM" miles dud h<lS ~..en conti",,""sly operateJ
<br />since 1927. Flows ~t both gages are net after having been reduced by
<br />lrrigat;ondiverslons.
<br />
<br />Year
<br />
<br />1970
<br />1969
<br />1963
<br />1967
<br />1966
<br />196~
<br />1964
<br />1963
<br />1962
<br />1961
<br />1960
<br />1959
<br />1956
<br />1957
<br />ICJ~6
<br />:955
<br />1954
<br />1953
<br />1952
<br />1951
<br />1950
<br />
<br />Supplementary material w~s obtained from U. S. Geological
<br />Survey, \'iater Supply Paper 997, "Floods in Colorado." The Lonqmont
<br />QailyTlmes-CallprovidedlmportantfIQOljlnformatlonandpl1otogr<lphs.
<br />Goulder County off icia Is <lnd the County Enqineer were also helpful In
<br />this regard.
<br />
<br />FloouuJ <lr"",,s in this n);>art "r-.. plutt..d un rupr<Juucfi<Jrls <Jf
<br />A.S.C.S. aerial photographs~de inJuly 1969. Detailed topographic
<br />i;lnd cross section surveys were provided by thc Urban Dralnaqeand
<br />Flood Control District, the City ot Longmont, and Boulder County, by
<br />cooperatlvedgreernent. These were used dS the bases for computations
<br />tordeterminingfIOQlJprofilesandfloodedarBdoutlir1es.
<br />
<br />Table~
<br />SUMMARY OF HISTORIC FLOOD PEAK DISCHARGES
<br />ST.VRAINCREEK
<br />
<br />At Lyons*
<br />Maximum
<br />Olscharge
<br />Date c.f.s.
<br />
<br />Jun29
<br />May 7
<br />Jun21
<br />AU930
<br />Jul20
<br />Junl7
<br />M"y27
<br />Jun 16
<br />Jun30
<br />Jun3
<br />Junia
<br />Junl5
<br />M"y 8
<br />May 9
<br />Jun3
<br />Jui 24
<br />May 2'
<br />Jun!3
<br />Jun8
<br />Aug3
<br />Jun 15
<br />
<br />958
<br />2,900
<br />0"
<br />2,010
<br />1,210
<br />1,840
<br />'58
<br />1,300
<br />1,140
<br />2,540
<br />717
<br />'"
<br />1,290
<br />3,060
<br />'"
<br />cao
<br />285
<br />'70
<br />1,610
<br />3,920
<br />m
<br />
<br />Neil r ~o\outh"
<br />Maximum
<br />Discharge
<br />Data c.f.s.
<br />
<br />Junl2
<br />",,8
<br />AuglO
<br />Jun21
<br />SeD 2
<br />Jul25
<br />May 30
<br />Junl7
<br />Jul I
<br />Jun4
<br />l.\3y6
<br />May 23
<br />M~y 9
<br />",,8
<br />Jul28
<br />JuniS
<br />Jul15
<br />Junl4
<br />~.\ay 24
<br />Aug4
<br />May 215
<br />
<br />3,470
<br />10,300
<br />590
<br />2,400
<br />1,300
<br />3,700
<br />52e
<br />2,650
<br />'"
<br />3,220
<br />1,210
<br />1,890
<br />4,420
<br />9,450
<br />589
<br />360
<br />",
<br />593
<br />3,480
<br />5,390
<br />715
<br />
<br />At Lonqmont***
<br />Maximum
<br />Disch"rga
<br />Date c.f.s.
<br />
<br />Aug 10
<br />Aug30
<br />Seo I
<br />Jun 17
<br />
<br />136
<br />1,570
<br />885
<br />1,810
<br />
<br />I
<br />~I RecordS from U. S. Geologic.. I Survey Surface water Records "nd
<br />W~ter Supply Paper 1680.
<br />. Flew partly rogulated by small di~ersionsa!>ove station.
<br />.. Flowpartlyregul"ted by mdny small r<eservolcsabovestlltlon.
<br />.., Records available frornOct. 1964 to S"r. IQfi7.
<br />
<br />,
<br />
<br />8
<br />
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