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Duration and Rate of Rise Floods In tne Boulder Creek Basin are produGed by Intense rainfalldurlngthunder,torm,. Typically, tne floods occur inthe springl)nd earlYSUrMler when snowmelt runoff is highest. Usually sovoral d<'lysofmoderateralnfall CO'"1binewlth thesno"",elt runoff to ~turatc the valleys and fill the streams. Tnen, when an intense rainstorm occurS, flooding Is produced. However, Intonse rainstorms, often ref or red to as cloud bursts, can by themselves produce flooding. The progress of a storm and flooding is illustrated by reports of the 1938 flood which occurred On South Boulder Croek and Boulder Creek below the mouth of South Boulder Creek. A heavy rain- storm which started upstream of Eldorado Springs about 4:00 p.m. extended down to Eldorado Spri~s by 6:30 p.m. and contInued for about 7 hours. Records fromthegagc near Eldo.-ado Springs showed 90 cubic fee-t per second or near base flow at 7:00 P.m., 970 c.f.s. at 8:00 p.m. and the peak of 7,390c.f.s. at 10:00 p.m. The peak di5charge held forn.."rly I hour and then gradually dimlnisned toa discharge of 1,020 <::.f.s. which was recorded 9 hours after the peak. Theflood- waters we.-e reported to have reached tne ~utn of Sovth Boulcer Creek by 10:30 p.m. Assuming tnat these floodwaters correspond to the olSGharges wnicn passed Eldorado Springs between 3:00 A 9:00 p.m. ratherthilntothepe<lkdischargewhlchbegandtIO:OOD.m. the "veragotravei rate of thefiood...ould be5mllesp<lrnour. After ontering the flatter ~"Ider Creek cn~nnel, the flood slowed down to an average tr<lvcl rate of about 1.5mlles per hour. It is noted that the f load occurrOd at n ignt whi 10 neavy ra; n$ were sti II 1~ II i ng "nd when conditions were not favorable for evacuation or flood fightlnq. Stroilrnflow increased fromnOr-mill stagctopeakfloodlng in:lhours bYt stayed wltninthl'stredmbanks for about the first I 1/2 hours. 29M<ly-2June 1894 Heavy rains fell over the mountains extending from the Colorado - .'yomi ng border soothward into tile ReDub I iCi,ln i,Ind Ar~ilnsas river basins. Rainfail over the Boulder and South Boulder Creek basins wdS particularly heavy. Rainfall records fora 96 hour period ending at 3,00 a.m. on 2 June 1894 show that the mountain drainage are<lrecelvedfrom4.5t06 inchesofpre<;ipitation. Rainfall amounts over the high plains gradually decre<lsed from west to east varying from 5 Inches at Boulder to approximately 2.5 inGhes at the mouth of 8oulderCroek. ThemountainrainfaIICC<rlblnedwithth<lsnowmeltrun- off to produce the greatest flood known at 8ouldcr, whiCh came roaring down the valley during the night of 30 May 1694. wilalngs,bridges, and even long sections of roads and railroads were wolshed away. Altnoughdamages were extensive, a dollar amount was not estimated at tnat time. I ~2 Juno 1914 Rains In the mountains comldned with runoff from iln oxceDtionallyheavysnowp<lCkproduced,whatnewspaperaccountscallod, "thewors-t flood On aouldor Creek followTng the 1894 flood". Boulder's watcr supply system and tne Boulder County farm were severly damaged. Numerous r~ldS and bridgos in the mountaIns were also damaged or destroyed. 2-7 June 1921 Little Is known 01 this flood oxcopt thdt itproduci>d tl1e higl1<lstpeilkdlsGhargaeverrecordadettheOrodal,lgage. Adiscnarge of2,5(}OG.t.s. was rOGorded on 5Junu. RaInfall totaled 3.:>6 in<;hes ~T JGWlder througn 3 pc~ioa of 2~7 June. flood DescriDtions are provlaed to illustratetnc flood potential . 3~la June 1923 Th is srorm cenrered over tt,e high P iai "s c~sr of -the " "