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PAST FLOODS TABLE 3 STREAM GAGING RECORDS LEFT-HAND CREEK This section presents the flood histories and sterm char~ acteristics at the Lett~Hand Croek gasin. Gage Loc<'ltion 1920 1930 1940 1950 1960 1970 I I I I I Hwy.287 I I I-I 3/27 9/42 6/5312/55 . . . . 6121 9/38 6/498/51 ,%, I 10/55 Boulder I-I I-I I-I 51299/31 10/4912/53 I 9/57 Flood Records Scattored data from unofficial sources and limited records Indi<;ateslgnlticanttloodingoccurrod in 1864, 1876, 1894,1921,1938, 1949. and 1951. Minor tloodingmay haveoccurrod inotheryoarsbut was not recorded. The tirst stream gaging station waS ostablished bV the State ot Colorado in March 1927 just downstream from U.S. Highway 287. In May 1929, a second gage was established in the mountaIns approximatoly21l2milesaboveStateHighway7. This gage was 1 <Iter reest<lblishedapproxlmatelyO.9mllesdownstream, but both locations are reterred to as "Near 8ouldor". The peak discharges for the last three major flOOdS wOre estimated by extrapolating thO gage rating curves or by taking slope area measurements. The I<lrgest discharge recordOd at U.S. Highway 287 was 812cUbic,fee1 per second In September 1938. T~e largeST flood recoroed at the gage near Boulder was 785 cubic feet per second in Augusf 19SI,hawever,adischargeof 1,140 cubic fee1 per sccond waS recorded at a location upstredrn at the 9<lge forT."eJun" 1949tlood. Table 3 shows >Jraohlc<llly fhe periods of vperatlon lor edch gage and the dates of recent major floods. Major tloods occ~rred at times Indicated by asterisk. RillnfallRecords RalntC"l11 record'; data for Tnese tloods <lremoager since no U.S. Weather Bureau precipitation stations are located within tl\Obasin. Theavailablcdataarefromunotticlal reports and from records tor the nearby Boulder and Longmont stations. DuratIon and Rate of RIse Left-Hand Creek floods are most frequently produced by Intense raintall during thunderstorms. Snowmelt runoff combined with runoff from spring rains of long duration also produce high streamflows. The tormer are characteriZed by a high peak diSCharge of short duration. The latter usually have lesser peak diSCharges and are of lonqerdur,,- tion. Bec"use ot the steep stream slopes, the flood pe<lks tr<lvel down the valley with such rapidity that 11ttletlrno Isavllllable to war n or evacuate residents. Flood Descriptions A general description of the last tour mlljOr floods occur- ring on L..ft-i-lilnd Cr....~ is provided to II iustrate the t lood potentid I. Heavy damages were not recorded for these floods since the tlood plain was rural Inndture. " ,.