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<br />'lo,,~ver, ch" rtt)..r i"lPorcant ....Se of the 100-year flood eveot lies io
<br />flood phin mana~e""'nt and land u." plaonirlJl: as SH forth io the "CaCe
<br />."'tures. The Scate of Colorado considers ch.. l(Jn-yenr frequency flood M
<br />the flood evont W be used i<> desil>;nir.g and protecting struccures and
<br />dwdlinl:s for human Q<;cupation. Therefore, all flood plaio ..,gulario".
<br />are based up<>o th" lOO-year flood.
<br />50o-Year Flood Event
<br />The 500-year flood eVeOt is useful io making cbe public aware that
<br />flood. ta...;er than the lOo-year flood can and do occur. JUSt because a
<br />person is liviD.'; above ehe 100-year flood boundaey does oOt "'ean thac he
<br />19 completely safe feom f!.oodioJ;l. The 5oo-y"ar flood eVent can also be
<br />used for r"lluladnll hillh risk develop,""nts ..ithin the flood ph1n such as
<br />nllclear power phnts, or tht' swra~e or ..anufacture of toxic or explosiv"
<br />""'tertals.
<br />
<br />(>Oint or: t~e reference Ibe, the hi~h water d"v.1t10ns can "" ~urve}'ed 00
<br />th" >(rounrt to ,~lle"[ate a"y disrrepa"des on the base "ao.
<br />
<br />c.
<br />
<br />Flooded A.rea~
<br />
<br />se~tions.
<br />
<br />Waur stlrfac.e "levati""s ~omp"ted ,~t: each cro.g sec"ion ...>tt'
<br />
<br />flood plain maps, sheets 1 throll~h 14, "ho.. tht' oou"dary of tht'
<br />IOO-yearilndSOO-year ilood plaIns. Th",iloodphinboll"dacieswere
<br />plotted froT:! the flood profiles by deter:nin1nll channel station1ru; of Hood
<br />COrl.tours at the sa"'", interval as the topo~raphi~ maps. Flood oontours,
<br />sl-oc>;1n as wi~llly li"es, .,xtend ""rpH,d!cular to the direction of flow 1ltld
<br />interse~t the ~round at the ed~e of the Hood plain.
<br />The nreas included ,..ithin che flood lir:.. bou<>d"ries are "~~ut ~S()
<br />acres for th.. WI}-year freqU<'ncy "nd 730 aCres f~r the 'iOo-ye"r.
<br />Upon official approval of this eePQrt by the Colorado Water
<br />Conseevation 80"rd, the aCt'" outlined by the 100-year flood bocmdary may
<br />be re~u1aced "ccordill~ly ':>y the local offtciah.
<br />o. nood""y
<br />~ncroach""'nCs on flood plains. such as arcHit:lal fill, ran r<,duee
<br />the ar""l e.xtenr ,,( " flood pl"-in if prOVisions are ",,,-de for In~re.1,.ed
<br />Hood ""i.o;hts. Its an alterna.ttv" to th~ Drt'S..nt Hoodinf\' "ltuatton. a
<br />possible floodway with flood plaln encroach"'''''t w,,-s analyzed b this
<br />atudy. This "a~ "imply a hydraulic a<lalvsis in which th" flood plab "as
<br />th,'orer lcally "",dified to contain floortin>; within selected ~""roach",,,nt
<br />boundar1es. The result!nll ehects on flood cl~va~ tons ar" ~howr: in an
<br />i\pp<'n.dh separ.,u from this report.
<br />
<br />3. Flood El"~"-tion
<br />'I'he indLlded tlX~ibics :!"d tabLes display study results. Hood cr"st
<br />"le"a.t.iotls for the 10-, ~()-. W()-. a.nd 500-year flOOd", as determind at
<br />each cross section. ,uy be found in Table 1 "Flood Frequent.y-Uevation and
<br />ni~char.o;e Da.ra". The. Cross Section Exhibics. 8-1 through B-1!. show a
<br />~ra.phtcal repr".entadoo of hil';h './<It,,r elevations at ty~tca.l valley cr09S
<br />
<br />",,'d to pre~"u ,lood profile~. "xhihits 1\-1 chtou~h A-16, wlllch show the
<br />"t",'"",b..d f'l"va.tio" in ""iation co hi>;h water "levado,," for the lo-y,'M
<br />'\()-year, lOO-y""r, ".,d5(\f)-year frequ,'ncyflo<>dg.
<br />
<br />rh~ flood ~nl(tle' :nay i)" lIs"J en ar,'.as "h..t.. ~ontrovers~ .,ris,'s c>v..r
<br />
<br />tht 1O',-vt'ar flood ""u~cta.ry sh"wn "0 rh~ ~lo"d olain 'lap", Sinee th.,
<br />fl(>(,d profi Ie ~xhibi<s lliv" the "at:~r ~ltrfa<" elevatioo at " Sl><'< Hie
<br />
<br />u
<br />
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