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<br />INVESTIGATIONS AND ~~ALY~IS
<br />Interpretation and Vae of Report
<br />A. Freque~cy and Discharge
<br />The j()~, 50-, 1n()~, ~nd SOO-year ftood events are used a. the flood
<br />frequencies for this floodplain analysis. Thus the data developed In thi~
<br />report will be compatl~le not only for re!,:ulation purposes, and ~.~, 1041
<br />desiRnation but also for Federal Insuranc~ Administration flood Insurance
<br />ratcstud1es.
<br />These various flood events ha"e ana"era"e Occurrence of once inth e
<br />nurtb<>r of years a" indicated. For example, the 100-yeat flood o~cuts, on
<br />the a"erage, once in a 100 year period, andha" a one percent ch",nce of
<br />hein!,: equaled Or exceeded in any glver y~ar.
<br />The parUcular u~es for t~e various flood events ln addition to those
<br />stated above are as fo l1ow~:
<br />
<br />.tatutes, The State of Colorado CO!l~ [ders the 100-year frequency flood '"
<br />th" flood "vent to he used in des1g"nlog and pfotectin~ strunure.. nnd
<br />dwellings for human occupation. Ther~'of", ,~ll floodplain re~uhtions ~re
<br />b8sed upon th~ lOO~year flood,
<br />SOO-YearFloodEve1\t
<br />11'e SOO-yeaf flood ev"nt is useful in ..aking the publ1c "waf" that
<br />floods larg"er than the 100-year flood can and do occur. Just because a
<br />person is l1vi">l above the 100-year flood bouClda<y doe. Clot mean thst he is
<br />completely safe from flooding. The SOO-year flood event can also be used
<br />for re>lulat1ng high risk developments within the flo<ldplain such a~ nucle8r
<br />power plants, or the storsge or manufacture of toxic or explosive
<br />"'aterials.
<br />
<br />10-Ye"r and SO-Y""r Flood Events
<br />InformAtion re!l:ardiClg these 10w"r f[e'luen~y flonds Is especially useful
<br />for future en~in",'rinp; "t"dif's and l"od ,,-<~ pL~nninr. purposes relllted to
<br />,"inorroadsysteflls,:tlinorchannelimprove"ents, the 10clltionof parks aCld
<br />recr"at1on~l fa~llitles, a!l:rieultural lands, and appurtenant "tructures,
<br />P<lr structur"s and use. of thh type on t~e smaller trlbut..ries or 1n at"ells
<br />whore the high risk of .trucrural failure ls economically r<>aslb1e, and tl",
<br />haz"rrl of life and property non.-xtstent, the use of thc lower frequency
<br />floods =y be conddered.
<br />
<br />B. FloodElevaUon
<br />T~e exhibits ,~nd t"I>l,,~ di~plAy Hildy c..sults by stream reach, ct" shalom
<br />On t~e index "'11.1" Flood ~rest elevations for the 10-, 50-, 100-, and
<br />SOO-year floods as detef1linedat each <:russ sect1on"",y be fOllnd in t he
<br />noed Pre'l"ency~nev"tion "nd Dis,:har;le D.H.. table, Table 1. The Cros"
<br />Section Exhibit., B-1 t~rou~~ B-S, show a >Iraphical representation nf the
<br />hi!l:h water elevations at typical valley ctOss sections t~rouf,h"ut the study
<br />reach. Water surface "levntion~ at t~e ~ross sections ""'re used to prep"re
<br />the flood proftles, exlllbits A-I through A-~e, which sho\ol t~" strea",bed
<br />eI.-vatlon in relation to hlg~ water elevation. for the lO~vear ,n-ve~r,
<br />lOO-year, anrl SOO~yea[ frequency floods.
<br />
<br />IOj)-Ye"rl'lMdP.vent
<br />
<br />The lOO~Year flood event lIay also be used f<>r engi"eeri,,!: de81~n
<br />purpose~ ,..her.. ~ 10\oler risk of f"ilure than the 1 0- or SO- yea r flood Is
<br />de.ired, flo...ever, t~r mOst I.mportant use of the lOO~year flo"~ eV,'nt lies
<br />in floodplain management and land u~e plal\nin.~ as ..H forth in tne ~tnte
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