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<br />FUTURE FLOODS <br /> <br />Table 4 <br />SLH-IARYfFPOTENTlALFLOCXJPEAKDISCHAR3ES <br /> <br />In order to study tho flood potential on St. Vrain Creek, <br />two floods, t~e Intermedi~te Regionai and Standard Project Floods <br />"er" doveloped. The Intermediate Regional Flood ;s one with an aver- <br />agefrequencyofoccurrenceot about once in 100 years and Isincreas- <br />ingly being accepted by the public as a mini'TIUm limit for "pplieati On <br />of local regulations. TI1eSt~ndardProjectFlood isofgrwtermagni- <br />tude and represents a reasonable upper limit of expected flooding. <br /> <br />Stream and Location <br /> <br />Intermediate Standard <br />Regional Project <br />C<ood Peak Flood Peak <br />Discharge Di5<;harge <br />c.f.s. c.f.s. <br />4,900 12,400 <br />6,450 16,000 <br />10,200 21,800 <br />10,100 18,300 <br /> <br />Intermediate Regional Flood <br />The dIscharge-frequency relattonshlps in the St. Vrain Creek <br />basin "ere based on a statistical analysis of the stream gaging <br />recordsot St. YrainCreekat Lyons and Platteville, Colorado. Flood <br />hyljrO>Jrephs"eredevelopedforroutingthroughButtonRo.::kDamand <br />for routing downstream from Lyons to determine the discharges through- <br />out the length of the stream. The IntermoolateRegional Flood peak <br />discnarges for each si'roam are shown In table 4. <br /> <br />North St. YralnCreek <br />(Entire Study Reach) <br />South St. Vraln Creek <br />(Entire Study Reach) <br />St.VralnCreek <br />at L'jQnsJ.! <br />$t.VralnCrook <br />atdownstreiYrllimltotstudy <br /> <br />II <br />At the Lyons gage. <br /> <br />Froquency <br /> <br />Ha<:ardsofLargeFloods <br />ihe effacts ot the Intermediate Region,,1 and $t~ndard <br />Project Floods were analyzed to determine potential flood ha<:ards <br />In the stwdy reech flood plain. Theanalyslsus.edfiel<.lcon<.lltlons <br />reprnsentedbybrldgeandvalleycrosssectlonssurveyed in 1911. <br />Fectors considered InclUde extent of aroa flooded. flood depths. <br />f l<XJd U"""'Y"&, "b",lrucl i"n", 10 f looJ f Io..-~, ....loci ti",& of fiwd <br />flows, rate of rise of stroam lavel, and duratIon of floodIng. <br />Oilmagesduring tloodlng are effected by both depth "nd velocity <br />of flows. ObstJ"UctionstofIOlOscanlncreasetlooddepths. In <br />regard to r..man ha<:ards, gonerally flood waters 2 feet or more <br />deep and flowing at avelocityot3 fe<lt or more per second croatos <br />a detinlte danger ot injury or drowning. These conditions "00ld <br />occur "tmeny locations during " large flood. <br /> <br />Stm'dardProjoctFlood <br />$formsil,,,twoul<.lproducett\eStandardProjectFloodar<il <br />~ncommon, and it is difficult to assign trequencies of occurrence <br /> <br />with any reasonable de<;jroo 0' accuracy. Howev<lr, II00ds of this <br />siz<l doo.::cur as evidenced Oy flooding In the Denv<lr area '0 1965. <br />T" Standard Project "000 peak discharges an' also ShOlOn '0 table ,. <br /> <br />Floods larger than the Standard Project Flood c"n occur. <br />HC\,c',.o~, f! oode """ liar tha~ +he I ~termed i>:lt", R<>g ;",,;0,1 Flood ;0,1'" "'Ore <br />frequent "nd althougl1 they IJlIJndate smaller are1lS they also cause <br />damdge. hardship, and inconveniences. The hIstoric peak discharges <br />;ntable3 illustratethesm"llormagnituceofthernorefreq.rent <br />floods. <br /> <br />18 <br /> <br />" <br />