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<br />JIIlboOd" <br /> <br />8. 1'lood Hydrographs - The coml>uted SPF hydrograph for the Yampa River <br />was adopted for the 500 year eVent (see paragraph '7e). The 100 year <br />hydrograph is considered to be I>rimarily a rainflood and was patterned <br />afte" the April 1974 event at Hayden. The 50 and 10 year hydrographs <br />are prtmarily snowmelt events al1d were patterned after typical snowmelt <br />hydrographs for the Yampa River at Mayb.e,lL <br /> <br />The 500, 100, and 50 year e\Tents on the small streams around Craig <br />are, :~rimarily cloudburst events. Flood hydrographs for these events <br />are 'based on the synthetic rainflood computations for these areas. The <br />10 yea~ event is primarily a sno"''lllelt flood. Hydrographs for the <br />snowmelt events were patterned after recorded snowolelt floods on <br />FOI,tification Creek taking into account differences in diurnal variation. <br /> <br />The 500 and 100 year events on FortH:lcation Creek are pd.marily <br />cloudburst events. Flood hydrographs for these events are ba.sed on the <br />syntnetic rainflood computations for th~,se areas. The 50 and. 10 year <br />eVEmts are primarily snowmelt floods. lIydrographs for the '3fLCl~nne.lt <br />evEmts were patterned after recorded snowme.lt hydrographs on Fortification <br />Creek. <br /> <br />Hydrographs are not presented in th.:ls report but aI'€! av.:d.lable. <br /> <br />9. Concurrent flows - Concurrent flows weI'e estimated xor several <br />index I>oints. Concurrent cloudburst flows were ba.sed on the rainfall- <br />runoff computations discussed earlier. Concurrent: sno"''1lIelt flows were <br />selected on an arbitrary basis since ther". is no <lata to mak" a more <br />precise determination. The 10 and 50 y,ear concurrent snowmelt flows for <br />an index point were selected as being (,quivalent to the 2 year and <br />10 year specific snowmelt flows, respectiv.,ly, at that tnde" point. <br /> <br />r <br /> <br />The concurrent flows on thEl Yampa RivE,r for use with the 100 and <br />500 year cloudburst floods on Fortificallon Creek should represent a <br />summertime Yampa River flow since a. cloudburst on Forti.f1.cation Creek <br />would most likely occur in the sunnnertJlme, An analysis of July and <br />August flows at Haybell was made to dete1>:dne these concurrent flows. <br /> <br />10. Results and Comments - Flovrs for ulle in estimating flood <br />platns for the various streams at Craig ar'~ listed on table 3. An <br />evaluation of the results of tilis study ..ms made by comparin:s 100 year <br />and 500 year peak flows with the envelope curve, Chart 'f. This comparison <br />ind:Lcates the results are reasonable. <br /> <br />As indicated in paragraph 5, ice jams have caused flooding in Craig. <br />An analysis of ice jams was not po"sible due to a lack of data. Ice <br />jams are not believed to be as serious nOT' on Forltificat~on ,as in previous <br />yea1:s because the channel has been imp:roved and straightcne,d, thus increasinf; <br />its capacity and eliminating many areas where ice jams occurred in the past, <br />In addition, considerable effCl:t is made by the C:ity of CraiB to remove ice <br />jam" before they create flood ccmditions. <br /> <br />10 <br /> <br />'J!!. " <br />.;1 <br />.' <br />1;,\' <br />