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PAST FLOODS TABLE 3 STREAM ~GING RECORDS LEFT-HAND CREEK This section pr~sents the flood histories ~nd stor~ C~3r- acteristics of tne Left-~and Creek Casino Gage Location I92Q 19}Q 1940 1950 1960 1970 I I I I I Hwy.287 I I H 3/27 9/42 8/5312/55 . . . , 6121 9/38 6/498/51 Near I 10/55 &lulder I-I 1-11-1 5/29 9/31 10/49 12/53 I 9/57 "Iood Records SCilttered data from unofficial sourcos and I imited records irldic<ltcsignifiCi.lntfloodlngoccurred in 1864, 1876, 1894, 1921,1938, 1949, Jnd 1951. ~inor flooding may have occurred in other years but w3snotrecorded. The first stream gaging station was estabJish<'XJ by the State of Colorado in March 1927 just downstream from U.S. HiGhway 287. In May 1929, a second gage wasostablished in the mountains approximately 2 1/2 miles above State Highway 7. This gage was later reestablished approximately 0.9 miles downstream, but both locations ar<>referred to as "Near Boulder". The peak discharges for the last three major floods were estimated by extrapolating the 9ago rating curves or by taking slope aroa measurements. The largest dlschargo recorded at U.S. Highway 287 was 812 cubiC' feet per second ir,Septemb<>r 1938. The l"rgostflood rocordod lItthcg:!gO near Rouldor was 785 cuoie feet per second j n .~ugust 19~1, however, " di seharg" of 1,140 CUbic f<>et per second waS recorded at a location upstream of the qago for The June 19>19 f 1000. Tablo 3 shOWS gr<~rhically the perlmh of Op~ration fOr e~Ch 91lge ~nd the d~Tes of recenT major floods. Major floods occurred at times indicated by asteriSk. Rainfall Reeords Rainfall records data for these floods are moagor sinc" no U.S. woatherElureau preclplt<ltlon stations are located within tlwl>d5in. Theavallablodataarofrornuhofflcidl reoortsondtrom recordS tor the nearby Bould<>r and Longmont stations. Duration and Rate of RIse Left-Hand Creek floods are most frequently produced by Intense rainfall during thunderstorms. Snowmelt runoff combined with runoff from spring rains of long duration also produce high streamflows. The for_r are characterized by a high pe<ll<. dlSCMrge of short duration, The latter usually have Ill'lsor p....l<.dischargas and are of longer dura- tion. Because of the steep stream slopes, the flood peaks travel down the vdlley with such rapidity that littlet!me is aVdilable to "a rn or evacuate residents. FIQOdOescriptions ^ goneral oescription of the last tour major floods occur. ...1 ~8 o~ Left-H~!'!d Cr~ek I s p~ov I ded tC' i! I uS+~l!+e The 'Iood po+enTl a I . Heavy damages were not rocorded for theso floods since the flood plain was rural [nnature. 13 "